Aust Wood Review article on bowl mounting

[rsser]

Current issue has a piece by Terry Martin outlining his use of expansion chucking for bowls.

Inc a v. interesting sidebar on truing your jaws.

He doesn't say it but I will: with dovetail jaws of course you need to be careful not to wreck the dovetail angle.

Also, with dovetail jaws and a recess wall to match, you have a keyed join that doesn't need much outward pressure.

Some folk bag this method of mounting. It's the way I was taught and probs have been rare; it's the way Raffan did thousands of bowls. So IMO it's not whether but how.

[artme]

I read that article a few days ago Ern - while standing in the newsagency!

You correctly point out the problen of the angle, and this can be difficult for most people

I think there have been special tools made to cope with this problem.

The fellow who taught me will not hear of this method. I do as he taught me and it has only evr been through my own carelessnee that I have had problems - twice.

we cut a recess with perpendidular sides that is an exact fit for the jaws of the chuck when closed. The Chuck is seated firmly on the base of the recess and tightened.

As I said, unless you are careless, no problems

[rsser]

Well done Artme, a low cost way of getting info!

IMO vertical sides will only work reliably with ribbed jaws and pressure.

Excess pressure I would say would be the cause of most problems.

And the ribs just leave marks that need cleaning up and so more work.

Yes, you can shell out $$ for so-called dovetailed scrapers, but the angle has to match your jaw dovetail, and anyway, you can shape your own out of a bit of HSS or an unused scraper on the tool rack. If anyone's interested I'll describe how I've done this.

[tea lady]

Yes, you can shell out $$ for so-called dovetailed scrapers, but the angle has to match your jaw dovetail, and anyway, you can shape your own out of a bit of HSS or an unused scraper on the tool rack. If anyone's interested I'll describe how I've done this.I just use the skew as a scraper. :shrug: Or should that be "back beveled scraper"? :doh: One trap for young players is measuring the top of the dovetail then transferring it to the top of the foot ring. You actually want the bottom of the foot ring to match the top of the jaws.:cool: a lack of outward pressure only results in the bowl spinning in the jaws rather than a UFO, if it is a dovetail rather than parallel sides:cool:!

[hughie]

Its interesting to note that the Leady chuck that was designed for secondary schools and I gather has been in service in schools for many years. Uses expansion and keying via a ridge or raised grip area.

The inventor claims that when used in conjunction with supplied cutter, failure rates a no greater than the experience mentioned here.

So what does this all mean? wrong sized cutter, over tightening, to little 'meat' to hold by etc

heres a previous review on the chuck

http://www.woodworkforums.com/f8/keyless-self-tightening-chuck-36662/

[Pat]

Don't mention this to Ken!:U

[colhu]

I'm with Tea Lady - I just undercut the recess a little with the long point of the skew used as a scraper. The angle of the skew is a bit steeper than the angle of the taper on the shark jaws on my Vicmark VL100, and the undercut serves to pull the square bottom of the recess hard against the end of the jaws.

I use the same technique to hold the body of my pepper mills while I bore them from the top. There are two potential problems:
1 if there is not enough meat around the recess, over-expanding the chuck sometimes splits the timber collar;
2 if the recess is deeper than the pitch of the "teeth" on the shark jaws (ie more than about 9mm) I need to taper out the neck of the recess to make sure it's only the end of the jaws making contact.

(Hope all that makes sense - it's really hard to describe in words what is easy to demonstrate with the hardware in your hands).

I've attached a couple of pics that might help the explanation.

cheers, Colin

[TTIT]

............Some folk bag this method of mounting................ .I've heard of this phenomena :o Why??? :? I've never had a problem with (tapered) recesses but I have snapped a spigot or two off going the other way :B

[Allen Neighbors]

Yes, you can shell out $$ for so-called dovetailed scrapers, but the angle has to match your jaw dovetail, and anyway, you can shape your own out of a bit of HSS or an unused scraper on the tool rack. ****If anyone's interested I'll describe how I've done this.****

Okay. I'm interested. I've not been able to do this correctly yet.

[robo hippy]

I don't imagine there is a link where I can read the article is there? I have been doing this for years. If you drill a recess with a big forstner bit, you never have to take the chuck off.

I won't use expansion chucking on end grain, too much chance of splitting.

robo hippy

[rsser]

RH: fraid not. Yep, Martin starts with a saw-tooth bit as well, one that closely matches his 50mm jaws, for mounting the top for outside shaping. then undercuts the recess wall with a spindle gouge.

Colin: yep, clear to me anyway, as a shark jaw user. Maybe 'ribs' is a better term than teeth.

Martin emphasises the importance of matching the recess circumference to the jaws'. And of having some bulk to take the pressure. But he shows 25cm plates, 6mm thick turned on a recess 47mm x 1mm.

Allen, I'll try to explain it and bear with me as I'm not much of a technical writer. My scraper stock is 1/2" wide, 3/16 thick. The scraper angle (long side on the left to the end) has to match the jaw dovetail angle (face to side). I grind a bevel both on the left side and the tip since I open the recess with a parting tool and want to clean up both the wall and the floor of the recess. But I relieve the tip so that not all is in contact, maybe just the left third, to reduce the likelihood of catching. First step then is to go in scraping the wall til the floor is contacted and then gently clean up twds the centre.

I used to start the recess with the long point of a skew vertical, so cutting not scraping, to leave a better wall surface, but found tool control difficult. It needs a pronounced skew angle for clearance in small diam recesses and there's little bevel support.

Raffan talks about recess depths of about 4mm.

I usually have a foot on bowls so the recess goes into this and often with not much bulk then to take any great pressure from the jaws, and have rarely had a failure. Course a deeper recess can help here but that can compromise the form, and with small bowls, sticking to a foot diam of c. 1/3 the bowl's, a 50mm recess is just too big so another method of mounting is needed.

EDIT:

Pat, Ken is right to warn about this method. If the wood is unsound and you apply too much pressure, it can split at speed with ugly consequences. You also have to moderate your hollowing method to suit. Big cuts with a 5/8 gouge with a piece in a shallow recess ain't gunna cut it, just lever the piece out.

To set the pressure I snug the jaws up and then add a bit of a turn on the key. With experience you can feel/hear it when it's right. You can always start with light pressure, try to move the piece with a hand either side, and if more is needed add some.

HTH

[Calm]

to get the angle of the dovetail jaws - lay the chisel blank across the end of the chuck (side of chisel touches jaws) and the angle of the end of the chisel should be a continuation of the angle of the "dovetail" on the jaws.

131511

Then you grind the releif that Ern desribed and you have what you were after

or you use the Skew as a scrapwe and adjust the angle (you cut at) to suit the dovetail. The point of the skew also gives a good clean corner to allow the dovetail to seat right in against the bottom of the recess.

The correct size of the recess is most important, it needs to be when the jaws are a perfect circle so even pressure is distributed arpound the whole recess. This perfect circle is usually when the jaws have a 2 to 3 mm gap between them. (just open)

[DJ’s Timber]

Just to be a bit different from Calm, I shape my 1/4" round skew this way.

