Overview

My interest in Saw Filing arose first from a desire to use older saws, all of which were dull when I bought them. Second, from the lack of a Saw Filing shop in my area. Initially I filed using only a file handle and various visual aids - lines on a piece of paper held in the saw vice to help with the bevel angle, a block of wood on the file tip to maintain the rake angle. The results were poor.

I eventually found a used saw file holding jig, but found it to be not quite good enough. I eventually built my own version of that jig, then a couple of more versions. These pages include the jigs and how to build and use them, along with other material I discovered along the way.

Contents

1. Introduction. Do you need a jig?
2. History. Patented jigs.
3. The Problem. Why saw filing is difficult.
4. The Jig. The jig I use.
5. Saw Filing. Tips from my experience, some particular to this jig.
6. Some Theoretical Issues. Are some filing patterns better than others?
7. Sloping Gullets Demistified. What demistified?
8. Quiet Version. A quiet pattern.
9. Quick Touch Ups. Joint free filing?
10. Reshaping Teeth. Tough enuf?
11. Other jigs. Shop made jigs by filers.
12. Jigs for Sale. Accept no substitute.

Introduction

While this level of skill if possible, most people would not achieve that time unless the files saws for a living. The problem seems to be that the skill is easily lost between Saw filing sessions. By the time you are back in the groove, you have already spoiled half the teeth on the saw.

Using this shop-made jig will reduce the number of variables to a manageable set, even after a long interval between uses.

History

This saw-filing jig was patented in 1876, patent number 173,866, by Elias Roth, of New Oxford, Pennsylvania. The circular part, B, allows you to set the bevel angle, the temporary guide E to set the rake. The jig slides in slots on the sides of the clamp that holds the saw, implying no ability to change the file slope.

While much praised in articles of the time, this jig did not get saw filers beating a path to Mr. Roth's door. There are many patents for variations on this tool, many much more complicated and non which you can build quickly out of wood.

I had seen pictures of similar jigs and finally realized that the arms are curved for a reason - they allow a full use of the file even when using bevel angles closer to 45 degrees. My Version I got pretty cramped in those cases.

The Problem

Saw filing requires that you maintain three angles during the filing action. Worse, you make contact with the saw at a single point on the file, and that point moves down the file on each stroke, so the relative pressure required of your hands changes continuously.

While filing a saw we must keep three angles consistent throughout the operation: the rake, the bevel, the slope.

Defining these 3 angle can be confusing - maintaining then during filing difficult. These definitions are based on having the saw held vertically in a saw vice with the teeth facing upward. So, the blade is vertical, the line of the teeth horizontal.

1. Bevel - the angle the file handle tilts back toward the saw handle in the horizontal plane. If the file is square to the face, the bevel is 0.
2. Rake - the tilt of the file face in contact with the tooth front. If this face is vertical, the rake is zero. For most saws, the file face is tilted so the top is toward the handle.
3. Slope - the angle the file handle tilts down from the horizontal. While most people can file keeping the file more or less horizontal, it is much harder to file while keeping the file tilted upwards. To simplify non-zero slope angles, most metal saw vices have a capability to tilt the saw blade from the vertical. To get a 20 degree slope, you tilt the vice away from you 20 degrees and work with the file horizontal.

   There was a brief time in the latter third of the 1800s in which tilting the saw during filing was a common practise. A saw filed with non-zero slope has been said to have sloping gullets. Filing with non-zero slope is rarely mentioned today. I have taken some illustrations from the Disston Lumberman Handbook of 1917 and included them in a discussion of Sloping Gullets.

The Jig - Version 3

Checking over the jig, it became clear that over time the hole in the dowel for the file tang has gotten a little lose. In fact, because the tang is 6-sided, it is not easily gripped. The tip is much easier to grip - it is three sided and a little larger.

Perhaps recalling the way Woodnut4 holds his files (see Other jigs), I decided to move the file holding dowel from the tang to the file tip. The result is Version 3, which in use is actually better than version 2.

As well as switch ends, I also increased the lengths of both braces by 1". This gives a little more room between the file and the back dowel during use.

