I just did another sample following the software measurements. Since I
have 3/8" bit depth, this made the rail 5 7/8". My final output total
width is 10 1/8" (instead of 10").

After the sample panel, I found the panel have (total) 3/8" gap (play)
and the top have 1/4" gap, is that a lot? When I did the paper/pen
measurements, the gap was much tighter.

If my bit are 3/8" depth, what measurements should I use for the side
width to make the rail minus 4" (example, for 10" width door, what it
take to make the rail exact 6")?

Are the popular bit depth 3/8" or there are other sizes? I bought the 3-
pieces for $60, to practice, along with pine boards (the pine sure
scatter messy...)

I guess I will have to play around some more to learn right.

Chuck

That is the best way I do it. My cutters cut 7/16 so my rails and
stiles are 2 7/16. You will loose the 7/16 with the cope cut so your
left with 2" on each side. Take the total door width and subtract 4"
and that's the mesurment from inside the tongue to inside the tongue.
It does not matter if your door is some odd ball size your rails will
be 4" narrower than the width of the door. Then take off another 1/16
to 1/8 for raised panels or just a 1/16 for plywood flat panels.