Can't see how to make this cut

[dmbLPVJ8]

I've stewed on this one for the last day, but no further forward, and I'm thinking it's probably an easy one.

I need to mill this part on two sides, and I've got most of the toolpaths defined but can't get the last perimeter cut right. 

My stock is 10mm acrylic, and my 0.8mm end mills have 6mm flute length so I've come up with the following strategy:

1. Drill the indexing holes with 3mm drill then mount the stock on M3 bolts through the spoil board; swap tools to the end mill;

2. Mill half of the rectangular hole with a 2D contour cut 6mm deep;

3. Clear out the top with 3D adaptive;

4. 2D contour cut the top perimeter to 6mm depth;

5. Flip the stock;

6. Mill the second half of the rectangular hole with a 2D contour cut 6mm deep;

7. Clear out the bottom with 3D adaptive;

8. 2D contour cut the bottom perimeter to 6mm depth.

I can't figure out how to select the geometry for step 8 - my best attempt ends up cutting through the stub at the side of the part. The final operation called "Doesn't work" in the attached f3d shows the problem.

I suspect there's something funky I should be doing with heights or something (maybe the part needs to be half above the XY plane and half below ?) but I have a tendency to over-complicate things 🙂

Any help gratefully appreciated,

David

[dmbLPVJ8]

Doh ! That's great, thanks so much Seth, I thought it would be simple ... I have a lot to learn but every step seems like a big achievement.

Much appreciated.

David

[seth.madore]

We all start somewhere 🙂