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Tiger
3rd April 2006, 02:28 PM
Dear all,

As we all know sharpness is everything in woodturning. I have tried woodturning sharp and not so sharp and sharp is definitely easier ;). Does anyone have any objective tests of sharpness that will help determine how sharp a woodturning tool is? I can get the skew-chisel sharp enough to cut the hairs off my wrist, but what about the gouges etc.?
I know I can tell by the end product ie the wood that is being cut but is there an another way without having to start the lathe and then go back to the sharpening equipment.

Hickory
3rd April 2006, 03:02 PM
I do two things, look at the edge, If it reflects light, it is still dull.... second I scrape my thumb across it. does it feel sharp, If so go for it, if not re-do the deed. You can't regrow hair fast enough to keep up that trial for long.

Approach the lathe and try, if it cuts right it is sharp if not then re-do the deed, There is no set point where sharp is sharp. Just do what you can and except what you can do. (I know there is a finite answer but be practicle here)

Also sudden pain and errupting blood often indicates a degree of sharpness when I feel of the edge with my sore thumb.

Tiger
3rd April 2006, 03:27 PM
I do two things, look at the edge, If it reflects light, it is still dull.... second I scrape my thumb across it. does it feel sharp, If so go for it, if not re-do the deed. You can't regrow hair fast enough to keep up that trial for long.

Approach the lathe and try, if it cuts right it is sharp if not then re-do the deed, There is no set point where sharp is sharp. Just do what you can and except what you can do. (I know there is a finite answer but be practicle here)

Also sudden pain and errupting blood often indicates a degree of sharpness when I feel of the edge with my sore thumb.

Hickory, are you saying it is easier to grow a new thumb than hair?

Seriously, though thanks for the advice but sharp is a subjective thing and scraping a thumb may not be all that definite. I know it may sound like I'm harping on this sharpness thing but it is so vital that without it you just cannot achieve anything worthwhile on the lathe and anything that will help recognise a good edge is valuable to us.

Bodgy
3rd April 2006, 03:54 PM
Tiger, two things I recently started doing.

1. I bought a Jewellers Loupe off EPay about $15 delivered. This has a 30x magnification. Its a pain to use cause you have to have the loupe real up close and the object too. V short focal distance. I does let you see exactly how your chisels and gouges are. I discovered that I would probably rather not know. I've found that 6000 waterstones are not enough and am negotiating a 2nd mortgage to buy a 12000.

2. I read in a WW book by an old Seppo woodie that they ever so gently try to slide the back of the thumbnail across the edge. If it slides its not sharp, it should dig in. Not convinced on this one,

ubeaut
4th April 2006, 01:02 AM
Tiger - Stop over analyse. If it's sharp it will cut if not it won't.

For turning tools 6000 grit is a waste of time, as is almost anything over 120 grit. Sharpening should take a matter of seconds then back to the turning.

Sharpening to high grits for woodcarving tools is excellent and a must but for turning it's ridiculous and a massive waste of time.

Just my humble opinion.

Cheers - Neil :)

PS Practise makes perfect. You will know when you've got it right, you won't need to look or feel the edge you will just know.
.

Skew ChiDAMN!!
4th April 2006, 01:14 AM
Hear, hear! Spot on, Neil. A few seconds use of a "high-grit" tool and it's down to the sharpness of a "120-grit" anyway. As Hickory already said: "Approach the lathe and try, if it cuts right it is sharp if not then re-do the deed."

Hint: I use a good diamond lap for a quick touch-up (just one or two strokes) during turning; when the lap doesn't freshen the edge then I go back to the wheel. This not only saves numerous walks to the wheel but also saves quite a bit of tool steel!

