Thank you very much for the info Michael. I should have asked for multiple formats, especially STEP. I had used this method before so I thought I was safe but some of the parts are larger than before.

Join seems to be doing it correctly, it's just super slow on larger parts. The time needed seems to really grow exponentially. I've had some success joining parts of the object first and then joining the whole.

It appears join is single threaded which makes it worse.

These parts came from Inventor but unfortunately the person providing them is not available right now so it'll have to do.

Nice to know about STEP for next time.

Cheers - Len