How to make Very Flat Optical Surfaces on Glass

[@mccallan2798]

I've got absolutely no idea why this video was recommended but I'm so glad it was. Fascinating. Well done.

[@robotslug]

Same

[@thekeyfox]

Same

[@BootyYeeter]

Same

[@88njtrigg88]

It's because your subliminally interested in light & optics.

[@mcpozzm6321]

It started when I clicked on a bartender showing how to make optically clear ice cubes for drinks, next day this was in my feed.

[@tombesson7293]

This video reminds me of the optician who fell into a lens grinder and made a spectacle of himself.

[@MikeWiggins1235711]

That's not as bad as the glass blower who accidentally inhaled and now has a pane in his chest.

[@yashsvidixit7169]

@@MikeWiggins1235711 Still not as bad as that chef who, while cooking some some chicken broth, fell into the pot and made a laughing stock of himself.

[@Cynthia_Cantrell]

Clearly, I didn't see that coming.

[@tombesson7293]

@@Cynthia_Cantrell Did you hear about the guy who wondered why the baseball kept getting bigger and bigger, then it hit him.

[@user-hv6wb5gk8p]

Reminds me of the lab technician who spilled some acid on himself. Really left him fuming.

[@TheWtfnonamez]

Totally counterintuitive. I've done a fair bit of metalwork sanding and polishing, so I naturally assumed that optical polishing would be similar, only using something harder and flatter to grind the surface. It never occurred to me that the rotational grinding process would use something ductile, yet get better results. Thank you very much for the excellent explanation.

[@stanrogers5613]

In metalworking terms, it would be very similar to using an aluminum, copper, or tin lap (as in watchmaker's "black polishing"). You want your lap to be softer than the material to be cut. Your lap becomes a matrix to hold the abrasive particles in place, and the cutting happens on the material that can't just grab and hold the abrasive. (Tin, by the way, gives absolutely amazing results when polishing steel. It's just _really_ stringy to machine when you're initially making the lap. Save it for your finest - sub-micron - grits.)

[@stc2828]

You polish silverware with fine cloth which is softer than silver. If you use sandpaper the result would be terrible.

[@gvidas1338]

Very informative yet old video on lapping metal parts by rotation. Check this: kzbin.info/www/bejne/nJ_Sh4ljh7x8jbs It vey clearly explains "how it's made".

[@sakelaine2953]

@@gvidas1338 This is great, thanks!

[@matter9]

I feel there’s a general misconception when it comes to lapping a polishing that is a result of focusing on the lap material. As the first comment responder noted the lap only hold the cutting media. There are three fundamental rules for cutting to occur, though I only usually remember two. The important one here is that the cutting “tool” (in this case lapping or polishing compound) MUST be harder that the workpiece. The second is that there must be relative motion. The third escapes me. But in either case it is not the lap that cuts the work piece but the embedded abrasive. Apologies for the lecture comment but lapping and polishing seem to be no different fundamentally than any other metal removal process; hard removes soft. In the case of polishing silverware presumably there is some residual polishing compound on the cloth that is the effective mechanism for removing the oxide layer. Also, if I’m glaringly wrong please correct me. 👍 Edited for autocorrect errors.

[@hydrocarbon82]

Flat-out the best vid on making flat optical surfaces! Clearly thought out well, I couldn't pitch in any criticism. It's almost like we're on the same wavelength.

[@digitalradiohacker]

What a cheerfully bright comment! I for one found the video very illuminating, and it seemed to polish out all the rough spots in my dull and hazy knowledge. You could say that it expanded my bandwidth....

[@yashsvidixit7169]

@@digitalradiohacker makes me wanna leave my daily grind and do something else

[@bellowphone]

Micronically inquisitive mind lapped up the precision explanations.

[@Asdayasman]

If y'all don't cease with immediacy I'm gonna jump into a woodchipper.

[@DocBree13]

😂

[@frog8220]

How did I end up watching 12min of "how to polish something to the nm scale?" But you explained it so well that I understood it without any previous experience in polishing glass or anything for that matter

[@Kargoneth]

It's rather hypnotic.

