Casting a light weight telescope mirror (all steps in the process)
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- Опубликовано: 21 сен 2024
- In this video I show how I designed, cast, slumped and coldworked a light-weight telescope mirror blank prototype. The blank is 10 inches in diameter, but only weighs 4 lbs 13 oz. It has a ribbed back design for rigidity, and is pre-slumped to f/4.9. Please visit www.mdpub.com/s... to see more of my astronomy and glass casting projects.
Previous light-weight mirror projects: www.mdpub.com/s...
My home-made kiln controller: www.mdpub.com/k...
Astronomy and telescope projects: www.mdpub.com/s...
My Blog: www.mdpub.com
Equipment and supplies used in this video:
Insulating FireBrick 9" X 4.5" X 2.5" in (6 Pieces) amzn.to/2WzFzky
Rutland Products Black, 10.3 fl oz Cartridge Furnace Cement amzn.to/3fclZB9
Spectrum PAPYROS Kiln Shelf Paper (20 sheets per pack) amzn.to/2THsKDA
Fireworks 1-Pound Kiln Wash amzn.to/2UYare9
RIP Mr. John Lowry Dobson your a legend and your still helping people today
These are the types of how-to videos I love. You show the exact process, and what you did to correct some imperfections. I really like the "What went wrong? What went right? Can I salvage it?". I'm new to making telescope mirrors and I think the whole process, especially slumping, would be a great way to do it.
Awesome video! Used to work for a commercial lapping machine manufacturer in Chicago. I built the machines from a pile of parts - 12", 15" 24" & 36" laps. The lap plates were capable of light bands of flatness. VERY fascinating!! Thanks for sharing. Jim in Phoenix.
was that by any chance Somaca... or whoever bought and absorbed them? I'm in the middle of restoring a skookum glass wet belt grinder from the 70s by Somaca, in or near Chicago.
Hi Mike, great video! I've been following your mirror builds for years now and just wanted to thank you for sharing your knowledge. I've been slowly accumulating equipment to attempt making my own blanks. I have a large kiln with a very heavy stainless insert that was previously used for fusing 3D metal prints at a university in South Carolina. The insert is cylindrical (bucket shaped) with a pipe that extends through an opening in the center of the kiln's bottom plate. I've built a drive unit that will spin the cylinder during the casting process. Let me know if you'd be interested in updates. I'll be working on it and posting videos sometime this fall. Again, thanks for all of your contributions to the telescope maker community!
Hello! Yes., I would be very interested in following your progress. Can't wait to see your videos. good luck to you.
Well done! Love the ingenuity
Great video. Thank you for sharing.
I found this incredibly interesting. I can watch for hours.
So much knowledge in this video. Great watch. You can get a $6 pump from ebay for the water spray on your grinding table and drill a drain hole with a coffee filter or 2 so you can recirculate the water. Or buy some vacuum funnel filter discs for $1. There are about 50 in a box and should get everything.
Fascinating vid, from someone with zero knowledge of telescopes, loved it
I can't wait till I see the next video I will watch this even if it was 10 hours long great stuff
WAY COOL !!!, I'm a hobby machinist and don't need yet another hobby, but very fun to watch you do something I've always wondered about. my only question is, why not use plaster for the outer rim of the mold, IE poor the plaster into a ring that doesn't touch the waffles so you end up with a one piece mold, you can still drop it into your firebrick ring in case it cracks.
Really everything I saw here is incredibly cool! Thanks a lot!
Great idea. I have my father 6 inches mirrors he started when he was young. Never wanted to finish it. I’ll try your way since I retired tried 3 d printing. Melted aluminium and the rest.
Excellent attempt! We are thinking alike, but you've taken action. I've been working on a design 'in my head' for years. What I've been thinking is making a slump form (as you've done in another video). Then slumping the glass (less than 1/4in thick over the form). Next strengthening the glass by 'fusing' glass 'ribs' to the underside. Finally, very gently grinding and polishing the mirror surface to its final shape. *as the glass would already pretty close after slumping, not that much material would need to be removed to achieve final shape.
Great video watching in post covid recovery
Oh man, so many great tips developed with great pains and expense over years- thanks for sharing! I'm definitely going to make one via your process someday... All materials and equipment for casting already on hand- save the R&R refac, which I've been waiting for a good excuse to order for years.
If there was a mention of glass type, I missed it... Assuming it's some type of leaded crystal. Would be super cool if you could use a colored frit, even if just for the undercroft. Folks would know at a glance "oh yeah, that's and Omegageek mirror". The optical contrast with a colored glass might help demolding and other processes after casting?
I hope you've made a start!
