What is an "optical" rotary table?

Tipsy · Dec 29, 2005

I have a nice 10" Walter rotary table, but am looking at an "optical" rotary table, it has two eye pieces and an illuminator in the main body of the indexer/tilting rotary table. What does one do with the sighting portion? Can such tables only be used for measureing? :confused:

Konrad · Dec 29, 2005

I would think the optic is somewhat a magnified viewing area....easier to read your angles.[only]
Konrad

Rumin · Dec 29, 2005

A very old design in 1969?

Maybe this site is helpful:

http://www.npl.co.uk/length/dmet/moy-scmi/moy-scmi-1-screen.pdf

Metal Slave · Dec 29, 2005

What does one do with the sighting portion?

When you look through the illuminated sight glass there is one stationary reference mark & above it (or behind it) you see the scale of the rotary table with however many increments it might be in.I have only used one optical rotab & it was built into a HBM , it only had indexing marks at 0,90,180 & 270.At those positions there was another reference mark and the idea was to line up the 2 marks with each other.It was amazingly accurate & surprisingly fast to index the table.

Metal Slave · Dec 29, 2005

I would think the optic is somewhat a magnified viewing area

And yes,as Konrad thought,it is magnified,very very magnified.

John Garner · Dec 29, 2005

Tipsy --

Up until about twenty-five years ago the highest-grade positioning-and-measuring equipment were often designed with "optical" measuring elements that were fully independent of the machinery-moving elements, making it possible to sense position with lower uncertainties than would be possible if the position-sense function was derived as a function of lead screw (linear) or worm-and-wormwheel (rotary) position. The machine makers typically bought the optical scales and readers from specialty makers such as Simpson Optical, Heidenhein, or E. Leitz.

A high-end "manufacturing" rotary table with a E. Leitz scale could resolve 1 arcsecond with total uncertainty in the plus-or-minus 3 arcsecond range; a metrology-grade table could do better.

This practice was exactly analogous to the present-day practice of using an electronically-sensed scale ("optical encoder", Sony Magnescale, Newall Spherosyn).

John

J. Elliott · Dec 31, 2005

I bought one of these on eBay, a nearly as-new 12" OMT. Tilting feature is what got me into it. Damn heavy table - almost 500 pounds, and built like a Rolls-Royce. (Not sure what I'll do with it eventually, but pretty rare for its condition and I like fine equipment.)

I think the deal is this - back in the day, a piece of glass with finely etched lines was the most reliable and accurately made thing with which to measure against. The optical rotary table has the scopes to magnify the vernier lines of the table moving in relation to the glass reference platten. (Or whatever is in there, don't quote me!)

High quality rotary encoders serve the same function now. I don't think you can find new equipment with optical measuring systems anymore. (Don't quote me on that either.)

[ 12-31-2005, 11:35 AM: Message edited by: J. Elliott ]

The real Leigh · Dec 31, 2005

I bought one of these on eBay, a nearly as-new 12" OMT.

This is probably not designed for machine tool use. Optical rotary tables are used in the optics field for precise alignment of mirrors, lenses, lasers, and other optical components. They're frequently quite massive, and could masquerade as machine tool accessories quite easily. But they're not sealed, and a little swarf, coolant, and lubricant would destroy the optical functions.

alwyn · Dec 31, 2005

The scale is photo etched,the same as the ones used on optical readouts,Linea scales that BP fitted,best thing since sliced bread,until the DRO and the rotary encoder came on the scene,
I have also used a optical OMT on a Newall jig borer, but they normally used as inspection tool,so Tipsy,yes they can used for measuring,
Over the years i,ve worked on all kinds of optical test equipment,and we always used Walter rotary tables,they do,nt come much better,and we did check them out first,with auto collimator's ect
Any body want a SIP 400mm rotab free,its too big and heavy for a BP and the likes,collect only.

J. Elliott · Dec 31, 2005

The real Leigh,

Thanks, I'd wondered about that too. Nice to get some verification of it.

Doug in Colorado · Dec 31, 2005

alwyn:

Any body want a SIP 400mm rotab free,

I do I do! At least I think I do. I have a Sip Jig Bore. How heavy is it? Where are you? Is it in okay shape? The price is certainly right.

Winfield · Dec 31, 2005

I own a Hilger-Watts TB80-1 optical rotary table with an accuracy of +-4 arc sec over 360*. It uses an optical disc with optical micrometer for readout from opposite sides of the disc . Also it doubles as a clinometer with a special split optical level.

Tipsy,
Hows it going over there in Fernwood? I have cousins living on Observation Drive.

The real Leigh · Jan 1, 2006

I own a Hilger-Watts TB80-1 optical rotary table with an accuracy of +-4 arc sec over 360*.

That's a beautiful item.

For those who haven't bothered to do the math, 1 arc-second is approximately 4.85 microinches per inch. That's .0175" at 100 yards, i.e. the length of a football field.

That's about the size of my five-round offhand groups @ 100 yards, so it's pretty good

Winfield · Jan 1, 2006

Actually the Hilger&Watts TB80-1 Microptic Rotary table/Clinometer has better accuracy than I stated: from the TB80 instruction manual:

Accuracy:
4 seconds of arc maximum error between any two readings

Resolution is better than 1/5 (0.2)arc sec using the microptic optical micrometer or 0.2 arc sec per div as stated on the fine adjustment knob.

alwyn · Jan 1, 2006

Doug in Colorado,i live in Wales,UK,the table works ok,its about 5 years since it was last used but it sits on floor on 2 pieces of 2x3 so its a bit dirty,at a guess it weighs about 250 pounds,
Iam not sure about the table size,it could 500mm i will check this out when iam back in work on Tuesday,by the way, its not an optical table.

evildrome · Feb 7, 2019

The real Leigh said:
This is probably not designed for machine tool use. Optical rotary tables are used in the optics field for precise alignment of mirrors, lenses, lasers, and other optical components. They're frequently quite massive, and could masquerade as machine tool accessories quite easily. But they're not sealed, and a little swarf, coolant, and lubricant would destroy the optical functions.

That's very interesting... I have a 14" OMT optical table and I had assumed (given the size of the hold down slots) that these were designed for quite substantial milling operations.

However, I did read an account of a chap whose optical scale had been fouled with coolant. That made me wonder at the time. I could not think that something made for milling wouldn't be proof against coolant.

Maybe explains why they're so unloved in auctions.

I use mine occasionally to pitch out PCDs on my drill press (which has no coolant).

Cheers,

Wilson.

sable · Feb 7, 2019

evildrome said:
That's very interesting... I have a 14" OMT optical table and I had assumed (given the size of the hold down slots) that these were designed for quite substantial milling operations.

However, I did read an account of a chap whose optical scale had been fouled with coolant. That made me wonder at the time. I could not think that something made for milling wouldn't be proof against coolant.

Maybe explains why they're so unloved in auctions.

I use mine occasionally to pitch out PCDs on my drill press (which has no coolant).

Cheers,

Wilson.

View attachment 249082

Those OMT tables were intended for inspection and jig boring use.

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