[@TickyTack23]

This is really good, so well detailed. It seems over the years there has been a lot of demonstrations of optical grinding/lapping, lots of "recipes" so to speak, without any detailed explanation as to why it works. I'm coming out of this with a deeper understanding of the process, only took 12 years, but better late than never!

[@tomtang2639]

jeez why didnt youtube algorithm recommend this to me earlier??? Its fascinating!!

[@Dukey8668]

I have been interested in optical engineering for a long time now and yours is the first channel I have seen that covers it well. So thank you for making such excellent videos.

[@stickyfox]

I used a machine like this in the 90s to flatten hydraulic motor parts. Instead of pitch, the wheel surface was steel, and the surface was kept flat by adjusting three rings which also kept the parts in position on the wheel. We'd check it a couple times a day by washing the abrasive off and placing an optical flat on the wheel. But other than that it worked the same way.

[@hindugoat2302]

its not the same as true level

[@stickyfox]

@@hindugoat2302 Reality is poison! I can't live like this!

[@stickyfox]

@Andrew Crews I worked on Eaton and Sauer-Sundstrand axial piston pumps and motors. We would replace pistons and cylinder blocks and send them out to be resleeved/refinished.

[@michaelmello42]

I appreciate this comment very much after having done very similar work in the 90s. I used to test lapped and partially polished parts with an optical flat to infer the concavity of the part (convex or concave). Once the concavity was determined, I inferred the lapping wheel's (opposite) concavity and would adjust the rings' position to correct the wheel.

[@subhashkulkarni1117]

Pl.explain the process in detail

[@movax20h]

Newtonian liquid is just a liquid / fluid. Classic. Water, alcohol, glycol, air are all newtonian fluids for example. So, it is not "special" in any sense. Optical pitch has just very high viscosity. There are fluids that are special, and they are called non-newtonian. There are many types of non newtonian fluids and they all have various applications and fascinating properties. :D There are some non-newtonian (visco-elastic with non linear sheer relationships), that are also used in optical polishing, but that is rather very different method.

[@HuygensOptics]

You are right about the fact that a lot of common fluids are showing Newtonian behavior. But there is also quite a lot that are behaving non-Newtonian such as paint, yogurt, ketchup, toothpaste, so in that sense non-Newtonian fluids are also very common. I guess, all fluids are special, but some are more special than others ;-).

[@movax20h]

@@HuygensOptics That is true. Non Newtonian fluids are also common. They are just harder to analyse :) ketchup is weird indeed for example. Or magnetorheological fluids, used btw for very precise polishing in optics. Learned about it just few days ago. :D

[@lolvivo8783]

@@movax20h which field do u study this?

[@noanyobiseniss7462]

The true test of whether someone has mastered a field is their ability to explain it to the uninitiated in a clear and concise manner, you sir are a credit to the field.

[@denisnikitin5894]

Thanks for the video, it's very informative. So the polishing table is an aluminum disk with a motor stator attached to it, and you press the pitch lap by using a granite plate, but I was wondering if you could share what the pitch lap substrate is made of? It looks like a few inches thick disk. Is it also granite?

[@HuygensOptics]

No actually in this particular case it is borosilicate, which has a thermal expansion coefficient that is about 3 times lower than granite (which is an advantage). You can however use granite without problems if you have good temperature control.

[@richardlee9685]

When you shut the machine down overnight, is it necessary to maintain the lab at a cool temperature to minimize pitch movement?

[@shannonpincombe8485]

Nah...you just use auto tune. Everybody does these days. Hehehe

[@tjsbbi]

@@shannonpincombe8485 That's how those T-pain sunglasses are made.

[@juliusfucik4011]

I think there is a tradeoff. It would certainly help, but investing in climate control may not be worth it. Also, it seems heating the plate and then weighing it down removes enough deformity in a small amount of time. These techniques are fascinating.

