Here is how I slot my guards:
After HT and final sanding/polishing of the blade -
Tape the Un-Sharpened blade up well, as you will be gripping the blade tightly during fitting. In the sanding stages, you should have sanded the tang to a smooth surface in the tang area near the ricasso. Also, slightly rounding the tang edges helps make the fit up smoother ( your drill bits don't drill square holes, do they?)
I use a set of calipers to mark the slot placement. First I measure the tang and assure that there is a good taper toward the ricasso, with only the last 6-10mm being the final fit area. Then I use the tips to scribe the cut out area on the guard material. The lines scribed will be 2mm longer than the tang width at the shoulder, and 1mm narrower than the tang thickness at the ricasso.
I drill a hole at each end of this box. Use a drill a tad smaller than the box width marked.
Next we put a #0 or #1 blade in the jeweler's saw and saw out the metal between the holes going up one line and down the other. Take your time, and change the blade as needed. Lubricating the blade with wax helps,too.
Now, take an #00 equaling file ( barrette or warding will work,too) and file the cut straight and smooth. Check the fit, and file a little more until the tang stops about 10mm from the shoulder. Use a sharpie and blacken the inside of the slot. Put the guard back on the tang. Put a few layers of tape on your vise jaws, and set the jaws about 8-10mm apart. Grip the taped blade and place the tang between the open jaws and give the blade/guard a few sharp bangs downward to seat it. Slip the guard off and notice where the sharpie has rubbed off. File a few strokes as needed, and repeat. When the guard will almost seat all the way, give it about ten or twenty good thunks down on the vise jaws to make the final fit . Adjust with the file very carefully as the final tight fit approaches.
If this is done right, the guard and tang will be a perfect press fit to each other.
The guard is now ready for final shaping and soldering in place. The fit should be tight enough that merely using epoxy or JB weld to seal the joint will suffice ( but I still solder the guard on most of the time).
Some tips:
Start with an oversized piece of guard material. It is nearly impossible to exactly place the slot in the center of a pre-shaped guard.
Milling the slot on a milling machine is a good way to get a perfectly straight sided slot. A small counter top "mini mill" will do this task. You can even use your drill press and an X-Y vise to cut the slot with an 1/8" carbide milling bit. (This isn't the best solution, but works if you feed the cut very slowly)
Make sure that every thing to be done on the blade is finished before fitting the guard. The only final steps I can think of would be final etching of the blade and etching the makers mark. Painting the tang/guard area with nail polish or a waterproof sharpie will prevent the etching acid from removing any metal where you just fit the guard.
The very last thing to do to the knife is sharpen it. Only on rare occasions is it necessary to sharpen the blade before final assembly. Failure to heed this is the most common cause of cutting yourself in knifemaking.
Taper and round the tang to make fitting into the guard and handle easier.
Tape blades well to prevent scratching the blade or cutting your hand.(Even unsharpened blades are still somewhat sharp)
When filing the slot, use even strokes, and don't "saw" the file back and forth. That damages the file and makes the slot narrower in the center of the metal as it minutely rounds the slot edges. I file the slot as a slight taper from the back side to make the fit at the ricasso easier to zero in on. No need for a big taper, but 5-10 degrees makes the final fitting much faster and more accurate.
On a big thick blade, like a bowie or camp knife, filing a slight shoulder across the tang at the ricasso for the guard to seat on makes the fit-up much easier. These knives were traditionally take-down types, and the "seat" made the assembly easier. Don't get crazy, a few hundredths of an inch will do. The tang should be 80% of the blade thickness at the ricasso. Thus, on a .250 blade the shoulders can be filed .025" deep on each side. I do not use this technique on smaller blades, as it creates a weak spot.
Avoid heat build-up in grinding the guard and handle, as it will break down the epoxy seal, or melt the solder joint on the guard .( don't you hate when that happens?) If you can't hold it with bare fingers, it is too hot.
Think the whole handle/guard process through before you cut the slot, or install the guard. There may be work that needs to be completed before the slot is cut or the guard is permanently placed. Shaping an "S" guard should be done prior to the slot being cut, for instance. You can trim the profile after the cut, but get the "S" shape defined and flat fit at the ricasso down before the cutting of the slot.
Doing most of the final shaping of the guard to center the slot is a good idea pre-assembly, as you can use a micrometer to check the placement.
Sand and shape the handle as much as possible prior to final glue-up. Some things can't be done until all is assembled, but do every step that can be done first.
Sand the guard surfaces to the final finish and tape them up for assembly. You only need to expose the glue areas. This avoids getting glue all over the guard, and scratches in final handle sanding. The blade should be taped up until all work is done on the handle/guard.
Dry assemble the blade/guard/handle and check everything....EVERYTHING.... several times before mixing the epoxy. I can't over emphasis the importance of this step. If it needs to be adjusted or changed, discover that fact now, not after the epoxy is cured. This is the one step that causes the most heartache in knifemaking. It is also the one that shows the worst when a knowledgeable person looks at your finished knife. The most common comments heard about an otherwise nicely made knife are, " You should "clock" the mosaic rivets before the epoxy hardens", and "Youi should have sanded the handle to fit the guard a bit closer on one side.".
So - Don't Forget To Clock the rivets, and double check the fit-up!
:foot
that I have done, I ended up doing an oversized slot, smashing the guard down from the side, driving it off and getting it back to flat, then repeating that a couple times until it really fit right.
