Traditional way of making a saya is to re-saw a block into two pieces and carve a cavity into one. Then glue them together, shape and medium grit sand them. Shaping is very basic - rounding spine edge and giving a slight bevel to the edge side and smooth the wood.
I like to shape sayas the way a knife is shaped - bevels, taper, rounded spine and edge. All of these can be done with hand tools (rasps) or a belt sander. All final rounding and finishing I do by hand. If done properly,
you won't see a glue line and the whole piece will look like a single bock. People ask me all the time how I carved the cavity without splitting the wood.
Some makers, including Carter and Tsil, use inserts, as Dan described in his post above. It works, but a fit is not as precise as in a carved cavity - a cross-section of cavity is similar to that of a knife, and you will end up with two extra glue lines, so I never considered it. However, this is not how Japanese do it. At least I have not seen a single Japanese saya done in this way. For Japanese this method would be too labor-intensive.
This isn't the same thing I was talking about, but it is the same method.
Tsills wife if pretty talented. But it seems like the the Marko route might make a more secure fit. Of course I have never tried so I am just basing this on observations.
That belt sander is to die for.
"Insanity: doing the same thing over and over again and expecting different results." --Albert Einstein
I know right! But the belts can't be easy on the wallet.
Tom, why would you need such a big belt sander? 6x48 is perfectly adequate for all I do. That big sander if probably less flat on sanding surface than mine. I have 6x48" Shopsmith. Fantastic sander. I also have 11" Shopsmith bandsaw. Fantastic too.