Preparing to Grind a 22" f/4.0 Telescope Mirror
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- Опубликовано: 5 авг 2024
- This video shows preparations for grinding a 22" f/4.0 telescope mirror. This is the first mirror of a pair that will become a 22" binocular scope! Gordon Waite shows how to evaluation the generation job on the blank, and decide on a grinding strategy.
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RUclips: I see you like CNC machining and restoration videos, here's a mirror resurfacing video.
Me: ok... I guess that'll do..
Same lmao
Exactly
Lol same
yep sounds about right
Yup
I like the slight hesitation at "A little bit of effort to grind it out" I interpret that as "This'll be a bitch!"
Yes, this was recommended to me too
I always enjoy watching Gordon’s videos. Been watching for years now.
Hope your doing well Gordon. Thanks for these great learning lessons in grinding mirrors.
Gordon, Thank you so much for sharing your expertise with us. It would be nice to know how the project turned out and if your customer has completed his/her scope.
Great stuff! I love seeing big light buckets being made, especially if they will be accessible by the public, as I think Time/Life/Nat. Geo astronomical photos tend to set up the public for a bit of disappointment when they go to a star party or open house and find that they cannot see similar visions live, through a scope , with their eyeball. Big scopes can help, but few are accessible to the public. When I was a kid, i was privileged to become a keyholder (the youngest, up to that point, I think) to both observatories of the Peoria Astronomical Society in Illinois, which included access to both a 20" and 14". The 20" was amateur-built yet of greater optical quality than many scientific instruments in private and government hands. There's nothing quite like the PAS in Colorado, and I do miss it. Am moving to mountains in a few years, and I'm already planning to get back into telescope making then
I am a disabled veteran so I know I will never have the opportunity to own such a magnificent piece of equipment. However, it is on my bucket list to be allowed the honor to look through one in my life. I have a Celestron Nextstar 8ES but I have not been out observing in years, my back cannot handle the weight of transporting and setting up my scope. I have always wanted to gaze upon the horsehead nebula, for me, it is the holy grail if astronomical observation. I bet with the light gathering capability of the 22 or 25-inch scope you can see it pretty easily.
I've never seen the Horsehead Nebula either. Sure would like to! It's funny that I've built hundreds and hundreds of mirrors, but I seldom get to look through a telescope with one of them. Do you live someplace with an astronomy club close by? Many have public observing nights where you might be able to check one thing off your list!
GordonWaite Yea I belonged to the Howard county astronomy league. However, we are sandwiched in between Baltimore and Washington DC so seeing condition are never that great. I had back surgery almost a year ago and my back was really bad for a couple of years before that so I have not been able to go out and observe which makes me sad. What is your favorite object to look at? I really like M81 and M82, I will never forget the first time I saw them and my brain tried to wrap itself around what I was seeing. Two galaxies with trillions of stars, billions of planets. I always imagine someone from one of those galaxies looking at my galaxy through a telescope and wondering if there is anyone out there.
GordonWaite If I ever win the lotto I will be ordering the best scope you have lol.
I'll be rooting for you!
Dear lord I hope you purchased a wider-tipped Sharpee since making this video...
Was thinking down the same lines with why not use Dykem.
Honestly I think he just enjoys the coloring lol
Mark Smolarek because it’s ten times the price
I would love to see a mirror done from start to finish. Opening the blank to packaging for shipment. I'm particularly interested in the final steps.
ruclips.net/video/snz7JJlSZvw/видео.html has what you're looking for I think
Great, another channel I have to subscribe to because its awesome.
There was a day and time when, especially being originally ground with a diamond bit that there would not have been all of those 2nd if not 3rd grade defects in a purchased item UNLESS one paid less for it due to the 3rd grade defects in the piece! BUT great work on your part, for both the work done and the instruction on the what’s how’s and why’s!!!