Wow, this is fascinating! You have a very impressive set up, especially given you've built it yourself. I have a ring saw and have done a fair amount of stained glass, but I want a kiln to do more technical projects like this and maybe labware. So, given the temperature and/or glass composition, would you consider this more of a slumping than a casting? Have you ever mixed together your own glass? Do you have any idea how many KWH or electricity $$ this used? Incidentally, filling the ring saw with _ice_ water greatly extends the blade life (and seems to cut better), though I don't know if that would apply to other types of diamond blades.
Please feel free to go into more detail in future videos, they're put together so well people can FFWD if they really _want_ to. I'm curious to see what else you do. Thanks for taking the time to make it! I subscribed for your gold videos, and this is quite a treat.
This is inspiring!! I am currently working on mirror blank casting project with a 203 trial. 400 is in progress now
how'd it go?
yeah, any updates?
Thx for video. Its pretty cool
you better the process and you can make a nice blank factory of yours...very nice job...
That's a lot of work.
Have you tested these designs to actually work?
I'm probably never gonna do this level of work but I want to try grinding a mirror, I have powertools that could be rejigged to make a workstation to speed the process up. Optics are fascinating and maybe the most interesting aspect of scientific history.
I watched the entire video. Fascinating. How do you turn the blank into a finished mirror? I love to see your progression in designs and see how they came out.
Regards water supply for your edge grinder: I've just built a machine for grinding decorative bevels on 3mm flat glass. I was going to use a pump from an old washing machine, but the cheap 12 volt aquarium pump I also had lying around with added speed control supplies plenty enough. Used water returns to a catch and settlement tank, then recirculated.
I'm just starting to learn the glass cutting, grinding & polishing techniques. Hopefully using recirculated grinding water isn't a step in the wrong direction?
so was your tool one of those sintered, stained glass grinding drums? sounds like a really interesting tool and I'm eager to know how (if) you have to polish your bevels. like, do you run several passes with several different grit cutters?
I've got a tile saw set up for glass and quartz, running resin bonded diamond blades. the resin bonded blades make super clean cuts with no tin smeared on them, ready for fire polishing.
I'm restoring a cool old wet belt sander by Somaca from the 70s or 80s. it seems that carbide abrasive belts are stupid cheap! (like $4 for a 4x64" belt)
I really enjoyed watching this video.. now I'm waiting on the actual grinding to an f4.7and then the aluminum coating. And then Fist Light..🙂
What an interesting journey. I didn't know exactly what our why you were making this blank, but it was a good watch.
Astronomy and telescope building have been big passions of mine since I was a kid (long time ago). Telescopes generally use very thick and heavy glass for their front-surface primary mirrors. About 10 years ago I started working on ways to make lighter-weight mirrors for telescopes. Just making the glass thinner doesn't work because it tends to bend under its own weight and distort the images. So I have been designing mirrors with various types of ribbed backs to support the glass surface. I came up with other more laborious ways to make the molds for casting the glass in the past. Now that I have a 3D printer and have gotten reasonably proficient with it, I can turn out molds fairly quickly and easily. Follow some of the links in the video description for more info.
@@omegageek64 Do you intend to silver it yourself? I'd like to see that if you do.
@@WaffleStaffel I normally have my mirrors aluminized at a nearby coating facility. Thy put down an enhanced aluminum coating and protective over-coats. Much more reflective and durable than silvering.
@@omegageek64 what type of coatings do they do with the aluminizing?
@@omegageek64 what was the mold made of?
Nice job, thanks
Wow! Very impressive work, im curious
How much money in electric power does this cost to cast a mirror blank?
Another pattern other than the square or hex is the triangle, there is
A guy name Peter Wangsness here in
Tucson who was casting large mirrors
With the triangular rib pattern that he
Claimed was superior to the square and hex and was ultra light weight.
He had a a kiln made of firebrick
That was roughly 12x12x12 foot
And would add bricks to thermal
Leaks detected with a thermal imager.
Wouldnt take much to scale up your
Process, and those plate glass blanks
Are very nearly as good as the over
Priced pyrex, dont care what anyone says.
I do not have any tools for this or knowlage but I am interested on this. Maybe next 20 years I can be on this level as you are. I really would like to make a perfect telescope by my self.
I don't need a new hobby, I don't need a new hobby, I don't need a new hobby.
Just what i want to do, been planning for years. Honeycomb grid.
Thank you for sharing this experience. It's very interesting. Do you have any idea how many Watt-hours of energy you used during the process? What is the value of the mirror at the end?
