Thread: Tensioning a backsaw plate

I did a quick search of this site and I didn't find (at least over the past couple of years that is) a posting specifically discussing saw-plate tensioning so here goes.

I've read and heard a lot of conflicting opinion on the subject of saw-plate tensioning. Some consider it a vital and often overlooked part of the processes of making and maintaining saws, others call it hokum.

In my experience making my own saws I have come to find that saw plate tensioning, for want of a better term, is vital to producing a saw with a straight tooth line. I only make backsaws using folded backs because I like the traditional looks as well as the servicability afforded because they can easily be removed and replaced without resort to heat-guns and/or solvents to remove the plates of saws made with slotted backs.

I make my backs by driving the back down the length of the saw plate, some call this the 'side-entry' technique. My backs have zero-clearance between the lips of the back when I'm done folding them which prevents driving the plate down on to the plate perpendicular to the long axis of the back.

Here's an illustration.

Saw plate stretching during back installation.jpg


As the back is driven from left to right down the saw plate the friction between the lips of the back and the top of the saw plate tends to stretch the plate ever so slightly. The tooth line however is not stretched and the differential stresses applied to the saw plate tend to cause the toot line side of the plate to wrinkle. This is a problem when using thinner saw plates and it is particularly acute when I put backs on my taper-ground 0.015" saw plates. These saw plates generally taper between 0.002" and 0.003" from the tooth line to the bottom of the back and unless properly tensioned they are impossible to get straight.

In the process of changing the position of the back on a saw I thought to document the process of tensioning on a saw build I have described on another thread in this section (https://www.woodworkforums.com/showth...=181862&page=2).

First here's the saw.

Here it is all fitted up and ready to test.jpg


It's my interpretation of a Disston #4, the saw plate is 0.0155" tapering to 0.0135" measured just below the back. When I was setting up this saw I originally fitted a stainless back but found that it was too light for my liking and switched to one of my 0.125" thick heavy brass backs. I got the saw back together and found that the projection of the back above it's mortise in the stock was higher than I like.

Some is okay but this is too much.jpg


This is how the tooth line looked before I started.

Starting out nice and straight.jpg


So I need to move it down and deepen the mortise to suit. First I took the plate/back assembly out of the stock and clamped the toe end of the plate gently but firmly in the vise.

Step 1, clamp the saw plate firmly but not enough to deform it..jpg


You want the vise tight enough to hold the plate without slipping but not so tight as to dent the plate with the vise jaw serrations.
Now to induce some flex to the plate I use my patent-pending saw-back remover to lever the back up.

Using the patent-pending saw back remover we apply a little flex..jpg


Now that's not very pretty is it?

Um, now that's a bit of a problem..jpg


So how to fix it? First clamp the plate up in the vise and then, with a soft faced hammer tap the back back down onto the plate VERY GENTLY.

Tap lightly on the toe end of the back.jpg


As you tap you will notice two effects. First the tooth-line will visibly straighten and second the ringing sound of the plate will decrease in frequency until it reaches a minimum.

better Getting straighter..jpg better still Straighter still..jpg good Just about done, still a little weave near the heel..jpg


Then, if there is any residual ripple in the plate toward the heel swap the plate around in the vise and tap lightly on the heel end of the back.

a little tap while holding the other end.jpg


And finally we're straight again.

Back where we started.jpg


And the back is down where I want it to be.

P.S.,

If the back is already stuffed all the way down on the saw plate you won't get anywhere tapping it down, you must first pry it up a bit using the patent-pending saw back remover.