AUTOCOLLIMATOR MIRROR SYSTEM

Brief description of how an autocollimator is used to measure straightness and flatness. Followed by my mirror system design and construction details.
#practitioner_of_the_mechanical_arts
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[@SyBernot]

This is how you lay out a fire zone in artillery. We used ours over distances of several KM. You can put an 8 inch round within a 2 foot radius over several miles with a well set and columated gun. They are incredibly accurate.

[@ThePlacehole]

Wait, what? By mapping the surface of the fire zone? Won't the people there object to, you know, getting shot at? I could imagine them getting quite funny about it --- even going so far as to try and prevent any attempt at being accurately targeted.

[@braxtonec]

Wow. Do they use lasers for that stuff? Are there gyroscopes involved to reduce vibration on a battlefield? Does GPS play a factor since its removed from the shock area? Thx.

[@tilliesinabottle]

@@ThePlacehole the trick is not to tell them why they're holding up a mirror.

[@ThePlacehole]

@@tilliesinabottle :D

I was about to "build something cool" in the shop before watching this then lying on the bed and crying now.

[@vincei4252]

Lol. You'll get over it and make something cool in the morning anyway!

[@tonyray4203]

Now you know how I feel when I watch your videos CJ!

[@ROBRENZ]

You are cool!

[@gambez]

Never give up!

[@andyZ3500s]

@@gambez Ca Lem never gives up.

[@glennstasse5698]

Although I’m not surprised at Robin’s skill, meticulous craftsmanship, or design capability, having seen other of his videos, I am amazed at all the effort that went into building these things to measure up just his own plate! And how does he know about all these special parts like the bearing washers and the funny screws and the pads the mirror gizmo spins on? If there was a Nobel prize for machining Robin would be a lock! Spectacular! (And thanks for showing all this.)

[@radardoug]

I'm always amazed to see laboratory grade equipment built in your home shop. I guess that just shows that while the tools are important, it's really the craftsman that counts.

[@camillosteuss]

Regarding the tools and the master, the humble cook is the best example... No cookery nor pots will provide a great feast worthy of toasting to it and the chef, lest the chef is dedicated and loving towards his trade... The fine pots may be nice to look at and good blades may slice and dice with ease, but without a knowing and loving hand, you will be served a frozen pizza deluxe, heated on a primo pan and cut with the costliest of knives..

[@johncollins719]

So many useful tips in 42 minutes. Wow! The tips on precisiongrinding alone were worth the time. Learned more about that subject than all previous research combined. Thank you very much.

[@ROBRENZ]

Glad it was helpful!

[@ThisOldTony]

Amazing work as always!

[@ROBRENZ]

Thanks Tony, I haven't had time to try the suggestions yet. ATB, Robin

[@tonyray4203]

You make the seemingly impossible appear possible to us mortals and along the way show simple but effective techniques that we can use e.g. the use of the toolmakers clamps. Looking forward to more on the Collimator if you publish it.

[@HanstheTraffer]

My jaw is on the ground watching the most precise machining I have ever seen and Rob is just ho hum.

[@Ryan-dz3jo]

An absolute privilege that you take the time time to share your technique and talent. So many lessons in a short video, thank you Robin, you are an inspiration.

[@ROBRENZ]

Glad it was helpful!

[@oxtoolco]

Pretty sweet sled you got there Robin. Can't wait to see the mount for the Kollmorgen collimator. I really liked the flag machining sequence. All the best, Tom

[@ROBRENZ]

Thanks Tom! I already did my plate with the system and it makes things go really quick. ATB, Robin

[@unclebobsbees4899]

The thought process involved for your order of operations always tickle my brain. The level of experience displayed is just awe inspiring.

[@2dividedby3equals666]

I'm quite speechless to be honest. This video is an absolute marteclass, not only in machining but also on design. Brilliant as always Robin, thanks for sharing and take care!!

[@ROBRENZ]

Glad you liked it!

[@mattm7535]

My "self-perceived level of intelligence" took a pretty big hit watching this video. I'm curious how many hours you have in this project. Thanks for sharing

[@rickhaass1133]

I had the same question...

[@ROBRENZ]

Roughly 24 hrs

[@mr.t.807]

Amazing work & video, thanks

[@braxtonec]

I feel like a dog watching origami every time, but I sip from the fountain of knowledge and get a little closer with repeated exposure.