131525

[rsser]

Ok, I hesitate to offer this pic as I'd reground the thing for another job.

It still works for the recess and I'll return it to a better shape by making the angle more obtuse and the top edge less rounded.

As you can see, it's pretty crappy steel and will soon need the top lapped again.

Here's a pic of Nova's job. Click (http://www.teknatool.com/products/Other/Dovetail_Chisel.htm). I'd reshape the tip so that only a third or a half contacted the floor while the side was scraping. And of course your dovetail angles may not be the same as Nova jaws'.

[robo hippy]

The tightening part took a while to figure out, and the proper amount of shoulder to leave.

Too tight, and you can blow it out, but that again can depend on the wood. Some woods you can really tighten, especially if you have a big shoulder. The problem with over tightening, if you don't blow it out first, is that if you do have a catch, the recess can fail because the extra stress of a catch can be just too much. You can get away with a narrow shoulder if you don't tighten too much, but you have to be dainty when you turn it out. I prefer the keyed chucks, and tighten a bit in one key, then rotate to the other, then back again, never getting it too tight.

I mark the recess by using a dedicated compass or dividers, which are super glued in place. First cut is just inside the line, then I just barely take the line. If the side of the dove tail is too fuzzy, I will use a small pointy spindle gouge and clean it up. I also let the scraper rest, just barely touching the wood, like a finish cut, to remove the run out you always get from going through end grain and side grain. This helps a lot when reversing the bowl.

As to depth (apologies, I never learned millimeters) I usually am about 3/16 of an inch. 1/4 inch is over kill, and proper fit is more important than more depth. This works fine for heavy roughing and coring. I saw Mike Mahoney turn a nice platter, about 14 inch diameter with a 1/16 inch deep recess. You need jaws that have never been hit by your gouge, scraper or coring tool, which for me is brand new ones. I can't go that shallow as I prefer green wood, the wetter the better, then turn them to final thickness, and let them warp. Some bottoms will warp so bad, that I can't remount them for sanding on any jaws, even with 3/16 inch deep recess. I do use extended jaws which are smaller, and they will get enough of a grip for sanding, which for these bowls is at a very slow speed, like 10 to 15 rpm.

robo hippy

[orraloon]

I just shaped an old scraper and get good results. I had the odd flyoff in the early days but that was more down to poor turning skills and getting big catches. The main thing is getting the depth of the recess right. I have the recess just shallower than the hight of the jaws so the rim of the jaws are snug on the bottom of the recess.
These days however I mostly use the Leady chuck with it's cutter as it is very quick to do and spot on every time. The only measuring is the depth and even that is not all that critical.
Regards
John

[artme]

Just had a bo peep at the bottom of a Red Cedar Bowl I turned. Recess is Only 3-4mm deep, vertical sides and just a poophteenth larger in diametre that the CLOSED chuck jaws.

I had no problems turning this.

Now if the recess is cut as I have decribed then all the pressure from the jaws is exerted into the bottom corner of the recess - Where all the meat is.

With the dovetailing method your angle could be wrong by any amount. If the angle is too acxute the pressure of the jaws will be applied to the top of the recess, where there is very little meat. The resulting problems need no description.

If the angle s too steep then the workpiece will move outwards on the jaws and grip will be lost.

[rsser]

Haven't found that a prob artme; doesn't have to be +/- 1 degree.

[artme]

Haven't found that a prob artme; doesn't have to be +/- 1 degree.

Hmmmm.....

[Allen Neighbors]

Ern, Calm, DJ, Robo. Thanks for the information. Now I'll try some of this when I get back home. I ran from the snow... and I ain't going back til it's well over.
Many thanks!!

[NeilS]

Have only ever used this method on (standard) bowls, not as many as Raffan, but guess it would be over the thousand nowadays (feels like it anyway).

I use:


Same method as HR to mark the diameter.
Same method as Ern with forming the recess.
Same method/s as Calm & DJ to make tenon scrapers.
But, like TL, I also use skew (slightly curved profile, similar to Ern's scraper, for same reason) at times. Call it a negative rake scraper if that does something for you...:U

Everything else said so far in this thread 'rings true' to me.

Once seasoned, I complete the outside of my bowls in one go through to wax finish and never return to have a second go at the foot with something like Cole jaws or vacuum chucks. I always use cling (Glad) wrap between the jaws and foot, to protect the finished foot recess from metal stains and marking, and to increase the gripping power of the jaws. Two layers of cling wrap on bowls over about 300mm.

I don't hold back on the hollowing out and have not found holding power a major issue. Recesses up to 5mm deep when wet turning larger bowls/platters to about 700mm, and up to 3mm deep for the same pieces when dry. Less depth on smaller bowls/platters by about 1 to 1.5mm. Can only remember losing half a dozen pieces over the years. If it was ten, then that's less then 1% failure rate. I can live with that given the benefits of completing the outside in one step.

Most recent grip failure was a faceplate ring (the metal sort) being let go by the PowerGrip jaws mounted on a 5" Nova chuck. The jaws were as tight as I could tension them up, but it was a fair lump of green wood hanging off them...:o. There was enough spring in the longer jaws to flex by about 5mm to let the ring go. Have only used the standard (short) bowl jaws since with no further incidents.

.....

[rsser]

Yeah, I've had one faceplate ring let go, or rather the shark jaws did, but I was asking way too much of it.

I only use cling wrap in the recess when the wood is green; never had a prob with stains on dry wood using oil or n/c lacquer & wax finishes.

[robo hippy]

I was using plastic and later the nitrile gloves to keep the metal stains off the wet wood, till I found out that concentrated lemon juice will remove it in a minute or two when the wood is still green, or 5 or so minutes if the wood is dry.

robo hippy

[rsser]

Neat idea RH. Thanks.

[Frank&Earnest]

Maybe it is beginner's luck, but I do all my bowls and boxes using jaws in expansion mode and have not had a problem in 3 years. For big blanks, I start with a 56mm Forstner on the flat side, round them supported with the tailstock and then cut the recess that ends up as being the foot. For the undercut the point of the skew works, but I have not had problems even when I did not bother. Unless you like turning as an extreme sport, the little give of soft wood and the resistance to higher pressure of our tough aussies seem to do the job anyway.

[Calm]

Where's Ken:? - he must be chewing his knuckle off by now - this is his pet topic - holding bowls in expansion mode.:D:D:p

Cheers

[NeilS]

I was using plastic and later the nitrile gloves to keep the metal stains off the wet wood, till I found out that concentrated lemon juice will remove it in a minute or two when the wood is still green, or 5 or so minutes if the wood is dry.



Will file that one away, thanks RH.

.....

[RETIRED]

Where's Ken:? - he must be chewing his knuckle off by now - this is his pet topic - holding bowls in expansion mode.:D:D:p

CheersMine too.
Ken has been away for the weekend, same as me.

