Another Frustration – Quill Runout

As many of you who’ve managed to wade through all the text on this site know, my main frustration with the Omni faceting machine is that I can’t cut rectangular stones or step cuts without extreme aggravation. Meet points just don’t meet, and I seem to have to do a lot of fiddling with the cheater and mast height just to get things to come close.

I identified the mast as not being vertical as one of the problems – and because of the mechanics of the swing arm, moving the arm means that the angle and direction of the mast mis-alignment changes continuously. To remedy that I aligned the mast as best I could and now cut stones trying to avoid moving the swing arm. I also mark the swing arm so I know where I had it adjusted originally when I come back with a different grit after moving the arm.

That seemed to reduce some of the problem, but it still has been frustating me. So the next obvious thing was to replace the sloppy transfer fixture. I ended up buying a Polymetric transfer jig on the recommendation of a couple other faceters and indeed it’s a much more solid and accurate device (you can get one from the Polymetric website). But much to my dismay I still experienced difficulties getting meet points and facets to align when cutting a square tourmaline this past couple of weeks.

I then checked my dops to make sure they’re not bent – which they are not. So then a horrible thought passed through my head: what if the problem is in the Omni faceting head itself? It’s the only part of the Omni I haven’t yet taken apart.

So… I put the head in the 90 degree position and stuck a dop in it. I set up my dial indicator to rest on the top of the dop, and I put the quill into free-wheel mode. Then I held my breath and rotated the quill while watching the dial indicator.

Bingo! I measured a total wobble of 0.003″ to 0.0035″ in the quill. I couldn’t believe it! To ensure I wasn’t using a bent dop, I tried 3 different dops in the quill. All produced 0.003″ to 0.0035″ total runout. So I then tested the quill barrel itself – and I got about the same amount of runout.

To put this in perspective – on a 10 mm stone with pavilion and crown angles at 40 degrees (for simplicity), that’s about 1/2 a standard 0.3 mm girdle width of wobble. And to compare with other manufacturers the Polymetric website (the only manufacturer I could find that publishes their stats) states their machines have a an adjustable quill to reduce dop total indicated runout to under 0.0002″. That’s less than 1/10th the runout I measured on my quill!

So now my task is to take apart my Omni faceting head and try to figure out how to adjust/repair this. This is becoming a very tiresome exercise as the one place I would have expected precision machining and construction does not have it.

I’ll be posting photos and commentary about this little adventure shortly.


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