Matt, not to criticize at all but curious, why where these cuts not made in the master before molding?
No worries, and definitely a fair question. Though it's already been discussed in the thread, I'll give my two cents again.
There are really two reasons. The first is a practical one. the main body is made out of MDF. If I tried to mill MDF like I'm doing with the resin, it would have turned it into a big mess. I didn't want to do that. As a few have suggested, I could have perhaps built the slotted piece separately, out of a different material, then grafted it into the main body. While true, my ultimate plan was to mill the grooves out of the resin pieces.
HOWEVER, the wrinkle is that I expected to have an actual mill on hand to do these grooves. I have a local friend that owns one, if my plan to acquire one fell through, but our schedules never lined up.
So my option was to wait for my friend to become available (and no insult intended to him. Either he is really busy, or I'm really busy. Our schedules do not align at all), acquire my own mill, or build one.
When it came right down to it, I thought it would be a fun and interesting challenge to build my own "machine" to cut those slots.
I guess the punchline is that for me, a big reason for doing it the way I'm doing it is because I wanted the learning experience.
ALSO, had I put the slots into the master, the seam line would have run right down the middle of them, and they would have been impossible to get as clean as the cuts are now. Since I'm only building a few of these, and will not be offering kits, I think it was the right decision considering the requirements and constraints.