Unexplained collision with 4th axis and roughing.

[ChrisKirchen]

I'm working on blowmold, specifically cutting the feature that makes the (SP400) threads for the lid in the molded part.

The block is mounted to our 4th axis so that we can generate clearance for the tool (which is a .02" ball mill).

I'm using roughing sequences with the rotary positioned at +45°, +22.5°, 0°, -22.5°, and -45°. Two of the sequences, the ones at +22.5° and -22.5° are not doing what they should; they cut much deeper than they are supposed to. The attached picture shows a correct sequence (at +45°) and one incorrect sequence (at +22.5°).

MFG_AUTO_REF_PRT_AS_CHK_SURF and CHK_PART_SURFS_PROFPOCK are both yes, but I don't think they apply to roughing sequences.

I've tried changing the angle of the rotary (i.e. 20°/22°/23°/25° instead of 22.5°), but the result was the same.

I thought that my mill window might be a problem, because two edges of the window were made from the edges of the thread (and those edges were splines), so I changed the window to a simple rectangle, but, again, the result was the same.

There is a similar groove feature, just to the left of the thread, that works just fine.

The block has been in the machine for the last 4 days, waiting for this one remaining feature...any ideas would be greatly appreciated.

I'm running 5.0 build M080.

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[ChrisKirchen]

Well, I managed to get it to work.

It turned out that the issue was with the mill window and the spline edges of the thread. I started from scratch and drew a very large rectangular mill window around the geometry (instead of the window that was created with the edges of the threads).

When it worked, I reduced the size of the rectangle until it failed again. I don't know if it is a consistent requirement, but in this case, when any portion of the vertical edges of the window is less than .01" away (i.e. the cutter radius) from the vertical spline edges of the thread feature, the tool path would fail.

The weird thing is that I have three other windows on the same feature, constructed the same way, albeit at different orientations of the rotary, and they all worked on the first try.

I'm still curious as to why the tool would be allowed to plunge so deep into the part and why changing the mill window in this way would resolve the problem.

On the bright side, the magnitude of the collision was so large that it was very easy to see on Play Path.

[NickMihelich]

That is really interesting i had been getting quite a few gouges in my roughing re-rghing sequences but could not understand why. Thank you for figuring out the issue i will adjust all my mill windows now.