That's really cool!
thanks for sharing your knowledge on the web for free
Gordon, I've recently been bitten by the telescope bug and I automate for a living. I've been watching videos about making mirrors and I can't help but wonder what technology has been applied to this. I see the defect on the glass in this video. If the table had an encoder suitable for position control, and a tool to measure the flaw from center to edge, the flaw could be mapped out on the entire mirror. A laser for etching glass could be used to remove the prescribed amount of glass necessary to correct the flaw. If the measuring device is also a laser, the process could be quick and accurate. The laser doing the measuring could monitor the results of the corrections as they happen. The etcher could be on one side of the mirror and the measuring laser could be on the other side. As the mirror is spinning, the etched spots would be checked by the measuring laser after perhaps another half turn. The finish would be poor and there might be subsurface fractures, but the surface would be close to true. Maybe there would be less grinding to do afterwards.
I work with PLCs (Programmable Logic Controllers) and to some degree with robots. There are probably a few robots in scrap heaps that work just fine. I think that if the above philosophy were applied to a robot, the process could be done with little supervision. It would be a dream to have a little shop with some cool machines that spit out a lot of high quality mirrors.
I figure that if I have thought about this in the last month or so, probably a lot of other people have beat me to it. Do you know if anyone has designed machines for this? Is there a huge gap in technology between amateur and commercial?
I very much enjoy your videos, thanks!
We use computer-controlled machines, but most companies in our class do not. We build them and program them ourselves, as we have a background in CAD, CNC and computer programming. The big commercial companies that make mirrors in the hundreds or thousands have pretty good machines available to them already, although they don't usually achieve the "premium" surface quality that boutique shops can produce.
Hi other people that this got recommended to
In the early 1970’s I Hand Ground a 10 Inch Mirror. It took Me forever. If I’d had this machine I would doubtless have been grinding larger mirrors too.
That's awesome, greetings
wow .its damn cool i cant even imagine where to start but i love stars. gratz from canada lac st jean
Thanks! Enjoy the sky.
I don’t know what I’m watching but I like it
Have you ever tried Dykem? It's a marking fluid used by machinists. It's effectively sharpie, but you can apply it with a brush very evenly and quickly.
I noticed the grinding stone was passively driven by friction with the glass. I wonder if the is any variation in speed and whether it makes a difference.
The speed varies a little bit, depending on how good contact is between the two disks. When it is in the proper "zone" then it is pretty constant. Basically, the speed takes care of itself!
Not sure if this message is helpful but they make powder guidecoat. You can probably find it in an automotive parts place. I hated using it with bodywork because it got a little messy when I was in a hurry. But it helped with my bondo. Thanks for the video. I am looking forward to making my own mirror.
Newport glass is really sketchy the secretary never got back to me after he said he would so I just got off united lens btw great video!
do you correct these, or are they for viewing only?
So how exactly does that grinder wheel lead to the desired curvature?
How long can it take to manufacture a mirror like this with this same machinery?
Just out of curiosity do you ever recondition mirrors???
Looks like fun. Y'know,Jjohn Dobson used to tell us that he made his first 24 - incher
from a surplus port- hole glass ( his standard material in the old days ) that he and a
friend sawed in half ( thickness ) with a HANDSAW ! , after they mounted the thing in
a wood frame. Good Ole' ... J. D. Gone but never forgotten. Cheers !
where you got that glass cylinder from what you grind a mirror ??
+Markko Two companies, United Lens and Newport Glassworks, are possible sources of mirror blanks.
Спасибо за ваш труд я тоже занимаюсь этим увлечением желаю вам здоровья и терпеия .Thank you for your Work i am also engaged inthis hobby i wish you health and patience.
Quick optical trick when the glass is spinning watch it carefully the entire time all the way up to the 4 min mark. So watch him mark it up with the sharpie and keep watching until it stops. As soon as he stops it at 4 mins scroll down and look at any text in the comments. Not sure how this will work on a phone or tablet, but on a larger computer screen the effect is kinda fun.
Would it not make sense to use 'Dykem' engineering layout fluid or something similar?
You could, but a felt tip pen is far easier. I have them on my desk, and in my pocket, and all around the shop. Much easier than finding the Dykem.
@@GordonWaite Fair enough, just a thought. Really enjoyed the video, very interesting so thank you for uploading!
Way better than the knees and bench work
Então a borda da ferramenta deve sempre ficar no centro do espelho? A tradução do RUclips não foi muito clara para mim.
Ok RUclips I watch the damn video! Happy now?