[@thedudeamongmengs2051]

@@shannonpincombe8485 I respect the pun

[@ai_university]

They run 24hrs

[@trex70]

Very nice thank's for sharing

[@nuramd]

Today is the day i understood why tires have grooves

[@gamemeister27]

If pitch is a liquid, couldn't flatness be achieved without a reference flat (like the bruiser or surface plate)? Enclose the pitch in a container with walls higher than it and heat it up enough to reduce the viscosity so it flows fast enough for the surface to find its level in a reasonable amount of time, then let it cool down. Surface tension would mess with the flatness near the walls, but closer in should be fine. I suppose you lose the grooves though, darn.

[@HuygensOptics]

You will have to wait for a long time before the surface reaches submicron flatness. Keep in mind that there is a volume contraction during cooling down. And of course it is not just about getting the tool flat, but keep it flat during processing.

[@tottedpotato]

Hello youtube algorithm...thank you for suggesting something I didn't know i needed to know

[@therealzilch]

I've always thought there was something almost magical about being able to make incredibly accurate optical surfaces, flat or otherwise, with no precision tools whatsoever. I ground my 6" parabolic mirror by hand, and figured it to 1/20 wave accuracy on a pitch lap, with no references other than the Foucault test. Very nicely done. Subscribed. cheers from sunny Vienna, Scott

[@robertmccabe8632]

if you like that; then the three plates to make a surface plate is another example of this principle (though wil hardish surfaces)

[@therealzilch]

@@robertmccabe8632 Indeed. I use this principle to keep my sharpening stones flat. Using silicon carbide abrasive, I grind A against B, B against C, and C against A.

[@DandamanV]

Here we are, reunited by the algorithm again!

[@markwilliams5654]

Could you make something optically flat in ancient times using something very similar

[@TungstenCarbideTempe]

The principle looks simple, its just a tar and turntable, but those who tried working with glass, especially polishing and making it precise, knows that its extremely hard, takes years of practice and patience. Great video.

[@adrianrevill7686]

Thank you, i always wanted to know how it was done. Very clear description.

[@mdevidograndpacificlumbera1539]

Do you always use the same grit to polish? If not, do the grits find themselves trapped in the pitch? Do you have to use different pitch plates for each grit?

[@HuFlungDung2]

Polishing is the final stage of producing an optical quality surface and there is only one compound used on a given lap. Grinding the surface to a desired rudimentary curve is called grinding, not lapping. Pitch laps do not grind but only polish. The amount of material you'd remove by polishing is miniscule and nobody wants to waste time doing any more polishing than necessary. Grinding a surface starts as a rough cut to quickly give a desired curvature and to remove casting irregularities. Then a succession of finer grits is used to remove the deep scratches left by the previous grit. This is done with a hard tool on the workpiece and an abrasive slurry is run onto the surface. It looks a lot like lapping with a pitch lap, but because the tool is hard, it can be reliably cleaned off when it is time to change to the next finer grit size.

[@MimicGriphon]

Am I the only one that loves this type of stuff, but at the same time, completely understands how boring most people probably would find it?

[@falcfire3093]

Fascinating stuff, the explaination is on point!

[@rapsod1911]

This is very interesting. I read somewhere that for lapping of silicium wafers they use some chemicals instead of abrasive particles. I can't imagine how precise they must polish wafers for 4nm technology.

[@HuygensOptics]

It's generally a combination of both. If you use a chemical that etches your surface while you are polishing, you can use a very mild (or soft) abrasive agent, which results in a smoother result. By the way, when you use Cerium Oxide to polish glass, chemical interaction also helps speed up the polishing process. For wafers the actual flatness is less important that the smoothness, since modern wafer steppers make a heigh map of the wafer to correct for the total thickness variation when clamping a wafer to the chuck. Modern technology wafers are indeed incredibly smooth and flat (from the dimension of individual components to that of the full chip)

[@Dak3]

Using interferometric fringes to test optics, what an ingenious setup!