The reason that both of us use contraction instead of expansion is threefold.

The chuck has better gripping power "crushing" the timber than splitting it.

The second one is that you are less likely to go through the bottom of the bowl because in contraction you can "see" where the timber is instead of "guessing" how deep the recess is.

The third is that you can maintain an even wall thickness right to the base.

Agreed that you have to reverse chuck the bowl to remove the tenon but you should do that even with a recess.

Ken very rarely uses chucks

Instead he glues a waste block on and uses a faceplate to turn the inside and outside at one setting and then reverses to clean up the base.

I have used all three methods depending on the situation.

It still comes down to personal preference.

[robo hippy]

,

I will agree that it comes down to personal preference as to using a recess, tenon, or waste block, but think there is no advantage to any style The one exception would be that a recess can be left as part of the design, where in most circumstances, a tenon or waste block has to be removed.

Better gripping power with crushing than with splitting mode. Well, to me, the biggest risk of splitting comes if you are turning end grain and use expansion. This is the same as driving a wedge into a log to split it up for fire wood. In expansion into side grain/face plate turning, you are pushing into side grain where the wood has a lot of resistance. You don't try to split a log by chopping through the side grain. The breaking of a recess comes from too small of a shoulder, too shallow of a recess, a recess that is too large for the chuck jaws, and/or over tightening. You can throw in a huge catch for good measure. Tenons can fail from pretty much the same reasons, though I would suppose that most of them fail from having too small of a tenon. Some say that when using a tenon, you should line up the jaws so they are quartering to the end grain, or avoid having one set on end grain, and the other on side grain because side grain will compress more than end grain, and your hold can loosen. Done properly, either works fine.

As to one style being more likely to go through the bottom, I don't know. I measure and check my depth. I remember to measure to the chuck jaws, and not the base of the bowl/recess, which would make the bowl bottom 1/8 inch or so too shallow. Pretty simple, just a different technique.

The only bowl I have seen that has the same wall thickness through to the bottom of the bowl is an 'earthquake bowl' that has a rounded bottom so it will rock when there is an earthquake, and this one will have the same thickness throughout the entire bowl. Other than that, if you have a flat bottom on a bowl, there is a thicker area where the transition from the side of the bowl to the bottom is. The smaller the bottom/base of the bowl is, the smaller this wall thickness variation will be. The larger the bottom of your bowl is the more thickness variation there will be. You can make a bowl where you go down the side to your desired bottom thickness, and then make a sharp turn to go across the bottom, but they just feel wrong to me. There should be no difference in the insides of two bowls, with the same shape turned either way, unless two different turners do them.

It really does come down to personal preference. I learned to use a recess before I heard about using a tenon. We use what works best for us as individuals.

robo hippy

[artme]

,

I will agree that it comes down to personal preference as to using a recess, tenon, or waste block, but think there is no advantage to any style The one exception would be that a recess can be left as part of the design, where in most circumstances, a tenon or waste block has to be removed.

robo hippy

This point about leaving the recess as a design fearure can be problematitic here in Australia. In competition Judges seem to deem that NO SIGN of a holhing methd should be left on the finished item. I personally think this is a stupid and pedantic way to behave as it does come down to a matter of personal taste.

I saw an example of a fellow's work that was stunning. Didn't even rate a mention because of the. Winning entry looked like a babies potyy! Bloody awful thing!!

[Frank&Earnest]

This point about leaving the recess as a design fearure can be problematitic here in Australia. In competition Judges seem to deem that NO SIGN of a holhing methd should be left on the finished item. I personally think this is a stupid and pedantic way to behave as it does come down to a matter of personal taste.

I saw an example of a fellow's work that was stunning. Didn't even rate a mention because of the. Winning entry looked like a babies potyy! Bloody awful thing!!

No problem at all. Just forget about competitions and put your work in a gallery. If it sells, you win. :D

[rsser]

Checking bowl thickness at the base can still be done with appropriate calipers if you leave a gap between the jaws. Doesn't have to be much. And a true round jaw arrangement will have a gap.

I agree with that it's a matter of preference and the skill you build up with one method or t'other. I've used both and with small bowls and a commitment to chuck mounting, a tenon is necessary. A glue block and parting off (or levering off a hot-melt bond) also work of course but the method doesn't ring my chimes.

[KenW]

Where's Ken:? - he must be chewing his knuckle off by now - this is his pet topic - holding bowls in expansion mode.:D:D:p

Cheers
Dave, you are correct, this is one of my pet topics.
As said I have been away,and just about to go away again.
has covered most of my views.
After seeing several people hurt, as their bowls exploded in thier faces. I never ever, hold anything using expansion mode.
I try to promote safe and accurate woodturning, holding work in expansion mode doesn't address either of these points.

[robo hippy]

Ken,

On this matter, given your stance, I guess we have to agree that we disagree. If using an expansion mode was inherently dangerous and inaccurate, then I should have been encountering problems with things flying off the lathe, blowing up, and not being able to remount them for turning the inside without there being a lot of run out. In the over 10 years and thousands of bowls where I have been using expansion exclusively, I haven't had these problems. While dumb luck could play a small part, this is way to high of numbers to attribute it all to that.

Have I had bowls blow up? Of course. Any one who turns bowls has. It is like turning through the bottom. If you haven't done that, then you have never turned a bowl, or just haven't done it yet. I have never had a bowl blow up in my face. I learned early on to stand out of the line of fire. I have never had a bowl blow up that was caused by turning in the expansion mode. I have had them blow because of tool catches, and some rather spectacularly. I have had them blow up because of flaws in the wood. These explosions were not due to the method of mounting, and no matter which way they were mounted, it would still have happened.

Have I had bowls come off while I was turning in the expansion mode? Sure. This was early on before I had learned to make the recess properly. I still have one come off once in a great while while coring. It is because I made the recess a bit shallow. Another case was with a very hard and brittle wood (Mountain Mahogany) and a case of too shallow again. I haven't had a bowl come off while turning in years. I do still have them come off rarely while coring. This is because of one of 2 reasons, flaws in the wood, or too shallow of a recess.

As to accuracy, my main problem is in reversing the bowls for coring and turning out the inside of the bowl. If my run out on the rim of a 16 inch bowl is more than 1/16 of an inch, I take it off and check for shavings in the chuck jaws, and some times rotate it 90 or 180 degrees. This solves the problem most of the time. Some times it is because I slacked up on pressure while I was tightening up the chuck, and the bowl slipped a bit.

If turning through the bottom is the accuracy problem, this is in measuring from the rim to the bottom of the bowl, and forgetting to include the depth of the recess.

If you tried the recess, and it didn't work for you, while it does work for me, it is because I figured out things about using a recess that you didn't. No other reason. I could probably teach you how to do it, but the tenon works better for you.

