top profile of slat; I see Brian is a proponent for dowels and his reasoning sounds good, debris/mites fall off. Has anyone taken this a step further and cut the slat tops to peaks..45 degrees from both sides?
That is all predicated on the assumption that natural mite fall rate is significant. I question that assumption. If it was significant, than screened bottom boards would be all you need for mite control, and we know that is not the case.
spacing; I see the plans over at beesource using 3/8 slats on a 3/8 spacing...others use slats approximating top bar width 3/4-1" and space 3/8....I believe most doing this are running the slats parallel to the frames and trying to align gaps. How well does this work out? does it make for blockage when spacing of frames shifts over time with propolis build? What happens if you decide to squeeze 9 frames in and 8 frame box...or gap nine frames in a ten? I believe it's Robo who has mentioned that with slats running perpendicular you always have min 50% free fall...that sounds nice and easy, especially if the tops are shaped to deflect mites/debris.
I have primarily used the 3/4 on 3/8 with the beesource plans and the Miller/Killion design, and have always run them perpendicular to the frames. I know the new fad is parallel, perhaps based on a false assumption
but definitely an assumption that market them over the traditional. Yes it was me that said with the perpendicular arrangement you have ~50% opening. With the parallel you can have anything from 100%, if your frames are perfectly drawn and aligned, to 0% if your frames are out of alignment. An as you stated, you limit your options when you run parallel, at least if you are bought into the mite fall off advantage.
related to spacing. Plans seem to have a great variety of difference in the space under the slats..not even accounting for the additional space a bottom board will add, anybody care to comment on that?
Not important. The bees see the top of the slats as the bottom of the nest cavity, so bee space is not an issue. The more space you have below, the more they bees can cluster without having to hang on the front of the hive. The Miller/Killion as 1-5/16" below the slats and I have never had an issue.