Thread: Saw Fettling

Originally Posted by pjr

ok, so that Disston D-8 Rip Saw that I started clean up, it starts at about 4 or 4.5 points per inch at the heel and graduates to about 5 or 5.5 at the toe. I guess I need to get the 7 inch regular taper file (according to the L-N table) and take a lot of care. Does that sound right?
I am daunted by the graduated tooth sizing so might leave this saw until I've done a couple of others. I don't want to mess it up.
(apologies basilg for taking over your thread a bit)

Peter - there is a bit of lee-way with file sizes, as you will see if you start searching around the various recommendations, but most seem to agree to within a size or so. It's not a mysterious art. The main reason to choose the 'correct' size file is to get the right sort of gullet for your teeth. The bigger the file, and the 'fatter' the taper, the more 'rounded' the corners. If you tried to use a large file to sharpen an 18 tpi saw, you would end up with all gullets & tiny shreds of teeth (try it on a rubbishy old saw & you'll soon see what I mean). The other consideration is to choose so that when the file sits in the gullet, the points of the teeth are no more than 1/2 way up each side of the file, otherwise you will get excessive wear in the middle part of the file as you rotate it on successive runs. Since this is the part cutting the business end of the tooth, you want it cutting as well and as cleanly as possible. A 7 inch file should be fine for a rip saw of that tooth size.

Don't be daunted by your graduated teeth, they should be no more difficult to sharpen than any other, particularly on a rip saw, which is filed straight & level. Let the file sit in the gullet, then just push evenly for the stroke or two it takes. The tricjk is to develop a nice, even & most of all, constant pressure. Most people (myself included) tend to bear down on the file a bit too hard, at first, but with a bit of practice, you will soon get the feel for how much it takes, and how to hold the file just firmly enough so that it takes an even cut on both sides of the tooth. A new file should cut very easily, so when it takes too much pressure to make it cut, you know it's time to break out a new one. It's impossible to say how many sharpenings you should get from a file, because it depends how much metal you take off each time, but the spring steel is a lot tougher on file teeth than mild steel, so you don't get all that many sharpenings out of a new file - maybe a dozen?

I found when I began that I tended to let the rake angle sneak forward on my big rip saw. It is standard practice to file with the trailing edge of a tooth leaning away from you. The file will cut this side more easily, so you tend to cut the back of the tooth & the bottom of the gullet ok, but less off the top of the leading edge of the other tooth. Over a couple of sharpenings, this will change the rake angle to a more aggressive one, making a big-toothed saw like yours bite & skitter instead of cutting smoothly. I make this sound complicated, but you'll soon see what I mean when you start sharpening. Perhaps it's not a bad idea to take a reading of your saws current rake angle and draw it on a sheet of cardboard you can keep for future reference.

It's quite easy to change the rake angle for a more or less aggressive cut, or correct it if it does gets out of whack. Use the same technique I used here,
https://www.woodworkforums.com/f152/d...8-copy-120653/
when forming teeth from scratch. The stick on the end of the file helps you to keep the angle constant as you go. In fact, you can use the stick guide when sharpening, the first time or two, until you feel more confident.

Cheers
(& apologies for another long-winded answer!)