Could you combine the two heat cycles into one by using a different mold? A single mold that the glass relaxes/flows into, the bottom is convex and corresponds to the surface of the mirror, then there is a gap, then the lattice structure that you 3d printed is suspended (somehow). A wall is all around so glass can't flow out the sides. The glass to be melted sits on top of the lattice and flows through it and fills the convex mold part then fills in between the lattice part way (doesn't overflow it otherwise you can't remove the lattice afterwards as it'd be trapped in the glass). Maybe you can make a ceramic lattice part instead of plaster that would allow it to be suspended over the mold like that. The back (which would be the top surface in this mold configuration) would be flat then too rather than deformed by the slumping (not sure if that is important but it seems like a flat back would make mounting it in the mirror cell easier?)
I've thought long and hard over the years about how to cast the glass to the shape I want with only one trip through the kiln. It's not an easy problem to solve. Glass is tricky stuff. Molten glass sticks to most everything it touches. It's also incredibly corrosive. So there are only a few substances that can make usable molds for glass. An ideal mold will be made of something that glass won't stick to, isn't chemically or physically eroded by the glass, and has sufficient strength to withstand the hydrostatic pressure and just plain dead weight of the glass, plus is inexpensive enough for me to work with. There are no good candidates that satisfy all those points. Some, like graphite, are expensive and difficult to machine to the shape needed. Others, like various refractory plasters, are relatively inexpensive and can be molded into shape easily, but lack strength at the temperatures of molten glass. A mold like one you suggest, made from plaster, would fall apart before the glass even softened. A graphite mold would be outrageously expensive since it would likely be one-time use. Pressing softened glass into shape inside clam-shell type cast iron molds is an option, but getting the molds made would be horribly expensive. I'd need to sell thousands of blanks to recoup my costs.
The curved back of the mirror isn't any real problem. the mirror will still sit on the support points of the mirror cell just fine. Plus curving the whole blank makes it stiffer. The blank essentially gets thicker by being curved, but without all the extra mass of a solid blank of the same thickness.
@@omegageek64 Thanks for the reply. That's very interesting. I was suggesting ceramic though, not plaster...would ceramic be structurally robust enough and not soften at the required temps? Although then you have the extra step of making/firing a ceramic piece... Also, have you tried this glass mold release spray? It looks interesting. www.artclayworld.com/product-p/sgm-014.htm, www.amazon.com/ZYP-Boron-Nitride-Mold-Release/dp/B07RX8TLBB
@@perspectivex Ceramic is just the sort of thing molten glass would stick to and chemically erode. Even if it worked as a mold, there'd be no separating it from the glass, ever. Yes, I have tried boron nitride mold release and graphite mold release. I just tend to use materials that glass won't stick to these days. Fewer headaches. I really do think that pressing the glass to shape in cast iron molds lubricated with graphite would be the way to go for mass production. For the dozen or so blanks I make per year, my methods are ok. Besides, I'm always tinkering with and trying to improve the designs. If I ever decide I'm really done prototyping, I'll look into better molds.
@@omegageek64 So the boron nitride was not as slippery for hot glass as you'd hoped? I wonder if you could make the ceramic with a glaze of some kind that would be anti-stick for glass. As for cast iron molds...is there something special about cast iron or could you use steel? (I'm thinking of this 3d print technology for perhaps making molds ruclips.net/video/e7hFOQTK5fg/видео.html).
@@perspectivex My early attempts at casting glass against metal molds were dismal failures. Boron nitride didn't help. I may have been using the wrong metals. I don't know. Anyway, once I discovered refractory plaster things got a lot better and I never went back to trying to use metal or anything else. All ceramics I have tried have been disasters too, unless coated with kiln wash. Even then it can be iffy. Unglazed ceramics are porous and glass loves to stick to it. On the other hand, kiln wash also sticks to it and kind of prevents glass from doing so. Glazed ceramics are too smooth for kiln wash to stick to, but glass sticks to it with no problem. I suspect the glazes melt and meld with the glass. Glaze is technically a kind of glass after all. The main problem with using ceramics even well coated with kiln wash is differential expansion with the glass. During the cool-down phase the glass will likely crack or even shatter violently as the glass and ceramic shrink at different rates. Cast iron is a traditional material for making molds for pressed glass. There is already an entire industry devoted to making glass molds from cast iron and artisans who know how to do it. I figured reinventing the wheel probably wasn't a good idea.
Interesting video. Since it's a front reflecting mirror, and no light actually travels through it, would one of the new high tech resins work as well as glass?
this is a fabulous idea.
You should have 3d printed it with support material which easily gets removed by a solvent..
And maybe roughly print the final glass anti shape for direct molding
Great video and a great project. It is long but worth the watch as you supply so much good information! I do have a question though. How did you attach the mirror blank to the turntable when you were cleaning up the outside edge?
Very interesting. How much lighter is the finished mirror made in that mold than it would be if it were made from just a solid flat piece of glass?