[@willsvideo]

Robin, I just want to say thank you for taking what are quite complex trains of thought and tricks that you’ve spent your entire career honing, and breaking them down into something even I, an amateur machinist can understand. I’ve been teaching camera operating for television and film for years (what I do for a living), and I’ve always found that there are so many people in the world who are incredibly good at their jobs, but can’t explain it, and it’s a wonderful treat to see someone who has not only the skills but the ability to explain why you’re doing what you’re doing.

[@ianpendlebury3704]

Simply fascinating ........ Thanks for making these detailed videos - always something to learn from them.

[@sharkrivermachine]

I particularly liked the set-ups on the grinder. I always learn something new when I watch your videos. Thanks for another great video.

[@forrestaddy9644]

Rob, I do like to follow your work. I've heard it said that explanation concurrent with demonstration is the most effective teaching method for technical material; you're proving this aphorism with your every video. Those considering adding silver brazing to your skill set should not be fooled by the apparently red heat seen in the silver soldering demonstration part of the video. Actual silver brazing temp is a bit cooler than that. Video cameras see further into infra-red, rendering what would seem dull red to the eye into cherry red on the screen. For the record, Harris SafetySilv 45 brazing temperature is1370⁰ to 1550⁰ F. Harris Safety Silv 56 is 1200⁰ to 1400⁰ F. Safety Silv white flux active range 1000⁰ to 1600⁰ F. Safety Silv black flux active range 1050⁰ to 1700⁰ F. The other difference between the two fluxes is the black flux has a boron content that extends its working time. Flux activity is time limited at brazing temperature. Silver brazing if done expeditiously is a sure and reliable method of bonding metals into strong permanent assemblies. The liquid flux oxidizes in air over time forming a tough film that inhibit joint wetting by the silver alloy. For that reason, plan your operation and have everything handy. IOW, do not dally. A final point is joint cleanliness. Clean the joint thoroughly, then scrub the joint surfaces with Comet cleanser, a stiff brush, and water followed by a hot water rinse. Do not follow with a solvent clean. Conventional wisdom decrees a final acetone wash. Acetone is a commercial product containing impurities, reaction fractions, wax, and tramp particulates. These pyrolyze and inhibit flux activity and joint wetting. Repeating: Do NOT solvent clean. Scrub the joint components with cleanser and water, etc then immediately braze the joint. A thoroughly clean silver brazing joint never misses.

[@AJR2208]

Good tips Forrest - Thank you.

[@ROBRENZ]

Thanks Forrest, I never thought about having a no water break surface before fluxing and soldering. That's a good one. Grit blast before soldering is also a plus. ATB, Robin

[@railgap]

@Forrest Addy - If you use acetone from the paint store, or typical industrial supplier of solvents, of course you will have problems. You can get "optically pure" acetone if you look - that is, a grade suitable for cleaning optics in the laboratory. The stuff is way above reagent grade, which is way above paint-store crap. It is absolutely chemically pure, anhydrous (if you keep it capped, heh) and free of contaminants. Comes in glass bottles. Anything in a can is useless.

[@forrestaddy9644]

@@railgap What you say about pure acetone is correct but consider $82/gallon at Lab Alley or $17/12 oz from Amazon for a low utilization shop supply when a simpler alternative is already on hand. And there is the fire hazard of acetone in proximity of hot work. Joint cleanliness is an inescapable requirement for success in silver brazing. How you achieve it is up to you. My position is Comet and hot water as a cleaning method for silver braze joint components is quicker, more convenient, non-flammable, and requires no special purchase. If you get poor wetting at brazing temperature, it's inevitably a consequence of joint contamination of some kind. I've tried alternative cleaning methods including electrolytic, ultrasonic, bead blasting (very effective BTW, particularly on cast iron, but generally a PITA), and abrading. All work but require additional steps, extra equipment and resources, etc. The shop sink is right there and the can of Comet and the retired toothbrush is handy on the shelf. You can flux, assemble, and heat within seconds.

[@jamies3190]

I want to know the 3 fools who would dislike anything robrenz uploads. He chooses to teach us some of the most informative information on KZbin. You 3 ppl should feel privileged to be blessed by a man with this type of wisdom! Thanks robben u sir are one of the best teachers and probably have forgotten more then they will ever know in their lifetime. Keep up great work

[@ROBRENZ]

I appreciate that!

[@vikassm]

Your channel along with Dan Gelbart's are the ones that Ive spent most time on, watching and re-watching countless times. Thanks again for uploading content like this, you're the best teacher ever. (And this video is just in time for lapping my "practice" granite plates.)

