cam newbie dimension problem

[Anonymous]

I am new to Fusion 360 - I am trying to make a simple part on a Taig mill with Mach3 and a 1/8" straight cutter.

The part should be a rectangle 3.500" x 2.750" with a rectangular pocket in it. The part is coming out 3.270" x 2.476", or approximately a quarter inch small. similarly, the pocket is coming out too large.

I looked at the gcode, and the rectangle outline is going to X+1.3125 and X-1.3125 which adds up to 2.625" width instead of the designed 2.750". This is 1/8" too small, or one cutter-width. the Y dimensions are similarly out by a cutter width. Of course, the hole in the raw stock comes out sized perfectly.

The pocket is too large. it's not as easy to measure since I made some mistakes in the drawing, but eyeballing, it looks like about 1/8 inch.

So, obviously, I'm missing something (probably simple) here. I'd really appreciate a shove in the right direction. I've attached an archive file - no idea whether that's the reight thing for you to look at - if there's a different file to include, just let me know.

Thanks.

[Steinwerks · Accepted solution]

Your issue is geometry selection. For the 2D Contour you've got the wrong side selected, which can be corrected by clicking the red arrow. For the 2D Pocket you've selected the surface and the CAM thinks it's an open surface instead of enclosed. This can be fixed by selecting the correct open contour chain around the inside of the pocket.

Screencast forthcoming here: