Optical Measuring Tool Query

http://www.kijiji.ca/v-hand-tool/st-albert/milling-tool/1233918232?enableSearchNavigationFlag=true

Anyone know exactly what this thing is? Is it a indexable rotary table ? Google gives me nothing.
Thanks

It's a rather beat up tilting rotary table.

I always wondered about those, normally the one's I see are in ebay and German made. I'd enjoy reading how they work. I wonder if they are they normally used just for accurate angles or are they fast enough to compete with a mechanical dividing head with plates for circular divisions? Are they far more accurate than a normal rotary table for dividing, or are they less accurate but faster?

partsproduction said:

I always wondered about those, normally the one's I see are in ebay and German made. I'd enjoy reading how they work. I wonder if they are they normally used just for accurate angles or are they fast enough to compete with a mechanical dividing head with plates for circular divisions? Are they far more accurate than a normal rotary table for dividing, or are they less accurate but faster?

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There not as fast as a dividing head with plates but much more accurate.

When you use one you really have to be on your toes it's real easy to make a mistake.

SIP6A said:

There not as fast as a dividing head with plates but much more accurate.

When you use one you really have to be on your toes it's real easy to make a mistake.

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+1 on both points as to being on your toes, I found the only way for me was to write down all my moves beforehand.

As for the tool itself, Yes it's a bit chipped but probably none the worse for it, .....in small shops ''stuff got put on them'' when they weren't in use.

FWIW, my old mentor used to refer to OMT kit as ''The SIP of England '' ......and Big Jim knew quality when he saw it.


To the OP;-

Redless - unless you need one, I'd class it in in the ''I've (say) $25 (or whatever) to spare '' class BOTOH - should there come a time when you need one, you will be in clover.

OMT kit was well made and accurate for its time. If I needed a table like that I would go for it without much hesitation if it all works. This is not just second hand opinion. I have an OMT toolmakers microsope with ALL the bits. It certainly is not a CMM but it is capable of measuring to the accuracy that I need and with a lot of versatility. It didn't cost me much and I wouldn't be without it. I also use it to solder tiny surface mount components via the microscope. Definitely not its original purpose.

OMT is definitely nice stuff. Certainly up there with SIP, Moore, leitz, Zeiss. I have the smallest optical dividing head they made. Has about 3 inch center height and reads to one second of arc

In my post I was timid about asking, but now I'll hold my shield high and venture forth. Is there a scale under the microscope of degrees minutes and seconds or is it degrees and tenths and hundreds? Am I way off in my suppositions? And "You really have to be on your toes" answers one of my questions, how are multiples calculated(?), which is really the same question as the first one. Assuming decimal degrees I can even still see it as a challenge, but with minutes and seconds I suspect it would really be difficult to keep up.

I think that only someone with access to that table or a manual would be able to answer for certain. I suspect OMT could fit a variety of optical scales - that is what they were good at.

My toolmakers microscope has a mixture of units, depending on what seems most natural. For example, the rotating table vernier is degrees and minutes. Some at least of the optical measurements are dms. Other optical scales measure things like radiuses where the units are in inches. The micrometer drums can be inches or metric. The slip gauge set made for it is inches.

As others have said, you need to get familiar with what the scales are telling you, making sure you are counting in the right direction etc. You also need to use a calculator (well I do anyway). It isn't like a modern DRO, but what you are looking is very precise and at that price a bargain if it isn't abused and you need what it does.

I would not be put off by having dms scales if that actually is the case. Just buy a cheap childrens school scientific calculator. This will do the conversions for you at the push of a button. You can do it manually on paper of course, but why work that hard.

It could be that you are concerned about setting up compound angles correctly. If so, it doesn't matter what the scales are, you need to get the theory right. I'm fairly sure from memory that this covered in Machinery's Handbook, but there are many other places that go through this.

I was just curious, having seen the Zeiss dividing heads in ebay.

It isn't like a modern DRO

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Hmm, a puzzle there, that seems like a natural.

partsproduction said:

I was just curious, having seen the Zeiss dividing heads in ebay.

Hmm, a puzzle there, that seems like a natural.

Click to expand...

OK, if so I apologise for stating the blindingly obvious.

But just to be clear, with a DRO you can set a zero anywhere. With optical scales you probably can't. That means you need to keep track yourself, which means a a fair bit of arithmetic. Doing that arithmetic is little different whether the scales are dms or decimal degrees provided you have a suitable calculator.

But just to be clear, with a DRO you can set a zero anywhere.

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Drifting here, but consider BC function in a two axis DRO, for a RT or dividing head that would be much simpler electronically.

Looks to be a plain degree marking on the table itself without vernier so I'd expect degrees minutes and seconds under the optics rather than decimals of a degree or maybe even both. Far as I remember the one I saw with decimals only under the optics also had a vernier plate. I had a 20" one in the lab for a while with both. Now that one really did insist you keep your brain engaged. Two, or maybe three, sets of double cross hairs in view too if I remember right. Nightmare to use and incredibly heavy. Be unsurprised if it created local gravitational field distortions. But really, really accurate. Interferometer fringe shifting was the only way I had to check it.

Generally I preferred a 12" bronze one from PTI (?) for that sort of work. Not tilting but at least you could move it without calling the heavy gang in and three sets of double cross hairs allowing accurate part division working are handleable on a degrees, minutes & seconds scale. Was soon glad when the PTB gave me a BBC B micro so I could program the conversion from d-m-s to decimals, mils and that obscenity the Russkies used instead of hacking it out by hand. Even a HP67 has its limits.

Clive