[@kellymoses8566]

If you think that is impressive the Laser Interferometer Gravitational-Wave Observatory uses interferometry to detect changes in length less than a 10 thousandth of the diameter of a proton.

[@BarneyDesmond]

@@kellymoses8566 luckily we don't need *quite* such precision for optics :)

[@movax20h]

Fascinating videos, with plenty of details. Thank you for all this useful info and diagrams!

[@williamcashion5262]

It's hard for me to believe but, I lapped and polished for 20 years (Gator Diamond, Inc) and didn't know half of this info. Thanks, Bill

[@ofeliawotsits6080]

Flat implies “not curved” when these are curved surfaces. It’s really about the size of the deviation from the theoretical shape of the required surface.

[@MaxRomantschuk]

This is the most satisfying and informative presentation I've seen in ages. As a photographer I really appreciate the craftsmanship required to produce high quality optics. My hat off to you Sir! 🎩

[@martinthemillwright]

One of the most clearly explained process ever seen on KZbin. Beautiful. I feel like building one of these now.

[@guymross]

4 minutes in and I have no idea what you’re on about and where the optical glass is

[@kochipj]

I work in the optics industry for a couple of years now and I have to say that your channel is a real treasure! Your videos are both, highly educational and entertaining. Keep up the outstanding work!

[@RobertMilesAI]

Does this type of pitch polishing give you any assurances of the parts being square or parallel? I imagine you might often want an object with two opposite faces both very flat and very parallel to each other, but my totally uninformed intuition says this process might not be able to give you that?

[@HuygensOptics]

That is correct. To create parallel surfaces, generally two-sided grinders and polishers are used that have two abrasive disks spinning in opposite direction while applying pressure.

[@ramkitty]

Excellent vector drawing demonstrating the constant angular velocity.

[@СергейХомяков-в7э]

I have been polishing precision optics for 12 years, I really enjoyed the video, thank you. I do the final polishing of the optics on a spindle in a zerodur plate with holes, I put planes with weights in them, according to a similar principle. pitch polishing pad for the night I turn over on a plate smeared with Regipol with good flatness

[@asdf35750]

Using a Fisher and Paykel motor driven by a VFD is genius! So much simpler than the old belt and pulley reduction.

[@electroflow3721]

Dear Jeroen, Inspired by this video I settled out to try taking broken Nd:YAG crystals and polish them to be usable again. I have already hand-lapped then using 3µm abrasive to about 3 wavelength flatness. Currently, I am finishing building a pitch polisher following your example here to bring them to final flatness. However, since they are not glass I can't use cerium oxide. I found a paper suggesting using .3µm aluminium oxide. Do you have any recommendations for the concentration of abrasive in the slurry when using your type of polishing machine? and do you have a hint where I could source this polishing compound as a private person in small quantity for a reasonable price? (Using the keyword "Linde A" I found a lot of North American sellers but none of them seem to send to Europe where I am based) Thank you for your inspiring videos and in advance for any tips you can provide!

[@vanaile9507]

Hi. I have the same your laser rod that need polishing aganst. Did you succeed?

[@markwilliams5654]

Great information thanks for sharing 🤠

[@The_Mimewar]

Yeah. No problem. Just GRIND the glass optically clear. Piece of cake

[@DarkMetaOFFICIAL]

This is crazy 😂 imagine someone asking what you're doing with that junk/scrap metal and trash parts.. Like uh, well.. you got an hour for me to explain? it's sort of technical. just a little. 😂😂

[@seditt5146]

Lol, grew up with a family that owned an HVAC business. As a result our shop behind my house contained tons of scrap parts to various household items. Combine that with my love ( obsession) of Science and my childhood was a constant stream of creating Lasers, Tesla coils, particle accelerators, different electro-static stuff and I found after a while.... people just stop asking what that thing is you built over there with junk :D . Funny enough one of my first passions was always Astronomy and I always wanted to make my own telescope yet felt mirror grinding was out of reach. I even made vapor deposition chambers using other junk so I could have coated it but this polishing stuff always felt out of reach so I just moved on to other subjects. Such a shame, I have a million ideas already of how I could have built something like this with no problem at all.