This is the far end of the jig, the end on the other side of the saw. The far brace (it is on the other side of the saw during use) is 5-1/4 inches long. Holes for the two dowels are drilled at 45 degrees. I use Forstner bits to drill these holes - they are able to handle entry at an angle fairly well. The file holding dowel is 3/4" in diameter, with a 10/64" diameter hole in the middle of one end. The triangular tip of the file fits into this hole, then the dowel is tapped on a hard surface to seat the file. The back dowel is 3/8" in diameter and about 5" longer than your longest file. This one is 14" long, but could be longer. Any extra length extends beyone the far end of the jig, where it does not interfere with anything. (Extra length is a problem only when mailing jigs!) The Slider controls the bevel angle. The slider is discussed in more detail below. This is the near end of the jig, the end you hold. The near brace is 4-1/4" long. The hole for the back dowel is at 45 degrees. The other end is mitred at 45 degrees. A 7/64" diameter hole to hold the tang tip is drilled into this mitred face. You should not drill this hole until you have done a test assembly of the jig and determined where the tip of the file should be so that the file is parallel to the back dowel. Since the file tapers the file cannot be parallel to the back dowel over its entire length, of course! My limited experience with this version of my jig (sharpened 4 saws) in this configuration confirms its superior file holding ability. However, it is a little tiring on the right hand. I am starting a modification to the near brace to solve this problem. Once built and tested, the new variation will be shown here.

Clamping Mechanism

This picture shows the simple mechanism that allows for both adjustment of the brace along the back dowel, and adjustment of the file holding dowel, but also allows locking of both dowels once the desired adjustment has been made. There is a fairly wide saw kerf from the edge to the dowel hole (I use my widest kerfed rip saw for this). A T-nut in one side, a machine screw from the other side. The end of the machine screw is visible in the "far brace" in first picture. I normally counter sink the t-nut to make the braces easier to hold. Tightening the screw once the jig has been adjusted quickly locks the position.

File Holding Dowel

The file holding dowel is a 1-1/2" piece of 3/4" hardwood dowel. The file tip (in version 3, tang in version 2) fits into a 7/64" diameter hole tightly enough that the file cannot rotate. The adjustment for rake is done by loosening the machine screw and rotating the file holding dowel. Notice the plier teeth marks on the dowel. Make sure you rotate the dowel rather than the file, since turning the file will put unnecessary wear on this hole.

The Slider

The slider is a small wooden block that slides easily along the back dowel.

The hole is at an angle to the length and determines the bevel angle. I use bevel angles from 5 degrees for Rip saws to 25 degrees for crosscut saws. I have many sliders with different dowel hole angles for special purpose saw filing. The hole is always square to the width and should be in the middle of the face. The hole in this slider is angled at 5 degrees. This hole should be just a little bigger than the back dowel to allow free movement. You can enlarge the hole slightly with a round file if it binds. You can also oil the dowel to reduce friction (thanks to Ken for suggesting this). Notice that the ends are not square to the edges. One end is at 5 degrees, the other at 15 degrees. These angles are used when setting the rake angle (see below).
There is a saw kerf down the middle of each side. The slider rests on the saw with the saw teeth in this saw kerf. Usually the slider is in contact with the saw vice, sliding on it rather than having the saw teeth in contact with the bottom of the saw kerf. In order that the jig slide along the saw from tooth to tooth, this kerf must be wider than the kerf on the saw you are sharpening. I initially worried that continued use would slowly saw through the slider. This has not happened yet and I have done many saws.
This view shows the two saw kerfs, ideally perpendicular to the face. If you want sloping gullets, you slope these kerfs.

Using the Jig

When filing, I almost always hold the near brace in my right hand and the slider in my left hand. So while my right hand does the actual filing, my left hand positions the jig relative to the gullet. When I want to file one side of the gullet more than the other, I exert a little force with my left hand on the slider, pushing it, and hence the entire jig, toward the tooth that needs more filing. For exotic filings, where the front and back bevels are not equal, this extra control over the jig position is essential. The file can be on either the left of right of the back dowel -- here it is on the right. In this position, the third or fourth finger press down on the file. This can be a little awkward. I normally work with the file on the left of the back dowel, pressing down with my index finger. After some use, I think yet another modification of the jig would make it more comfortable. More soon.

Saw Filing

1. Select a file appropriate to the size of the teeth. I use Extra Slim for most large saws, switching to Double Extra Slim for the finer toothed saws (over 10 ppi). Generally the file should be large enough so that the teeth cover less than half of the file face during filing, theoretically allowing you twice as many filings before the file becomes dull.

