Basil, I just made my own fly cutter after reading though your thread so thank you for the inspiration! As for the surface finish in the slot, I has the same "rippled" finish. I made my 3/8" slot with a 3/8" end mill and found that by bumping it over just a hair (so I was only cutting one wall) I got a much better surface finish. Next time I think I would use a slightly smaller cutter and finish up to the tool width so I could get a good surface and a nice sliding fit.