[@Santibag]

The closest thing I do is knife sharpening, but I always wondered about stuff like straightness, flatness, and smoothness. This videos was very interesting.

[@royalgilpin4922]

This video reminds me of how profound our technological advancement has been. Just think of how many different people had to cooperate and dedicate basically their entire lives to engineering better solutions in the relatively niche field of precision optics. Using a high viscosity fluid as a lapping surface? How the hell did anybody come up with that? Stuff like this just blows my mind.

[@janpoppeliers8619]

Very clear and detailed explanation, best I found so far (and no irritating background music). Cool how you built the turntable from a washing machine motor and rollerblade wheels!

[@JBantha]

I'm still trying to process 0.05 um. Wow. Heroes. That's insane.

[@fearlessjoebanzai]

I can't shake the feeling that I'm learning knowledge that I will never need to use!

[@Bill.Pearson]

Agreed. Like watching This Old Tony.

[@yashsvidixit7169]

Dear Huygens Optics, Please accept me as your student and hire me as an intern. I'll work hard and be a great asset.

[@maxenielsen]

Excellent explanation! I’ve been aware of over-arm polishers for lenses, but not aware of this method. You openly share a lot of which others would consider trade secrets. Even so, I have to believe that if I were to set up a similar polishing system, using everything you show here, I probably wouldn’t get results as good. Thank you!

[@chuckhightower2730]

Not an optical engineer by any standards, but this could be adapted and computer controlled to make concave mirrors for telescopes, etc?

[@carlosescobar9010]

Thats exactly how telescope lenses are made!! But with very high precision instrument and no computers.

[@chuckhightower2730]

@@carlosescobar9010 yes, a la Gordon Waite, but I’m much lazier and less coordinated in adjusting stroke parameters etc. keep in mind I have never, and probably will never make my own mirrors. I have plenty of telescopes and accessories as-is but a 16” mirror sounds awesome.

[@satankarmukesh3552]

Thank you for nice video, will you please let me know how to make single 40 to 80mm discs flate up to 1/6 wave or 50 nanometre regards.

[@joyztik]

Sometimes I wish I had really forced myself to understand math as a teenager. I would've loved to learn optics.

[@davidwhite769]

I love how he’s been talking about super high-precision techniques and equipment… and then says that the rotating platform is driven by a washing machine motor and supported by rollerblade wheels 😂 (I know that this is fine and makes sense, it was just unexpected XD)

[@zusclhz]

That's AWESOME! Thank You for Teaching 🙏🚂🎼🌹🎶🎵🧰🛠⚕🕊

[@MikeyMystery45]

I would give anything for a decent sized, fast, telescope mirror.

[@IllSkillz]

that would be usefull for CPU die lapping

[@bekanav]

Very good stuff. I've done my share of glass pushing, long long hours of manual work. I tried to make 200mm flats but I constantly got into troubles in 1um (two rings) level... Perhaps I return to them sometimes, even though I hardly remember why I started making them LOL (ok it was some cassegrain telescope idea, and another for testing other flats)

[@CHITUS]

I've got absolutely no idea why this video was recommended but I'm so glad it was. Fascinating. Well done.

[@АндрейЛенин-п2у]

таким методом шлифуется кремнивая пластина в производстве полупроводниковых кристаллов, только сейчас уже есть скоростные, с материалом дисков на подобии наждачной бумаги, там шлифовка всего пару минут идет, ну и абразив не мышьяковая пудра

[@RobotN001]

В РФ его бы уже посадили за выдачу сверхсекретных технологий.

[@speedx5803]

@Huygens Optics. Excellent video! thank you so much, it is very clear explainned. I have a question, what material do you use for the part rings which shows up at 6:20 and 7:22? is it also made by pitch? thank you!

[@HuygensOptics]

The rings are cut from granite using waterjet cutting.

[@speedx5803]

@@HuygensOptics Thank you so much!