I do turn very aggressively. I will turn a 10 inch bowl at 1700 or so rpm, and use a scraper for roughing, removing shavings 1 inch or more wide. Please note, this is production turning, and not suitable for most people, and can be very dangerous. The recess is every bit as safe and accurate WHEN PROPERLY MADE.

robo hippy

[Calm]

Pull up a chair guys this one is just getting interesting:D:D - Your turn Ken :2tsup::2tsup:- boy i cant wait for the next episode.:cool::cool:

Cheers

[Frank&Earnest]

Yep, it is always worth waiting a bit before shooting off an opinion. :D I was going to answer Ken's post above starting with " I do not think anybody would seriously deny that expansion chucking is inherently less safe and accurate than some other methods..."
... and robo hippy appropriately chimes in to say just that. :D The problem, rh, is that absolutes are rarely correct and require a level of proof rarely attainable with our limited resources. While you can see above that I also had a positive experience with the method, it does not mean that one can extrapolate that to make assertions on the qualities of the method as compared to others. There will be better ones and worse ones.

What I was going to say to Ken is that, in the end, the issue is a philosophical one: what level of risk are we prepared to accept to obtain other benefits. After all, it is a fact that exposure to wood dust is detrimental to our health: to what lengths are we prepared to go to reduce it? Would you stop turning because it is less safe than not turning at all?

[Old Croc]

Interesting points of view, "what is snow"? :D hot as hell up here at present.I only use contracting as it is so much easier to finish the base by tidying up the small grip ring. I only use about 3mm or 1/8". To mark up the base for the correct diameter, i have made up a series of guages to speed it up. These consist of a piece of resin board with masonry nails glued into the edge for the centre and one each for the different closed diameters of all my different jaws,
regards,
Crocy.

[Pat]

Almost as good as the old "Pins or Tails first" debate:U

I recognise the differing points of view and am enjoying the well assembled arguments. I am also happy at the mature tone of the arguments.

I'll grab some popcorn and beer for the next installment.

As a declaration, I use both methods depending on the timber first, then inclination.

[stuffy]

:rant:
slap2:
It is ignorant to say one method is always better than another.
In the end we all choose the method that suits us best but the factors that determine that vary for each person.
For production turners it's getting the best result in the shortest time that matters, for us amateurs we can fiddle around for hours trying to use the "best" technique.

Before we can judge one way as better than another we have to be proficient in both and know the advantages and disadvantages under different conditions.
For example how many people turn a bead with a skew? Do you give up because it's potentially dangerous or has a higher failure rate? Or do you learn to do it properly and enjoy the accuracy and better finish it provides?

:(

[jefferson]

I will enter the so-called debate - with some reservations.

I've had smallish bits fly / fall off the lathe due to tenon / recess failure. No damage done, aside from some to pride.

But make no mistake, Ken W. teaches extensively and always takes the SAFE option. So I listen a lot when he says xxx approach is best, particularly for beginners / intermediate turners.

Aside from being an above-average turner, Ken always aims at the lowest common demoninator. A good approach IMHO. Like most demonstrators, he bleeds a little, but his eyes in particular are still in tact.

[Calm]

.

HE's back

Where you been Grasshopper we missed you
:fireworks::thewave:

:wave:


sorry about the hijack ----- not really

Cheers

[Frank&Earnest]

I will enter the so-called debate - with some reservations.

I've had smallish bits fly / fall off the lathe due to tenon / recess failure. No damage done, aside from some to pride.

But make no mistake, Ken W. teaches extensively and always takes the SAFE option. So I listen a lot when he says xxx approach is best, particularly for beginners / intermediate turners.

Aside from being an above-average turner, Ken always aims at the lowest common demoninator. A good approach IMHO. Like most demonstrators, he bleeds a little, but his eyes in particular are still in tact.

Hi Jeff. Yes, we all had well identified flying objects, it goes with the territory :D. I owned up to one just recently. But if my skills do not allow me to turn a 150mm plate with a sub-mm edge and a 3mm thick tenon as a foot I can hardly blame the chucking method, can I? :wink:

[NeilS]

A belated thought on the topic.

The 'orthodoxy' about contraction being a safer method of holding a blank for inside turning developed before swivel heads lathes. The swivel head allows you to stand in front of the bowl as you turn the inside, which puts you out of the firing line. It also puts the toolrest between you and the blank.

Of course the blank may still ricochet around the workshop and get you, eventually... :U

However, in group settings such as classes, turn-fests or demonstrations, with people standing in every direction, there is still a danger to bystanders. It's therefore understandable that those that teach and demonstrate in such settings teach and practice the safest chucking option.

What we and they do in the privacy of our/their own workshops may diverge from this orthodoxy.

.....

[rsser]

Good thoughts Neil.

I'd say again that how hard you go in with the hollowing is a big factor; it's not hard to overdo it and lever a bowl recess out of the jaws. For a production turner, going in hard is a matter of their livelihood; they can't afford to pussy foot around.

Jeff commented once something like that I look light cuts or went slowly. Well, I'm not in a rush. On the other hand, we were working a bit of his rock hard redgum! Recently with a 30cm lump of green Deodar and a 5mm recess, I was using most of the left wing of a 5/8 gouge and going gangbusters.

I have also never bothered to match the recess to the jaws OD while circular, and typically use recess depths of 3-4mm. It seems 4 vertical points of contact with the jaw faces flush against the hole is enough. However, with Terry Martin's shallow recess of 1.5mm I'd certainly think about matching the circumferences to spread the pressure.

[tea lady]

I think this is of of those "depends" sort of debates. My recent cedar turnings I have been doing using expansion mode, but with quite a wide (As apposed to deep) foot ring. Mainly cos I wanted the foot ring ultimately to be thin but out nearrer the edge, but I've only got a little chuck. But turning a small bowl with a cedar off cut I had a grip on a bowl using compression, and I think it crushed the wood and precipitated the whole foot breaking off. Cedar is the other end of the hardness spectrum, and expansion mode actually gives it more wood to hold on to. :shrug: Blackwood s another wood that you need to be careful off. I also don't turn a square bottom corner to the outside of the foot ring, but a curved profile so it has support from the surrounding wood. :cool:

[rsser]

Yes, cedar is soft (least your WRC and Aust red are) so matching circumferences in compression mode will reduce crushing of fibres at the jaw ends and spread the load. Again, in this mode if you are using d/tail jaws, matching the foot angle should provide a keyed joint. That may of course not suit your design intention so remounting and final shaping of the foot is called for.

Blackwood doesn't usu give me any grief but the pieces you had from my group buy were on the brittle side. Air dried but in a tin shed with one long side open so at a guess it got fairly warm at times.

[KenW]

Ken,

On this matter, given your stance, I guess we have to agree that we disagree. If using an expansion mode was inherently dangerous and inaccurate, then I should have been encountering problems with things flying off the lathe, blowing up, and not being able to remount them for turning the inside without there being a lot of run out. In the over 10 years and thousands of bowls where I have been using expansion exclusively, I haven't had these problems. While dumb luck could play a small part, this is way to high of numbers to attribute it all to that.

