Minimising sanding on bowls etc

[rsser]

So we spend a sh*tload of time sanding and it's a pain in the proverbial.

http://www.woodworkforums.ubeaut.com.au/showthread.php?t=51740

At least a good thing about it is that you have a margin to retrieve shall we say some roughness in technique.

But how to get a better finish off the tool?

Over to you ... :U

[Cliff Rogers]

......But how to get a better finish off the tool?.....
Go straight to the 80grit gouge on an angle grinder. :2tsup:

Sorry, it is beer o'clock. :D

[rsser]

Champers o'clock down here :2tsup:

(New contract will keep the kid in baked beans and her dad in a few gadgets for six months :B .)

So, Cliff raises the modest question of THE PREPARATION OF THE TOOL EDGE :no: :no: :~ :C and then ducks out for an ale. Geez :doh:

[cedar n silky]

Well, apart from really sharp gauges, and chisels, (and good attitude and skills) I discovered something recently. I had a small "dent" in the tool rest, and I lived with it for a long time, but decided to file it out the other day after another one appeared. The odd lapse of concetration, and not holding the tool down, no doubt caught me out. Well it made a lot of difference, bcause the little dent was actualy being transfered to the wood!:doh: A good flat and true tool rest is a good start:2tsup:

[Skew ChiDAMN!!]

Turn something besides bowls? :innocent:

[powderpost]

Shear scraping with a sharp tool is the answer. Will reduce sanding time to about 25%, maybe less.
Jim

[BernieP]

G'Day all

After reading Jim's (Powderpost) comment on shear scraping went for a browse and came up with the following interesting article http://www.sydneywoodturners.com.au/site/articles/techniques/scraping%20bowls.html (http://www.sydneywoodturners.com.au/site/articles/techniques/scraping%20bowls.html) Makes it a lot clearer for me, hope all info is ok?

Cheers
Bernie

[reeves]

good point Ern.

As far as I can tell from experience and reading about such things is the same as Cliffs response, getting a better finish off the tool.

Nice sharp chisels will obviously help here, mainly scrapers or skew. Where they are sharpened with a wet wheel, dry white wheel or whatever, given its specific grade, will affect this. I used a diamond hone to keep my chisels sharp between grindings. Also when you are sanding taking the speed up in different grits can have a similar effect as going up a grit, try getting as high as you can in speed terms with each grit. Some epopel recomend going up to high grits in stages some just go to 240 or 400. I find it depends on wood hardness and texture.

The speed you are using combined with the hardness or texture of the specific wood will have a lot to do with it. Harder the wood higher the speed in general terms but i guess finishing the final scrape as yr highest speed helps. Reading yr wood in what its needs for a good smooth finsish could also help as could having the optimum angle as yr chisel touches wood.

Lets not forget about sanding sealer, i haved the specialist bowl turners nitrocelluose sealer and its easily the best thing i have used. Makes a great finish that last heaps longer than wax, oil or shellawax. A couple of coats and hit the high grit and yr there. I odnt use it all the time as its costly and more of a proffesional thing, also stinks like knocks u back with its fumes. The ubeaut sealer is pretty good tho not as industrial strength as the nitro.

so in summing up

1) consistently sharp finishing chisels
2) correct speed for final finish
3) correct chisel technique on final finish (watch raffan videos ;0)or shearscraping
4) correct speed for sanding
5)using sanding sealer on the lower grits or adpat its use before adding polish or finishing laquer

what do you currently use for finishing ?

cheers
john

[Skew ChiDAMN!!]

I'll second shear-scraping. :thyel:

Because I turn goblets that tend towards hollow-form shapes a bowl gouge is impractical, so I use oland style tools for aggressive hollowing and a scraper for finishing cuts.

I've also developed a habit of using the same two tools for turning the outside of my goblets, simply because they're what I have to hand. :- It's sheer laziness, I know, but it works for me and I hate sanding! :p

[rsser]

My two bits ... for bowl insides mostly:

Finishing cuts that are as fine as you can get them; fresh edge, small gouge, light cuts.

Avoid tool chatter, so aim for min. overhang.