[@MegaFrankels]

When you go through the grits of silicon carbide or cerium oxide, dou you change pitch plates or clean it very well? How do you make sure some coarse grit doesnt ruin the later polishing steps?

[@HuygensOptics]

The silicon carbide grinding is not done against pitch but against other glass or granite plates. You have to carefully clean and rinse between grains (not only the plates, the work space, but also your hands) in order to avoid contamination.

[@WaschyNumber1]

So you could make your own glasses 😊 also telescope optics 🤔

[@T____K]

well explained, no questions, sir! great video

[@ktmfour1007]

So for a lake too reflect a perfect mirror image it must be perfectly flat

[@fatihdurmaz9826]

well i have a few hundred questions :))

[@HuygensOptics]

Asking one is a start...

[@aniksamiurrahman6365]

Yes, I have a question. How on earth you do these sorceries?

[@jlmknight]

Very fascinating seeing someone so specialized and advanced in their field, thank you for sharing.

[@ОливерКарески]

Can a copper disc be very flat polished?

[@Sirmellowman]

is this similar to how they make the large telescope mirrors?

[@hamzadriss1358]

Many thanks. So same thing for seal faces

[@jacobrose9606]

I have no idea what I just watched, what the purpose of an optical surface is, or why someone would need something like this… but I feel smarter.

[@1NicholasWeir]

Thank you for making and sharing this video! Great content and very informative!

[@perspectivex]

Like the other people have said, really great video and clear explanation. One question: What's the relation between the maximum size of flat you can grind vs. the minimum size of the large pitch plate below? I mean, how small can you make this machine vs. how big of a flat can then be produced. I am wondering about grinding flat mirrors for star diagonals for telescopes, not sure how big yet but maybe up to 90mm (?).

[@HuygensOptics]

If you have a round mirror the size can be up to 35-40 percent of the pitch ring. However it is more difficult for rectangular objects like star diagonals. You need to contain them in a ring. For a 90mm diagonal you need at least a 350-400 mm pitch ring. Also you cannot attach this type of object at the angled surfaces to the holder, but only at surfaces perpendicular to the pitch surface. For example using hot glue. If you look carefully at the connection of the elliptical mirror at 6:58 in the video you see that it is connected at the short side with two dots of hot glue (on each side) to the aluminum holder.

[@perspectivex]

@@HuygensOptics Could you just create the flat in whatever shape is most convenient for the machine then water jet cut it out or something like that to get your desired shape (ellipse, rectangle, etc.)?

[@HuygensOptics]

It's possible, but it depends on the flatness you require. Generally the cutting will introduce stress/cracks in the material at the cutting interface, which can seriously deform the objects in the um scale range. If you require high quality optics it's not an option. Also the abbrasives in water jet cutting can very easily damage your optical surfaces, even with protective layers applied.

[@perspectivex]

@@HuygensOptics hm... maybe you could use the larger blank of 'convenient shape' and cut out the desired part(s) about 99% of the way with a small diamond grinding bit of some kind, leaving a holding ring or maybe tabs, then do the flatness grinding/polishing, then just snap the parts out by breaking the thin retaining glass. Or maybe try EDM using one of the techniques for non-conductive materials. But, yeah, at that point there's probably not really an overall cost/effort savings. :)

[@HuygensOptics]

That is a trick used with for example with the central hole in telescope mirrors: you drill almost completely through except fort the last 2mm or so. My personal experience with this method is not positive. Generally, if there is residual stress in the material, it will be partly released when cutting parts out, deforming the piece. I always bring the object in its final shape and then start grinding and polishing and focus my efforts on a good mounting method and the correct tool shape.

[@pjbth]

1:25 I love how that's a huge piece of what I'm sure is expensive equipment using off the shelf roller blade wheels. You can clearly see the painted design on them lol

[@lrakschmidt2880]

I'm wondering if you can put the pitch lap in the freezer when not in use for weeks or months?