Didn’t know Cody’sLab had a third channel where he grinds mirrors. Cool!
link please
Hmm how will you get a spherical grind with this grinding setup? I can is the tool exactly 90 degree to the glass or are you using a spherical tool? But if so the high spot in the middle of the tool will only grind on one circle on the glass in this setup
The tool sits flat on top of the mirror. It is well offset from the center, and loose abrasives like silicon carbide or aluminum oxide are ground between the two disks. The mirror-to-be is sitting face up on a turntable. When the turntable spins, the friction causes the tool to spin on top of it, thus grinding both the mirror and the tool. The mirror on the bottom slowly goes concave, while the tool gets convex. The radius of the spherical surface on the mirror is controlled by changing the offset of the tool on top.
Ahh, thank you very much. Tool and glass are grinding each other, now I understand how the glass will get its spherically shape
Do you use a fixed post machine for all your work? I am re-watching all your videos.
We use fixed-post for almost all grinding and polishing. Then we switch to stroking machines for figuring.
Greetings from Brazil
Is that a some sort of special glass blank manufactured using a cast or just plain thick glass blank( float glass)?
This is special glass, borosilicate glass called Supremax-33 which is made by Schott. It is cut from sheet stock.
@@GordonWaite glad to hear from you. Here I'm into manufacturing of glassware from borosilicate glass 3.3.
Hi gordon.. I am looking for optical mirror for making telescope.. Do you know where do i get this..
Waite Research for a good one, GSO for a cheap one.
Hola Gordon. estoy haciendo un espejo de 14 pulgadas con una herramienta de 11 pulgadas. cuánto tiempo que sobresalir la herramienta del espejo para que salga esférico el espejo?
Start at about 1.5" and experiment with your spherometer.
+GordonWaite gracias Gordon.
I do have one question, why do you have to spend so much to make mirrors by melting glasses and moulding it, taking care in grinding to the exact point required. Wherein you can get it done in a metal place with mirror finish coating and use it the same way as glass mirror..my question may not be that exact but this is just my thought...
"Get it done in a metal place " ? Wha ...??? You mean a machine shop ? They don't do this stuff.
Most metal work is accurate to a thousandth of an inch. Telescope mirrors are more like a millionth of an inch. Plus metal expands and contracts too much with temperature change.
What does f/4 mean?....can anybody explain please?
If u pause it
The disc turns backwards
How do you determine the f rating? In glass, its the purity of the glass, yes?
F ratio is noting to do with glass type geometric shape of it. Where the light focus. When miror placed if you masure focal length and appeture and dive FL to a appeture that is f ratio.
is the mirror actually spherical or parabolic?
Telescope mirrors start out as spherical through the grinding and polishing. When the polishing is finished you start figuring the mirror to take it from spherical to parabolic.
@@GordonWaite Thanks. After watching almost all your videos I have basically figured (pun intended) that out. However, for you it's probably so obvious that you never explicitly explain as to why this is so. Why is it easier to create a sphere first? Why do the methods of grinding you use produce a sphere (and not an ellipsoid for example)? And also how exactly do you know where to remove material to make it parabolic?
do you need to find the center of the mirror before drilling a hole in it??
I don't know why you would drill a hole in it? Could you please explain? Thanks!
Why are you drilling a hole in it?
@@GordonWaite hmm i guess the only time you would do that is if you are building a telescope such as a maxutov or something.
Out of curiosity - what's the ballpark cost for a blank of this size?
If you have one made from Supremax-33, Blanchard ground plano/plano, and beveled, plus typical shipping, you will spend between $1,500 and $2,000 for the blank.
Although this is an awesome video I must say something here and I truly hope that I strike a nerve but at the same time I do not offend anyone by doing it. So here it is: There are tens of videos on how to grind your own telescope mirror and they are all awesome made by awesome people who get to do this. My problem is with the videos that are missing from the online medium and those are the videos where someone actually uses these DIY/homemade mirrors and actually shows us some sky photos taken with them.
Hope I am wrong here but there's my 5 cents n the matter.
Most DIY mirrors go into Dobsonian-style telescopes and these just aren't very good for doing sky photography. I have done a lot of lunar photography, though. If you are interested, please drop me an email.
I'm making a cassergrain/reflector dual just like the takahashi cn212
Very cool! What size is that?