[@ROBRENZ]

Wow, thanks!

[@rhysd5410]

I really like the trick of coming in the other side of a threaded hole with a set screw to set a depth. It never occurred to me before. I can think of a few times when that would have been the right thing to do. Instead I used Loctite and felt uneasy about it!

[@EPaulIII]

Nothing wrong with the Loctite. I have even used fishing line to provide a locking but adjustable mechanism for adjustment screws. What you do need to do is carefully think out exactly what is happening when you lock it. Does your locking mechanism tend to take up the slack in one direction or the other or is it neutral. A lock nut pulls one way or the other. Loctite is neutral and so is my fishing line. You should use whatever is appropriate to the situation.

[@danmartinrc]

Wow! There was a lot of knowledge packed into those 42 minutes. Thanks!

[@ROBRENZ]

Glad you enjoyed it!

[@joell439]

Stunning work. I sure wish I was 1/10th as clever and thoughtful. Thanks Robin for sharing. I learn more than I ever imagined watching you, the humble master, at work. 👍😎👍. Joel......

[@ROBRENZ]

Glad it was helpful!

[@zagmongor]

I love your videos. Every decision you make has a purpose and is very well thought out, both in regards to how you will go about machining the parts as well as how those features will work in the end product. I strive to design parts with as much intent and purpose as you do. Every video I see just shows how much more there is to learn. I always click on your videos because it seems like an interesting topic, not knowing there are about 20 new tips and tricks and knowledge about materials thrown in throughout the video. I will be adding dowel pin holes to my tapped fixture plates from now on, that seems like a very efficient way to quickly line up parts to the mill.

[@lopezepol75]

Looks like I'm not going to bed tonight. Time to bust out the notebook and gain some knowledge.

[@txm100]

Out of curiosity: what are you writing down?

[@rootvalue]

tm Probably doctors who will prescribe Ritalin. 😂

[@andyZ3500s]

@@txm100 I do the same thing. I will make a simple drawing of something that could be useful to me, or I write down a product that I'm not familiar with but could also be useful to me.

[@maikeydii]

I'll have to start to do exactly the same. Rob's videos are a treasure trove of knowledge in the (fine) mechanical arts.

[@Watchyn_Yarwood]

You are a genius! A genius is a person who displays exceptional intellectual ability, creative productivity, universality in genres or originality, typically to a degree that is associated with the achievement of new advances in a domain of knowledge.

[@ROBRENZ]

Thanks for the kind words.

[@Saki630]

Beautiful video. I am allergic to metal and milling but I still paused my pr0n to dedicate an hour to this amazingly informative video. Keep up the high quality content. There are many people who learn from your channel.

[@bcbloc02]

I watch this and all the precision fits and pieces while I am beating together pieces with a sledge hammer in my shop. I feel like I barely rate caveman status. lol When I first saw those parts I thought they were castings. Not sure what is more impressive the level of fit detail or that you could make all that in 3 days. Just WOW, Impressive!

[@ROBRENZ]

Thanks Brian for the very kind words. ATB, Robin

[@gravyblue]

You're not alone....

[@Rob_65]

If Tom Lipton is 'Q' (from James Bond), then I am wondering what you are. At least a master in the arts of fine mechanics and a very good teacher too. We mere mortals are very glad that there are people like you, Tom, Stefan and some other guys who show us all their magical tricks for us to try to do this too.

[@hairyfro]

I picked up a Hilger & Watts autocollimator on eBay to measure my own surface plate only to discover how difficult it is to find proper target mirrors. So, I started designing my own. Needless to say, I'm feeling a little less confident in my own design now. This is a really well thought out and executed design. Well done! Also, I guess need a bead blaster now. Such pretty finishes on those parts...

[@ROBRENZ]

It can be as simple as the one I showed first.

[@jeffren70]

Robin: you are on a whole other level than 99.9% of all other humans. Great work!

[@smitty2868]

A treat every time you upload, thanks for the work.

[@woodscreekworkshop9939]

Simply beautiful, I shed a tear 😢👍🏼

[@Aeroeng92]

Incredible work. Thank you for sharing this with us.

[@mortezarahimi6784]

Sometimes selfish people like me need to watch this kind of videos to recall that: "there are people out there that you can't imagine how smart and skillful they are and you think that you are the smartest person in the neighborhood!!!!" Thank you sir! as always people like you aren't on TV or in the center of media attention but Humanity definitely owes a lot to people like you! and if you are in the Practitioner Level, what Level am I ?????? Salute to you, From Iran!

