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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