People don’t always realize that it can often be easier to file off all of the teeth and recut than to try a reshape to each of the teeth. Here is a method that works well for me and you may want to try if you have a saw that has highly irregular teeth. An eBay Disston came to me with a real orthodontic problem. Crowded teeth every other three or four teeth, some, many, missing. Uneven tooth height along the whole length caused the saw to trip and jerk into the cut with every forward thrust and accuracy went out the window altogether. The teeth in this condition would be almost impossible to straighten by eye and by hand except by the most skilful saw doctor and here is where in normal circumstances we would send the saw for recutting the teeth. Yes, there is a Foley Belsaw saw tooth recutter that mechanically recuts the teeth before sharpening. The recutter stamps out the teeth into the saw plate very quickly but of course we don’t have a recutter!!! It takes about an hour to file off all of the saw teeth and refile new ones using this method and the results are surprisingly accurate. Here is what I do and it works:
Firstly, I file off the teeth with a 10” single cut flat file. All the teeth should be removed to the lowest gullet point Any compromise can lead to another hollow spot or a missing tooth, depending on where the low point sits in regard to the teeth you recut. Some time back I had hoped to come up with a resistant material that I could cut teeth into that would guide my saw file for recutting perfect teeth – the material was sitting right there in my shop and I had hundreds of options. Wood is fairly resistant to saw files.
Don’t leave any spots unfiled
By cutting accurate channels, in a matter of minutes I had my saw file guide for recutting and I was able to recut the Disston. Because the best size teeth for almost all tenon saws and dovetail saws is 16 TPI (teeth per inch), I used a rule with 1/16” divisions to map my stick-of-wood saw-file guide. Begin by holding the rule or, in my case, the combination square beam, against the 1/2” by 1” piece of wood. An 8” long piece is sufficient. I marked only about 3”. The stick can be then be moved along and carefully aligned with the last tooth cut as you progress to the end of the recutting process. With the points marked onto the wood with a sharp, pointed knife, I square the lines across the full 1/2” width. Then I take a sharp 3/4” chisel and make an incised cut from one line to the adjacent line. This creates a definitive wall that then aligns and guides the point end of the file perfectly. Starting with the point end in the far side of the guide, i file the tooth front.
Before cutting, I align the guide with the start of the saw and fractionally below the saws edge, perhaps 1mm or 1/32”, and then, with a second wooden stiffener at the front of the saw, clamp the whole assembly into the vise. It’s important to note here that the guide is purely to set exact distance between teeth and not an actual depth controller, which unnecessary. The first pass with the saw file simply places the front of each tooth on the steel saw plate. Subsequent file strokes deepen the cut and it’s the number of passes combined with sighting the narrowing light on the saw edge that determines the depth and size of the teeth. This is not hit and miss effort, but truly accurate, provided care is taken not to go too deep with the final file cut. Traveling from toe to heel, left to right when the handle is on your right as you file, simply align the file with the squared line and the saw file locked in your hand at an angle where the top of the file is tilted slightly downwards toward the toe of the saw as shown in the drawing. This gives a rake to the fore part of the saw tooth. For a more aggressive cut, tilt the file further forward. This creates a more vertical
This is how the teeth will look after recutting using my method.
cut to the cutting face of the saw tooth and it’s this that makes the saw more aggressive for faster, deeper cuts. Take care to cut to the exact line and press harder in one direction, left or right, to align the file to the knife line. Once you have say 1” of alignment cuts that position the teeth, go back and file the teeth to depth. Work methodically from left to right. Go down to depth. This is gauged by filing until the light on the top of the adjacent tooth to your left becomes super thin. The final, partial stroke removes the light and the cutting edge of the newly cut tooth is level with the edge of the saw. When the saw teeth are cut to the extreme of your guide, move the saw guide along and align the cuts in the wooden guide with the last tooth you just final cut and start the next section. The whole process of recutting the actual teeth should taken no more than 20 minutes. This system also works well for simply changing tooth size.
All that remains is setting the teeth. Worth noting that in thin wood or soft woods, you may choose not to set. I keep a saw with no set for super-fine dovetails in thin stock.
If you are new to saw sharpening, go along to The Home Depot (US) or B&Q (UK) and buy a piece of sheet steel plate or floating and taping trowel. The first time I tried this was about 8 or 9 years ago on such a trowel. It actually made a working saw.