Amateur Telescope Making (UPDATED 9/23/18) - 20" f/4 Nearly Complete

[_Augustus_]

2 minutes ago, Adstriduum said:

Did I say aperture length? (－‸ლ)

 

I have a 4" and a 6". I WOULD go for a 12" IF my budget wasn't so tight. A 10" would be best. My head is just in the clouds  

So do you plan on grinding your own mirror?

[Adstri]

1 minute ago, _Augustus_ said:

So do you plan on grinding your own mirror?

Depends. I have the equipment but I am busy/lazy so not for a while.

[_Augustus_]

So....

The mirror and lap got permanently stuck together. I tried everything (heating, freezing) to get them apart, only to find that my mirror now has several 1 cm chips in the edge, and that's just the part that isn't covered by the lap. I could probably just mask off/bevel out the edge, but I don't know if separating the mirror and lap is possible, at least not without further damaging the mirror.

RIP this project

Edited June 12, 2017 by _Augustus_

[Green Baron]

Gosh ! Well, it so happens with many hand crafted things that the first try is for learning. My list of failures is long and it is still growing ... :-)

Don't be too frustrated !

 

[Starman4308]

Sorry to hear it didn't work out Augustus. It's not an easy project you got yourself into, and I find it plausible that something happened to the pitch after that long in storage to make it a bit more sticky. I wish you better luck when you try again; hopefully you'll have learned a fair bit from trying to get this mirror ground.

[_Augustus_]

14 minutes ago, Green Baron said:

Don't be too frustrated !

 

I just wasted $100 of my own money and my parents are not very understanding - here are some of their responses:

"Let's go to a glass shop and see if they can separate it" - Ignores the fact that the mirror and lap are held together by a tight vacuum, the fact that if you somehow ripped these apart you'd probably leave pitch residue on the mirror, the fact that a glass shop wouldn't even have the tools to rip them apart, or the fact that a glass shop would refuse to help with this

"Maybe a glass professional could file it down/fill in the chips" - Ignores the fact that the mirror and lap have to be separated first, as well as basic understanding of how the curve of the mirror works

"Take the Stellafane class" - Ignores the fact that once the initial guilt/sympathy (of which they have little) goes away they'll never be willing to drive 5 hours each way every month for me to take that class

 

8 minutes ago, Starman4308 said:

I find it plausible that something happened to the pitch after that long in storage to make it a bit more sticky. I wish you better luck when you try again; hopefully you'll have learned a fair bit from trying to get this mirror ground.

It was also probably the higher temperatures in my garage yesterday.

Edited June 12, 2017 by _Augustus_

[Elthy]

Maybe they could be seperated in a vacuum chamber?

[_Augustus_]

3 minutes ago, Elthy said:

Maybe they could be seperated in a vacuum chamber?

IDK if that's possible. The pitch is also now sticky and has perfectly conformed to the mirror.

Also, you'd need a vacuum chamber with a way to pull on the mirror or lap (robotic arms?) which would undoubtedly cost more to use than several of these mirror kits - and that's assuming I'd know where to find one that I could use.

Edited June 12, 2017 by _Augustus_

[Starman4308]

Well, worst case, eventually you'll be on your own and can pursue this at your own pace. Assuming you go to a university*, most of them will probably have an astronomy club, and many of those probably will have ground their own mirrors as well.

Plus, if you get a driver's license and your own vehicle at 16-17, you could drive yourself to that Stellafane class, assuming that's something you'd actually want to do.

*Don't feel like a 4-year college/university is the only way to go, though; many people just straight up aren't suited to it, and might be better off either with a technical degree or trying to find a job straight out of high school.

[Green Baron]

36 minutes ago, _Augustus_ said:

I just wasted $100 of my own money and my parents are not very understanding - here are some of their responses:

"Let's go to a glass shop and see if they can separate it" - Ignores the fact that the mirror and lap are held together by a tight vacuum, the fact that if you somehow ripped these apart you'd probably leave pitch residue on the mirror, the fact that a glass shop wouldn't even have the tools to rip them apart, or the fact that a glass shop would refuse to help with this

I can imagine that the residue and water have formed sort of cement and the two parts have realized that they are one. Since the cement is from the same material as the mirror (SiO2) you have a 50/50 chance of damaging the one or the other. Chance has been taken :-/

SiO2 won't dissolve in acid, like the Ca-part of a "real" cement would, so trying it with vinegar-cleaner or so wouldn't work either.

Quote

"Maybe a glass professional could file it down/fill in the chips" - Ignores the fact that the mirror and lap have to be separated first, as well as basic understanding of how the curve of the mirror works

You can't fix it on a turning machine (and it would probably be too expensive) to remove the lap mechanically ...

Quote

"Take the Stellafane class" - Ignores the fact that once the initial guilt/sympathy (of which they have little) goes away they'll never be willing to drive 5 hours each way every month for me to take that class

But they offer it, they want to help get over the frustration :-)

 

Edit: that reminds me of one of my early failures: i made a bow, i mean i wanted to make a real strong longbow, medieval style. It turned out to be a hiking stick. So i took a weekend course. And another one. Since then i have made some 50 longbows, the best one had 80 pounds of pull force, the arrows flew through a fire protection door.