[@ROBRENZ]

Thanks for the very kind words.

[@JesseHersch]

I am astounded truly. Incredible work.

[@dgoode-ys3nx]

Another fine clinic, Thank You for sharing.

[@ianrobertson8313]

This is a must see channel, well done

[@wash3141]

As soon as I stop weeping, I am going to sell all of my tools! What an amazing job Rob. Thanks so much for sharing!

[@middleroad00]

*Amazing* ! Conception, design & fab, all-by-one. Back when I started out as a 'Tool' designer there were: -General Machinists, multiple levels. -Tool & Die Makers, again - multiple levels. -Instrument & Gage Makers. I can't recall what comes after that, but this project is at that 'atmospheric' level.

[@eliduttman315]

The Japanese have living national treasures. Folks, that's EXACTLY what Robin is. How scary good can 1 person be? To date, Robin seems unlimited.

[@jhueth3969]

Awesome! I’ve been waiting for you to do a video on autocollimators. Your videos always help me understand the tools I use a whole lot better.

[@fredgenius]

Wow! I'm blown away by your skill again.

[@1Maxsophie]

Nothing can be said except OMG, Legend.

[@zachaliles]

I don't know why it surprised me when I got to the part where you showed making them. I've been watching you long enough I should just assume you've made everything in your shop unless you say otherwise.

[@MegaCountach]

Really informative Robin! Thanks for your time! Cheers, Doug

[@charlieromeo7663]

There are so many takeaways in this video its crazy! Very cool vid, Robrenz.

[@hitchandcartow]

Bravo! Thanks for sharing this. I’m a big fan of the 2-speed kinematic mirror adjustor system.

[@someoneoutthere7512]

Very impressed! I like watching someone make laboratory grade tools!

[@holry7778]

Wow. Simply amazing and gorgeous work. Great job Robin.

[@bob_mllr]

Great video and job Robin. Always a treat looking over your shoulder and learning. Thankyou!

[@agie170hss2]

Very, very impressive work and great explanation, as always!

[@Garthinyus]

Can't wait to see you Robinize a surface plate using this tool.

[@anathaetownsend1894]

Educational as always. Thank you, Robin.

[@kevinbasto5611]

Just a mad scientist, in the best possible way!!!

[@mahejeah]

just dense packed with great machining tips!

[@NicholasMaietta]

For whatever reason, this reminds me of my days as a fusion splicer. Cool stuff.

[@JohnK8]

Gorgeous work.

[@tombellus8986]

Great work, and thanks for sharing your knowledge and skills. Medicine for the home-bound.

[@FCleff]

The explanation, design and execution were magnificent!! Thank you.

[@ROBRENZ]

Glad you enjoyed it!

[@hinz1]

Those mirror stands are totally awesome.

[@ROBRENZ]

Glad you like them!

[@longlivepunk]

Wow Robin, great work as always! I love to see the thought you put into your projects.

[@ROBRENZ]

Thank you! 😊

[@gwharton68]

Absolutely beautiful. I have no use for an autocollimator, but it would be fun to have as a conversation piece. Great job as usual.

[@davidandrews8566]

Robin that was a delight to watch thank you

[@markusn1365]

i have no words ... except, absolutely impressive work

[@886014]

Nice one Rob. I like that finish. I guess you're going to do a part 2 and I'm curious to see how you prove that mirror perpendicular without a master. FWIW I've found old hard drive platters make very good auto-collimator mirrors. They're manufactured to extremely high tolerances, are double sided so perpendicularity can be self-proved if required. Best of all they're free ... something that can't be said for normal 1/10th etc first surface mirrors! They make accurately checking all manner of things very easy as the mirror becomes essentially disposable. For anyone considering dropping down the rabbit hole of optical metrology, Rob's work is spectacular just because that's the way he works. However despite the extraordinary accuracy in the process, accuracy in the mirrors etc isn't generally required for most measurements as the AC is generally used as a comparator and it's all about repeatability between sightings.

[@ROBRENZ]

Thanks Pete. I hate to disagree but mirror flatness matters unless you can guarantee the exact same spot on the mirror is used for the total sled travel.