##besten#Liebe##Episode
So where is video 2
I guess grinding is where the precision comes in, but my first thought would have been, “Can I get my money back?” (Not having any experience with mirror stock or grinding.)
Deviations from perfect are pretty common. They all are fixed in the first grinding stages without any extra effort, so we don't get very upset. Worst case you have to start one grade above.
a 10in version of the takahashi cn212 i need to make a 2in hole in it
Time to break out the diamond hole saw. I would recommend only a partial cut out of the hole. Cut out the last little bit after the mirror is finished. Having a hole in the middle makes it harder to make and press polishers. Having just a narrow ring isn't so bad.
So how did your 22" binos come out? Any pictures of it? Maybe RUclips videos?
I built a 20" f4.5 binocular scope that was featured in Sky and Telescope back in 1993 (I believe)
It was an amazing scope(s) the problem too was that if I was going to spend as much as I did on the scope I of course had to have the best eyepieces. So that meant 2-35mm Panoptics, 2-16mm Naglers and so on! Eee$$$kk!
I think at f-4 you're gonna have issues with getting the stars to merge without knocking the scope out of colimation.
Had a lot of interesting adventures with that scope before I sold it. :-)
I was only contracted to produce the mirrors. Somebody else was to build the telescope itself. Don't know how it came out!
@@GordonWaite I asked because back in 1993 I built a pair of 20" f4.5 binos...they were amazing. It was featured in Sky and Telescope that year too. Got the optics from Pegasus optics in Ariz.
Amazing! One lens like this one in video costs? 3000USD?
Actually a 22" f/4 mirror costs about $9,000.
@@GordonWaite you mentioned building huge binoculars. Do you have video of that? Would gladly watch. It is amazing what people can do with their skills. All the best
@Greg Moonen thank you. I hope i can find those on your channel. Quick links would be of much help
@Greg Moonen no. No building. Just wanted to watch. But i guess i will look it up myself
hi there. How did you calculate 176 inches focal length with f-4 and 22 inch diameter mirror? Wouldn't it be for 44 inch mirror? Or is it because you are making binocular? I didnt think it made difference, thanks!
For someone like me: It's aperture is about 550mm and focal length about 2200mm
how much is a blank like that cost
Around $1,700 to $2,000 at the moment, without any processing
That defect looks like the diamond tool kept spinning while the lens stood still.
Actually it is the combination of two problems. The mirror itself wasn't perfectly centered on the turntable. And the edge of the diamond tool wasn't perfectly positioned over the center of the mirror. We see these all the time, although most are less dramatic than this one.
@@GordonWaite I had to think about that for a moment, but now I see it so clearly. Thanks a lot.
Why not use Dykem?
Felt tip pen is way easier and faster. The "Sharpie" test is a decade's old classic tradition.
If the grinding stone is just sitting on the mirror, then theoretically it wouldn't make a complete even finish since the contact point of the two changes. No reference hight.
And yet it works so marvelously well! The grinding stone isn't "just sitting" on the mirror...
You need a bigger marker
who cast the blank? i assume no centrifuge was used or that was a botch job
The blank wasn't cast, it was cut from a large sheet of borosilicate glass. The sheets are produced by Schott, a huge glass company. The artifact is from the generation of the blank, and is a trivial thing, not a problem at all.
@@gordonwaite1697 Oh I sure got that backwards! I was so sure you said somewhere in the video that it was a cast blank. Watching too many videos to keep them apart.
i was whatching dragonball z clips and now im here. ok. i guess.
5:50 where the grinding starts
maybe I am slow, but that looks like a lens to me. not a mirror.
It will be coated with a reflective coating.
@@vladimirvlad2563 ooo. Awesome. Thanks for the reply.
i dont even have a telescope, wtf am i doing watching the entire video ·_·
me too....wtf!?
Must be a nightmare to do it right, a lot can go wrong.....
It is, indeed, detail oriented.
That looks expensive
2:49 Aaand SOLD! at Southeby's for $ 485.000
my god, these godless communists and their nasty periods in place of commas
Why is this in my recommended videos? xd
Какой большой кусочек колбаски....
Who else the thumbnail was a big piece of processed meat
aw crap... 11:23 minutes of getting excited to be left drolling..... come on, put on the entire work video.