Re: Saw re-toothing question - long
L. Hanson - N. Idaho
>I can't say what would have caused a retoothing machine to bow a saw blade like that, much less three of them, as I have almost no experience with them - though it says to me it must have been the fault of the sharpener or his machine to do it consistently like that. My experiences mirror most people's, I think - hand saw sharpening by others is a hit and miss proposition.
For straightening a slight bow in a saw, I first look to see if I can identify where it is bowed - is it bent in one place, or is it bowed for it's length? The much more common is that it is really just bent in one place which just makes it look bowed. If it is bent like that, it's off to the anvil with a large flat faced hammer (very slightly rounded - I think they are referred to as 'planishing' hammers) to work the bend out, working with the bend up, hammering the area immediately surrounding the crown of the bend. I sometimes hold the saw slightly bowed in the direction I want it to bend - but that's mostly so I can use the light reflections to better judge where it is I can do best with the hammer than anything else.
If that isn't the case - and it is a gradual bow, I then mark the spot that is the center of the bow on the blade with a marker (use one that isn't permanent), then outward to where I think the bow ends. I then work the bow using my bench and my right forearm as the crux point, working against the bow. I'm sure some are better at using a hammer for these purposes than I am, and that may be the way to do it, but these are just my experiences. I can work a sharper bend out with a hammer, but working a long bow is tougher for me with one.
If that doesn't get it - I sometimes have had success clamping a 2x4 to my bench on top of a couple 1/4" plywood cauls (one at each end) and sliding the blade of the saw - bow up - underneath it. Then, I bring the edge of the mark made previously to just in front of the 2x4 and gently begin working it upward, pulling it out to check often, and moving it, never doing too much each time. Keep working the area that you've marked off until the bow comes out, concentrating on the parts of the bend that are the most severe, keeping them just ahead of the 2x4.
Once it's close, I usually joint the saw fairly heavily and re-sharpen the teeth, followed by resetting them. I find that the act of setting the teeth will sometimes get that final little bit straightened out. That's usually because I am straightening a saw that I am also restoring, and haven't sharpened yet. But for me - the act of setting the teeth is sometimes enough to get that last little bit of the blade straightened out.
I think, as always, The biggest trick is not to bend it too much - work gradually and cautiously, back and forth until it approaches being straight. It isn't always a 3 minute job, it can take quite a while to properly work the steel back to straight again. It's best to have a bit of practice on a couple cheapies, if you can, to get the 'feel' for it.
I hope that wasn't too long winded - I'm also sure there are others with more experience in the matter that may disagree with my methods, and I'm always willing to listen to a different point of view...
HTH
Leif
norsewoodsmith.com