Shallow Sperical Radius Dimple

[mach-4]

I have a "dimple" that needs to be cut out of the surface of my part. It is a SR of about 30000mm and .01mm DP. This gives me a visible circle of about 49mm on the surface. I have revolved a cut and used the hole option. Before I hit the green check mark the model is highlighted to create my geometry correctly, but when I hit the check mark my part goes away and leaves a solid where there needs to be a cut(the cut direction is correct). I have tried the relative and absolute accuracy at .000001. Without the accuracy turned up it will error out altogether. The best I get away with is .05 deep. Our customers do it on the same type of product with the same crazy dimensions and their models are good. What can I do beyond the accuracy that will help?

 

[moldman]

Try giving the cut some more material to remove. Create a cylindrical protrusion above where you want the dimple to be that is .49mm in diameter. Now revolve the cut to make the dimple. I have seen this before both with revolved cuts and protruded cuts. If there is not enough "meat" for the cut to bite into, it seems to slip out of it's mouth. Make some more meat and it works like a charm. You could also make a standard hole where the dimple is supposed to be, and then fill it up. You can probably bump up your accuracy back to a reasonable amount - it will speed everything up.

 

[mach-4]

That did it. I created a cylindrical protrusion above it then I made a revolved cut. The only hang up was it gave me an error when I cut exactly to the edges of the cylinder. I had to cut a little past and no problems. Thanks!

 

[whatttup_G]

i bet its a boundary failure, what you drew in sketcher is too skinny or small compared to the model... when it revolved, there was no area cut compared to your accuracy numbers, thats why it previewed, then failed, then you had to crank up the accuracy to fix a bad sketch with insane resolution

since adding extra material to cut away worked, the problem was probably that side of the sketch. if you are making a dimple, and revolving a ball shape to do it, make the sketch bigger than the cut, don't use a 'use edge' to make the top of the cut... that approach is fine for normal cuts, but you are shaving a tiny bit so things are different, you need a robust approach, you need the cut to slice out a huge shape, but only have a tiny intersection with the model.

say you have a big beach ball, and a small tennis ball... you want to dimple the beach ball with the tennis ball, but only a tiny shallow bit... you revolve the tennis ball shape, and use way more sketch than you need... like draw half the ball, or the whole ball, and revolve that, not the tiny sliver you wind up with...

and yeah, it just happens that 99% of this oversized sketch cuts air, but in this way you have a sketch that is rock solid, a cut that is legit, and no tiny edges or radius's from hell... i bet you can push your accuracy back to normal (not that it matters ususally) just to see if this method repaired your problem