Thursday, January 17, 2013

Saw sharpening and the 80/20 rule

For a long time, I was dissuaded from trying to sharpen handsaws and backsaws by reading too many forum posts by saw experts.  Passionate arguments about the effects of being off on rake or fleam angles by a degree or two, the need for absolute consistency etc. left me scratching my head.  I knew there was no way I could meet the standard they were setting.  They made it seem like small errors would ruin the saw.

Fortunately, there were a few voices expressing a different point of view:  that you can make a saw cut acceptably well with less than perfect sharpening.  Viewed from the perspective of the 80/20 rule, this made sense to me.  In case you aren't familiar with it, the 80/20 rule suggests that you get 80% of the effect (a sharp saw) from 20% of the cause (sharpening skill).  Not literally or exactly, but as a very general guideline.  On top of this, I asked myself the following question:  what if it's wrong?  In my case, the answer is I may have damaged a nice old saw I paid $3 for and spent a few hours on, but probably not to the point where it can't be salvaged.  It really doesn't matter very much if you screw it up; you just have to get over your fear of failure.

So, with this in mind, I got myself a good file (Grobets are available from Lee Valley, Lie Nielsen and others) built myself a vise, read and watched what I could find online, got from Lee Valley the filing guide described previously and a magnifier and found a suitable patient:  a nice old 11 ppi panel saw in good condition with truly terrible teeth.  Starting with bad teeth is more difficult, but that's what I mostly find at garage sales and I wasn't about to start on one of my good saws, so that's what I did.

The first thing I did was joint the teeth about half way off.  Then I did my best to even up the gullets by "moving" them in the right direction and making their depth uniform, not worrying a whole lot about rake or fleam.  My biggest challenge was seeing clearly; the magnifier has a focal length of about 6" which I find awkward.  I repeated this process several more times until the gullets looked about right.

At this point, I put the filing guide on and started shaping the teeth.  It went better than I expected it to, just slower.  I had to keep stopping, looking at the saw in profile and adjusting to make sure I was getting the teeth even.  I made a number of passes before I was satisfied.  Then, I gingerly applied a small amount of set and gave it a try.  I hadn't applied enough set, so I had to do it again.  Trying the saw again, I was very surprised.  It cut to a line and took almost 1/4" per stroke, as far as I am concerned good for a small panel saw.

Did I do a great job sharpening this saw?  No.  To the naked eye, the teeth look uniform; under magnification, not so much.  Is the rake angle just right?  No.  I used 10 degrees, which makes it start easy but cut more slowly.  Is the fleam angle optimal?  Doubtful, and I know for sure that it varies a degree or two at least.  Could an expert do a much better job?  Absolutely.  Forget all that.  The saw is very serviceable and I can make good cuts with it.  That is all.  


  1. Exactly! It's fine to strive for the perfect edge or the perfect tooth. However, the fear of falling short of perfect should not prevent one from trying. You can't learn if you don't try. And an imperfectly sharpened saw or plane or chisel still works better than a dull one. No saw that ever leaves my shop is perfect. But they all cut really nicely anyway.

  2. Bob's is one of the other voices I referred to. Check out his excellent podcast on saw sharpening: Other episodes in the series cover sharpening of the main tools in your shop.

  3. That's great! Too many people these days are forum woodworkers. Talking about woodworking all day and never getting out in the shop to try things. Maybe a large part of it is fear of failure. You've demonstrated here that you can gather a little knowledge, give something a try, and who knows, it may just work out. Inspiring post.

  4. Congratulations on stepping outside your comfort zone.
    Perfection is a worthy goal as long as it doesn't prevent you from trying. Even mediocre saw sharpening is better than a dead dull saw. Besides it can be fun to learn new things.
    I've been practicing for a while and this is what I've come up with. Not perfect but pretty good.

  5. Outstanding Andy, I keep telling people that saw sharpening isn't that mysterious and most of it is just sitting down and doing it. That reminds me, I have a sash saw that needs a touch up, gotta go!

  6. I am not sure perfect regular shape is desirable.
    Small teeth shape variation prevent excitation of vibrations.

  7. Thanks! That's my story and I'm sticking to it. :)