OK, So I bought an autocollimator. Now what?

To increase my number of unneeded precision metrology items, I purchased an ex-university Hilger and Watts autocollimator... When it arrives it will probbaly be a TA3 model.. As expected incomplete in so far that the electronic meter unit is MIA along with any mirrors...

So what now? Or what mirrors are suitable for this unit? Optical square be nice as well

Nice looking unit. I also find myself in the "too-much unneeded metrology tooling" category... Just received an eBay K&E alignment telescope, so I can do some calibration/alignment on my Leitz autocollimators...once I check out the alignment of the alignment telescope.;-)

I guess the real question is what do you WANT to do with it? For checking variation in flat planes (e.g., surface plate), or other line-of-sight applications, a fixed front-surface mirror in a solid, stable right angle mount of some sort is useful. The better the surface quality of the mirror, the better the return to the autocollimator. Tenth-wave surface quality is pretty usable for most everything. Poorer quality such as quarter-wave will limit light return, especially at distance.

Sort of a different issue. Assuming the typical center wavelength of visible light at 550nm (~0.5micron, roughly), the 9x12 surface plate specified to 275 nm is effin' decent, assuming that the specification is the typical "two planes separated by the spec distance", into which every point on the surface supposedly falls. For optical surfaces, especially those that are smaller and need to return as much light back to a source instrument as possible (especially with non-coherent sources), the flatter the mirror surface, the better. You want the test equipment to be as above reproach as possible, and easily usable to boot. If you have the mirror across the shop, 10 or 12 feet away, finding the return is sometimes a challenge, made worse by a poor mirror dispersing light over a wider angle (due to less flat surface shape). Less energy back to the instrument.

Manual and mirrors.

Here is a link to a russian web page that looks like a manual. It goes russian but has enough english. Not familiar with the file format and didn't try decoding it.

I like buying mirrors from surplus shed. They have lots of interesting stuff at great prices.

RC99 said:

To increase my number of unneeded precision metrology items, I purchased an ex-university Hilger and Watts autocollimator... When it arrives it will probbaly be a TA3 model.. As expected incomplete in so far that the electronic meter unit is MIA along with any mirrors...

So what now? Or what mirrors are suitable for this unit? Optical square be nice as well

Click to expand...

Thanks everyone... Primary playing around with this would be my newly aquired 8ft by 5 ft surface plate.. If it arrives in only one piece..

Reading up this model is supposed to have an electronic part to it that if connected can display the tilt in 0.1 arc second increments..

I have been informed mirrors can be made out of hard disc drive platters, that are extremely flat and double sided..

I did get that manual off the Russian machining site a few days ago... It is a manual for a TA3..

HDD discs will certainly work, although they won't be as flat as a decent optical mirror. The most current drive platters are being made to some fairly stringent standards for localized flatness, but global flatness is still typically in the fractional micron range, say something around 300nm (1/2 wave, sort of). Disks DO make good general purpose mirrors if that's what you have to work with. The older drives won't be quite as good; like everything else, improving technology for making the platters drives the specifications. I haven't reviewed the IDEMA specs in the last couple of years, but the glass disks were being made with some better performance numbers in the last few years.

Ahh, yours has the Lewis Pads I see. I was able to snag a couple of those autocollimators off the bay many years ago. I had since given one away, but have kept the one that has the analog meter unit. It uses an electric eye to confirm splitting lines easier than the ole human eyeball. Yours should be completely usable without it, as long as you get power to the bulb. I would think a suitable penta prism and one optical flat mirror to be be a good starting bit of kit. I was lucky to acquire an H&W mirror w/90deg base , but have never located a penta prism. But, this is not something I use on a daily basis.

Thanks Daryl...

Been reading through your thread http://www.practicalmachinist.com/vb/metrology/need-h-w-ta-3-autocolimator-manual-237126/ and the TA3 manual..

Makes you wonder how hard it would be to make a unit to interface with the electric eye in the device... Seems it works by an a narrow slit oscillating over I assume a light dependant resistor and when it reads darkest, it means you have alignment.. Being 1960's tech, I doubt it is that complicated, not that I know much about electronics.

TA3 pdf manual.. -->> https://dl.dropboxusercontent.com/u/46279918/Hilger&Watts autocollimator TA3.pdf

Exactly. I actually set up the TA-1(the one I gave away) to check the ways on my Monarch EE. The hard part is setting up a proper platform outboard of the end of the ways. I used the bottom of the tailstock base as a sled and mounted the mirror on that. Once everything was aligned, which probably took a full day, I was making measurements, like really precise measurements, which proved quite a bit of fun ...really. I have since played around with the TA-3 after I made a new power cable, and it works perfectly. After you use one, you'll figure out why they came up with the electric eye model. Update...Thanks RC99 for the download manual. I am almost positive I have downloaded one in the past, but can't seem to locate it. And the one you posted does not look familiar to me, but it is the correct one.