[@886014]

@@ROBRENZ ??? I'm not sure I follow you Rob. Mirror "flatness" in optical metrology is measured in fractions of a wavelength of light, waaaaaaay beyond any of the accuracies even your machining is capable of ;) If the mirror was so far off "flat" that it was affecting measured sled travel measurements you've got bigger fish to fry! What happens when the mirror isn't "flat" in optical terms (and that is generally referred to in fractions of a wavelength of light ie circa 50 nanometre range) is the reflection will be blurry and can never be bought in to focus. You can try it if you want, just polish up different objects and you'll see. Shiny doesn't mean flat, as we both know. That's a whole different discussion on lapping vs polishing. Optical metrology can be very counter intuitive, especially with autocollimators. Another misconception is the mirror size, and that doesn't need to be as large as the instrument's bore. The only affect mirror size will have will be the brightness of the reflection. I've used gauge blocks as mirrors for example, and they do work, but the reflected image isn't bright, nevertheless the image is crisp and their surface finish is optically accurate. This can be confirmed with an optical flat, pretty much a must have for anyone serious about rolling their own optical gear and they're not expensive if purchased used. Optical flats are also excellent for checking gauge blocks for any issues, and I check mine from time to time. BTW the reason old hard drive platters work so well is because they ARE very accurate. Even a consumer hard drive flies the heads in the circa 3 nanometre range average above the platter. Crashing in to the platter would instantly destroy the disk. We sometimes take for granted some of the extraordinary manufacturing and physics we buy for peanuts these days, but when developed that level of accuracy wasn't easy to mass produce, never mind for the price they sell for! The disadvantage is they're fragile, but given they're free I'll take that!

[@hasanzakeri8708]

@@886014 I have to agree with @ROBRENZ here. The surface quality of the mirror is everything. And those few nanometers of inaccuracy in the surface will show itself in distance and would be equivalent to seconds or large fractions of seconds. Similarly, you can easily identify a quarter wavelength of inaccuracy in a telescope mirror just by observing a star.

[@xmachine7003]

@@ROBRENZ Are the mirrors optical flats?

[@ROBRENZ]

@@xmachine7003 basically yes but with a reflective coating on the flat face

[@shane9338]

over the years i have been watching Rob work, Ive wondered if the absolute precision caries over to the rest of his life's adventures? I guess OCD can be a good thing at work as long as you can turn it off at home. My Dad always told me "if you are not going to do it right, then don't do it at all." He also said spend your money once, and buy the top of the line best available, and you will always be satisfied with it"

[@LeoMakes]

This is so thoroughly impressive! I especially liked the machining of the flags and the glass bead finishing. Super interesting project!

[@tsviper]

Robin's breaf information is PhD level for most people......

[@465maltbie]

A lot to absorb, will have to watch again later, which will be a pleasure. Charles

[@Totalis1989]

As usual, you have presented a beautiful precision assembly and I have learned many things. The component used to lock the differential screw is wonderful and I shall be using that idea on a current project of mine. Thank you for freely sharing you knowledge.

[@brianstyrczula9466]

Incredible talent

[@bhimapandava7767]

Wow, this is fantastic!

[@phillipyannone3195]

Another spectacular video. Thanks for sharing your vast store of knowledge. So many great tips. Turning dreams into reality.

[@MrPianoKnee]

Really is spectacular. Mechanical eye candy, even for the less informed. One hundred percent pure science except for the part that is one hundred percent pure art. Will have to save and re-watch this one on the big screen.

[@x0urce942]

this is just mindblowing...the radius you made on those pins...

[@workucet6788]

Fantastic, as always! Such a good teacher...

[@ROBRENZ]

Wow, thank you!

[@stumccabe]

Absolutely beautiful workmanship and design (mechanical and aesthetic). Thanks for the video.

[@ROBRENZ]

Thank you very much!

[@thomaslizon2594]

Amazing work as always. Such a level of precision. Impressive and inspiring. Thank you very much.

[@ROBRENZ]

Thank you very much!

[@TheTsunamijuan]

Love the finish on the parts. You always have interesting stuff, and impressive levels of detail. But this video blew my mind. Probably cause I am starting to understand machining and the processes around it better. So I have a greater respect for what is being accomplished and why.

[@ROBRENZ]

Glad you enjoyed it!

[@pierman69]

Fantastic and impressive as always Robin!

[@ROBRENZ]

Many thanks!

[@bobloblaw7879]

great video Rob. I learned quite a bit about autocollimators and their use - thanks!

