Shaping the Teeth
Even though its still early in the process, its a good idea to file the teeth using the rake angle geometry you want to end up with - either a rip or a cross-cut profile. These are two distinctly different styles of teeth, and you need to decide now what you want. Rip saws are for sawing along the grain, crosscut are for across the grain. Rip saws are somewhat easier to file for a beginner, but get a few crosscut saws under your belt and you'll wonder why you thought they were so difficult.
Since the saws being made here could be used for either purpose, I'll discuss both. A fairly recent "innovation" is that dovetail saws should be filed rip, since that is the direction in which they were cut, and recently more and more dovetail saws are being sold in this configuration. This was not the case when I was learning - a crosscut profile was considered to be more useful than a rip, because while you can use a crosscut saw for short ripping functions (albeit slower), the opposite is decidedly not the case.
This is because a rip saw leaves a much rougher edge than a crosscut saw - you can get away with this when sawing with the grain, but not going across it (it's for much the same reason you need knickers in a dado plane, but not in a rabbetting or grooving plane). Using a rip saw invariably means you must use a marking knife of some sort to cut the edges of your dovetails - or use a backer - before you saw them, else you will get a ragged edge on the back side of the cut. The chance is less so with a crosscut saw, because the teeth act more like knives than the chiseling cut of the rip saw. Here, you can see what the differences are in the two types if you were to sight down a saw from the end:
Dad always told me that you could slide a needle down the valley that forms between the teeth of a well-sharpened crosscut saw. I say this just to point out the slicing cut that it makes. Personally, I have used each for cutting dovetails - and I can't say I prefer either way. Regardless, a cross-cut saw is needed for making some shoulder cuts for tenons, so having one of each seems like a good idea.
For rip teeth, you can use the following as a guide for setting the rake angle (note, the heel - or handle - of the saw would be to the right, and the toe - end - of the saw to the left)::
The top one is the more aggressive pattern, which can be more difficult to use if you're not as experienced with hand saws as you'd like to be. If starting cuts is an issue with you, you might consider the lower diagram (or something between the two) which relieves the angle of attack slightly to make for a less aggressive cut. It'll be slower, but easier to use. Disston started using the lower profile at some point after the turn of the century for some of their saws, so there's no need to feel like you're cheating if you do decide to use the less aggressive cut. I know users who sharpen their dovetail rip saws up to a full 15 degrees to make them easier starting. I would suggest you experiment with your own to find out where you are most satisfied.
Much the same is true for a crosscut profile, but it starts out with a less aggressive angle. Here is about the most aggressive angle I would use on one:
You can increase the 12 degree angle for a less aggressive cut, if you prefer. There is more discussion of these angles on the Vintage Saws site, if you are interested.
Truth be told - I never sit there with an angle gauge to determine what exact angle I'm filing. I stick the end of the file into a block of wood at what "looks" to be about right, and go with it. I often jam the other end of the file into another block of wood to help me maintain a consistent angle, however, and use a bevel gauge so I can repeat the angle when I turn it around for the other side.
To initially shape the teeth, I work from one side only, and perpendicular to the blade. Trying to skip every other is difficult at best, and unnecessary at this point, as I'll finish sharpening them later by doing every other tooth.
I'm not going to worry about the fleam angle (crosscut saws only) at this point, just getting the teeth properly shaped. Starting from flat, this will be the progression of the teeth as I file them (note - I'm showing a rip profile, but a crosscut would be similar):
For shaping the teeth, I try slowly bring it to the next to the last diagram, leaving just a little bit of flat space on the top of the teeth. This helps me by serving as a guide to maintain the appropriate size of each tooth as I'm filing away. I stop there, and leave the remainder for the final sharpening.
A bit blurry - but I think you can see what I mean...
Adding Set to the Teeth
Now is a good time to "set" the teeth. "Setting" the teeth simply refers to bending every other tooth over slightly one way (the remaining are bent the same amount the other way) to increase the kerf size cut by the blade. You can see the end effect in the rip and crosscut profiles diagrammed above. The reason for this is to keep the blade from binding against the wood its cutting. Softwoods need more set, as they "spring back" more. Wet woods need the most set. Hardwoods need less, and for cabinet grade hardwoods, it's best to try and get away with as little kerf as possible. It's been my experience that you need at least some.
Setting the saw is done with a tool called, surprisingly, a saw set. Stanleys are among the most common with the 42x being my preferred - but others can be just as serviceable. For teeth finer than 14 PPI, it might be necessary to file down the hammer of one of these so it fits properly over the saw tooth. The ultimate goal is to end up with a set where about 1/2 of the tooth is bent over. Subsequent sharpenings reduce the amount of set simply by filing it away as you file down the tooth, therefore requiring you re-set the teeth at least every third sharpening, and maybe more often with finer teeth.
Using a saw set - notice the mark I've made on every other tooth with a marker:
Start by setting every other tooth on one side, then flip the saw around and set the remaining teeth the other direction. At this first set, it might help to start over again and do it twice to make sure the set is consistent on both sides. You may want to do this second round of teeth setting after you have sharpened the saw, especially if you are too eager in your sharpening and file away most if not all of the set you've just put into the teeth.
A word of warning - if you set a tooth one way, then decide you need to set it the other way, you could break the tooth off. It is generally good practice to avoid doing it, so heed the following advice. One problem I always seem to have when setting teeth this fine is that I lose my place while setting every other tooth. To overcome this, I often take a marker such as a Sharpie and mark every other tooth for reference, as I mentioned above. This helps me avoid problems like mentioned above where you accidentally set the teeth the wrong way. If you do - don't fret, it's not the end of the world. Subsequent filings will essentially remove the set, and at some point in the future you can start over. Till then, it won't make a huge difference in how the saw performs so long as you are consistent in the set from side to side. But do try to avoid it.