Ponderings

**Toolin Around** · 30th December 2007, 11:58 PM

I thought I'd put up a few thoughts on sharpening I have that may or may not be of use to y'all. It's the holidays - I have too much time on my hands.

Many if not all at some point in time have used the shaving technique to test an edges sharpness. It's one technique I abandoned years ago as in my woodworking journey never found it really told me anything other than I can shave my arm with the tool. And all the girls couldn't understand why I had bald patches all over my arms. Take for example the axe in pic one. It's not easy to see but it's fresh of the grinder and I can shave with it. So! should the axe then be considered sharp - hardly. Another thing about shaving. Try shaving something more sensitive like your face next time with a freshly "sharpened" chisel or plane blade. You'll be very quickly coming to a painful conclusion that the tool ain't all that sharp.

Another method that has always completely escaped me as to how someone could determine if a blade is sharp or not is to rub their thumb lightly across or along the edge. In the past I've had people pick up a chisel of mine and do just that and say something like "now that's sharp". Now I've never had a good poker face so I can only guess that the look I give them would be similar to the one that usually is accompanied by "huh?!?". If you have no idea what that look is... next time you're over at my place take one of my chisels and do just that - that's the look. In my mind I'm thinking how did you do that! My fingers are just not that sensitive. A butter knife doesn't feel much different to me.

The fundamental to sharpening since the iron age is that the finer and cleaner an edge the longer it lasts and the better it cuts. Though the tools and such have dramatically change over the last couple millenia the need for a finely honed edge hasn't.

So keeping that in mind how do I determine if an edge is well honed. There are two tests I use. Both involve my finger nails. First test determines if I have any imperfections that need to be honed and or ground out. And whether I need to use a finer honing compound. The second actually determines if the edge is sharp.

The first test is in picture two. I, gently, drag my nail along the edge of the tool. It helps if the nail is just slightly longer and extends a bit past the skin of the finger tip. As I slowly drag it along the edge it acts like the stylus on a record player and registers even the smallest nicks in the edge. Also as I drag it along the edge I can feel if there is any resistance to it sliding along the edge. The feeling of resistance is something you'll have to get to know as what you feel is honed enough may not be the same as mine. If all you hone to is 200 grit the resistance on your nail would be very high. I use a MDF disk charged with buffing compound and a soft cloth wheel to hone the edges of my tools so the resistance on my nail is next to zero.

That test has told me how well I've honed the edge but not how sharp the edge is.

Pic three is the test that determines how sharp the edge is. An edge that is truly sharp should be able to "stick" to the nail at any angle above 0 (in theory but for the most part is true), relative to the the surface of the nail. As the tool gets duller the angle has to increase so the edge can grab and hold to the nail. When really dull the edge won't grab at even a 90 degree angle. I gently touch the nail to the edge all along its length to make sure its sharp the whole way. Or if it's a very long edge, every couple inches or more. It's important to remember not to drag your nail along the edge as in the first test, only lightly touch and move on.

This methods doesn't work as well if you're the sort that likes to buff the back of your blades. The buffing will round the edge which means the tool will need to "stand up" more so the edge can contact the nail. You'll still be able to determine sharpness as the blade will still be sticky sharp but not as well if the back is perfectly flat. My personal opinion is that the backs of chisels and similar shouldn't be buffed. Or at least kept to the faintest touch to remove the remnants of a wire edge. The rounding of the back of the blade blade comes back to bite you in the ???? later in most aspects of woodwork - YMMV. Carving chisels are exempt from this.

Another method of determining sharpness, though I strongly recommend you don't employ it... Is how long you bleed for after you cut yourself with an edge tool. The sharper it is the longer you'll bleed. It's true - honest

Hope that's of use... Happy new year.

**Toolin Around** · 31st December 2007, 12:00 AM

The pics didn't make it onto the post so here they are

**zenwood** · 31st December 2007, 12:57 AM

Some interesting ponderings. Sharpness tests involving fingertips etc. sound a little dangerous: I'd at least recommend pointing the tool towards the TIP of the nail rather than the BASE, in case of slippage.

The ultimate test of sharpness is to use the tool to do the cutting it was intended to do. For chisel or plane blades, I sometimes test them by seeing if they can make end-grain shavings in pine. More frequently i make bald patches on my arm. But I'm almost at the stage with my waterstones and veritas honing guide that I'm confident of a sharp edge without needing to test. And when I'm working too hard planing or chiseling I know it's time to sharpen (hone) again. With an axe, straight off the grinder or file with the light thumb rub across the edge is fine.

To detect nicks in the blade, you can often see them by holding the edge up to the light and checking for uneven reflections. You can usually see the result of a nick in the surface left behind by a nicked edge. Holding the edge against a straight edge such as a square or rule and sighting against a lit background will show light where the nicks are.