After posting on this thread, I thought I'd have a looksee on the ole bay and see where prices are at. Wow. Looks like the collectors are in charge now.I had bought 3, two working, one for parts, all from different sellers, like all total for a small percentage of what the average one is selling for currently. I figure I was buying toolroom clean-out clearance in those days , never to be seen again.

When I was at the Litton Company, autocollimators were commonly used. They used them to check the flatness of mounting for the two gyroscopes on the stable platforms in their guidance systems.

It was me who suggested old HD platters to RC as that's what I use, however there is some incorrect information in this thread. Firstly, modern HD platter disks are made of aluminium, and they are VERY flat. I can't recall the figures off the top on my head, but they're ever bit as flat as some if the best optical mirrors. They are also polished to an exceptionally high finish, around 1 angstrom before coating. A benefit of the platters is that they are coated with a very tough coating to resist damage with head crashes, so they stand up to workshop use much better than schmuck optical mirrors.

A poorer quality mirror doesn't necessarily produce a a dimmer reflection, instead the reflection won't be in good focus. The reflected line appears to be "fuzzy" for want if a better description, and it's difficult to align anything properly. Indeed that can be a potential use of an AC in determining mirror quality from samples, although as far as I'm aware the results are only ever subjective. The brightness of the reflection is instead determined by the size of the mirror and the distance from the autocollimator.

Don't overlook the humble HD platter for this type of thing, it's something we take for granted, especially given the cost, but the science and technology within them is truly astounding.

thermite said:

A great deal of this sort of gear had been part of 'somebody's MIL-Industrial production or field-maintenance rice-bowl.
Time was, even the guidance system core components were showing up in cheap newsprint (pre-internet) monthly mailers.

I s'pose someone finally twigged that poor countries with military ambitions resembling open-air museums [1] were still hungry for the unfriendly use of some of that and it went to different destinations when taken out of service.

Bill

[1] At an 'undisclosed location' ....whole rows of Mig 17, still lovingly maintained by a Reserve Air Wing and gleaming in the afternoon sun. Not much point wasting costly camo-paint on a suicide-kit, after all.

Click to expand...

Yes, and the Litton Company is now just an unpleasant memory for myself and many others. All of their "stuff" got sold off and probably the only place where it's remembered is at the Grumman Aerospace Corporation of Peconic, Long Island. Grumman bought them so that they couldn't lie to Grumman anymore or screw them on production schedules. LOL.

Daryl, what is the code number on your auto collimator meter unit.. The meter units seem to be as rare as unobtanium... Google is not showing me a single picture of one except for the one you posted several years ago.. Quite a few auto collimators that use it, but no meter unit..

Pete F said:

It was me who suggested old HD platters to RC as that's what I use, however there is some incorrect information in this thread. Firstly, modern HD platter disks are made of aluminium, and they are VERY flat. I can't recall the figures off the top on my head, but they're ever bit as flat as some if the best optical mirrors. They are also polished to an exceptionally high finish, around 1 angstrom before coating. A benefit of the platters is that they are coated with a very tough coating to resist damage with head crashes, so they stand up to workshop use much better than schmuck optical mirrors.

A poorer quality mirror doesn't necessarily produce a a dimmer reflection, instead the reflection won't be in good focus. The reflected line appears to be "fuzzy" for want if a better description, and it's difficult to align anything properly. Indeed that can be a potential use of an AC in determining mirror quality from samples, although as far as I'm aware the results are only ever subjective. The brightness of the reflection is instead determined by the size of the mirror and the distance from the autocollimator.

Don't overlook the humble HD platter for this type of thing, it's something we take for granted, especially given the cost, but the science and technology within them is truly astounding.

Click to expand...

I agree that HDD disks are excellent mirrors, and that they contain a substantial accumulation of technological expertise. There is a distinction between surface roughness (polishing) and flatness, though. Angstrom-level polishing is indeed a feature of the micro-roughness characteristics in modern disk manufacturing, but the planarity of the disk, both in terms of waviness and global shape, is a differently-assessed characteristic. Both aluminum and glass are in current use for disks, at least have been up to about 1 year ago, the last time I measured some production glass samples from one of the major Japanese players. They were 65mm diameter, and quite good for such thin glass. Glass was introduced as a way of attempting to get better stability of the substrate for ever-increasing performance, especially for smaller HDDs. The typical 95mm diameter is still largely aluminum substrate.

