Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free
How hard and how long would it take to make the mirror (yes, I'm attending the SLAS meeting this month) for someone who hasn't done it before? What would the estimated cost be for the materials for the mirror? Is there anyone here or in SLAS who would be available for advice? I'm interested in making my own mirror but it depends on cost (you know, the wife/CFO). If all these add up I'd take the dob tube and the rocker box. I would assume the first step would be to make the primary mirror, then to get a secondary and a focuser. So I guess if this is a project that I can assemble over time as money comes up, I'd try it. Thanks, Jay On 2009-01-06 22:56, Patrick Wiggins wrote:
I understand the "how to make a mirror" video that we were not able to screen at the solstice party last month is going to be shown at this month's SLAS meeting.
Perhaps after watching that several people will want the carcass to use with their new homemade mirror.
Grins,
patrick
On 06 Jan 2009, at 09:48, Josephine Grahn wrote:
We have the empty carcass of a 13.1 inch blue Coulter dob, if anyone would like it. No optics, no focuser, just the empty tube and rocker box. It does have the mirror cell, but no primary mirror, and it does have the support for the secondary, but no secondary mirror. Free, you just have to pick it up. Located East side SLC.
Oops, For the benefit of those new to SLAS I should have mentioned that the video is a joke and not to be taken seriously (among other things the "opticians" start with a bunch of sand and use a household oven to fuze it into a blank). On 06 Jan 2009, at 19:47, Jay Eads wrote:
How hard and how long would it take to make the mirror (yes, I'm attending the SLAS meeting this month) for someone who hasn't done it before?
I think there are a few people on the list that have made mirrors but, to be honest, if you value your time you might be better off buying a finished mirror. The exception to that would be if you want to do it so you can say "I made this" and not to save money. Brent Watson who occasionally monitors the list has run mirror making classes in his hanger at the Bountiful airport in the fairly recent past.
Is there anyone here or in SLAS who would be available for advice?
Steve Dodds of Nova Optical (http://www.nova-optical.com) in Herriman is a SLAS member and might be a good person to start with. Bruce Grim (he's the SPOC director) is another. And maybe Chuck Hards here on the list (Chuck have you made any mirrors recently?). patrick
On Tue, Jan 6, 2009 at 8:12 PM, Patrick Wiggins <paw@wirelessbeehive.com>wrote:
And maybe Chuck Hards here on the list (Chuck have you made any mirrors recently?).
Not recently...not in this century, lol! These days, it's not really cost-effective to make a small mirror, but a 13" home-made mirror could be made at tremendous savings. For example, you can get finished 8" Chinese mirrors of decent quality for under a hundred bucks, but a full-thickness (6:1 diameter-to-thickness) 12.5" mirror could run you a thousand dollars, easily. Larger than that, and some serious cash can be saved- like the price of a used car! That said, figuring a large diameter, "thin" mirror isn't generally a good first project, although having said that, some people have done it and done it well. With all of the ATM experts in the SLAS and OAS clubs, I'm sure anyone seriously contemplating grinding their own mirror could easily get all the help they need.
Jay, If Brent Watson was still around he could probably tell you exactly, but I think Chuck’s amount was probably about right. I took a class from Brent about 6 – 7 years ago and as I remember it cost like $350 - $400 for the mirror kit, another couple hundred for the Craford (sp?) focuser, $75 - $100 for either the 1/4th or 1/8th wave secondary, and of course you will need at least 1 lens. But lenses are like potato chips; you can’t eat just one. We started our class in January and ordered our stuff. I got a 12.5” mirror. It took a few weeks for delivery and came with all the materials for grinding accept the grinding wheel which we made ourselves. We ground our mirrors one night a week (7 -10 pm) under Brent’s tutelage and finished our mirror and scopes, which we built at home (Carcass part), by May. Oh yeah we also made our own Ronchi (sp?) tester which you need to complete the figuring of the mirror. I kept copious notes, but like most things, there are stored away in a box somewhere…lol. I guess my point is, if you have never made a mirror before, don’t do it alone. The other point is that making your own is a very rewarding experience. If it costs you about the same either way, making a scope at least once in your armature career, I think, is very worth it. But you need the right guidance. jg --- On Tue, 1/6/09, Jay Eads <jayleads@gmail.com> wrote: From: Jay Eads <jayleads@gmail.com> Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free To: "Utah-Astronomy" <utah-astronomy@mailman.xmission.com> Date: Tuesday, January 6, 2009, 7:47 PM How hard and how long would it take to make the mirror (yes, I'm attending the SLAS meeting this month) for someone who hasn't done it before? What would the estimated cost be for the materials for the mirror? Is there anyone here or in SLAS who would be available for advice? I'm interested in making my own mirror but it depends on cost (you know, the wife/CFO). If all these add up I'd take the dob tube and the rocker box. I would assume the first step would be to make the primary mirror, then to get a secondary and a focuser. So I guess if this is a project that I can assemble over time as money comes up, I'd try it. Thanks, Jay On 2009-01-06 22:56, Patrick Wiggins wrote:
I understand the "how to make a mirror" video that we were not able to screen at the solstice party last month is going to be shown at this month's SLAS meeting.
