When you finally work up the courage to make a handle for a hand saw, the shaping is not the most intimidating part. At least it wasn’t for me. The most exacting part of this whole endeavor is letting in the plate. There are a few things you want to simultaneously accomplish. Most importantly, you want the kerf for the saw plate to be straight in line and plumb with the handle. You want the kerf to be wide enough for the plate to slip in without forcing the kerf open (to avoid slowly splitting the handle) but you want it to be snug enough that it’s not sloppy. Also, you don’t want it to look like crap. Here’s how I do that.
I’ve found that there are two things that make all the difference here. Careful layout and good, old-fashioned paying attention. Begin by making sure your stock is even thickness. Find the middle with your marking gauge, and mark the kerf all the way around from wherever it starts on the top of the handle to wherever it ends on the bottom. The first one you make will require a little experimentation here, so I err on the conservative side. You can always cut deeper but the inverse is not true. A good guess can be made by laying the handle on the plate in what looks like the final position and putting some pencil marks on the top and bottom.
Notice I haven’t given any measurements? You don’t really need them. Outside of making sure your template printed out to the right scale (the danger is real. I have a lovely scrap handle cut out at 105% scale) and making sure you start with stock that is ~4/4, the rest is somewhat subjective. The kerf will effect hang angle, so after the it’s let in, you’ll probably want to try it out and adjust it until it feels right. I’m not a fan of sloppy kerf work where the kerf is deeper than it needs to be. All of that just robs you in the end so I’d rather work 1/32″ at a time and have everything snug as a gun.
The most accurate way I’ve found to do the actual sawing of the kerf is to begin on the top of the handle at the tip. The first cut is essential here, so make it count. Start on the push stroke if you can, because you’ll get a cleaner result. Also make sure to split the line.
Stopping every couple of strokes just to check, I saw all the way down the top of the handle like I’m sawing the most important tenon of my life, and just through the tip as it begins to curve down on the other side.
I use that kerf to line up my second cut by placing the toe of the saw in the kerf and the heel on the line of the rounded part of the body of the handle. A few light strokes lines everything up and from here I cut as far as I can with the dovetail saw. Again, stop and check every few strokes just to make sure something hasn’t gone entirely wonky, but if you start well, it’s likely you’ll be fine at this point.
Here’s what that looks like without the saw:
My tenon saw finishes the work and does two things. First, it makes the kerf deep enough, but just as importantly, it makes the kerf just a tad wider to accept the saw plate. This is your only chance to “fix” any inconsistencies from the dovetail saw. I say “fix” because you can’t really change the kerf at this point, but judicious use of the tenon saw can help even out any minute inconsistencies you left behind. It can also make them worse, so pay attention. Saw until you have a level kerf (i.e. the saw enters and exits without rocking on any material at the base of the kerf).
Insert plate. Drill for saw nuts. Done.
I mentioned that you want the plate to sit straight and plumb in the handle. The wood doesn’t have an opinion on the matter, so you have to define these two planes. Straight refers to what you see as you look down on the handle from the top and plumb means looking at the handle as if you were staring down the barrel of a gun. Here’s why the method above works. Made with care, the first cut will ensure the kerf in the handle is straight and if the first cut is straight, the second cut (resting on two points) will give you plumb. There, now it’s no big secret.