The thing that gave me the biggest fit starting out was getting a guard filled to fit perfectly. I'm a bit of a professional and any visible gap drove me nutts,even though I could look at factory knives and see even more of a gap than on mine.
I learned two tricks to make the guard look as if a blade grew out of it. The first one was to file to fit as close as possible and then peen the entire top surface of the guard with a very small ball peen hammer. This works best with brass. what it does it to mash the surface of the brass into your filled slot so that you have a very thin layer that will fit perfectly against the blade. You have to tap the guard back into place with the blade in a padded vice,using a slot cut in a block to tap the guard into place. The thin layer that you peened into the slot will deform into the blade bit fit so tight that there will be no visible gap. If you peen the top surface of the brass guard and the pommel,and then highly polish it gives an attractive mottled finish.
The second trick is to use a dremmel and thin down the underside of the guard all around the edges of the slot and pound it into place. You have to be very careful as there is a fine line between thin enough to form to the blade properly and making a bigger hole.
Lots of tricks like this in hidden tangs.
Another is to coat the top of your guard and the slot area very well with Vaseline,so that epoxy doesn't get onto it during glue up. Epoxy can be very hard to remove from your finished polished guard top without making any marks.
Another when using multiple pieces in the handle is to made surfaces by sanding them against a piece of glass backed with sandpaper. This way you can get perfectly flat surfaces without any glue lines.You may need to sand by single strokes, in a single direction, depending on the material to keep it flat.
Another tip is to always create mechanical bonding points inside a block or piece of horn and on a tang for epoxy to bond the pieces together. That way you will not rely on glue bond,but you will have a mechanical bond. My favorite epoxy to use is original Accraglass. Do not use the gel but the original runny stuff. It has nearly zero shrinkage and will easily pour into a wood block or piece of stag.