Bevel rubbing with the gouge. This will often mean pushing the edge high above the rest before arc-ing down to the centre ... that bit always makes me nervous. Having one with a short bevel can be very helpful for 'turning the corner' and coming across the bottom. Or else use an Oland tool, a Munro or Proforme etc.

Stopping or slowing when the piece starts to flex (first thrumming then screeching = sanding nightmare).
Some use getting the fingers to damp it down from the outside. (One US turner has programmed his Stubby to vary the lathe speed as he turns so as to reduce flex).

Only use 1/3 the edge of a scraper (when flat scraping).

Aiming for pig tail shavings all the time with a gouge (no, some timbers won't let you).

When shear scraping, looking for fine strands, not dust.
Shear scraping can also be done off the wing of a gouge. On the outside this gives a less polished surface than cutting with bevel rubbing but depending on tool handle positioning can help refine a curve. (It works on the inside but produces corduroy.)

For hollowing: going down in stages, though with curved rests and small gouges this isn't usually necessary.

Only turn green wood :D

Added: for straight-sided insides like pencil jars, after drilling go in using the tip of a square scraper, not a side-scraper which tends to strip the fibres off.

John: what finish you ask. Whole new thread here but... DO except for pale timbers when its n/c sanding sealer (thinned) and wax. Shithot Waxstik for elm.

[Cliff Rogers]

Back again, about to climb on the roof & make more holes for another flue, this time for an exhaust fan over the hob.

The question was... how to get a better finish off the tool?

I agree with sharp tools & shear scraping but I'm going to add a few obvious but often overlooked things.

Practice, practice, practice & experience.

The type of timber you select.

Knowing how what tool works best on what timber.

Knowing what tool you can use the best & in what mode.

Number one things to avoid is tear out.

To avoid it, lets look at what causes it.

Tear out usually happens in end grain in softer timbers but can be made worse with brute force, ignorance, & cutting unsupported fibres. (AKA cutting uphill)

When you know what causes tear out, you can avoid it with a combination of the things mentioned above.

Number two thing to avoid is bruising, burnishing, compressing the side grain with the heel or bevel of the tool.

(Small qualification for the picky ones here... I know that you can do some nice spindle work with a skew leaving a burnished surface that doesn't need sanding BUT, look at the title, we are talking about bowls etc.)

To avoid it, lets look at what causes it.

Rubbing the bevel with too much pressure.

My opinion is that you can NOT burnish the surface evenly by rubbing it with the heel/bevel of the cutting tool at the same time as you are cutting so, to get an over all 'polished' finish, you will have to do some sanding & it all comes unstuck if some of the grain has been compressed & other parts haven't, so, in my opinion, if you want an even overall polished finish, you will need to do some fine sanding so, do NOT burnish the surface with too much tool pressure.

I can think of at least one other thing that causes compressed fibres that need sanding & that is the tips of measuring & marking devices.
Calipers, sizing tools, divider points, even hard tipped pencils can crush the fibre while marking out & that will lead to need for extra sanding.

Number three thing to avoid is chucking & re-chucking muck ups.

To avoid it, lets look at what causes it.

Crappy chucks. (out of round, mismatched jaws, loose fit, etc)
Poor quality mounts in/on the blank.
Over/under tightening the chuck.
Removing & refitted the piece in the chuck more times that is necessary.

The first one is easy to fix with money, if you don't have the money, you have to first identify what the problem is & see if you can come up with a work around or a repair for it.

The second requires attention to detail when you are cutting the foot/mount in the blank & practice/experience. I also recommend that you get or make a dovetail cutting scraper with an angle to match you chuck jaws & KEEP IT SHARP.

The third is just practice/experience, trial & error.

The fourth is obvious. Get your work flow in an order to avoid it.

OK, that is a start, I'll go & get stuck into my roof job now.

[Skew ChiDAMN!!]

Tear out usually happens in end grain in softer timbers but can be made worse with brute force, ignorance, & cutting unsupported fibres. (AKA cutting uphill)

Ignorance is the main one there, IMHO. Or lack of understanding of the principles, anyway. Once you understand the basics, brute force, uphill cuts and blunt tools become only minor factors, only done in cases of sheer frustration or the rare occasion when there's no real choice with the tools you have to hand.