Oh... and another reason that seemingly sharp tools won't cut is setting the RPM incorrectly for the dia. you're cutting. Too fast or too slow... same thing. Selecting the right RPM is just as important as sharpening...

hughie
4th April 2006, 01:30 AM
Tiger,

Good advise here, Skew and Neil are on the money. There are many ways to test the sharpness and most if not all are subjective. Its an experience thing, for me a run my thumb [ a la Hickory ] across the edge at 90' [roughly]with a little experience you soon know sharp as to dull. If all else fails try it:D
R.Raffan recommends leaving the rag or burr on the edge as it will cut better. This is my experience as well, although it would bad news for a razor:D But it cut wood real well.
hughie

Lance Stunning
4th April 2006, 07:03 AM
I would agree the object of sharpening is to get back to the lathe asap. My grinder has 36 and 60 grit wheels which either touch up an edge or reform one with no problem. The one exception is with the skew. When I'm turning down or roughing I usually resharpen on the 60 grit wheel. But, when I make the last finishing passes on a bead, I will hit the belt sander which has a 15u 3M Trizact belt. It's the same belt as most knife sharpeners. A sharp skew makes such a nice surface, it is ready for finish.

21589I converted an old 2 speed motor for my belt sander. It uses standard 1 x 42 belts. The other side is a felt wheel for putting a final hone. Another idea never used much.

Tiger
4th April 2006, 01:47 PM
Thanks guys for your opinions. I know that honing/sharpening is a controversial topic amongst woodturners. I absolutely agree that the quicker you can get back to turning the better. I have found though that when I hone the skew chisel I get a very nice finish that needs virtually no sandpapering. What I can't attest to is whether I would get the same finish straight off the grinder, maybe I'm expecting a better finish after the hone :confused:. Also I understand that with the speed that a lathe generates, it will knock off a nice edge in no time. I am mainly talking about finishing cuts where I would go for a hone to save on sandpapering time and dust.

Bodgy
4th April 2006, 02:25 PM
I'm an idiot, should have seen this was re Woodturning not general sharpening!

You should see what my gouges look like under 30x magnification, not a pretty sight.

Tiger
4th April 2006, 02:43 PM
Bodgy,

I like your idea about the magnification, for only $15 that could be a worthwhile investment. Rather than mortgage your home for a new waterstone, have you considered wet and dry sandpaper up to 2000 grit?

TassieKiwi
4th April 2006, 05:19 PM
Lee Valley are running a special on loupes at present.

A good test that will save your nail-job is to do the same on the side of a Bic or similar pen. If the edge digsin - sharp. If it slides-not so sharp.
Try it.

Bodgy
4th April 2006, 05:47 PM
Tiger

I started off with sandpaper, the scary sharp stuff, but prefer waterstones, although I'm getting a bit tired of having to keep flattening them.

I might resurrect the scary sharp board just for one grit, but dont know if you can get 10,000 W&D?

ubeaut
5th April 2006, 01:46 AM
Tiger - The finish on the timber has far more to do with your expertise with the tools than it does with your sharpening. The sharpest tools in the world are still bordering on being useless in the hands of someone who doesn't know how to use them correctly.

Getting a clean cut at the right angle with just enough bevel dragging will give you a brilliant finish that won't need sanding. It isn't hard to do once you have mastered the skill of controlling the tools, but it may take a lot of practise to get there.

I can get these finishes using many tools to cut cleanly and in the past have demonstrated doing just this using such things as an axe, pocket knife, plane blade, draw knife, glass and many other edged instruments. I am talking about a clean glazed looking cut not scraping. It is all in the handling of the tool. And no you can't do it with a blunt tool, but it also doesn't have to be sharpened to the inth degree.

Cheers - Neil :)

PS the above demo's were done to prove the point to students, that you don't need to have the best and most expensive tools to do woodturning. I do not advocate doing this as a turning practise.

Schtoo
5th April 2006, 02:16 AM
I use a bench grinder that has a buffing wheel on it.

Sharp enough to cut arm hairs is where I call it adequate.

Also sharp enough to turn cedar without any problems, and helps prevent the brittle woods shattering because I don't have to work the tools very much. Let the tool do the work and all that. ;)


(I used to think off the grinder was sharp enough. Maybe for hardwoods it's enough, but I already have them that sharp so why downgrade?)

Bodgy, I know 3M makes a #10,000 film, that it's expensive for what you get and waterstones don't go even that fine so it's pretty much pointless.

I wouldn't bother, and I usually don't let a tool touch wood unless it's as sharp as the steel lets me make it.

