One note about sharpening such fine teeth - even your stance at the vise can make a difference in how you apply pressure to the file - and if you don't move as you progress down the saw, it will make a difference in how the saw is being sharpened. Stop every so many teeth and adjust yourself accordingly! Besides, you need to make sure you can see what you are doing.
For rip-filed saws, you're nearly finished. All that's left is to run a file across every other tooth from one side, then flip the saw and run the file from the other direction on the remaining teeth. This is done so the filing is consistent from each direction, and any inconsistencies that are created by your technique are repeated in an opposite and equal manner. The angle should be the same one chosen previously (the lower is the less aggressive pitch):
It often helps to use something to darken the teeth so you can see which teeth you've filed and which you haven't. You can use chalk, layout dye, or "Sight Black", which an anti-reflective aerosol spray used by gun-owners for reducing glare when sighting through their scopes. It wipes off easily, leaving nothing behind. Another great method is to use the soot from a burning candle or alcohol lamp.
As shown in the above diagram, file the teeth at 90 degrees to the blade, using the same angle used in shaping the teeth above. Here's the real-world shot:
This last step usually only takes a light stroke or two of the file, just enough to remove the "flat" part left behind in the step above (see the "shaping" diagram). The flat will help you as a reference, filing the very last of it away should leave all of the points of the teeth in the same plane along the length of the saw, as seen in steps 4 and 5 of the diagram below - which goes through the entire shaping process:
The process for crosscut saws is much the same as for rip saws above, but with two very important differences - the first being the angle the teeth were cut at - which will be the same angle you chose when shaping the teeth previously, similar to this (the 12 degree angle is the minimum, most aggressive angle I would use on a crosscut saw - more rake angle will give you less aggressive, easier starting, but slower cutting performance from your saw):
The other difference is the fleam angle. For our purposes, fleam angle is just the angle that you file the teeth at, which basically means 20 to 25 degrees off of perpendicular, as shown below, whereas a rip saw is file perpendicular. File every other tooth, then flip and file the remaining. Always file pointing in the same direction relative to the saw - if you do one side angling the file towards the toe of the saw, make sure that you also file towards the toe of the saw when you flip and file the other side.
Or, using a real-world photo, something like this:
Because you are just introducing this angle to the filing, it may take an extra stroke to remove enough material to properly form the teeth. Just be careful, and watch that you don't remove too much that it makes it difficult to file the teeth from the other side. If you have to, just file a little, flip the saw file the other side, then repeat until you are finished. It's easier if you remove too little than if you remove too much.
It is important that you file the proper teeth for crosscut, and how you file them is determined by the set of the teeth. I tend to pick a side (i.e. the tooth bent away from me will always be on the right), and then file towards the toe of the saw. It seems silly, but look at how the teeth are forming in this diagram, with the cutting points of the teeth on the outside edges of the blade:
I know this might seem trivial, but I've caught myself filing the teeth backwards! So watch yourself! To help clarify the angles a bit more, here's an overhead view of how the files should be held:
For back saws. I use about a 20 to 25 degree angle. A steeper fleam angle results in a sharper saw, but also one that dulls quicker (on panel saws I use a 15 to 20 degree angle). You should end up with evenly shaped teeth, as below:
It can be hard to tell (and even harder to photograph), as because of the sharpening every other tooth might look small - so look at it against a light colored background and look at the entire tooth.
For a final tuning, after the saws are complete and assembled, draw a straight line on some lumber (with the grain for rip, across it for crosscut) and do a test cut. There are two things you are looking for - the first is that the saw tracks along the line correctly, and the second is that the tooth marks left in the wood don't show an obvious tooth pattern, like if one tooth is set more severely than the rest. The fix for both of these is to draw a stone (I have an old broken oil stone I use just for this purpose) along the side of the teeth. To correct a tracking problem, stone the side of the teeth that the saw tracks to. It should only take one or two light draws with the stone to correct. If it takes more, you may need to re-set the teeth on the saw.
- A few generic tips on sharpening that might prove helpful that I've not mentioned previously, but should be:
- I've seen or heard reference to this statement many time in reference to sharpening a saw: "When filing the teeth, it can help to count the number of strokes so as to remove the same amount of metal on each tooth". While I agree with this statement in principle - and can be a great help to a beginner, a better method is to joint the teeth, then gauge your filing according to removing the "flat" left behind by jointing.
- When sharpening - always "lift" the file on the backstroke to avoid dulling the file more than necessary.
- To reduce the amount of set on each side of the blade equally, take an equal number of stroke on each side using an old oilstone.