It broke one day, i grilled a sausage with the remains :-)

Edited June 12, 2017 by Green Baron

[YNM]

Oh... well...

Could it theoretically be salvaged ? Dunno, perhaps destroying (cutting off) the lap as far as possible ? After that, if the pitch was to undone itself in some heating, I'm sure the vacuum will somewhat lowers and you could pull it off.

Also, if you don't mind getting a smaller mirror afterwards the chipped portions could be cut off. No one told you that the mirror have to be perfect circles...

Edited June 12, 2017 by YNM

[monophonic]

2 hours ago, _Augustus_ said:

I just wasted $100 of my own money and my parents are not very understanding - here are some of their responses:

"Let's go to a glass shop and see if they can separate it" - Ignores the fact that the mirror and lap are held together by a tight vacuum, the fact that if you somehow ripped these apart you'd probably leave pitch residue on the mirror, the fact that a glass shop wouldn't even have the tools to rip them apart, or the fact that a glass shop would refuse to help with this

"Maybe a glass professional could file it down/fill in the chips" - Ignores the fact that the mirror and lap have to be separated first, as well as basic understanding of how the curve of the mirror works

"Take the Stellafane class" - Ignores the fact that once the initial guilt/sympathy (of which they have little) goes away they'll never be willing to drive 5 hours each way every month for me to take that class

Your parents may not be very understanding of mirror making, but they do sound rather understanding of the frustration you are going through. They have offered you three ways forward, some of them less workable than others but nevertheless they are willing to go through it with you any way they can think of. Plus there may be one more option no one seems to have mentioned yet.

First sleep on it though and let the immediate frustration wash over. You have put immense emotional effort into that mirror in addition to the physical work and money. Its breaking is giving you a big backslash on that. You will make better decisions after you let the emotions calm down some.

Then go check the blank and tool. I suspect you still have two almost pristine glass surfaces on their back sides. You can grind either one into another mirror with a plaster and tile tool - google will find you good instructions on those. The page I read never mentioned any need for pitch either, which should greatly reduce the chances of getting the tool stuck on the blank. Of course you probably have to have the parts sawed apart and sanded smooth to prevent cuts from the broken surfaces. Any glass shop should manage that at least. And you need to get more grit, some plaster and epoxy, I hope those aren't very expensive where you live.

Edited June 12, 2017 by monophonic

[_Augustus_]

I'm making progress removing the pitch. Might be able to salvage this.

[YNM]

Good luck with your endeavor, again !

[_Augustus_]

50 minutes ago, YNM said:

Good luck with your endeavor, again !

Bit of an update:

The pitch is fragmented but the mirror is holding it together. Leaving them in the freezer overnight. If they still won't separate in the morning, I'm doomed.

[qzgy]

4 hours ago, _Augustus_ said:

Bit of an update:

The pitch is fragmented but the mirror is holding it together. Leaving them in the freezer overnight. If they still won't separate in the morning, I'm doomed.

If you really don't mind sacrificing the pitch, can it be heated off? Like, with a blowtorch or something?

In any case, good luck with fixing this minor setback.

[_Augustus_]

10 hours ago, qzgy said:

If you really don't mind sacrificing the pitch, can it be heated off? Like, with a blowtorch or something?

Heating it would heal the cracks and make it stick more. Freezing it should shatter it but that hasn't happened.

[_Augustus_]

I left the mirror/lap in the freezer for nearly 20 hours. No progress in separating them. 

 

[_Augustus_]

I think I'm going to give up on separating them. I left them in the freezer all day today and still nothing. 

I will post updates on future projects on this thread. If you are making your own telescope(s) then feel free to post on here as well.

[munlander1]

3 hours ago, _Augustus_ said:

I think I'm going to give up on separating them. I left them in the freezer all day today and still nothing. 

I will post updates on future projects on this thread. If you are making your own telescope(s) then feel free to post on here as well.

Will you try again soon? 

[_Augustus_]

26 minutes ago, munlander1 said:

Will you try again soon? 

If I can get the money.

It'll be a larger mirror. I'm going to Stellafane next month - might get multiple blanks in different sizes if I can.

Edited June 14, 2017 by _Augustus_

[YNM]

Send them over here ! Maybe I could do something with it 

[_Augustus_]

I think I'm going to start with a 10" f/8 planet killer. If I have some $ left over for more blanks, I might get supplies for a 12" Dall-Kirkham and a 16" f/6.
 

Edited June 19, 2017 by _Augustus_

[Racescort666]

Would colder temperatures help to separate the lap and mirror? Dry ice and denatured alcohol can get it down to -78.5 C which is way colder than your typical freezer. 

[_Augustus_]

8 hours ago, Racescort666 said:

Would colder temperatures help to separate the lap and mirror? Dry ice and denatured alcohol can get it down to -78.5 C which is way colder than your typical freezer. 

That would probably shatter the tool, mirror, or both.