Hickory
5th April 2006, 04:48 AM
I think you are trying to get too high tech on the keen edge and sharpness factor. The question is rather or not you can make it sufficiant enough to do a good job turning. I use a 1"X30" belt sander with 120 grit. Set the table at the angle I want and buzz off a new edge each time I start a new piece, Sometimes a true up or two is needed to complete. I consider myself a woodworker not a tool sharpener and prefer to spend my time standing in front of flying chips than holding a loupe to my eye to see if an extra grain of steel is shaped to the max. Rubbing across the thumb nail is a good indicator, I do that with my fish hooks to see if they are sharp (but sharp hooks are not the usually problem, not hungry fish is the usual problem) Just as super sharp chisels and gouges are not as much a problem as techniques and toolrest placement to how well the tool cuts.

Ease up on the technicalities and get back to just having fun. Watch the pros, not once have I ever seen them Eyeball the edge. They hit it a lick and go back to the job.

Bodgy
5th April 2006, 10:44 AM
[quote=Schtoo]
Bodgy, I know 3M makes a #10,000 film, that it's expensive for what you get and waterstones don't go even that fine so it's pretty much pointless.

Schtoo you can get Jap waterstones up to 10,000 in Oz, 8000 = $129, 10,000 = $149. Most of the usual suspects stock them.

Outsider
5th April 2006, 02:02 PM
Bodgy Hi,

I'm a novice but think I saw a chart comparing Japanese numbers and wet N Dry and the numbers are nowhere near each other. Like 2000 or 3000 Wet N Dry equated to 8000 Japanese Water Stone.
I'm sure someone will correct me if I'm Wrong, usually am ask SWMBO.

Bodgy
5th April 2006, 03:44 PM
Outside, you're probably right. The grading of grits seems absolutely chaotic for sand paper and W&D. You'd think it a simple matter to standardise, either by micron size of grit or # of particles per mm.

Bit like screw threads, there's a real nightmare: BS, BSF, BSW, ANC, UNC and so on. So much easier now metric is becoming most common.

Auld Bassoon
5th April 2006, 07:10 PM
There are a number of reference books on sharpening that tabulate the numbers used by various regions and for various abrasives. Do a 'Google'!

zenwood
5th April 2006, 10:33 PM
The question is about objective tests for sharpness. Apparently there is an ISO standard (8442.5) for sharpness testing, involving a measurement of the pressure required to cut through a standardised piece of material: sharper blades need less force.

See here: http://www.catra.org/products/testing/knives/sharpness_tester.htm

There is the legendary japanese sword, which could cut through a silk cloth when the cloth was draped over the edge...

Bodgy
5th April 2006, 11:49 PM
Zen

Not convinced re the Samurai sword. I'm sure they were sharp but the floating silk being severed?????

I think thats the Tokyo version of alligators in the sewer, crop circles, I slept with Lord Lichfield and oops got piszed, cold bath and where's my kidney/liver/spleen/left eyeball etc???

zenwood
6th April 2006, 08:26 AM
Bodgy: I saw it on "Highlander", so it must be true.

Don Nethercott
6th April 2006, 10:40 PM
When I got an aluminium oxide wheel for my grinder I was told the coarser grit (60) was better as it sharpened quicker and thus less chance of overheating.

Anyone else agree with that?

Also it is my understanding that the edges on the woodturning tools are not "clean" edges but have a burr on them which is best left on as it helps with the way wood is cut on a lathe (unlike with wood carving tools which are pushed to cut).

Don

Skew ChiDAMN!!
6th April 2006, 11:36 PM
When I got an aluminium oxide wheel for my grinder I was told the coarser grit (60) was better as it sharpened quicker and thus less chance of overheating.

Anyone else agree with that?

Not me. I sharpen in quick, light passes that only hold the tool to the stone for maybe a second per pass; usually only 2 to 4 passes to sharpen the tool. Overheating's not a problem I have... now.

Where the problems start is when you're either putting to much pressure onto the tool/stone, taking too long to do a pass or are taking a lot of passes without adequate cooling time between. The first won't really change with the grit, the second & third are best cured by practice.


