Help with patterning extrude cut along helix?

Eleanor_Coffin

Hi all, I'm looking for some help with patterning a cut along a helix path. Screenshot below to show what I'm working with. The preview it shows is the result that I want, but it's erroring out and won't complete the pattern.

Some extra info: My sketch plane is 1mm offset from the surface. My original extrude is thru all, both sides. I'm patterning along a helix that is tangent to the sketch plane (at the 1mm offset).

I know I can pattern the sketch and extrude each cut individually, but I feel like there has to be a better approach. Any advice? Thanks!

bradley_sauln

If @John_P_Desilets suggestion doesn't work you can always create a part to be a cutting tool and perform a part pattern with the remove option.

John_P_Desilets

@Eleanor_Coffin Have you tried checking apply per instance? 

bradley_sauln

If @John_P_Desilets suggestion doesn't work you can always create a part to be a cutting tool and perform a part pattern with the remove option.

kevin_o_toole_1

Seems likely this issue is not with the pattern, but the boolean. Subtracting a box which is exactly tangent to a cylindrical face is not valid geometry in Onshape (there's a non-manifold edge created at the contact point), and I imagine it's not the result you want – you to subtract material all the way through that inside face.

If this is the issue, you can fix it by adding a second direction to the extrude, extending out a bit in the other direction, so the boolean will drill through the rest of the material in that curved face.

Eleanor_Coffin

@bradley_sauln This worked perfectly, thank you!

As an academic exercise, answers to the other two suggestions:

@John_P_Desilets Yes, I did try that. The pattern preview disappears when I check Apply per instance.

@kevin_o_toole_1 I considered that too. That's why I offset the sketches 1mm from the helix's surface. My extrude settings were set to Remove, Through all, Symmetric as well, in an effort to avoid that issue.

Thanks all for your advice!