[@HuygensOptics]

Sure, that is the way to store them over longer times. It also avoids the evaporation of the more volatile components from the pitch so it keeps the right viscosity. However, even then you have to put some effort in bringing them back in a usable state, because, they will loose shape on the sub-micron scale.

[@bdblazer6400]

Everytime he says pitch. Take a drink. Perfect fun.

[@SqueakerT]

At work here in Germany they got mad at me for filing like this....that you work in nm tolerances and do so as well made me really happy. The understanding of why one would do it so they just couldn’t understand. Also an amazing video, very informative. Keep up the good work!

[@machinetoolswarehouse]

Awesome work! I am going to try this...

[@DarkMetaOFFICIAL]

I wish you would have firstly explained, briefly even, what the heck any of this is, or what it's for. This looks amazing tho whatever the heck it is

[@juliusfucik4011]

I think the idea should be pretty clear, but there are other videos to get up to speed in the description.

[@ernestgalvan9037]

I think, this is one of those esoteric art forms, that if you need to ask what it’s for, then you don’t need it… 🤓 Although I am absolutely fascinated how a machine built from an old washer and skateboard wheels can possibly create something SO exact, measured in fractions of a lightwave….and he is SO nonchalant about it all!! What’s next, a Hydrogen Fusion Reactor Core from a Tesla Electric motor, a pair of old Apple watches and a Zippo Lighter???

[@youcancallmeque]

i have no idea why KZbin recommend me this video. What more fascinating is i watched it until end, and still have no idea what is that.

[@DANTHETUBEMAN]

I'm lapping this video up!

[@midship_nc]

we use rotary lapping tables like these to manufacture mechanical seal faces with flatness better than 2 helium light bands

[@brianmahoney4156]

I love the combination of washing machine and industrial PWM

[@matiKRK]

As a Polish, I approve of this video

[@zekeroche7915]

I've been polishing for a year now. This was super informative. Putting images to techniques helps me understand more of what I do all day long lol

[@haldorasgirson9463]

Grinding 3 surfaces flat against each other is how metrological surface plates are made. Does this work for optical flats?

[@HuygensOptics]

Yes, that can be done in the same manner, at least for the grinding part. But of course you cannot polish plates against each other, so during polish you use a separate tool and compare plates against each other by counting fringes.

[@haldorasgirson9463]

@@HuygensOptics Fascinating channel. I ground a 6", F8 Newtonian mirror while in high school (45 years ago). It ended up mediocre at best. My 4", F10 refractor kicks its butt. You are way over my head most of the time, but I enjoy what I have seen anyways.

[@raguaviva]

physicist here, every single video of yours is mesmerizing, I have no words!

[@lschmidt2405]

When the pitch drapes off the sides, how do you get it back up on top? Do all the different grade abrasives get mixed into the tar? Do you then have to replace the tar? How do you setup for lens grinding as opposed to flats? How are multifocal optical lenses ground? eg for spectacled?

[@ccaissie113]

freeze then chip it off and melt and recast. the polishing compound is micon sized...not grit. used to use rouge, but there are better compounds not so messy.

[@shripadwarudkar6487]

Hats off to your narration... I simply was thrilled. I am a retired engineer, 73 yrs.

[@Saki630]

its amazing how a bumpy surface can grind down to the nanometer range

[@Asdayasman]

It's only bumpy on the macro scale.

[@Sirmellowman]

this is extremely interesting.

[@MindbodyMedic]

this filled in some gaps in my knowledge, really great stuff.

[@sandroac34]

Hi, to make a "Economic bruiser" can I use a large granite disk with small disks of Soda Lime glass glued on face? Or best, can use a disk of thin sodalime glass (same size in diameter) glued on face of these granite disk? I can not pay for zerodur or fused silica... I´m changing a large 1,10 meter CG to CP... and the bruiser is my biggest concern... I purchase the book recommended by you, but doesn't suggest alternatives! thank you a lot.