Reminds me of a bloke I know, who saw me hollowing one of my bowls and couldn't help himself but correct my technique with the bowl gouge. "Start the cut from the middle and work to the edge," he said. Admittedly, it's good advice when applied to the average "open" bowl, but it's usually followed by an explanation along the lines of "so that the fibres are being supported by the ones underneath them." I wonder if he ever understood that last part? Because I was undercutting the lip of a semi-enclosed bowl, so the grain was inverted, as it were. (I rarely do plain ol' open style hollowing. :-)

I asked this bloke why he thought I was cutting the wrong way and he couldn't tell me anything except "that's the way he was taught by so'n'so." :rolleyes: Turning by rote? Not a good idea! :no:

[soundman]

Ive been doing a couple of bowl like things of late is fairly soft timbers in situations where the edge cuts from cross grain thru the end grain.

I supose you would call them cross grain bowls.....no matter how sharp the tool, which tool, or the presentation, the endgrain seems to bend over before it cuts making it difficult to ge a good finish on the end grain.

so by convoluted means I found the applying a very thin shelac sealer then cutting with the tool of choice I get a much finer finish and the end grain stands up to be cut much better.

we often think of a "sanding" sealer....... I'm now using a cutting sealer.... hell why not.

cheers

[powderpost]

I have found it much more efficient to scrape hard, hardwoods than to use a gouge. Softer woods are no problem with the bowl gouge. The 'bruising' from too much pressure on the softer woods can be relieved by wetting the bruised area with a well wetted rag. I have been using the shear scraping method now many years. I first saw it demonstrated by Del Stubbs at a woodturning convention in Brisbane in the late 70's. He actually finished inside a bowl without a tool rest. Spooky???? Not really because it is a gentle finishing cut. At a demonstration session I finished a "sugar" bowl using the shear scrape, the finish was good enough to polish. The timber was a bit of caribea pine. The last bowl I made was from cooktown ironwood. It was finished and polished without any sand paper at all.
Jim

[Alastair]

Hi Ern,

For a change I have some pics at hand, so herewith my take:

All of the above....

Good advice all, but having suffered at length, I have also done some borrowing, and adapting over the years, and have developed a technique which works (for me anyway!!).

For years, I used the conventional, square ground bowl gouge, probably at ~ 45 deg. This was too "blunt" to cut well across end grain, and too "shallow" to allow cutting on the bevel across the transition on deeper bowls, and thus was a compromise at best.

With building a jig, the possibility of more exotic grinds became a reality. As pioneered by Ellsworth et al, these variously named "Glaser", "Ellsworth" or "Irish" grinds are really designed for rapid stock removal while hogging out bowls. (pics 1 & 2). Some detail on this here: http://www.woodcentral.com/newforum/grinds.shtml
Being of miserly extraction, especially when it comes to grinding away good steel, I inched my way forward in this direction, trying as I went. While I never fell in love with the original concept and purpose, I did find an alternative technique, on my way to a more restrained version, (pic 3).

Outside is done in two stages. While aggressively roughing out shape, I use the BG with handle low, and flute "up", (ie conventional), with the left wing peeling away waste. I find this allows quite a heavy cut. Once the initial shape is there, I then change to holding the BG horizontally, handle out to the right, flute up, and take a slicing cut, using the 'vertical ' section of the right wing. The bevel is kept rubbing, while the handle swings from way across the bed to the right, out to clear of the lathe on the left, as the cut follows out to the rim of the bowl. I find this gives a clean 'slicing' cut across fibres, and also gives fine control while refining the bowl shape.

To explain the hollowing, see pics 5 & 6. As you can see, the angle at the 'wing' is quite fine, (maybe 30deg?), while that at the "bottom" is much steeper, (50deg??). Once into the bowl, I start a pass with the flute on top, cutting well out on the left wing. This means I am using the "sharp" part of the profile. With the handle horizontal, I am also taking a 'slicing' cut across the end grain, as above.
As I go deeper, approaching the transition from side to bottom, I rotate the BG clockwise, transferring the point of cut from the wing, down to the base of the flute. This changes the cutting angle to ~50deg, allowing the transition without having to move the handle out so far to the left, or coming off the bevel. You are also cutting with the "blunter" edge, but this is less critical, as you are cutting across the base, where there is little end grain. For this more conventional section, I also lower the handle slightly, coming back to horizontal as I approach the centre of the bowl.