Have I had bowls blow up? Of course. Any one who turns bowls has. It is like turning through the bottom. If you haven't done that, then you have never turned a bowl, or just haven't done it yet. I have never had a bowl blow up in my face. I learned early on to stand out of the line of fire. I have never had a bowl blow up that was caused by turning in the expansion mode. I have had them blow because of tool catches, and some rather spectacularly. I have had them blow up because of flaws in the wood. These explosions were not due to the method of mounting, and no matter which way they were mounted, it would still have happened.

Have I had bowls come off while I was turning in the expansion mode? Sure. This was early on before I had learned to make the recess properly. I still have one come off once in a great while while coring. It is because I made the recess a bit shallow. Another case was with a very hard and brittle wood (Mountain Mahogany) and a case of too shallow again. I haven't had a bowl come off while turning in years. I do still have them come off rarely while coring. This is because of one of 2 reasons, flaws in the wood, or too shallow of a recess.

As to accuracy, my main problem is in reversing the bowls for coring and turning out the inside of the bowl. If my run out on the rim of a 16 inch bowl is more than 1/16 of an inch, I take it off and check for shavings in the chuck jaws, and some times rotate it 90 or 180 degrees. This solves the problem most of the time. Some times it is because I slacked up on pressure while I was tightening up the chuck, and the bowl slipped a bit.

If turning through the bottom is the accuracy problem, this is in measuring from the rim to the bottom of the bowl, and forgetting to include the depth of the recess.

If you tried the recess, and it didn't work for you, while it does work for me, it is because I figured out things about using a recess that you didn't. No other reason. I could probably teach you how to do it, but the tenon works better for you.

I do turn very aggressively. I will turn a 10 inch bowl at 1700 or so rpm, and use a scraper for roughing, removing shavings 1 inch or more wide. Please note, this is production turning, and not suitable for most people, and can be very dangerous. The recess is every bit as safe and accurate WHEN PROPERLY MADE.

robo hippy
Sorry for the slow response, I have been away again, still.

Before we agree to disagree, I will try and expand on my comments.

As Jeff pointed out, when I post a comment / advice I assume that a beginner will be reading it. Whenever I demonstrate I also assume that there a beginners in the audience.

I therefore try to show the safest most efficient way of performing a task.

I teach beginners / novices on a weekly basis at my local club and my own workshop, therefore I have a fair idea what they do wrong.

Why I don’t like expansion mode for mounting a bowl (keep thinking beginner).

An internal spigot is harder to make than an external. Ern correctly stated that making a special tool makes this job easy, beginners rarely make tools, they just want to make shavings.

Therefore they make the spigot using a gouge to start and a skew as a scraper to finish.

Given that most starter skews are sharpened at 20 to 30 degrees, they rarely get the angle correct.

If the internal spigot doesn’t have a sharp bottom corner, the face of the jaws may not touch the bottom of the recess.

If the recess is made the correct size (chuck jaws form a circle) you cannot see the face of the jaws to see if they are correctly seated. (I am aware an experienced turner can feel if the jaws are seated properly).

This is the first safety / accuracy issue.

When part of the jaws are hidden inside a recess, there is no easy point of reference to measure from, making it easy to go through the bottom.

Second accuracy issue.

To overcome this problem most turners leave extra wood in the base of the bowl, making it bottom heavy.

When the bowl is spinning you cannot see the chuck jaws, this makes getting a line on the inside and outside a bit of a guess.

I production turn bowls for a number of galleries, and none of them will except work with any signs of how it was held in the lathe.

To remove evidence of an expansion spigot requires a fair amount of wood to be removed at the base, changing the original line of the bowl and creating a lot of extra work.

None of these problems occur with compression mode.

Most of my competition bowls are around 1mm to 2mm thick, it is not possible to hold a bowl this thin in expansion mode. It is however quite safe in compression mode (although I prefer face plates).

You said that a few bowls have exploded on you, due to unseen flaws. I have seen many, and more than a few people hurt. The odds of this happening in expansion mode are far greater than compression, especially if you turn thin bowls.

Our hardwoods often have invisible cracks. If one person is hurt by an exploding bowl, that’s one too many.

I have only made hundreds of bowls, not thousands, however I have never gone through the bottom of one.

This is more likely due to the fact that I am anal about templates, jigs and measuring, and nothing to do with mounting methods.

To me, scrapers are, and always will be finishing tools. I think it would therefore be irresponsible of me to say your way of making bowls is safe or accurate.

I would however agree that you should be able to make bowls in your workshop however you see fit.

[powderpost]

Interesting discussion. I taught woodturning for many years for TAFE. In those days the Woodfast super chuck was the "in" thing. There were a lot of failures by students due to poor technique, blunt tools and over zealous cuts. I used the same chuck successfully for many years.

I have used the scroll chuck, mainly in expansion mode, successfully for many years, on platters out of 19mm thick timber, with 2mm recess. These start on a screw chuck with the outside profile coincides with the bottom of the recess. That overcomes the problem of not knowing where the bottom of the recess is.

I will not leave chuck marks on the bottom of a bowl or platter.

I have found the best method. in my opinion, for what I do, is the glue block method far superior. A system used before the advent of current range of chucks that eliminated the need to wait for glue to set properly. The size of the foot is determined by me, not a chuck manufacturer. To clean up the foot, I rechuck using the Longworth chuck. Previously, I used a disc of 19mm ply with screwed on blocks to hold the bowl in place.

The bottom line is that all these chucks have an application but do require an understanding of their limitations, sharp tools an an efficient technique.
Jim

[robo hippy]

Ken,
After reading your response, I could go through and counter every point you made. Then after thinking about it, realized that I encountered every one of those points with both a recess and a tenon. I solved every problem with both ways of mounting bowls, and can teach both methods. I just prefer a recess. I can find no inherent advantages to either way, whether the turner is a beginner, or experienced. For me, it was a matter of there was a problem, and what was it that I was doing wrong? With some experimenting, I solved the problems, and I can teach others my tricks, which aren't really special or difficult. I will never forget one of our club meetings when the topic was a round robin (open) discussion of mounting techniques. The recess was mentioned, and several turners spoke up about how they had tried it and it didn't work so they went to some thing else. Me, being pretty much a newbie, kept silent. I had been using it with no problems for a while, and couldn't figure out why it didn't work for them.

We do turn different styles. I prefer green wood turned to final thickness (1/2 inch max, which I think is about 10 mm), and then let it dry and warp before sanding. The more it warps, the more I like it. These are bowls intended for daily use. I sell directly to people at shows, and don't sell to galleries. I did go through a phase where I was turning as thin as possible, and used a recess on them as well. Again, I was able to work out your points so that a recess worked. My bowls probably wouldn't sell well in a gallery as they are too utilitarian, while the really thin ones don't sell well at my shows, plus, they tend to want to blow away. I doubt that you teach beginners to turn that thin. I consider that a more advanced project.