I'm sure if one was to actually measure the reflected illumination intensity of the poorer vs. the better mirror, in terms of shape, say a half-wave vs. tenth-wave mirror, you can indeed measure a change in brightness of reflection. The micro-roughness of the surface (quality of polish) has a lot to do with the amount of light coming back as well. I don't disagree with your comments, generally, just clarifying that there are a number of factors that affect the ultimate quality of reflection from a specular surface. Assuming that the light source coming from the autocollimator is collimated as it exits the instrument, a plane mirror that is the size of the aperture of the autocollimator will return the maximum amount of light possible. A 10" diameter mirror won't be of any additional help in this regard, if the objective on the autocollimator is 35mm diameter. On the other hand, using a 1/2" mirror is a sure path to difficulty. As you note, distance is a factor, and largely so due to scattering of light from both micro-roughness and global shape issues, as well as the internal imperfections of the autocollimator, such as dispersion or chromatic aberration, or just plain dust on an older instrument. The practical effect of the numerous sources of error and aberration is a fuzzy focus as observed in the AC.

Looks like the part#for the meter unit is FA70. There is a ser# and that is the only numbers on the box. This is the reason I got this one years ago, as even then, the meter box was quite rare.I just googled FA70 and I see there is one for sale in some eastern country, probably Russia. That might be a difficult transaction.

specfab said:

I agree that HDD disks are excellent mirrors, and that they contain a substantial accumulation of technological expertise. There is a distinction between surface roughness (polishing) and flatness, though. Angstrom-level polishing is indeed a feature of the micro-roughness characteristics in modern disk manufacturing, but the planarity of the disk, both in terms of waviness and global shape, is a differently-assessed characteristic.

Click to expand...

Yes, hence why I specifically mentioned the two. Both are excellent in my experience, more than capable of being used for AC mirrors. If there is a deviation in overall flatness across the mirror it won't affect the operation of the AC (unless of course it's so bad as to make them unusable). A mirror that is "perfectly" flat and polished will produce an image that is both crisp and bright. A mirror that is polished but not flat (regardless of whether it's not flat on the micro or macro scale) will produce an image that is bright but is blurry. Completely useless as an AC mirror (an excellent example of this is a domestic mirror, you'll get a bright reflection off one but it will be blurry and useless). A mirror that is flat but not highly polished will produce an image that is crisp but not bright. Collimating off a surface that's not highly reflective is an example of this. If using a standard size HDD platter, the mirror produced will be smaller than the aperture of the autocollimator due to the large hole in the centre of the platter. For all intents and purposes that's unlikely to affect the operation of the device for what most of us here are doing. Indeed I spoke with RC off the forum and related the story of how remarkably bright the reflection is off a tiny gauge block if orientated along the measurement axis for ACs that measure one axis at a time.

Bill don't ask me what happens to all the AC mirrors, as you say, there should be at least as many out there as there are autocollimators, and maybe more. I presume people don't understand what they are and they simply get discarded. Those that do come up command a considerable premium, to the point of being ridiculous considering the alternatives that are essentially free. Of course it still means fabricating bases for them, but because the platters are double sided, proving them is no big deal.

With regard the electronic versions of these, I too understand they're some form of vibrating slit and null indicator. I don't think that would be a trivial thing to fabricate from scratch. What I think would be more realistic to make would be to remove the eyepiece and replace it with a camera. Looking in to an AC for any period of time is tedious and after a while hurts my back as it's at an awkward height (at least for me). It should be relatively straight forward to put a camera in its place and project on to a screen large enough that you will gain the same sensitivity improvements but at little or even no cost if you can bastardise an old web-cam or similar. It's certainly something on my "to-do" list, though sadly it doesn't feature prominently.

thermite said:

[1] Narrow-spectrum monochromatic light behaves differently traversing a lense than broadband 'white' or visible light.

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Other than chromatic aberration not being an issue, visible wavelength photons of all wavelengths behave the same when traversing a lens designed for that wavelength range so I'm not sure what you meant by this footnote.

The behavior of lenses at different wavelengths (speaking only of visible) varies over a wide range.

This effect can be quite obvious with a simple (single element) lens.
The effect can be controlled by using multiple elements of different characteristics.

Photographic optics are optimized so that two or three wavelengths will focus at the same point.
Achromats are optimized for two wavelengths: green and blue.
Apochromats are optimized for three wavelengths: red, green, and blue.

In contrast, lenses designed for industrial use may be optimized for only a single wavelength, like red from a laser.

The bottom line is you cannot __assume__ anything about chromatic behavior of any lens.
You must consult the manufacturer's datasheet, and believe what it says.

- Leigh