The one disadvantage I have found, is that since you are cutting so well on the bevel, there is a tendency to "follow" a previous poor cut or ripple. To avoid this, I usually freshen the edge, and up the lathe speed before taking finishing cuts, and take these lightly with little pressure on the bevel.

As usual with these things, the description above is crystal clear to me, but probably confusing for everyone else, and I apologise for this!!!!

regards

[Cliff Rogers]

My bowl gouges all have a grind very similar to your first pic.

[rsser]

Thanks for the post Alastair.

I tried an Irish grind on my P&N Supa gouge and the wings ended up too fine to last long. Looks like the tool needs a more rectangular cross section with a shallow flute to get the grind pictured on woodcentral.

[Alastair]

Hi Ern

I agree. The flute shape of the P&N is not ideal, and that is also another reason why Ihave remained with a relatively modest version of the grind. The flute is too "U" shaped, compared to the Glaser/ Superflute profiles. What I find is that unless you are very careful in developing the profile, there is a tendency to "hook" the wings into a concave rather than a convex profile.

However, as I remain a fan of P&N in general, it is a case of adapting to suit.

regards

[rsser]

Exactly.

The finish on mine is poor too ... machining marks on a flat section of the flute wall.

But it's fine for hogging out.

[Alastair]

Not to mention the black hands when you turn a tannin-rich timber like Oak or Willow!!

[rsser]

Ah yes!

So many mornings when on the train I notice the black crud still stuck under the fingernails. Got used to public manicures now :(

[OGYT]

The finish on mine is poor too ... machining marks on a flat section of the flute wall.
Ern, I recently bought a couple of Doug Thompson Cryo Bowl Gouges - unhandled. The man that originally tested Doug's gouges, honed them to do the tests, so I thought it would be a good idea to hone mine to give 'em a try that way.:?
I built a honing wheel out of two layers of 20mm MDF, glued/screwed together, and mounted on my outboard spindle like a handwheel. I shaped one to fit the flute on my 5/8" gouge, and the other to fit the flute on the 1/2" gouge. I charge the MDF with rouge, reverse the lathe and lay the flute over the wheel. When honing, it polishes the flute like nobody's business. It works a treat for honing the inside of the flute and I can hone the bevel on the flat. :2tsup: The idea isn't original with me... saw it somewhere.
You might get those machining marks out with something like that. Just a thought.

[rsser]

Hi Al,

Thanks for the tip. Appreciate it.

I'm happy to use the P&N just for hogging out and with the little shed time I have, my technique ain't pretty but is fast.

I think I suffer from a kind of semi-religious aversion to honing ... if you know what I mean? Freshening the edge with a few swipes of a paddle hone is fine. But the bench already has a grinder with two kinds of wheel, a platform before one and a fingernail jig for the other, and beside that is a cheap GMC wet grinder (no longer used) on one end and a 3M type abrasive wheel on the other. ... as they might say in Tel Aviv, enough already ;-}

I have ordered an Ellsworth Signature gouge as I want to have the experience of a tool with a short bevel at the tip and kinda straight up and down at the sides. Don't know really whether the tool cross section and my fingernail jig will do that for me but the tool was on special at a place that goes 'Bingo' whenever they get an email from me.

Curiously, I got an orphan gouge in an old set of bench chisels I recently acquired, and it sure as hell looks like a turning gouge of the dimensions I mentioned earlier. It's a Berg of CS so I've been able to play with bevel geometry without seeing too many $$ sparking off the tip ;-} Good steel but not a patch on the Oz Titans for bench chisels ... but that's another story ... and I've got a bit of Reeve's sheoak waiting to be hollowed.

btw, I love your sig. Got a brother whose a tech whizz on concrete and I'll forward it to him if that's OK.
.

[scooter]

Like to see some pics of your setup, Al. :)