I have never understood the obsession with the 'finished' bottoms. I leave the recess, it is cut cleanly, sanded, signed, then a soft (Mahoney's Walnut oil) oil finish put on it. It makes no difference to the people who buy them. They don't sit flat, even if I turn the bottoms off. Wood moves, and one day it might sit flat, and the next day not. There is no mystery about turning off the bottoms, as there are only so many methods of doing it. It is an extra production step, and I can't charge any more for it. Some turners are very picky about it. I figure this is from the old habit of leaving the screw holes from a face plate, or the hole from a screw chuck which was plugged, or had a sticker covering it. If I was turning a very thin bowl with a tiny bottom/base on it, I would turn off the bottom. Some of my favorite bowls warp so badly that I couldn't turn the bottom flat if I wanted to.

I am curious if your stand on the recess comes from your attempts to use it and not getting along with it, and/or watching beginners attempting to mount bowls. I don't work with many total beginners as I find it difficult to anticipate the mistakes they will make. I have been amazed at some of the things they will try just because they don't know any better. But, then, that is how I learned to use a recess. Hmmmm.........

As to the scrapers, long before I started turning, they were the go to tool for bowls. I started playing around with them just to see what those who knew how to use them knew that I didn't. They are an excellent tool for roughing. Think of it this way, the primary roughing cut on bowls is a scraping cut, with the flutes rolled side ways. What better tool to do a scraping cut than a scraper? For finish cuts, I NEVER have the scraper flat on the tool rest, especially any where near the rim on the inside of the bowl. I have lost more than one bowl by the vibrations that happen with this cut and damaged more. Always at a shear/45 degree angle. Much less pressure on the wood and a much finer cut.

This is another one of those occasions where I wish the Star Trek technology was available and I could beam down under for a week or two turning session. I haven't met any one that I couldn't learn some thing from yet (some thing I learned from my Dad).

My biggest advise to beginners are start slowly, slow speed on the lathe, and small cuts. High speeds and heavy cuts make for rather dramatic blow ups. Stand out of the line of fire. I learned this from turning a lot of sloppy wet wood.

robo hippy

[rsser]

This is a bit beside the point re this discussion but for many of our woods (even green) roughing out with a scraper would be an exercise in frustration. They're just too hard. I was gobsmacked when I read Nish's Creative Woodturning about this use of scrapers.

As for a gouge actually scraping when you use it to hollow, as far as I'm concerned if the bevel is rubbing it's cutting.

To be a bit provocative, a scraper taken straight off the dry grind wheel is also cutting, with a jagged edge standing upright (aka the burr).

[KenW]

Jim,
Just like you, I rarely use a chuck to make a bowl.
I glue a scrap of ply to my blank and screw on a small face plate. This alows me to turn the outside and inside in one operation. I reverse the bowl onto a ply disk to clean up the bottom.This is also the way I preper to teach bowl turning. Beginners however seem to want to spend their money on chucks.

Robo, Ern has a good point about our wood, and I never turn green. One on my favoutite woods is Red Mallee Burl, if you try to rough it with a scraper it will tear out several mm deep (1/8"or more).

If a bowl is going to sell in a gallery for large prices it has to look special. The bottom needs to be finished so it matches the rest of the bowl. I always carve three small feet on the bottom of my bowls, this stops them rocking as the wood moves.
If you went to this much trouble with your bowls you would go broke.

I also use scraping cuts (shearing) with my bowl gouge, when roughing out a bowl, but only on the outside.

It would be fun to turn together and exchange ideas, I know we would both learn something from it. It would also give you a chance to try some hard, cranky Aussie wood.
Maybe one day.

[NeilS]

First rate thread this one.

Valuable input from everyone and conducted in the best spirit of the forum.

The aesthetics of the foot recess and the current influence on this from competition judges and galleries deserves further discussion, but in a separate thread (which I might start another time).

.....

[NeilS]

To be a bit provocative, a scraper taken straight off the dry grind wheel is also cutting, with a jagged edge standing upright (aka the burr).



Seems to me to be so, Ern.

Viz attached diagram.

.....

[Tim the Timber Turner]

Neil

By my definition both drawing are showing a scraping action.

There is no support or control of the cutting edge by the bevel.

With regard to the cutting/scraping discussion I’ll add the following.

I hog out the centre of most of my bowls with a scraper. A 10mm round nose held in an arm brace. If the timber is worth it, I’ll bowl save.

The outside I'll turn with a gouge. I currently favour the Woodcut double ended 13mm bowl gouge held in a collet handle.:2tsup:

Reason for the arm brace is that it’s quicker and puts less strain on my elbow and forearm than a gouge. This is more so in hard desert timbers and timbers like mallee burl.

My arms and elbows are showing wear and tear of too many years of standing at a lathe.:C

I probably only got another couple of thousand bowls left in my right elbow. (I wish).:roll:

Cheers

Tim:)

[KenW]

Neil

By my definition both drawing are showing a scraping action.

There is no support or control of the cutting edge by the bevel.

With regard to the cutting/scraping discussion I’ll add the following.

I hog out the centre of most of my bowls with a scraper. A 10mm round nose held in an arm brace. If the timber is worth it, I’ll bowl save.

The outside I'll turn with a gouge. I currently favour the Woodcut double ended 13mm bowl gouge held in a collet handle.:2tsup:

Reason for the arm brace is that it’s quicker and puts less strain on my elbow and forearm than a gouge. This is more so in hard desert timbers and timbers like mallee burl.

My arms and elbows are showing wear and tear of too many years of standing at a lathe.:C

I probably only got another couple of thousand bowls left in my right elbow. (I wish).:roll:

Cheers

Tim:)
Tim, I agree with you, both drawings are scraping. The one with the grinder burr is a bad idea IMHO, I think we have been down this road before.

You need an arm brace, poor old fellow you must be getting old and wearing out.

[rsser]

Yeah, Tim, join the decked and the wrecked members; we should start our own sub-forum ;-} Ken can't lift a terrier; Neil has to monitor his energy carefully, and I can't even wipe my backside with the best tool.

...

This comes down to microscopics. My reading is that with a grinder or even honed burr on a scraper, the thing won't work unless that turned up edge is penetrating the wood. So the wood side of that edge is providing cutting support. Call it a micro-bevel if you like. There'll be SFA in it of course, so any slight drop or rise at the end of the handle will lose it.

OK. Perhaps a bit on the Jesuitical side but it is Sunday ;-}

[Tim the Timber Turner]

Tim, I agree with you, both drawings are scraping. The one with the grinder burr is a bad idea IMHO, I think we have been down this road before.

Jees Ken, now I'm realy worried.

Next thing will be agreeing with me and I won't have anyone to disagree with.

You need an arm brace, poor old fellow you must be getting old and wearing out.



Ken

If you live a clean healthy lifestyle, like me, and keep off the grog (and in your case the roof:oo:) You may live long enough to need an arm brace.:D)

On a serious note I'll buy into the scraper burr argument.

