Cabinet door question on inside 90s

[Warnsdorff]

I'm stumped on tool paths for inside corners. With this ogee bit, I ran a simple profile on a 2d square geometry. I'm using bobcad/cam for programming. I'm assuming I need to build full 3d geometry and use a tapered ball of some sort to finish corners, but would love some additional insight.

[sgodding]

There are a few ways to address inside corners:

1. Use a small ballnose to carve the 90-degree profile. In Aspire/VCarve Pro you can do this with a moulding toolpath, using a small angle in each corner as the drive rail (I usually make the angle .01" on each side) and the profile of the ogee bit for the profile. No idea how that would be done in Bobcad. I use a 1/8" tapered ballnose for this. The taper doesn't really come into play at all on most of the corners I do. You have to be very exact with the profile vector, and your machine needs to be really solid for this to look good at the end. Otherwise you will get witness lines where the corner meets the rest of the profile. The moulding toolpath in the Vectric products works much better than a 3d carving toolpath for this kind of work - faster and better result.

2. In the Vectric products you can also use a moulding toolpath to cut the entire profile. This is very slow, but gives a very nice result, especially when you can't get a profile cutter with exactly the geometry you want.

3. Fake it by using either a straight or v-bit at the top of the ogee. Don't bother trying to get a crease on the corner -- instead, make sure the step at the top of the ogee is square. I usually use a 1/8" straight down-shear end mill, and may also then run a 45-degree v-bit to give a really sharp corner by lifting the bit at the corners. This does leave a small angle rather than a straight vertical face for the top step, but most people won't notice. By making the corner sharp, it creates the illusion that the corner is square and you don't notice the missing crease unless you look closely.

Oftentimes people who make MDF doors commercially will minimize the use of profiles with curves (like ogees) so that they can use v-bits and straight cutters to make sure the corners look sharp. My customers want curved profiles, so the above approaches are what I use.