I haven’t spent a lot of time on the blog talking about the process of filing as I don’t consider myself a particularly good writer, rather I have a good friend who edits my incoherent thoughts and the web already has a few good sources. I think the most popular is Pete Taran’s, “Saw Filing–A Beginner’s Primer”. No single text can cover all the finer points so I thought I’d dive into some of the problem areas that are often not covered.
I’ll start with a common and frustrating problem — broken teeth.
Regardless if you’re starting today or have been filing for years, a broken tooth or worse yet, breaking one when setting, is just one of the things you deal with from time to time. There is truth to the fact that you tend to find more broken teeth on the higher end “London Spring Steel” due to the extra-hardened steel but most often the cause is resetting a tooth in the opposite direction after it’s been set.
But however it happened you’ll need to joint the teeth even with flats on the tops. This would be SOP for starting the process of sharpening any saw regardless of the condition.
The difference with a broken or chipped tooth is that the amount of jointing will vary depending on how low the tooth breaks. A small chip may just be an extra few swipes of the file but if the tooth breaks below the gullet you’ll need to repeat the process, making two passes or joint flat and cut new teeth, the latter being more tricky and time consuming.
Here’s a tip on selecting a file for jointing. Many use an 8″mill (shape) in a smooth cut (grade) and this is a good overall size that works well with a lot of the jigs, commercial or homemade, to help file the teeth square to the tool’s face. The goal is to flatten and not round the tops of the teeth while jointing. The simplest jig is a scrap of hardwood with a kerf in the block that allows the file to be held with a firm friction fit. The file should sit proud of the block at least ½ the thickness of the file.
Over time I’ve found a larger 10″ or 14″ file slightly coarser, bastard or second cut, works better, faster and with the larger size I don’t need the jig.
Another pitfall to watch for is not jointing enough. MAN UP and make a few passes. Don’t worry about taking 1/8 off a 5 or 1/16 off an 11 point. Unless the saw has been recently sharpened, chances are the teeth and gullets need some help and you can’t do that with a flat that will be gone in 2 swipes of your file.
Also note, if you’re adjusting rake angle by more than a few degrees it’s really important to make sure the file is seated in the gullet otherwise the file wobbles resulting in hooked teeth. You’ll run into this hooked tooth problem more with rip saws as people tend to use a wider selection of angles than cross cut.
The easy solution when changing rake angles significantly is to joint way down on the gullets. This is relative to the tooth size as a smaller file is easier to control in hand. One common example is changing a rip saw from the old standard of 8º to something a little more contemporary like 0º on a 5 points per inch saw. In this case I would joint down to around ½ the size of the teeth and really pay attention to holding the angle correctly.
Ok, enough on the jointing. With the teeth now flattened you can shape them. I find when shaping teeth after a deep jointing I like to work in stages. I’ll do 3 or 4 passes on every tooth but leave some flat at the top. It’s really important to let any short teeth go and resist the urge to file them! Look a few teeth down the line. If you’ve got a short tooth coming up let the tooth before and after go. Finish getting the rest close so there is just a hair of the flats left. If you know you’re going to be jointing again, do get fussy at this point. That said it’s good practice if need be.
Now bite your lip and joint the saw again till those short or broken teeth are the same height. The point of jointing and shaping twice allows not only to correct the short or broken teeth but also to even out the spacing or pitch and gullet depth.
One thing often neglected when reading about filing is the importance of consistent gullet depth and keeping them even to the tooth height. I find two things help.
First don’t get fixated on JUST the flats when you sharpen. Drop your head and look at the baseline of your gullets. Is it as straight as your tooth line?
The other tip is a technique that’s often used to prevent cows and calves, or big and little teeth, a hurdle many Jr. Smiths face. The fix is to file each tooth a set amount like 2 strokes then move to the next tooth, leaving some flat on each tooth. This way they all come into shape at the same time. The added side effect I find is your gullets are more even. I personally prefer this method most of the time. The exception is a really short plate or if the shape of the teeth is very good from the outset.
Keep in mind if you’ve got a really bad saw where the pitch or space between the teeth is inconsistent you’ll need to adjust the spacing.
With practice you’ll find there are limits to how far you can push and pull a tooth by filing the front or back BEFORE you run out of flat. Depending on the inaccuracy of the pitch you may need to joint a few times. Above all keep in mind you just need to resist filing the tooth past its flat.
I’ll leave off here and talk a little about setting and sharpening another time.
Saw Monger & Advocate