All this stuff about burrs on scrapers is bull sh*t.

This is how I see it.

You grind a scraper and you get a burr.

You either hone it off or you leave it on.

If you leave it on, after 10 seconds of using the tool, you have no burr left.

You are then cutting with the intersection of the top and and the bevel. This is whatever angle you ground the tool at. 45 degrees = very sharp and gets blunt quick, 15 degrees = not so sharp but takes longer to go blunt.

If you don't belive me try it for 10 seconds and see if you have a burr left on that part of the tool. Well you might get 20 seconds on soft timber.

Ern, No personal offence ment but, sorry but micro bevels = more Bull Sh*t.

How can you tell if you are rubbing a micro bevel??

Thanks Ern I'm safe now as I have you to disagree :no:with.:)

Cheers

Tim:)

[RETIRED]

Poor Tim. :wink::D I agree about the burr bit too.

[rsser]

Hah, small letters for a big turner. You don't get away with that ole mate!

Tim, there's whatever practice of turning that works for you. Fine. Whatever. There's also an emerging science of scraper use. PM me if you want to read some of it. It may surprise you, as it did me.

[Tim the Timber Turner]

Hah, small letters for a big turner. You don't get away with that ole mate!

Tim, there's whatever practice of turning that works for you. Fine. Whatever. There's also an emerging science of scraper use. PM me if you want to read some of it. It may surprise you, as it did me.

Thank but no thanks Ern.:no:

I'm too busy making things on my lathe.

Cheers

Tim:)

[Tim the Timber Turner]

Poor Tim. :wink::D I agree about the burr bit too.



Speak up man.

You are a long way away and I'm a bit deaf. (along with my crook elbow and dicky leg).

I had to turn your volume up so everyone else can hear you.

Now you have gone and done it, you have publicly agreed with me.

Cheers

Tim:)

[Calm]

What a pack of pussies you lot are - this thread had the makinbgs of a good ol stoushe but no you are like a few old chaps - oh my knee - my arm-brace - i use tenons not recess's - i prefer glue blocks - oh you agree do you - bah get into it and tell him what you really think.

Bloody chaps you lot - and we know what the "rules of the shed " say about chaps:D:p:p

[Chipman]

I find this discussion really interesting, especially since I am a novice turner. I supect that many of us find a way that works for us and then refine it. I have used both expansion and compression methods (as well as glue blocks etc) and with due care all work well.

Curently my preferred method for a bowl is to
1.Bore a hole the required depth with a forstner bit into the top of the bowl (will become the inside) and mount it on the chuck with dovetail jaws. Plenty of wood thickness/diameter to avoid it splitting.

2. Shape the outside and produce a tenon on the free end (to become the foot of the bowl) I prefer this for the reasons some have discussed already.

3. When the outside is finished, reverse chuck it and hollow out the inside and finish it.

4. Often use a disk sander (bench type) to take most of the tenon off and then reverse mount it to clean up the foot (often use a jamb chuck or Cole Jaws (esential for ME to wrap duct tape around the mounting blocks to avoid finger injuries, especially if I slip while sanding))

Any comments/advice appreciated.

Chipman

[rsser]

Thank but no thanks Ern.:no:

I'm too busy making things on my lathe.

Cheers

Tim:)

Are you?

So tell me, how much do you like sanding?

There's busy, and there's efficient :rolleyes:

[artme]

Burrs are ########!! I remember bringing this up before!

If you take a tool straight from the grinder with a burr edge on it, that burr will last not time at all once the tool is applied to the work. To pretend, theorise and think that it does otherwise must bring your cognitive and reasoning powers into question.

[artme]

Must also agree With Ken's comments on the recess. I noted this earlier on in the thread. Some judges simply will not countenance any sign that the work was somehow held in order to complete it.

Is this only true of woodturning judges?

[robo hippy]

The difference in burrs on tools is like the difference in profiles on gouges, there are many variations.

Scrapers will cut fine with the burr honed off. You can do scraping cuts (both pics in the attachment are scraping cuts), you can ride the bevel, and shear cut with it.

There are huge differences in burrs from grinders. If you just kiss the bevel on your grinder wheel, you get a very delicate burr that is gone in seconds. If you use a bit of a push into the grinding wheel, you get a more durable burr. With my CBN wheels (see thread on diamond grinding wheels), I get a burr that is as durable as any cutting edge on any of my gouges. Excellent for heavy roughing, riding the bevel cuts, and shear/finish cuts.

Then, there is the burnished burr. Hone off the grinder burr, then use a burnisning tool to create a burr like on your card scrapers, which most of us who do flat work are familiar with. I was never able to get a good burr from a round burnisher (screw driver rod, drill rod, or other really hard metal like shock ablsorer struts). With a trinagle burnisher, I can raise a good burr. Lee Valley/Veritas tools has a table mounted burnisher with carbide rods that you can buy. If you gently kiss the surface of the bevel, you get a dainty burr, that is great for shear/finish cuts, but not so good for roughing cuts. If you press harder, you get a more sturdy burr that is excellent for heavy roughing and finish/shear cuts. The burnished burrs seem to curl over more than the ones from the grinder, and don't work as well for riding the bevel.

Now, I know some of you are wondering about riding the bevel of a scraper. I may be crazy, but I'm nuts. It is a specializes tool I have for the center bottoms of the inside of my bowls. The profile is a quarter round, or swept back design to the left side like an 'inside' bowl scraper though it comes to more of a point. It is almost like half of a swept back profile on a gouge. I would never use a round nose scraper for this cut as I want to be cutting on the tip of the scraper, not high up on the center of it as this will have a high risk of catching. Bevel is steep like a bottom of the bowl gouge, and gives a high shear angle. I could use it on the outside, but don't, as a shear cut with a scraper or gouge is easier.

I need to win the lotto, so I can ship myself and a container of my woods to you, and return with some of your woods. I did a trade once with a guy there who makes penny whistles and he was looking for American woods with specific gravity of 1.0 or higher. I had some Mountain Mahogany (not mahogany, just called that because of the color) which was growing at 8500 feet just outside of Las Vegas. On the flooring hardness scale, Oak is about 8, bubinga is 12, and lignum is 20. This stuff is at 18. He was telling me about heading out into the desert for some acacia with a specific gravity of 1.5. Does your postal service have flat rate shipping boxes like ours? I can send 20 pounds max for pretty cheap, and would be willing to trade.

robo hippy

[rsser]

Burrs are ########!! I remember bringing this up before!

If you take a toll straight from the grinder with a burr edge on it, that burr will last not time at all once the tool is applied to the work. To pretend, theorise and think that it does otherwise must bring your cognitive and reasoning powers into question.

As RH says, burrs ain't burrs, but one of the first studies, done by Farrance, indicates that on a spindle gouge the burr off a dry grinder was hard, compacted, difficult to hone off, and lasted several minutes on ash (Fraxinus). If you'd like to test your own reasoning powers by studying the test report, PM me your email address.