Maybe you could add glass fibers to the plaster to give it some tensile strength?
Have any of these blanks been figured? I’m curious how well they hold a figure.
Enjoyed the video a great deal. That hexagonal 12.5 inch mirror.... You would be a wizard if you can pull that off. Do you think it would be viable to create a larger homebuilt telescope using hexagonal clustered mirrors (say, about 48.75 inch accum dia with 7x15 inch mirrors) without having to resort to computer controlled/actuated mounts? Reason for this would be reduced weight for a large mobile hobby telescope
Parabolical and spherical shapes are easier to produce, because they're symmetrical around the central axis. It would become pretty hard to produce mirrors with the correct off-axis shapes.
@@DoNotHackMyAccount Thank You for your reply, DNHMA. Quite the conundrum. a fixed platten at the right degree tilt for grinding, may make such an endeavor possible. Regardless, the mirror mounts would make the whole thing too heavy and imprecise to be portable and functional though. I was thinking about a telescope large enough requiring a dedicated mount to an RV/Toy Hauler.
Could you melt cast cordierite pizza stones. Low expansion for mirrors.
Hello , fantastic work , i wanted to ask you how much Current does this kiln pull , at my house im limited to 16A , but on 220V , not 110V like in USA , so im limited to 3KW power , if i use 3 phase i can go as high as 9KW , would this be sufficient for this kind of kiln
Super,
what is the difference between buying a thick glas and grinding it directly without so much effort?
First of all, as it is not flat, you have a chance to brake it while smoothing the surface. I really dont get the idea. if I had the equipment to bavel the glass, I would simply do it on a thick enough glass. Not too thick obviously.
Hi, those ripples were in all likelihood just insignificant cosmetic blemish, not worthy of your consideration. Being properly annealed is absolutely paramount. Considering how long you took in allowing the glass to cool, the annealing process was most likely acceptable. Now, on to more important considerations. After you've slumped your glass to f/ 4.9 you could, if desired grind it in the more traditional fashion with abrasives to an ever lower focal length. That depends on how thick the glass is, especially at the center of the mirror blank. Nice job by the way. Follow up question, how large of a glass blank will fit in to that kiln??
Wondering if considered a honeycomb/hexagonal design, and why you ended up choosing rectangular backing?
What are the thermal flex implications of this design, my intuition and simulations indicate that it would be significantly less stable than an equivalent single thickness mirror, or a sandwich-style construction. Have you completed and used any of these lightweight blanks yet? I find the idea very intriguing.
This technique of making 'ribbed', light-weight telescope mirrors has already done by scientists. I believe on of the telescope in Ariz. or Chile.
@laminaytrap Already proven technique, but go ahead and flex your ego on that arm chair.
Pretty funny you came up with simulations without knowing any thing 😂
@@richsoftwareguy trolling people that ask reasonable questions and for further resources on science and engineering videos is not a good use of your time
Thank you for sharing. I got the opportunity to witness a rocket launch in 2018. Memorable experience. I uploaded a pretty fun video of the trip to my page.
To even and flaten the blank out try a wood planer.
Brother can I buy one of those mirror ?
Your website has innapropriate ads and it's http and says not secure
Also why do you use a checkered like shape in the blank? Does it pre curve it?
The webbed back is to add rigidity to the blank without adding the extra weight of making the whole blank full thickness. The pre-curving happens by heating the blank over a convex form in a kiln.
Do you sell these blanks?
Another question...
Is the glass stress-free?
yes.
what is the end result, is it good or does the mirror have distortions?
Unfortunately, I can't tell yet. The lab where I have ground and polished many mirrors to perfection has shut down. I need to figure out how to do it at home on my own. Working on setting up my own lab. May be a while before I have results. Based on my experience grinding and polishing honeycomb back mirrors, I think these will work just fine.
@@omegageek64 Ok friend, thank you for your attention, you gave me an incentive to continue my 600mm f/4 project, could you help me, with what measures should I make the honeycomb, to guide me?
Telescope mirror like 8 inches 🤪 please 🙏 I wanna build my own
At 28:22 if other materials are used instead of plastic It would be Better they don't stick
Круто😀
I wish i had you for a neighbor!
Most. Fragile. Manhole. Cover. Ever.
What was the mold made of please respond
The mold is built up from refractory plaster as the base with the pattern impressed in it from the 3D printed part (PLA). The outer mold is made from K23 firebrick lined with refractory fiber to prevent the molten glass from sticking to it. Fine silica sand fills the gap between the plaster and the firebrick to prevent molten glass from escaping the mold.
@@omegageek64 I don't have a 3d printer sadly, but could this mold be made with just plaster?
I don't have a 3d printer
Poor cad work, really crappy