I want to make a primary mirror. A six incher "maybe an eight incher at f/8" at f/10 with a fantastic figure. I have the time and the ability to learn. What are the minimum tools I will need to accomplish this project ? Will mirror grinding kits have what I need to make it a near perfect mirror or would I need something better ? I have choosen Pyrex with the focal point already set "easier for me". I really want to try this as I'm tired of the mirrors that poop out at 200X. I cannot afford a good one from all those you know who's. What are my chances from 1-10 with 10 being the best chance ?
Can I do it ?
Started by imgary, 05/13/2003 09:08PM
Posted 05/13/2003 09:08PM
Opening Post
Posted 05/13/2003 09:20PM
#1
"What are my chances from 1-10 with 10 being the best chance ?"
Zero. You have no chance. You will fail. You're not an optician, you're just some poor schmuck.
There. Now you have to do it, just to rub it in my face. :-)
Zero. You have no chance. You will fail. You're not an optician, you're just some poor schmuck.
There. Now you have to do it, just to rub it in my face. :-)
Posted 05/13/2003 10:39PM
#2
If you are really interested in making a really good mirror, I suggest making two. That way you can figure one as well as possible, and then try to do better with the second. By going back and forth, you could probably get a darn good mirror. However, the time you spend could easily be spent making enough money at some part time job to buy a top quality mirror.
Posted 05/14/2003 01:37AM
#3
Gary,
If you've got access to a group-- be it A) a Special Interest Group, B) workshop (like some of the Clubs run periodically), or at least C) a glass-pushing friend, it will be far easier. I went with option B-- a weekend workshop run by a club (Delmarva Stargazers) for my initial foray this past February. In about 14 hours of hard work I ended up with decent 10" Pyrex mirror (1/10 P-V, 1/45 RMS, super smooth polish). It isn't rocket science (but it is an art!), and mistakes (other than breakage) aren't critical since 'anything you grind in, you can grind out.' Try it, you'll like it! Doing it solo out of a book would be a lot more daunting, though. Jim
If you've got access to a group-- be it A) a Special Interest Group, B) workshop (like some of the Clubs run periodically), or at least C) a glass-pushing friend, it will be far easier. I went with option B-- a weekend workshop run by a club (Delmarva Stargazers) for my initial foray this past February. In about 14 hours of hard work I ended up with decent 10" Pyrex mirror (1/10 P-V, 1/45 RMS, super smooth polish). It isn't rocket science (but it is an art!), and mistakes (other than breakage) aren't critical since 'anything you grind in, you can grind out.' Try it, you'll like it! Doing it solo out of a book would be a lot more daunting, though. Jim
Posted 05/15/2003 12:47PM
#4
The primary (pun intended) tool you need is patience and the ability not to get frustrated. Bad, or I should say unpredictable things WILL happen, and you need to be able to objectively analyze what's going on to figure out what to do when things don't go according to plan. This is where the help of someone else or a group with mirror making experience is invaluable. All the books and all the web sites simply can't cover it all - there are too many variables.
If you want to save money then don't do it. You'll end up spending nearly as much as what a finished mirror costs. But if you enjoy building things yourself, there is nothing like the personal satisfaction you get when you finally get a good mirror, accurate across the entire surface to within a couple millionths of an inch, that you made yourself literally with your bare hands.
That being said, if you are working alone, then you have two chances of getting that nearly perfect mirror on your first try - slim and none, and slim just left! Seriously, there is too much to be learned with just one mirror, unless you are willing to have the project go on for years. My personal suggestion is that you try to make an OK 6" mirror, then go for a better 8".
I made my first mirror when I was 14, a 6" f/9 (it was supposed to be an f/8, but I had trouble getting the curve deep enough), by myself using Thompson's "Making Your Own Telescope". It probably came out no better than 1/2 wave - I don't know - I really didn't know how to test well yet. After using it for a while, I re-ground it to f/4.5. This ended up a little better, maybe 1/3 wave. Next I made an 8" f/8, which ended up about 1/4 wave. Then I refigured my crappy 1 (yes one!) wave Coulter 13.1" f/4.5 to about 1/4 wave. Now I'm finally refiguring my 8" f/8 to be as good as I can get it - I won't settle for less than 1/10 wave.
My point is most people NEED the experience of easier projects before going on to more difficult ones. There's as much (if not more) art as science when it comes to figuring, which simply takes time to learn.
Regarding getting a blank and tool with a pre-generated curve, it may save a little time, but you kind of have the cart before the horse. Rough grinding the curve is probably the easiest part of the job. Fine grinding without leaving larger pits behind is a little harder. Polishing it out completely is a little harder yet. Figuring is by far more difficult, by maybe an order of magnitude. If it's your first mirror then I would say grind the curve yourself - you'll learn from it.
Regarding kits, Willmann-Bell sells nice kits and supplies, well packaged, and they have friendly service. Their mirror making supplies unfortunately are not on their web site, so you'll need to either call them or get one of their catalogs.
If you want to save money then don't do it. You'll end up spending nearly as much as what a finished mirror costs. But if you enjoy building things yourself, there is nothing like the personal satisfaction you get when you finally get a good mirror, accurate across the entire surface to within a couple millionths of an inch, that you made yourself literally with your bare hands.
That being said, if you are working alone, then you have two chances of getting that nearly perfect mirror on your first try - slim and none, and slim just left! Seriously, there is too much to be learned with just one mirror, unless you are willing to have the project go on for years. My personal suggestion is that you try to make an OK 6" mirror, then go for a better 8".
I made my first mirror when I was 14, a 6" f/9 (it was supposed to be an f/8, but I had trouble getting the curve deep enough), by myself using Thompson's "Making Your Own Telescope". It probably came out no better than 1/2 wave - I don't know - I really didn't know how to test well yet. After using it for a while, I re-ground it to f/4.5. This ended up a little better, maybe 1/3 wave. Next I made an 8" f/8, which ended up about 1/4 wave. Then I refigured my crappy 1 (yes one!) wave Coulter 13.1" f/4.5 to about 1/4 wave. Now I'm finally refiguring my 8" f/8 to be as good as I can get it - I won't settle for less than 1/10 wave.
My point is most people NEED the experience of easier projects before going on to more difficult ones. There's as much (if not more) art as science when it comes to figuring, which simply takes time to learn.
Regarding getting a blank and tool with a pre-generated curve, it may save a little time, but you kind of have the cart before the horse. Rough grinding the curve is probably the easiest part of the job. Fine grinding without leaving larger pits behind is a little harder. Polishing it out completely is a little harder yet. Figuring is by far more difficult, by maybe an order of magnitude. If it's your first mirror then I would say grind the curve yourself - you'll learn from it.
Regarding kits, Willmann-Bell sells nice kits and supplies, well packaged, and they have friendly service. Their mirror making supplies unfortunately are not on their web site, so you'll need to either call them or get one of their catalogs.
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