Omni Platen Vertical Runout AKA “Platen Hop”

My platen – the flat part the lap rests upon – is not flat. This means as you cut a stone, the lap has high and low spots as it rotates which continually tap-tap-tap on the stone. I had a Topaz I was working on cleave which I attribute to the stone continuously being hit by the high spot. The faster you run the machine, the more this causes vibration and a jack-hammer effect on your stone and faceting head. Not what you want on a precision machine.

In machinist parlance, this hop is called “vertical runout”. Using a 1/1000th inch dial indicator, I tested my platen near the edge, approximately 5.5″ from the center. An acceptable runout would be 0.001″ (1 thousandths of an inch) or less, and I know of several fellow faceters locally whose machines (not Omni) came from the factory with less than 0.001″ runout.

Originally I complained that my vertical runout was 0.0015″ (1-1/2 thousandths of an inch) which was slightly annoying. Foolish me.

My vertical runout is now 0.007″, almost FIVE TIMES WORSE than what it was before I sent it back to the factory. I repeat: This is *after* it came back from the factory for alignment.

Here are some photos demonstrating the problem:

Omni Platen Vertical Runout Image 1

Dial Indicator zeroed at the high point.

Omni Platen Vertical Runout Image 2

Turned 90 degrees clockwise… 0.0025″ difference…

Omni Platen Vertical Runout Image 3

Low point on the Platen. Only out by 0.007″!

Omni Platen Vertical Runout Image 4

The Platen at 9 o’clock position. Out by 0.005″.

These measurements were taken at about 5.5″ from the center of the platen.

When I emailed the well-known owner of about this, here’s the response (typos are his):
“You are kidding me right? .007? There is not a machine out there that will get any better. Facette and UT on brand new machines send them out with those numbers. Why dfon’t you just go cut stones…?


Quoting from UltraTec’s page:
THE PLATEN – This critical subassembly (L) which holds the lap provides exceptional accuracy–.0003 inch maximum vertical runout.

For the record – UT publishes their platen runout here:

So Ultratech machines their platens (4″ diameter) to 23x tighter specs than my Omni. If any Facetron or Fac-ette owners care to chip in their factory-spec platen runout numbers I’d be happy to post them for comparison. I’m not interested in modded machines, only factory-shipped specifications.

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1 Response to Omni Platen Vertical Runout AKA “Platen Hop”

  1. Stewart Mitchell says:

    I don’t own an ultratec or fac-ette faceting machine but I would like to chip in my specs. I own a VJ faceting machine. Run out on this machine is 0.0001″ (on a 5″ platen) I have spoken to three owners of VJ machines and the greatest run out I have encountered has been 0.0005 on a second hand machine. This run out was reduced to 0.0003 when the bearings were replaced.

    I was considering purchasing an Omni-e before I got my VJ. After reading this page I am glad that I didn’t. The shoddy workmanship I have seen here is appalling.

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