Tuesday, August 2, 2016

Some thoughts on Sharp

I carve with carbon steel in dry basswood.  I'm not offering new advice, rather supplyiing a bit of reason behind some good advice I have learned to follow.

In the search for sharp I read somewhere there are two enemies to an edge- friction and chemistry.

Assuming we avoid conditions that cause rust, I think as carvers we can ignore chemistry.  That leaves friction.  Lubricants are out of the question- whittling oily bass?  I think not.

We deal with friction by polishing our blades.  How much polish?  Good Q.  Lets use a 10x magnifying glass to help us determine the answer.

Sorry I can't take 10x pics, you'll have to trust me or look at your own stuff.

I hone to 1200 grit till I get an even burr on an edge, at that point the blade looks pretty smooth to the naked eye, any reflection is getting clear.  Under 10x we see a different landscape, scratches deep enough to drive your car into, and the edge looks like a sawblade.

On to the strop- for me its a power strop with green compound (mfr recommends the compound for high polish on hard metals- that's what I want).  I don't strop forever, I do spend a minute or more alterrnating each side of the blade- the equivalent of a few hundred strokes on an average hand strop.  I look for the wire edge to disappear, then I test the edge cross-grain on a piece of bass I keep next to the strop. I feel I gain some consistency by testing all my knives on the same piece of wood.  When I get continuous shiny scratch free cuts on the wood I figure I'm done, and I give the blade 10 more passes each side on the strop to finish.

Back under the 10x, the blade looks better, but many scratches are still there.  Truth is, they'll be there for quite a while- it takes a long time to polish them all out, and likely there are a few leftover 600 grit scratches in there too.  Every trip back to the strop will remove more scratches, eventually they'll all disappear.  I don't think you'll get better than that.  I have a blade I've been using for a couple years; I'm not a prolific whittler but the edge is nearly scratch free.

Unless you go back to the stones and start yourself over.

Here's the advice part:

Strop only:
- stay away from the stones if you can and your edge will improve over time.  Return to the stones only to repair a damaged edge.

Take slicing cuts:
- let's recall the edge under 10x right after honing with 1200 grit- the sawblade look.  The sawblade will never go away, the teeth will get smaller and finer with additional stroppings, it will not show under 10x but it's still there.  I'll bet somewhere on the web you can find a microscopic view of a sharpened edge.  Slicing cuts take advantage of the micro-sawblade we are creating.