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 Faceters.com 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…?
Jeff”

I call BULLSHIT.

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:
http://www.ultratec-facet.com/V2Base.htm

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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