Tuesday, October 29, 2013

The Why?

Perhaps you've seen my video showing how the Drawsharp works, and, as with most advertisements, your natural reaction was to think that this was just another gizmo that attempts to replace a valuable skill with money. I'd usually be right there with you, so I hope you'll bear with me, because I want to go beyond how the tool works, and to "the Why?", which regardless of whether you are interested in the Drawsharp, will hopefully offer you some useful information about the drawknives and how to deal with them.

The top knife was polished on the back while the bottom was a rusty pitted mess
Here are a couple of drawknives that my current students brought to the shop. The polished blade on top was a breeze because there was no chipping or pitting to deal with, but the bottom blade, which showed signs that someone had started and given up, was definitely in need of serious attention.

The bevel wasn't much better
I have tuned hundreds of drawknives and I always started with flattening back and grinding the bevel. I am happy, and a little embarrassed to say that this is wrong, plain old wrong. The reason that I used to flatten the back and grind the bevel was to create a proper bevel angle and stable surfaces to register on the waterstones. Hollowing the bevel and back made it easier to consistently reach the edge, which let's face it, is the only part that cuts the wood. And that would be the end of the story if we were talking about chisels, which always keep the flat geometry off of the stones. But a drawknife requires a slight rounding just behind the edge on the side that rides on the surface of the wood. This is so that the tool can enter and exit a cut, otherwise, when sharpened flat like a chisel, it will dig, like a chisel.

So after honing, I would strop the edge, which gives a subtle rounding and allows the drawknife to follow the fibers and come out of the cut on command.  Just the right amount of rounding has always been tough to accurately reproduce. The problem is that once the edge is rounded, resharpening means either reflattening the bevel and back on the stones to reach the edge and then stropping it again to re-establish the correct shape or simply stropping the edge until the rounding becomes too much for a good cutting angle, at which point it's back to the grinder. Does this sound at all familiar?
The back is still largely a rusty mess, but after 10 minutes of work, the edge is sharp
As much as this process would give me pause before taking on a drawknife in sad shape or sharpening one that was good but not great, it would also keep me from really addressing and understanding what what going on on the real business edge of the tool.

I suppose my understanding started to change when a student, Steve Kinnane, came up with the idea of grinding the drawknife using the back (spine) of the tool as a reference. I adopted this wholeheartedly for it's ingenious simplicity. You can grind a curved or straight knife with control and ease after smoothing the spine of the tool, which is almost always soft enough to be done quickly (and only once) with a file and some abrasive.

Then one day, I thought, why not use that same unchanging reference to hone the edge? And the wheels started turning, leading to the Drawsharp. I suppose my reluctance to spend time tuning my collection of drawknives should have highlighted the problem sooner. Flattening the back of a drawknife is really just labor, not skill. Yes, honing a ground edge freehand is a valuable skill for some tools, but doesn't offer an advantage to drawknife geometry or sharpness.

I use the drawknife from the time that I split a piece from the log to the last cuts on a finished chair, so it must be as sharp as any tool that I own. Using the spine as the correct reference has made sharpening knife easier and I can honestly say that I no longer have a "favorite" drawknife. I used to coddle certain knives, never letting them touch green wood. No, these were my finish knives and unlike the other lugs, they were kept in top shape, mainly because of their seldom and restricted use. Now that I know the exact geometry of my edges and have a way to quickly and repeatedly tune them, I can get all of my blades singing. The only difference between my knives is the quality of the steel and the comfort of the handles. As far as top performance and geometry for cutting wood, the mystery is gone.

I appreciate that you've stuck with me through this and hope that you understand my intention in enlisting the help of Benchcrafted to make the Drawsharp available. I want folks to work with sharp tools instead of fussing about and eventually giving up thinking that a razor sharp drawknife is limited to those experts who possess skills that they cannot muster. After much practice, I can freehand grind a drawknife and hone it beautifully on my waterstones, but honestly, it's no longer a skill that I value. Sharpening a drawknife to work at it's peak is no more complex than using the correct references, the real skill building belongs to using the tool to make great furniture, and having fun doing it.

Soon, I will be posting a video of fully rehabilitating a drawknife in hopes of getting more folks using the most versatile tool in my shop.


9 comments:

Andrew Jack said...

I cannot beleive no one has commented on this yet. I hopefully sent some folks your way after this past weekends show. Lots of interest!

Harry said...

Hi Pete,
It arrived yesterday and I immediately put it to use. It worked beautifully. I expect it will be even better when I remember to use some oil.
Thanks
Harry

Philip said...

Fantastic info Pete. I'll be saving my pennies...

Peter Galbert said...

Thanks for the feedback Harry!

Anonymous said...

After using my drawsharp on a few different knives, I realized how easy it would be to add a micro adjustment knob on either end of the tool. I struggled slightly to move the columns a miniscule amount.

Alex Bond said...

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Michael Fontane said...

Pete,
I used my drawsharp this past weekend. It is a fantastic tool and very easy to use. Thanks

Styles said...

Thanks for designing and making a great tool! My favorite thing about it is that there is no time consuming fiddling that plagues most sharpening jigs. It takes the room for error out of sharpening without adding any complexity or extra time. You don't have to plug it in and it doesn't need a "station" to reside on. It works fantastic for my drawknife and is great for the outside edge of my scorp as well. I tried to make my own at first with some dowels and some sandpaper and wish i didn't waste my time. The materials and design of yours is fantastic and worth every penny.

Peter Galbert said...

Thanks Styles, that's great, I'm happy that you find the tool so useful, I use mine all the time!