[@bostedtap8399]

Excellent demonstration Rob, brilliant design and manufacture of the instruments. I've used a 0.025 mm per Metre level on tables and machines, and plotted the flatness deviation using a spreadsheet (took me several days to get the formula) Great vlog, thanks for sharing and best regards John.

[@andyZ3500s]

You sure do a good job at explaining the engineering and making of a complicated project. Thanks for your valuable time.

[@ROBRENZ]

Glad it was helpful!

[@nickolaguez]

So much valuable information. Incredible Robin.

[@ROBRENZ]

Glad it was helpful!

[@outsidescrewball]

THANK YOU for your time to create and share..SO many lessons

[@ROBRENZ]

Thanks Chuck! ATB, Robin

[@BackeB]

Wow this is both inspiring and humbling to watch. The silver solder part was satisfying!

[@ROBRENZ]

Glad you enjoyed it!

[@d37tae]

14:49 with my AirPods in was like scratching my teeth across a chalkboard. I haven't had every hair on my body stand up like that for months. Haha. But in all seriousness, your work is fantastic and it is such an inspiration. Keep it up!

[@toolbox-gua]

Excelling in taking consideration to minute details to achieve excellence. Awesome and beatiful.

[@ROBRENZ]

Glad you liked it!

[@saschaoswald480]

Nothing my small intellect could come up with would add anything useful to this. Simply spectacular. Thank you so much for sharing your knowledge...we are not worthy!!!! I think you should have made a few of these while you were at it, I bet you'd have some eager customers...

[@ROBRENZ]

Glad you enjoyed it!

[@pierresgarage2687]

Hi Robin, This is loaded with information about how to get the most of every situation when requiring "Real precision". Hope you're planning another part where you elaborate on adjustments and make actual measurements. Thanks for what you already released... Pierre

[@ROBRENZ]

Will do Pierre! ATB, Robin

[@Kvasir87]

You’re an absolute beast!!!

[@slausonm]

Robin, you are on a much higher plane of machining than I but you talk about basic things in your videos that I try to teach my high school engineering and tech students. Thinking about planning and order of operations is very important. Thank you for posting this video, I enjoyed every bit of it.

[@ROBRENZ]

Great to hear!

[@AmateurRedneckWorkshop]

Very impressive to say the least. It is nice to watch an expert work. Thanks for the video.

[@ROBRENZ]

Glad you enjoyed it

[@smithparkins4862]

Wonderful break down. The finished product is sending a shot across Clickspring's bow... I have a lathe project in the works now, and I will definitely be using lessons learned here...

[@gasworker3042]

Brilliant! Thanks for sharing!

[@MCEngineeringInc]

Amazing work! 👍🏻👍🏻

[@feedback-loop]

Very impressive. Thank you very much for sharing.

[@braxtonec]

Didn't know what one was, but thanks for the thorough and detailed explanation. I have a greater appreciation for the finer points of their use and even more so for the construction of the 'accessories'. Outrageously refined and clean design. This is my second time watching and it just keeps getting better!

[@ROBRENZ]

Thanks for watching!

[@Volcker1929]

Fantastic video sir, thank you.

[@bobolander]

always love your videos, this one was awesome as per your usual. i thought "he's pushing that sled with a skewer to avoid inputting heat" and then you said you were doing it for that very reason. i learned that from you. thanks for teaching and it never ceases to amaze me how much i learn every time i watch. you've multiplied your talents over a lifetime. respect on multiple levels!

[@ROBRENZ]

Thanks again!

[@txkflier]

Wow! That was the best engineering and machine work I've seen in years. Your corner mirror unit and mirror sled are way better than what we used on our US Army surface plates. Of course, you'll be able to use them for many other things. It was many years ago, but I don't recall that it was important that the auto-collimator and corner mirror didn't move between each of the union jack runs - only during each one. Yes, it's handy that you can make three runs without moving the auto-collimator. One thing we did do after each run was to return the sled mirror to the starting point to make sure that the zero was still good. If it wasn't, we'd redo that particular run. The calculations we ran tied the three runs at each of the four corners together and connected the ends of the center runs to the midpoints of the side runs. The calculations also gave us the error of the four crossovers at the center of the plate which told us how accurate our measurements were. And, we typically avoided the outer 2 inches on our larger plates..

[@ROBRENZ]

Thanks!

[@TomChame]

Amazing, thanks. I was really happy when I understood the 3 legged gizmo......

[@helicopterjohns]

Beautiful Tool! John