[@HuygensOptics]

It is an option. Float glass and granite have approx. the same CTE (7-9 ppm/K) so that is good and I have actually done this in the past.The problem that you will encounter is changes in shape due to temperature changes and gradients. It will be very hard to get your process stable. So for example using a thick slice of Pyrex (CTE=3.3) has major advantages over granite. Pyrex blanks can sometimes be found for fairly low prices on Ebay.

[@sandroac34]

@@HuygensOptics Amazing... I have a pyrex blank 24" diameter end 1,5" thick and I can use that as a bruiser... You save my day again! Thanks! in few days I can put a video about this machine on my channel and invite you to see.

[@HuygensOptics]

@@sandroac34 looking forward to that!

[@flat-earther]

Interesting, I always wondered how glass in binoculars and optical instruments is made so flat.

[@SuperAWaC]

i am a machinist by trade and when i was initially linked this video, and i only saw the title, i thought "oh great some charlatan is going to talk about taping sandpaper to a piece of float glass" but i was pleasantly surprised to see that was not the case and this is the real deal. subscribed. have you considered trying a cast iron master surface for the weight? as long as the room is at least loosely climate controlled, you could theoretically have a more economical option for a even flatter surface than the granite plate

[@HuygensOptics]

In principle cast iron would work just as well as granite. The CTE is around 10-11 ppm, so compared with granite (8ppm) this is only slightly higher. And because of it's higher thermal conductivy, it will get to thermal equilibrium (and retain it's original shape) quicker than granite. So it would in fact be a better choice as a material. However, don't know how easy it is to make a cast iron disk of 400mm in diameter with a flatness of approx 1um. By the way, granite is not an expensive material.

[@SuperAWaC]

@@HuygensOptics i know that in metrology cast iron is preferred for master surfaces, because it is more dimensionally stable and easier to make very (beyond AA grade) flat. for your specific use, it would also help as cast iron is denser so it would be heavier for the same size. that is why it came to mind.

[@movax20h]

@@SuperAWaC Actually in some super accurate machines, aluminium with internal cooling channels can be preferred too. This is because aluminium has way higher thermal conductivity (about 3 times higher than iron) and can be stabilized better, down to 0.1°C. Of course if you deal with big loads and need very high stiffness the cast iron or granite are preferred, but with low loads, aluminium counter intuitively can be even better. I can't find source and machines doing that right now, but I do remember seeing some year ago.

[@CaskStrength777]

I am a Tool & Die machinist and horologist and it made me happy to see there are other intelligent machinists watching things like this. I would second the use of a cast iron master plate. There is a guy who comes once a year to certify the multitude of granite surface plates we use in my shop and the man that does this is one of the rare ones who actually can re-lap the granite plates back into spec for flatness using a Master cast iron plate using aluminum oxide abrasives of various grades. Cast iron master laps are always made in pairs of three to get true flat reference surfaces- I know they are still made but I am not sure who you go to to buy one but if you had one I am certain you would get better results since they are what are used to correct even the granite surfaces

[@SuperAWaC]

@@movax20h I do know that many coordinate measuring machines have ways that are aluminum which is hard anodized and then lapped to extreme tolerances. It wouldn't surprise me if the very high end ones are also liquid cooled. I do know that they are kept in tightly temperature controlled environments with any heat sources removed (such as computers and humans) and put into different rooms, which is probably enough. But it would take longer for the whole machine to soak back to equilibrium if that environment were disturbed.

[@Allan_aka_RocKITEman]

@Huygens Optics >>> 👍👍

[@WhatAWondWorld]

Спасибо. познавательно

[@luderickwong]

can i understand this way, i can use this machine to recondition old guage blocks for flatness and bring them back to live? it is a pity to see gauge blocks find in old basement turn rusty by age and water damage. ordinary files and sand paper will destroy its flatness immediately, at least they should be still good to be use as parallels in a milling vise....

[@HuygensOptics]

You can use this principle also for your purpose. However, you cannot use pitch. For metals you need to use a metal ring and abrasive with different grain sizes.

[@fhgx32]

Very good explanations with great schematics. Great video overall.