2. Select an appropriate bevel angle. I usually use a 5 degree bevel for Rip Saws, 25 to 30 for crosscut saws. Assemble the jig with appropriate slider, then tighten the braces. Make sure the braces are level and tight on the back dowel.

3. Arrange your saw vice so that you are in a comfortable position while filing. I sit while filing, with the saw vice just below shoulder level. I can comfortably reach over the saw to hold the far brace, but am close enough to be able to see the tips of the teeth, and the flats left by jointing, clearly.

4. Set your work lighting to make the flats clearly visible. You have to be able to see the flats while filing, so find a position that gives the best reflection of light off the flats when you are in filing position.

   I have found that in my shop, the flats are more visible with the saw handle on the right end of my saw vice. The flats are easier to see on the first pass, since they are wider. It is much more important to be able to see them on the second pass, when you are removing them completely. So, always do the first pass with the saw in the direction in which the flats are harder to see.

5. Joint the saw. Most of the loss of metal in a saw occurs during jointing, with only a small amount being worm away during use. I find the existence of the flats produced by jointing very helpful during filing, so I joint very lightly almost every time I sharpen a saw. If you do a lot of saw filing, you might be able to sharpen without jointing.

   Jointing should put a small flat on the top of each tooth. If the teeth are not about the same height, some of the teeth will not get a flat after a light jointing. If there are just a few short teeth, don't worry. They won't do much cutting now, but will eventually. It is not worth it to remove a whole lot of metal here just to get a flat on every tooth. If most of the teeth have no flat, joint a little harder.

   Charles Johnson recommends removing most of the teeth on one side of the jointing file: "place it on a large true faced carborundum whetstone, and grind one face only, until it is nearly smooth". He recommends jointing every time, but is able to joint very lightly.

6. Set the saw, if there is currently not enough set or the saw is badly set. I only set about every third to fifth sharpening, if I noticed the saw was binding during the last use. If the existing set is really bad, you might do another light jointing after this setting.

   Most saws I have bought have too much set. They may have been set for wet softwoods and I mostly saw dry hardwoods. A tapered saw requires very little set for use in dry hardwoods. All saws will need more set in wet softwoods. More on setting saw teeth using a drawing from an old Chas. A. Strelinger & Co. catalog.

7. Shape the teeth, if necessary. If there are few gullets that are much smaller than their neighbours, do these teeth first. You would file this gullet until it is as big as its neighbours, even if that means filing away more than half of the flat. This step is only necessary if the saw has been badly sharpened. Again, don't worry if a couple of gullets are bad. Clean them up a little each time you sharpen.

8. Select a sharpening strategy! There are sharp disagreements on which gullets to sharpen from which side of the saw. I have my own strategy, which I describe here. I work from the heel to the toe, with the tang of the file always closer to the handle than the toe. This means that the tooth on the handle side is pointing away from me, the tooth on the toe side toward me. Put another way, I am sharpening the front of the tooth with the set, the back of the tooth against the set.

   You can do it other ways. You can file with the file tip pointing toward the saw handle, or toward the saw toe. You can work from the handle toward the toe, from the toe toward the handle, or alternate. Make sure your strategy gives you the best possible views of the teeth tips on the second filing, when you have to just remove the jointing flats. Find the filing strategy that works for you, lets you produce the most consistent filing, and stick to it.

9. Set the rake angle. Loosen the screw holding the file dowel. With the slider on the teeth and the file in the gullet, rotate the file dowel so the file has the correct rake angle.

   If the saw teeth already have the correct angle, fitting to an existing gullet works fine. If you want to change the angle you need a jig to help. My sliders have angled ends - one end at 5 degrees, the other at 15. I set a spare slider on the teeth at a gullet, turn the file to match the slider, then tighten the machine screw, locking the dowel position.

10. File alternate gullets from the handle to the toe. This means that the slider will be on the toe side of the file.

    As you start each gullet, check both neighbouring gullets. If the gullet you are filing is noticeably bigger/smaller than its neighbours, file away less/more than half of the flat. [When using my jig, take a couple of practise filing motions to make sure you are lined up correctly. If you are not lined up the dowel will jam in the slider. If the dowel does jamb in the slider, let go and the jig will move to the correct position. Take a light grip and slide back and forth a couple of times, then resume filing.]

