Back saw curve after handle attached

[Bram de Jong]

Hi Neanderthals,

I have an old back saw which has a slight curve. A while ago I removed the back, cleaned the groove, put the saw in again and, yay, perfectly straight!

Then I attached the handle again and what do you know, there's the bend again! So somehow the screws must be tensioning the blade somehow.

How do I correct this, or rather how do I figure out exactly what the problem is?

Bram

[Andrew Pitonyak]

How man screws?

A few things I might try:

If you place the blade in place, does it look like the holes on the blade align with the holes on the handle?

Do the holes look like they are drilled perpendicular to the face?

If all the screws are in place, but NOT tightened, is it warped?

If not, which screw, when tightened, seems to cause it to warp? I might try tightening them a bit at a time, see how that works, then try a more aggressive tightening on one screw at a time... You might need to change the order in which the screws are tightened to see if you can tighten two out of three without warping the blade.

Just a few things I would look at to start.

[Jim Koepke]

There could also be some misalignment with the handle and the back. If this is the case, tightening the screws my be tweaking the back, causing the bend.

You could try placing the saw handle in a vise to watch the back to see if it moves when the screws are tightened.

jtk

[Pat Barry]

Possible that the handle itself is warped? Maybe just slip in the blade and check for gaps between the slot and the blade all around before tightening. If the handle is warped it is probably time to make a new one.

[Pete Taran]

This is a pretty common problem for those versed in the saw doctoring arts. The problem is that the blade, back and mortise are off somewhere. By off, I mean that handle is slotted slightly off center from the mortise the back fits in, or the back is not completely uniform in thickness from one side to the other.

The fix is relatively easy and straightforward. The side which is concave needs to have a paper shim inserted between the blade and the handle or the back and the handle depending on where the inequality exists. When the screws are tightened, this counteracts the force from the other side and with any luck, will fix the problem. You could also try to scrape the handle cheek where it meets the blade on the convex side of the curve, though that is pretty hard to do on a slot that is only .040" wide. Hope this helps.

[Mike Allen1010]

+1 for Pete's suggestions.


I like using shop built tools – marking gauges, planes, back saws etc. That said, the issue you're describing is the reason why I think most people are better off buying a quality back saw (either new or vintage), rather than trying to build one themselves. Getting the alignment of the blade, back and mortise in the tote exactly right is a real challenge – the tolerances your talking about are extremely tight (especially if you prefer a thinner than typical saw plate).


Pete's suggestions are IMHO 100% on target (not surprisingly, Pete is an "expert" in the world of handsaw's in every sense of the word).. However, as you try to execute go suggestions, I think you'll find it's easier said than done. Good argument for buying a quality back/joinery saw from some one who knows what their doing.


For me, because joinery is one of my favorite parts of hand tool woodworking and because the quality of your back\joinery saws makes a big difference in your ability to execute quality joinery and have fun doing it, my view is this is an area of the tool budget where you definitely get what you pay for and and investment inequalities saw is worth it.


All the best, Mike

[Bram de Jong]

Thanks for the suggestions guys... Will experiment and come back with some results!

[Derek Cohen]

As Pete mentioned, the problem is a high spot inside the blade slot in the saw handle. This may have occurred as a result of the wood moving over time. The fix is to scrape away the high spot using a thin scraper blade. This will increase the kerf, which can be shimmed with paper or foil.

Regards from Cape Town

Derek