**Clinton1** · 31st December 2007, 09:37 AM

I've been using your "sharpness test on the fingernails" since you showed me up in Toowoomba.
Very, very happy with it... after I got past the initial nervousness.

I agree that shaving is a pretty low sign of 'sharp', although I've never bothered to do any actual tests as to a 'low level of sharp' (shaving) and the 'polished edge sharp' to determin actual useability and any benefits incurred.
I am satisfied that for planes and chisels used in a paring motion that the extra level of sharpness generally equates to longer service life in the edge.

So... the fingernail test works well for me.

**scooter** · 31st December 2007, 02:31 PM

A tip I've read is to do both the fingernail tests with a bic pen barrel. Smoothness test with the end (minus the refill), sharpness test with the barrel itself.

**kkperth** · 31st December 2007, 02:50 PM

Get yourself a microscope like this guy on the internet http://www3.telus.net/BrentBeach/Sharpen/qx3.html and check the sharpened edge - saves your hair, fingernails and pens!

This will give you visual proof of the condition of the edge, although this may be a bit OTT.

**Tiger** · 1st January 2008, 08:16 AM

Agree with all you've said Toolin. Only thing I'd say is that the shaving test still tells me how sharp something is. When razor sharp, the hairs jump and fall quickly without any effort, when moderately sharp, there is a bit of pulling, when there's still some of the wire edge left, it leaves a tiny ragged cut on my skin and bleeds.

**Pops** · 1st January 2008, 01:16 PM

Hi TA,

The method I have always used for testing the quality of an edge, particularly for those tools needing the very best edge, (axes are not in this group for me) is to use my fingernail to run along the edge. Think I picked this up from my father when I was a kid, a very long time ago now I guess.

A bit differently to how you are doing it, but principly the same anyway. First I run the nail lightly along the edge from the flat side, at about 90 degrees and then I do the same from the bevel side, again at about 90 degrees to the bevel. I get a good indication of the condition of the edge doing this. Well to me anyway.

These days I tend to do this without also trying to look closely at the edge, i.e. no visual inspection. Why you may ask. Simple, I don't see so good up close without having to change my specs., which I can never find when I need them.

Gave up the hair shaving thing many years ago, too much blood for my liking.

And then I use the tool to confirm it is sharp enough, (for me). Sometimes I just try to pare off some end grain from a bit of pine scrap lying around.

Zenwood - Great minds think alike on this one. Also like your tips on using light and reflections to check for nicks. I do this too, when I have my specs handy.

Having a window with natural light coming into the shed is much better than fluoros etc. for this I find.

So I'm with you mate.

The fingernail is a useful low tech. method of edge checking. Also agree with you about not buffing the backs of chisels, for me a real no, no.

Happy sharpening, and checking, and using, your favourite chisels and other sharp stuff in 2008 all.

Cheers
Pops (looking for his specs. still)

**kman-oz** · 2nd January 2008, 11:01 PM

Can't say I've tried the nail tests, I'll give that a go tomorrow, but I can't say I've ever needed a better method than the one I use either. My nails don't really protrude past the finger tips, so it might also get bloody!

I think Pops method seems more logical because it looks for imperfections on both surfaces, where the single edge nail test doesn't. As an example, I'd sharpened a chisel this morning... well defined burr from the 1200 stone, visually the bevel was perfect, honed down to 0.5 micron, yet it wouldn't par the bit of Oregon I use to test the edge when finished. I hadn't bothered to inspect the back of the chisel, so when I did I found the edge had folded over tpwards the bevel. Pops method would have picked that up I think.

**Wolfs** · 3rd January 2008, 06:47 PM

My method for saving the hairs on my arms is to hold the sharpened edge against the side of a piece of paper and push. The really sharp blade slices effortlessly through the paper while the not so sharp ones falter and produce a ragged edge. Only takes a second and matches other methods well.

**m2c1Iw** · 3rd January 2008, 08:15 PM

Originally Posted by Toolin Around

An edge that is truly sharp should be able to "stick" to the nail at any angle above 0 (in theory but for the most part is true), relative to the the surface of the nail. As the tool gets duller the angle has to increase so the edge can grab and hold to the nail.

TA very interesting.
I have never subscribed to the shave method, recon it is particularly dangerous with narrow blades.

Instead I also use the finger nail, actually LH thumb but without knowing why as I can't remember how or who told me. What I hadn't cottoned on to is how the variation of angle can provide the extra bit of feedback as I usually touch nail at about 30deg.

Your tip on finding nicks is also appreciated, thanks.
Cheers Mike

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