Perhaps after watching that several people will want the carcass to use with their new homemade mirror.
Grins,
patrick
On 06 Jan 2009, at 09:48, Josephine Grahn wrote:
We have the empty carcass of a 13.1 inch blue Coulter dob, if anyone would like it. No optics, no focuser, just the empty tube and rocker box. It does have the mirror cell, but no primary mirror, and it does have the support for the secondary, but no secondary mirror. Free, you just have to pick it up. Located East side SLC.
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Jay, The general rule of thumb is that it takes about an hour per inch of aperture to grind a mirror. I have ground several mirrors and built several telescopes. I would recommend that you start out with a long 10 or 12.5 inch mirror. I also would make it at least f/5 and preferably f/6 or bigger. The higher the f-ratio the less work you need to do to grind and figure the mirror. There are a couple of places that sell mirror kits. Willman-Bell http://www.willbell.com/Default.htm has mirror kits that include two Pyrex blanks. You are supposed to use one as a tool. You could go in with someone and grind two mirrors out of the kit. You can make a tool out of plaster and ceramic tile. Newport glass sells kits as well. The tool is usually plate glass in their kits. Their website lists prices, you will need to call Willman-Bell. http://www.newportglass.com/ngwkitp.htm Also, you should consider the plate glass as an option. It is much thinner and lighter than the full size Pyrex blanks. You just end out needing to support it with more points. There is software to help you design the mirror support. Most ATMers just use concrete form sonotube to make the tube. You can get focusers for about $100 dollars for a really nice Reverse Crawford for JMI. Secondary mirrors for longer f-ratios are cheap. They will be less than $30. I usually order this from Newport. I always order the 1/4 wave and they ship the 1/10 wave because they don't actually have any 1/4 wave mirrors. As for books on telescope making, "The Dobsonian Telescope" and "How to Make a Telescope" are both good books on the subject. How to Make a Telescope is better for the ginding part. The other book is better for building big truss tube telescopes. Dave -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Jay Eads Sent: Tuesday, January 06, 2009 7:48 PM To: Utah-Astronomy Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free How hard and how long would it take to make the mirror (yes, I'm attending the SLAS meeting this month) for someone who hasn't done it before? What would the estimated cost be for the materials for the mirror? Is there anyone here or in SLAS who would be available for advice? I'm interested in making my own mirror but it depends on cost (you know, the wife/CFO). If all these add up I'd take the dob tube and the rocker box. I would assume the first step would be to make the primary mirror, then to get a secondary and a focuser. So I guess if this is a project that I can assemble over time as money comes up, I'd try it. Thanks, Jay On 2009-01-06 22:56, Patrick Wiggins wrote:
I understand the "how to make a mirror" video that we were not able to screen at the solstice party last month is going to be shown at this month's SLAS meeting.
Perhaps after watching that several people will want the carcass to use with their new homemade mirror.
Grins,
patrick
On 06 Jan 2009, at 09:48, Josephine Grahn wrote:
We have the empty carcass of a 13.1 inch blue Coulter dob, if anyone would like it. No optics, no focuser, just the empty tube and rocker box. It does have the mirror cell, but no primary mirror, and it does have the support for the secondary, but no secondary mirror. Free, you just have to pick it up. Located East side SLC.
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If I were making a largish mirror today (10" or larger), I'd make it from plate glass, figure it as a sphere, then use Bill Kelley's flex mounting system to pull the parabola. That would result in probably the most accurate surface possible to the amateur, with the least amount of work or cash outlay.
participants (5)
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Chuck Hards -
Dunn, David -
Jay Eads -
Jim Gibson -
Patrick Wiggins