Online educational material on using autocollimators and alignment telescopes

G'day guys, I haven't used an autocollimator before and wondered if there was any online material on the basics of using one in the context of machine tool surveying etc. So far I have only got as far as the basic "sketch" type diagrams that explain the principle of autocollimation but nothing really further. The only other thing I've seen are text books, which probably contain more depth and detail than I'll need. This optical side is all a bit of a mystery to me to be honest and I don't understand the difference between an autocollimator, an alignment telescope, and an autocollimating alignment telescope. I'd be grateful to be pointed in the right direction as to where I could read more about this field.

Thanks very much for the help.

Pete

Pete --

Brunson Instrument Company of Kansas City -- the last US maker of a still-fairly-complete line of optical tooling instruments -- offers an online outline of optical tooling instruments and how they are used at Online Learning Center AND offers a number of instrument manuals, for both current and no-longer-manufactured Brunson instruments and the most popular Keuffel + Esser instruments. (Brunson purchased the remains of K+E's optical tooling business a while back.) Product Manuals and Publications

John

John, thank you so much for that. A lot of good information there.

Can I confirm I have the basic idea? Say we want to establish the "straightness" of a way in the vertical plane. If I understand correctly, in a nutshell an autocollimator will do so by measuring the angular rotation of a target mirror and by a series of measurements over the length of the way and with a known base length of the mirror and distance between measuring points the vertical displacement can be established. On the other hand, an alignment telescope will use a target to establish an optical base line, and either the target's or an intermediate target's deviation from vertical can be calculated. Something like that?

I know an autocollimator can be used over quite short distances quite successfully, for example checking a surface plate. But I get the impression that an alignment telescope is really more suited to larger applications ie longer lathe beds and up. Is that true or is it merely the applications that I have seen? Is there any difference in overall accuracy between these two techniques, especially over short distances?

Pete

John (and others) having devoured the information in the link, apart from my questions above, I wonder what the next step is in learning how to use these things from a practical perspective? Are there any practical texts that basically spell out the process of, say, mapping a surface plate using an autocollimator? Better still anything online?

I take it an alignment telescope like the Brunson model 83 can be used as both an alignment telescope to a target and an autocollimator with a mirror? Hence would it be considerably more versatile?

Finally, there seems to be an extraordinary spread of pricing on these, from under US$200 to several thousand and I'm confused as to why there should be such a massive difference.

Thanks again for the guidance and help.

Pete

Pete F said:

Finally, there seems to be an extraordinary spread of pricing on these, from under US$200 to several thousand and I'm confused as to why there should be such a massive difference.

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Precision costs money.

The first thing to do is read the specifications to determine the true accuracy of the product.

The more important thing is to note the name of the manufacturer to determine whether or not you can believe the specifications.
It's common knowledge that the specs from manufacturers in certain countries aren't worth the rice paper they're printed on.

- Leigh

Thanks Leigh, that of course makes perfect sense, and that's where I start to run into trouble as I really don't know what I'm looking at/for. It's why I'm trying to learn more about the topic if I can.

By way of an example, listed on ebay at the moment are a number of Davidson Optronics autocollimators. One model D-656 is listed at $7K (or, rather generously, "best offer"). Meanwhile an identical model D-656 is listed at $1K. Now it's quite normal to see variation in asking price of different tools, but 7x, that's a heck of a spread!

Pete

Hi Pete,

The bay is not an accurate source of prices. Many sellers list stuff at exorbitant prices in an attempt to make a killing on junk inventory.

Unfortunately, there are too many buyers out there with more dollars than sense.
It only takes one to buy something way over-priced to make a seller's commission for the month.

The entire business model of the bay is to lead those fools to sellers who will happily take their money.
Of course the site makes much higher fees from such sales than it does from sales that are reasonably priced.

If you monitor the activity for a while you'll see the same vendors hawking the same over-priced items month after month.
They don't care if they have to list an item 20 times. Eventually some fool will buy it.

- Leigh

True enough.

Perhaps to explain what I'm after. I've obviously seen countless times in metrology and machining books autocollimators in use. Do I need one? Well, I've lasted 48 years so far without one so I guess the answer is no, however I've been quite interested in the optical area and would like to teach myself more about it. It's an interest but as I mentioned from at the start, not something I know much about at all so I'm not about mortgage my house to drop a bunch on optical tooling that will no doubt spend most of its time in a cupboard. The links kindly provided by John, have certainly whet my appetite for more however; a bit like peering over a fence and maybe wanting to join the neighbour's party! I'll admit to still being somewhat confused with regard alignment telescopes beyond the obvious bore, part alignment etc. as I now appreciate these tools can be set up in myriad configurations. I'm looking at tooling in the bottom end of the price market, but not if it's useless in terms of use.