    When you near the toe, the slider will drop off the end of the saw. Flip the back dowel to the other side of the file, reset the file rake angle, continue to the toe. If you move back to a gullet you just filed, you can use that gullet to set the rake angle. Having to reset the rake angle for the last few teeth is a real nuisance - you are down to a few teeth on a part of the saw you don't really use. I do it anyway, so the saw is uniformly sharpened.

11. Switch the saw in the vice. Working from the heel to the toe, file alternate gullets with the tooth closer to the heel facing away from you. On this pass you must remove the flats on all teeth.

    Before you start in a gullet, check the size of the flats on either side. If the flat on one tooth is larger than on the other, you will have to file the tooth with the wider flat harder. It is actually quite easy with my jig to work only one side of the gullet. If you do not force the corner of the file into the bottom of the gullet, you can file only the tooth face of interest.

    When the flats are almost gone, rotate the file away from the teeth so you can check both teeth to compare the size of the flats. When you are almost done, ease up on the filing pressure a little. The advantage of this jig is that you can move the file away from the teeth to get a good look at the flats, then bring it back with exactly the same file position.

Some Theoretical Issues

From Charles Johnson's Saw Dictionary - work with the file handle toward the saw handle.

From the Disston Lumberman Handbook - work with the file handle pointed away from the saw handle.

The Burr Argument

If you use Method II, the burr appears on the inside of the front of the tooth, on the outside of the back of the tooth. If you use Method I, the burr appears on the outside of the front of the tooth, on the inside of the back of the tooth.

Why does it matter where the burr is? It matters because these burrs are broken off by contact with the wood as you saw. The breaking off could produce a degraded cutting edge. If this is true, then it makes sense to have the degraded edge on the back of the tooth rather than the front of the tooth (for saws that cut on the push stroke). This suggests that Method II would provide a longer lasting sharpening.

I will take some microscope pictures of teeth filed each way and include them here.

The Visibility Argument

Charles Johnson says: "[a right handed filer, working with the file handle toward the saw handle, gets] ... the better view of the teeth points on the second filing [saw handle on the right], and is best adapted for rapid work, while the [saw handle on the left during the second pass] gives the better view for accurate filing of the teeth.

This is important - the filer must be able to see the teeth clearly, in particular the points and the flats on those points created by jointing, with visibility most important on the second pass.

There are 4 permutations of the two saw positions (handle on the left or right) and file positions (file tip poiting toward saw heel or toe). A third factor is whether you are right or left handed (left handers please reverse all terms in this discussion.) Each complete saw filing involves having the saw handle on the left during one pass, on the right during the other.

In these drawings of a saw as viewed from above, the zig zag is the gullets, the lines going to the edge mark the cutting tips of the teeth (the most important part when filing). The position of the saw handle and the filer are labelled and the file position shown by the dark line. The bevel on the front of the tooth is marked in green, the bevel on the back of the tooth in blue.

	Filing with the set on the tooth front, looking at back of next tooth. As bevel increases, filer crammed into blade. Filing even numbered gullets.
	Filing with the set on the tooth front, looking at the front of that tooth. Filing odd numbered gullets.
	Filing against the set on the tooth front, looking at the back of the next tooth. Filing odd numbered gullets.
	Filing against the set on the tooth front, looking at the front of that tooth. As bevel increases, filer crammed into blade. Filing even numbered gullets.

Using Method II (drawings 3 and 4), file tip toward saw handle, the filer is still on the wrong side of the file for one pass down the saw.

With my jig, I can rotate the file away from the tooth for a quick visual check of both sides of the gullet, then rotate it back into position with no loss of accuracy. Since this is easy no matter which direction the file points, I don't think the visibility argument favours one file direction over the other.

The Surface Quality Argument

When you file with the set, the file moves easily and smoothly across the face making little noise. When you file against the set, the file skips and bounces as the teeth contact the leading edge of the tooth, making quite a bit of noise. It is my belief that the surface on the with tooth is much better than the surface on the against tooth. I believe that this effect is as great as the burr effect, if not greater.

I will take some microscope pictures of teeth to see if any effect is detectable.

The Sloping Gullets Argument

The sliders determine the slope of the file. If you want a slope, make sliders with angled saw kerfs.

