Bent/Wavy Back Saw Plate

[Matt Hunstiger]

I have a recently acquired Disston No 4 Backsaw, 14" plate, ~3 3/8" deep at the toe and heel (spine removed, so I'm talking just the plate). It's got split nuts and "Disston and Son" on the spine and medallion, so it's about 1865-71. The problem is a bend/wave in the plate along the tooth-line, about 9"-11" from the heel, and a shorter bend/wave 11"-12" on the top/spine side of the plate. What I've mostly seen online and on youtube is people fixing bends where the whole plate curves to one side or the other, but this plate is straight with a wobble along the top and bottom, so if you pinched the blade just above the teeth you'd feel this up/down wobble, and there's a shorter one on the top side. I first noticed the teeth side one, and then when I took off the spine to see what was going on I saw it was bent along that edge too.

I knew the saw was going to need some work, because the handle was needing replacement (and wasn't very expensive), so I was hoping to fix it up to be a user saw, but I'm not sure how to go about addressing this wavy issue along the top and bottom edges while it's still flat in the middle. It still has nice flex too it. I can bend the blade either direction so the toe and heel are near each other and it flexes back to normal. I'm relatively new to woodworking, and I've been getting some new tools as well as some old stuff, so I would appreciate any suggestions. Thanks.

[Jim Koepke]

Hi Matt and welcome to the Creek.

There are a few causes for the wavy plate you describe. One could be the back has become jammed in the spine/back.

This can often be corrected by holding the saw plate in a vise at the toe and lightly pulling from the handle end.

If the handle has been changed and the saw nuts are a little off, this could be the cause of warping the saw plate.

If the plate has actually been bent, it may be possible to re-tension the plate through a planishing process. This involves using a hammer on a solid surface.

Finally, with such an old saw plate you might find it may be better to replace it. If my memory is working you want 1095 steel for a saw plate. Or you may be able to find a second hand saw and use part of the plate from it.

jtk

[Matt Hunstiger]

Thanks, I will look into these possibilities and see if I can fix it!

[Jim Koepke]

Thanks, I will look into these possibilities and see if I can fix it!

There is some information on saws in the archive > Neanderthal wisdom/FAQs > https://sawmillcreek.org/showthread.php?103805

Bob Smalser posted (section 9) on rehabbing saws, unfortunately his images were hosted off site and the links are broken. It may be possible to discern enough information from the text.

jtk

[Rick Whitehead]

Before you do anything else, I'd clean the existing plate and put the back on it.On a back saw, the back holds the plate in tension, so it's difficult to see what's happening unless the back is on the plate.
By tapping the back up or down on the plate , you can sometimes get the plate to straighten out.
I has an old Disston back saw that was slightly newer than yours. It had quite a wave along the tooth line. By turning the saw upside down and tapping the back on my bench, I was able to get it to straighten out. Note: the plate may not end up the same distance from the back at the heel and top. That's OK, as long as the blade is straight.
Rick

[Matt Hunstiger]

Thanks for the additional information.

[Pete Taran]

In my experience, the wave you describe is due to the heel or toe of the spine being driven down on the blade which grips the plate unevenly causing the wave. The cure is to take the back off, or tweak it to be parallel again and reassemble. Are you saying that the plate is still wavy even after the back has been removed? If it is, a better plan it to just to make a new blade and reset in the back, especially if the blade is pitted and in tough shape.

[Matt Hunstiger]

The blade was wavy along the teeth before I took the back off, and when I took the back off, the blade was wavy (still) along the teeth, and there was a (newly discovered) wave along the plate that was previously inside the back. So it's flat in the middle, but wavy along top and bottom edges. Overall the plate is straight, as is the back. It's a 14" plate, and the toothline wave is about 9-11" from the heel, and the upper wave is about 11-12" from the heel, so the top wave is a bit shorter. Maybe I should just find a supplier for the right gauge steel, 14" x ~4", 1095 steel, as was suggest earlier.

[Mike Allen1010]

Lots of great suggestions here for straightening a wavy back saw plate. Given the purpose of the backsaw is cutting precision joinery, a less than perfectly straight saw plate is real, significant limitation. I think you might be able to get a replacement saw plate with teeth already roughly established from Ron Bontz here on the creek. I believe he also offers saw backs and saw nuts if you're looking to build your own. I'm not positive, but probably worth a try.

[Matt Hunstiger]

Thanks for the suggestion. I tried a metal supplier (Admiral Steel I think) last week, which I found online, but they didn't respond to my inquiry. Might be too small for them to bother.