Pete

HI Pete, hummm one thing at a time … do you need an autocollimator most likely not, same goes for an alignment telescope. Are they useful devices yes, depending on what your doing. Alignment telescopes are to check off sets between targets and surfaces on a given plane by using there built in optical micrometer and a precision scale, if it’s a combo collimator it can also check the alignment of bore and surface targets it’s level of precision is in the.0002-.0005 with all the correct tooling and an operator that knows what he’s doing. An autocollimator is good for straight line only if I’m scraping in a 30 foot long way my autocollimator works very nicely and will work in the less then .0001 range if I mind my P & Q’s. If I wish to know the height of the table on a HBM compared to the ways, a precision scale and my alignment telescope can tell me that information with +- .0002 precision. I’ll see if Ihave something I can scan in that covers checking surface plate flatness withan autocollimator when I’m back at my shop. As for price and brands to look for ... price is as Leigh already covered. top quality is to be expected from K&E ,Brunson, Letz/Lica, Hilger and Watts and Davison Optronics.
Cheers Don

Thanks Don, I appreciate the information on the accuracy. 10ths is definitely very good, especially if there is no mechanical way to otherwise measure. Expect this operator to be a bumbling idiot however. Realistically, the work I'm doing is small, my work envelope is maybe an office desk size, small machines and plates etc. K&E, Brunson, and Hilger are names that I've seen in the price range I'm grovelling in.

A hypothetical question, if you could choose between an autocollimator and an alignment telescope, which would it be? Most of the information I have is regarding autocollimators, and that's what got me started down this path. I still don't know to much about how useful an alignment telescope would be to me.

Speaking of which, here is some information that was extremely enlightening to me, it looks as if the paper basically goes through proving tools that can then be subsequently used to prove subsequent operations http://www.vermontphotonics.com/VT_Photo_Applications.pdf

Finally, most of the autocollimators I've seen don't have mirrors in the sale, and the mirrors I have seen were up in Leigh's La-La-Land territory. If I understand the operation correctly, the mirror is brought in to proper alignment from the first reading, and then subsequent measurements are compared to this datum. I wondered then if it would be realistically possible to grind and/or scrape a cube to 90 degrees and mount a first surface mirror to it? Is it correct in presuming that the accuracy is not reliant on the mirror's precise perpendicularity to the surface, as the series of readings are differential?

Pete

Edit: some more application notes http://www.davidsonoptronics.com/images/pdfs/Autocollimation.pdf I was especially interested in the angular displacement example when using an alignment telescope with a concave mirror.

Pete F said:

A hypothetical question, if you could choose between an autocollimator and an alignment telescope, which would it be? Most of the information I have is regarding autocollimators, and that's what got me started down this path. I still don't know to much about how useful an alignment telescope would be to me.

Finally, most of the autocollimators I've seen don't have mirrors in the sale, and the mirrors I have seen were up in Leigh's La-La-Land territory. If I understand the operation correctly, the mirror is brought in to proper alignment from the first reading, and then subsequent measurements are compared to this datum. I wondered then if it would be realistically possible to grind and/or scrape a cube to 90 degrees and mount a first surface mirror to it? Is it correct in presuming that the accuracy is not reliant on the mirror's precise perpendicularity to the surface, as the series of readings are differential?

Pete

Edit: some more application notes http://www.davidsonoptronics.com/images/pdfs/Autocollimation.pdf I was especially interested in the angular displacement example when using an alignment telescope with a concave mirror.

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Hi again Pete, for what I do the autocollimator has paid for itself many times over, the mirrors should be as close to a perfect 90 as you can be made or purchased and yes they are harder to find then the autocollimator. Performing the same task are my electronic differential levels , they are easier to use then the autocollimator plus I have a program in my computer that graphs the error I input in arc seconds and gives me a graphical representation in millionths of an inch . I have rarely used the alignment telescope, but when I need it, its the only thing that will do, that I have.
soooo if I was going to buy just one .... it would be Fedral or Wyler electronic differential levels. I know that was the answer to a question you didn't ask :-} my apologies.
Cheers Don

bebop said:

soooo if I was going to buy just one .... it would be Fedral or Wyler electronic differential levels. I know that was the answer to a question you didn't ask :-} my apologies.
Cheers Don

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Ha Ha! I have been looking at them too! However I can't see myself owning any in my lifetime, maybe the next. The more I delve into this optical field, the more applications I discover that I would never have thought of. It seems there's an awful lot that can be done with an autocollimator, a mirror or two, and an optical square! It's funny you mentioned that program as I was only thinking today that surely something would exist to do the same thing with autocollimation data and wondered if it was out in the public domain. First to find a suitable instrument.

Pete

Hi Pete,
I' m restoring a lathe, scraping the ways by hand, but the length is about 10' . So messuring with a straight edge was not an option .. so I looked and checked and found a H&W autocollimator for somewhere around 600$. After reseiving the case I took it all appart ,checked everything and put it back together, tested is with a led light and was ok for me. Now i needed a mirror , and like Don says, they are harder to find. So I bought a new one from Edmund Optics, witch is the next one .. http://www.edmundoptics.eu/optics/o...-wave-precision-optical-flat-mirrors/43420577 .. and with a "cel mount" so i can tilt the mirror int he set-up, and withe the cell assembly the story was complete. Then I was looking for a wayt to calculate the messurements, and you can't find mutch on the internet, but it is there. So if you are in need , i can send you a blanc sheet witch will calculate the angles messured into a deviation. I used some blocks as a base to messure, sometimes good, sometimes not .. now i made the mirrror onto a King-way allignmenttoom i made , and those messurings are good to work with. Accuracy is about 0.000039.
The pictures a add ,one is the setup from the mirror on the Kingway allignment tool , one is the setup from the autocollimator on its rest, the last one is from the sheet a use to calculate the meassuring