Test of sharpness

[Tiger]

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]

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]

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]

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]

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!!]

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]

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
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 But it cut wood real well.
hughie

[Lance Stunning]

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.

Attachment 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]

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]

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]

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]

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]

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]

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]

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.