Sharpening the Disston Acme 120 No-set Handsaw
by Daryl Weir
This statement first appeared in a thread on theWoodNet woodworking forum. It was compiled and reproduced here for easier public consumption. All Text and Images are the property of Daryl Weir.
I know I've talked about sharpening a acme 120 but never went into detail on the process. Thought I would share some info and pics as I go.
I picked this old acme 11ppi panel saw up from ebay and yes, I probably paid to much for it but I thought it was worth it. This is only the handle as the blade is in the vise.
This is the first acme with patent dates stamped in the handle that I've owned. I'll show the etching later but the early ones didn't have the secondary etching stating that basically the saw being very hard should not be set.
Jointing needs to be done as one side of the teeth were a little higher than the other and aren't properly shaped. This shows up after jointing as one side having a bigger land than the other.
I have made some gauges for a cant saw file. Yes, I do use those darn blocks that some people seem to hate. I only use them for initial shaping to maintain the angles and them loose them for the bevel filing or final sharpening. These have always worked for me and have never seemed to be a pain in the, well you know what as some say. As close as I can tell from the Disston book the included angle of the tooth is 47 degrees instead of the normal 60.
The one marked 9 degrees is for the initial shaping,
the 15 degree is for the rake or the front of the tooth
and the 32 degree is for the back of the tooth.
Initial shaping starts with the 9 degree to try and make the gullet a uniform depth and even up the lands left after jointing. Yes, I do count strokes. The ones with a shallower gullet might get a little extra stroke of the file. It's all kind of a hand/eye thing to gauge and judge your progress as far as depth, spacing and shape.
Starting to get pretty equal results so I think its time to start doing the front of the tooth.
Red Dykem is applied so you can see what you're doing. This is a great help and something I always used in the machine shop for layout work. Just dawned on me one day when I was first sharpening to use it for this purpose.
Next the 15 degree gauge is used for shaping the front of the tooth with one stroke:
You can judge your progress by the flat on the top of the tooth and which way pressure needs to be applied.
Next I switch gauges to the 32 degree and do the back of the tooth with one stroke.
Next it just a matter of jumping back and forth between gauges to get the teeth to the correct shape. I know it's kind of a pain but it's worth it in the end. Some people say it doesn't make to much difference in the geometry (one tooth being a little higher, not quite the same shape, etc. ) and the wood won't know the difference. Well the wood might not know but I do and the person using the saw might see a difference too. I know perfection is unatainable by human hands but shouldn't it be strived for in everything we do? I know there's a limit but sometimes people give up to easily. There seems to be an art form in these old tools that has been pretty much lost today in this disposable world we live in. After all this is an "acme" which means the pinnacle/the best, shouldn't every attempt be made to return it to that state.
Anyway here are the teeth shaped to the best of my ability.
Next comes the 30 degree bevel gauge that straddles the saw plate. Just slide it along and use it for a guide. This is were some time gets sucked up as any misguided stroke can ruin the point of the tooth and make it too short. I'm just getting a good start on bevel filing the one side. When this is done I'll have to flip it over and do the other. It was time to stop so this is where it ends for now. I'll keep everyone posted as I continue and the saw is finished.
Finished the first bevel up, it took about 5 strokes in each gullet to get the front and the back of the tooth cleaned up and get to the apex of the each tooth. The regular cant saw file (not safe back) when filed at a 30 degree bevel or fleam angle and held perpendicular to the side of the saw plate will just about produce the right geometry from the initial shaping but does deepen the gullet up which is O.K. The red dykem helps you to see where you're removing material and if you're holding the file in the correct orientation. You just have to look and correct angular rotation of the file.
Then flipped it over and started on the second side: and here's the completed profile.
While I know it's not perfect, it's probably as close as I'm ever going to get. The saw still retains a nice breast to it after all these years.
I had to make a trial cut in a piece of old red oak I had. You won't believe how fast this saw cut for an 11ppi. As I've said before the Acme's have a different feel to them than a normal saw with set when cutting. There's some slight friction but each stroke removes quite a bit of material while leaving a good finish. The cutting edge on this one measures in at .040" while a D-8 panel saw I have from close to the same period measures in at .033". The back is a few thousandths thinner than the D-8 also. The extra taper grind provides sufficient running clearance for no set.
Here's a few pics of the finished saw.
Like I said in the first post, notice there is no etch as far as a warning about not setting the saw. There was some discussion I had with another saw collector that the early ones might not be a "no-set". The theory was this being the new skewback that Disston had just patented was the skew back version of the premium No.12 thus becoming the 120 and that the Choice 80 was the skew backed version of the No.8. It's kind of interesting to think about but this saw is definitely a no-set because of the extra taper grind.
I'm glad I bought it!
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