Also it is my understanding that the edges on the woodturning tools are not "clean" edges but have a burr on them which is best left on as it helps with the way wood is cut on a lathe (unlike with wood carving tools which are pushed to cut).

This is true for scrapers; it's the burr that does the actual cutting. No burr = torn grain.

For gouges, skews and other "cutting" tools it's not really true but if it's sharpened enough to have a burr it's sharp enough to use and removing the burr is really a waste of time. IMHO.

There are those who'll remove the burr anyway (and polish with jeweller's rouge with a loupe :D ) and there's those who'll just move along and get the job finished. You could say it's the difference between an artiste and a bloke who's doing it for a living. [shrug] There's nothing wrong with either way, but I really don't think the benefits of xtra sharpening merits the time spent.

Lance Stunning
7th April 2006, 04:20 AM
When I got an aluminium oxide wheel for my grinder I was told the coarser grit (60) was better as it sharpened quicker and thus less chance of overheating.

Anyone else agree with that?

Also it is my understanding that the edges on the woodturning tools are not "clean" edges but have a burr on them which is best left on as it helps with the way wood is cut on a lathe (unlike with wood carving tools which are pushed to cut).

Don

For sharpening HC steel I agree with you on the 60 grit wheel. Adding to that the more friable (grit breaks from the binder) it is, the less heat will build up. A fine grit wheel builds heat faster than course. Wheels that are dressed exposing new surface minimize heat build up. 3600 rpm grinders should use softer wheels than slow speed (1800 rpm).

There's a different set of rules for tool making and serious reshaping. It assumes one will be tempering along the way. Therefore heat build up is not a concern. Anyone making tooling from old leaf springs?

Schtoo
7th April 2006, 04:56 AM
Bodgy, last time I had some #10,000 paper in my hands, the back felt rougher than the front.

More academic than anything else really. #8,000 in a water stone is enough for most things, maybe #12,000 if you wanted to go a little further.

That's just me though, and my turning tools never see waterstones anyways. :D

JackoH
7th April 2006, 09:41 AM
I think you are trying to get too high tech on the keen edge and sharpness factor. The question is rather or not you can make it sufficiant enough to do a good job turning. .

Sharpening causes more angst to the new turner than anything else. As with everything to do with this craft the beginner must get a few lessons, or at least join a club where the basics of all aspects can be learnt.
Then there is no substitute for experience, and that only comes with time and practice.I have four sharpening jigs purchased in the first few months after I started and now I use none of them.
I have an 8" grinder with 60 & 80 grit white stones and a $50 adjustable tool rest in front of each and that's all.
As Dick Sing (Pens From The Woodlathe) told me some years ago-"Grind once Sharpen each time after"):)

Don Nethercott
7th April 2006, 02:29 PM
JackoH,
What is the adjustable tool rest you have?
I find the tool rest that comes with the 8" grinder a pain to use.
Don

JackoH
8th April 2006, 10:05 AM
JackoH,
What is the adjustable tool rest you have?

Don. Carbatec used to sell them under the name 'grinding jig' for about $40, I haven't got a Timbecon catalogue but I am sure they could supply , as no doubt could Jim Carroll.

Skew ChiDAMN!!
8th April 2006, 06:51 PM
In one of my threads I posted this pic (http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=20792&d=1142682208) that includes a view of my grinder station. The rests are only quick knock-ups made from scrap ply & pine and probably took all of half-an-hour each to make.

Most of my grinding is done freehand, but I still like to use these rests to ensure a consistent angle. The RH one was my first attempt, if 'tis ever rebuilt it'll become more like the LH one... which is a bit more solid. The two bolts that can be seen on the LH one allow the entire rest-assembly to be moved in/out and immediately underneath the rest is another coach-bolt/wing-nut that allows me to adjust the angle. Both of these have been in regular daily use for a couple of years now. :)

The horizontal slots in the rests are where I used to mount sliding jigs, similar to mitre guides. I've no idea where they are... I haven't used 'em in years. :rolleyes:

JackoH
10th April 2006, 02:22 PM
Don. Jim Carroll has a jig similiar to mine in his current newsletter. (Mine don't have the attachments).
See www.cws.au.com