New Teeth

Project: Cut new cross cut teeth on a 12” backsaw
Required ReadingSaw Filing – A Beginner’s Primer and The How’s of Setting Saws, both of which can be checked out from the Vintage Saws Library. Print out both, read twice and high-light the angles mentioned. If you actually do that, this post is superfluous. Required Tools: Saw vise, a new saw file (you’ll wear out at least one side), saw set, magnifying lens, good lighting.
Alternative posts: Norse Woodsmith, Sharpening Hand Saws, Sharpening Handsaws by Bob Smalser
Video: Fine Woodworking: Sharpening a Dovetail Saw

clampedSawThis backsaw has 12 TPI (teeth per inch) filed rip. It also needs a heavy jointing as the middle teeth aren’t at the same level as the end teeth. I want a cross cut at the same TPI. The saw is jointed, which removed most of the teeth, and every other gullet marked. For me, marking is invaluable because I can’t keep track of fleam (the angle at which a tooth edge meets the wood,  think chisel bevel angle) and I make multiple passes. Don’t bother for rip, the fleam is the same on each side. I draw the fleam angle on the vise jaws for constant reference.

levelIt is important to have things level so you have a reference for the rake/hook angle (the angle of the tooth from a vertical). Ready to file. Note that, in the photo, the plate extends above the vise much more than it should. At this height, as you file, it markedPlatewill vibrate, squeal like a pig and the file won’t cut very well.

fileMake the file guide shown in Pete Taren’s Primer. I’m going for a beginners saw in all aspects so I’m using 15 degrees for both fleam and rake. Use your smallest file (4” 2X (double extra) slim taper or smaller). As you file, keep the file level and parallel with the fleam guide lines and the top of the guide level. I make a complete pass on each side, handle to tip. I also only file from one side and don’t flip the saw, which is why I draw the fleam angle on both jaws (the reference lines look like a chevron). Read the Primer again, there are a lot of details to get right. You might note that my file guide is much taller than the one in the Primer. This is sub-optimal as it hits the vise and effectively halves the length of the file.

fleam jig2Another guide for the fleam angle, which I like better, is a slotted block of wood. And, of course, Lee Valley is here to help you.
fleam jig

How do I know when to stop filing and the saw is sharp? When you can’t see the tips, same as when sharpening a chisel. This is where good light and a magnifying lens are crucial. In the photo, you can see the teeth that reflect a lot of light. These are the teeth that still have a flat tops and need to be filed. When they no longer reflect, they are sharp.

newTeethFinished. Sharpening anyway. I have a long ways to go to achieve a consistent tooth profile.

Setting: Not much to add here, read Pete Taran’s guide. I have the Somax No. 250 set (fine), which I have mixed feelings about. I like the quality but it seems like the pin (that pushes on the teeth) is too tall, which makes it hard to register on a tooth. The width of the pin is just dandy. The other problem I have is the anvil; for the tiny amount of set on these saws, I’m right at the edge of adjustment and it isn’t easy to tweak. And either I have a gorilla grip or the anvil is soft as it has dented after setting two saws. This is the only set I’ve used so it might be the nature of the beast and my ham fistedness. Make super sure you pushing each tooth the correct direction. This gives me fits. Here are two tips: each tooth is a tiny chisel (flipped on edge, bevel towards the middle of the saw plate), the cutting edge is pushed out so it can cut. This also happens to be the direction of the fleam bevel. So, looking down on the teeth, towards the front of the saw, if the file line in front of a tooth points left, the tooth goes left. The other tip is, when looking at the side of a tooth, if you can see file marks on both sides of the tooth, push it. If you can’t see file marks, don’t push. The file marks are the trailing edge of this tooth (ie the cutting edge is on the other side of the tooth) and the “waste” edge of the trailing tooth. (The reflections are gullets).

testIf you over set your saw (as I did, after making two short test runs, grrrrr), you can lap the teeth to reduce the set. Just like a chisel back. I have a strip of sand paper semi permanently mounted to my bandsaw table (I do a lot of lapping), swipe the the plate on each side, measure, repeat. Take it easy, you’re removing a tiny bit of metal from tiny teeth, it goes really quick. You’re making a subtle change to the teeth, I would be surprised if it affects the cutting action. For all I know, it may improve it: the tooth tip will be stronger (no point only engagement), the set will be more consistent and it may wear longer.

Even better, if you have a mill vise (hardened & ground flat jaws), is to over set the teeth, place a piece of paper the thickness of the set on each side and clamp the tooth line in the vise. The paper acts like spacers and any teeth that are over set are pressed back to the width of the paper. Thus, every tooth has the same set. Mike Wenzloff video showing how to do this.

Addendum: Read this posting by Daryl Weir in the woodnet.net Woodworking Hand Tool forum (Refurbing an old 1880’s Disston No.12 thread):

I got the new teeth filed in and started setting them at about .005″ per side with my Stanley 42X. This is a little much for a No.12 but I side dress ever so lightly with a dull file. I never used to do this but Disston recommended this for a smoother cut and longer lasting point on the blade, I haven’t looked back since I started doing it.

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One Response to New Teeth

  1. Pingback: Brooksbank backsaw rehab | ZK Project Notebook

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