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F8thful
super member
Reged: 06/14/05
Posts: 153
Loc: Camas, WA
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Greetings ATM'ers
A couple years ago I attended a telescope making class, taught by John Dobson.
In 30 days we ground, polished and figured our mirrors and built our telescopes.
John's method of mirror grinding is to set a plank (2x12) across two buckets, drive a few nails in to hold the mirror and start grinding. By maintaing a "W" pattern and rotating the tool and mirror frequently We were able to acheive a very good parabala.
I see most of the rest of the world grinds on top of a barrel and spends a lot of time moving in circles around the barrel.
Can anyone tell me the advantage of the barrel method?
Thanks
Glen
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10" Dob project
New 10" 10 Yr. old Dob project
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neo
professor emeritus
Reged: 02/12/08
Posts: 616
Loc: Iasi, Romania
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I guess some people find easier to rotate the mirror in one way and themselves in the other.
Your method it's very useful especially when you don't have enough room to move around a tall stand/barrel, for example if you grind on the kitchen table . 
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Dobson's method works very well. You can grind outside on the porch or grass and not worry about contamination. I'd recommend screws sunk a little beneath the top of some heater hose for the stops, though, exposed metal parts have a cunning way of sooner or later connecting with the glass in the wrong place.
It's what we did in a his class about 15 years ago, BTW. 
I don't know that there are any real advantages to the barrel method, if you're more comfortable standing I'm sure it works too.
Best,
Mark
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3124
Loc: Northeast
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I have a tremendously heavy steel grinder stand, with a 24" piece of thick lab countertop for a surface, lagged to the concrete floor. Very similar to a barrel, but it works very well, never moves. I have screws that can level/warp the top. I use a shelf liner mat under the tool/mirror. An occasional rotation of what's on this top is all that's necessary to eliminate problems. My personal version of a barrel. I note that the plank idea needs more attention to rotation of the mirror.
Mark
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So many projects, so little time!
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