Making cabinet doors

[4DThinker]

Boy, I've been trying to create a simple 5/16 roundover form tool for the last hour or so. Drawing the right half of the bit using 0,0 as the center bottom point I can get the tool database to show what looks like the right profile. The bit has a 1/4" center flat on the bottom, so the total width is 7/8". The Diameter of .875 shows up and is hard coded into the panel, but the pass depth and stepover are variables as are the feed speed etc..

The problems show up when creating a profile path using this tool. Pick the edge of a 4" square and it doesn't cut anything off. Appears to think of the bit as a 7/8" diameter end mill. Draw an offset 5/16" into the square, and it'll try to roll around the corners instead of leaving a nice mitered seam like the bit actually does in use. I've tried all sorts of changes to the starting profile line and can not get a result that renders a preview view accurately. I get accurate cuts using a 1/4" end mill description and simply cutting to the depth of the radius described, but Vcarve sure doesn't know how to handle rendering the true profile of the bit around corners.

The dimension flaw shows up in rendering as well. For some reason an offset line set 5/16" into that 4" square results in a little edge step left using the form tool description. I move the offset line in 1/64" and I'll have a little flat left. There doesn't seem to be any dimension I can pick inset from the 4" square that will leave a perfect flush roundover top-to-edge. The tool profile was drawn in Vcarve as a 5/8" circle (5/16" radius) and two polylines extending out at 0 and 90 degrees from the circle. Cut and delete 3/4 of the circle, and join the two lines to the remaining arc. I'm guessing that the internal math can't handle 10,000ths lke the 5 in .3125. It either rounds it up to .313 or down to .312. In other words, .3125 inset is an impossible position for it.

[hdtheater]

I watched the video for two rail sweeps last night. Looks like that could be my solution. I am about to order some bits, I think I can can get it all completed with an 1/8" ball nose, maybe 1/16". One case where bigger is better!

Once I get a few jobs off my plate, I will start working on these.

-Eric