When filing sloping gullets, it is usually easier to tilt the saw in the saw vice than to tilt the file. My saw vice only tilts away from me - the geometry of the vice and the bench clamp prevent tilting toward me. This means I can only file up the gullets, not down the gullets. Since the gullets always slope down toward the handle, the file handle must slope back toward the handle as well.

So, with standard saw vices, it is difficult to use Method II if you want sloping gullets.

Quiet Version

This allows you to perform an experiment on noise and effort depending on whether you are filing with or against the set. I think you will find the difference considerable.

Based on this observation, you might want to try a saw filing system that takes 4 passes along the saw, rather than the usual 2 passes. Given the extra saw handling, the gains in noise and effort would have to be considerable.

Pass 1 - Start at the heel, file in the gullet with the tooth set away on the saw handle side, jig set with the file handle toward the heel, and file just the front of away tooth, removing half of the flat.

Pass 2 - Working from the same side of the saw, from the saw toe, with the file handle pointing away from the saw handle, work back toward the saw handle filing just the back of the teeth done on the first pass (the away facing teeth). Since you are finishing the tooth, on this pass you file to just remove the flat. Now both front and back of the away facing teeth are done.

Pass 3 - Working from the other side of the saw, file handle toward the saw handle, file in the gullet with the away tooth on the saw handle side, file just the fronts of the away facing teeth. On this pass you are removing only half of the flat.

Pass 4 - working back from the toe to the heel, file handle facing the toe, do the back of the teeth facing away from you. On this pass you are finishing this set of teeth, so you file to just remove the flat.

This takes twice the passes, but the filing of each tooth goes much faster and is much quieter - you can easily do it this way without hearing protection. Since you are only filing one tooth at a time, you need only look at that one tip. As well, you put the best possible surface (filing away surface) on both the front and back of each tooth.

So, there are three filing systems to try. If you detect an advantage to any one of them, let me know.

Quick Touch Ups

Set the jig up as usual, then without jointing or setting, work from heel to toe just filing the fronts of the teeth. One smooth filing stroke to each tooth. Such a light filing will change the height of each tooth by at most a few thousandths of an inch. Such a small change will not put the saw seriously out of joint.

Reshaping Teeth

Changing the filing on a mitre-saw from 15 degree rake and 20 degree bevel to 10 degree rake and 40 degree bevel took me two complete filings to get most of the teeth into the new shape. The first filing was very difficult, as the file kept getting stuck on the edges of the old bevels. Many of the teeth looked pretty ugly after the first complete filing.

On the second filing, the teeth were more uniform, but some tooth backs were still not flat.

Removing set is more difficult than tapping the teeth back with a hammer. After several passes down each side there were still teeth that were uneven. Side filing seems to be required to make the teeth uniform. I suspect that there is a lot of spring back since the teeth are not being hammered against an anvil. Do this before reshaping.

Other jigs

Ken Brownlow has made a jig like mine. Ken says: "It's not as pretty as yours, but it's been well used. I used spray oil on the dowel which helped a lot, and that's some left over chalk on the file." Looks pretty enough to me. Anyone using a jig like this or like mine will soon realize how important it is to have soft corners on the parts of the jig you hold. A few minutes with a file to soften all the corners and you will be a lot happier when filing. The idea of putting oil on the dowel to improve sliding is one of those things that knock you over when someone points them out. Why did this never occur to me?
Woodnut4 is the eBay handle of woodworker who does excellent work sharpening his saws, and the saws he sells on eBay. His jig just help with the rake angle and help it does. If you can find pictures of any of his saws on eBay, they are incredibly regular. In his words and picture, his jig: It's a simple wood block with a hole drilled in it a little smaller than the end of the file you are going to use. Draw a line of what rake angle you want pretty close to tangent to the hole. Push the file in lining up one side of the file with that line. As long as you keep the top of the block fairly parallel to the top of the saw edge you'll hold the angle pretty close.
Bugbear, aka Paul Womack, has a simple jig that combines a file handle and a pointing device that makes any small change in rake angle very clear. Check it out and hunt around his site for other ideas and links related largely to old tools and woodworking with hand tools.

Jigs for Sale

The jigs are finished with Boiled Linseed Oil. The jigs are made of various woods, the standard is oak or beech, but exotics are available for an extra $5 per jig set. Shipping included.

Questions? Comments?