PS I did my own microscopic edge study of a scraper burr raised on dry grinder. Then compared it with the same tool slammed into a bit of hardwood. No detectable diff. Partly this was a test of the old chippy's way of getting rid of a burr or wire edge after sharpening a bench chisel, and it's not the same bevel angle we're talking about, but it was enough demo for me of how hard the burr can be.

[Tim the Timber Turner]

Are you?

So tell me, how much do you like sanding?

There's busy, and there's efficient :rolleyes:

Ern

I don’t think I have ever met anyone that enjoys sanding, not for any length of time anyway.

As for being efficient, I must have been doing something efficiently because I have made a very good living for 20 years, all with things I have made on my lathe.

In these 20 years I have educated my kids and built a small business with regular customers in 10 overseas countries. All this with stuff I made on my lathe.

I wouldn’t have achieved any of this if I spent all my time worrying about what sort of burr I had on my scraper.:no:

Having said that I will defend to the death your right discuss and research scraper burrs for as long as you live.

Whatever rows your boat. We all get something different out of our hobbies or in my case a hobby that got out of control.

Woodturning has been very good to me; I make a good living; I have a great lifestyle and have met and enjoyed the company (along with a few glasses of red) many hundreds of like minded turners from many parts the world.

Duty now calls and I’m heading off to York Peninsular fishing for a few days. That’s a lie really, I’m not that keen on fishing. A white sandy beach, a good book and maybe a small glass of red. Or two. Life can be tough at times.

Cheers

Tim:)

[rsser]

Sounds good Tim; hope the weather is kind to you.

FWIW, I was a honing sceptic re turning tools in general and have posted against it in this forum. Wasn't what I learned; didn't see any professionals doing it. Only one ref to it, in one of Darlow's books. Was happy with my way of doing things.

Well I've had to eat my words. When a turner like Alan Lacer does the microscopic studies of edges and resulting finishes, I take notice. When our local pro's, Ken W and Vic Wood, in the shear scraping thread, mention that they lap the top of their scrapers, that's worth reflecting on.

As my hands are slowly weakening due to age (give or take a broken wrist in the meantime), anything that'll give me a cleaner finish off the tool and reduce sanding is worth a close look. Shear scraping is light work; wielding a power sander is heavier work.

[robo hippy]

This is a bit beside the point re this discussion but for many of our woods (even green) roughing out with a scraper would be an exercise in frustration. They're just too hard. I was gobsmacked when I read Nish's Creative Woodturning about this use of scrapers.

As for a gouge actually scraping when you use it to hollow, as far as I'm concerned if the bevel is rubbing it's cutting.

To be a bit provocative, a scraper taken straight off the dry grind wheel is also cutting, with a jagged edge standing upright (aka the burr).

The gouge, because of the rounded nose, and wings can be scraping (wings) and shear cutting (nose) at the same time. You can have the tool at the same angle, and make the same cut, rubbing the bevel, or not rubbing, depending on where the handle is relative to the cut and wood. This can be done only on the outside of the bowl, and not on the inside, because of the differences between the concave and convex surfaces. Well, maybe you could do it on the inside, but it would be difficult, and you couldn't do it down inside the bowl. The wood doesn't really care if the bevel is rubbing or not, the angle the cutting edge is presented to the wood and its rotation is what makes the difference in how the wood cuts, Rubbing the bevel or not doesn't make any difference in how smooth the surface is, or how clean the wood cuts. The only difference I have been able to notice is if the bevel is rubbing, you burnish the surface of the wood, which does make it more shiny.

The differences between a pushing cut and pulling cut comes in here when done on the outside of a bowl. Almost all cuts on the inside of a bowl are push cuts, while on the outside, you can do either. A pull cut you generally are not rubbing the bevel, while on a push cut, you do rub it. You can again, get the same finished surface with either cut.

I do know that I am pretty much alone on this thinking, but think about it a while. It may make some sense.

Boy, did we get side tracked or what?

robo hippy

[Frank&Earnest]

I had some Mountain Mahogany (not mahogany, just called that because of the color) which was growing at 8500 feet just outside of Las Vegas. On the flooring hardness scale, Oak is about 8, bubinga is 12, and lignum is 20. This stuff is at 18. He was telling me about heading out into the desert for some acacia with a specific gravity of 1.5. Does your postal service have flat rate shipping boxes like ours? I can send 20 pounds max for pretty cheap, and would be willing to trade.

robo hippy

Looks like your desert acacias are on par with our desert acacias, then, in the 15-20 range. But specific gravity 1.5... are you sure? IIRC haven't seen any here over 1.3. Can anybody confirm either side?

[rsser]

Did we get sidetracked?

Yep, most enjoyably ;-}

Whatever unconscious competence I had with expansion mounting is now blown out of the water and next time I do it I'll be thinking about all the things that might go wrong :( which is not a bad thing.

[Sturdee]

Shear scraping is light work; wielding a power sander is heavier work.

Ern,

In that case you might be interested how TTIT has his power sander (http://www.ttit.id.au/gadgets/gadgets.htm) set up with a long flexible shaft.


Must be easier to handle.


Peter.

[rsser]

Thanks Sturdee.

I did try to copy Vern's neat idea but couldn't find a shaft to take a chuck big enough for my discs that wasn't also junk.

Now I use a 90 degree angle drill which I don't have to fight so much to keep in the right place as with a std lekky drill.

[Sturdee]

T
I did try to copy Vern's neat idea but couldn't find a shaft to take a chuck big enough for my discs that wasn't also junk.




Ern,


I picked up a flexible shaft many years ago from Bunnings for use with an electric drill. One end has a comfortable plastic handle grip with a standard 10mm drill chuck and the other end is clamped in the drill, so you can drill around corners in awkward places. Used it a few times for that but it's on my roundtoit list for adapting for sanding.


Peter.

[Frank&Earnest]

I did try to copy Vern's neat idea but couldn't find a shaft to take a chuck big enough for my discs that wasn't also junk.



I had the same problem with a good German flexible shaft, and IIRC Neil S mentioned it also. The 6mm chuck couldn't take the 50mm sanding pads I bought from Jim Carrols. My solution was to grind off the corners of the exagonal shaft of the pads. Works a treat.

[rsser]

Ah. So simple. :doh:

[NeilS]

My most recent flex shaft from UK has been the most successful. At current exchange rate it was a reasonable price. Unfortunately seller is about to close down. Anyway here is link.

PRO QUALITY FLEXIBLE DRILL SHAFT FREE UK P&P on eBay (end time 11-Apr-10 12:39:48 BST) (http://cgi.ebay.co.uk/PRO-QUALITY-FLEXIBLE-DRILL-SHAFT-FREE-UK-P-P_W0QQitemZ380205592729QQcmdZViewItemQQptZUK_Hand_Tools_Equipment?hash=item588604f099)

After some experimentation I have managed to allow reverse direction without the chuck unscrewing.

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