davidpitre
Post Laureate
Reged: 05/10/05
Posts: 3183
Loc: Central Texas
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I have found stainless steel to be impossible to cut neatly with an acetylene torch. I assume it is the high melting points of materials like nickel.
I'm leaning towards mild steel because I can work with it easily. Of course I'll give it a decent paint job.
Anyone want to convince me otherwise?
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David
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John Jarosz
Astro Gearhead
Reged: 04/25/04
Posts: 3026
Loc: Chicago area, IL
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Well, cutting the triangles out of aluminum with a band saw or table saw is much easier. The mirror cell will be lighter too.
SS is hard to cut with a torch.
Just my opinion.
John
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6" F4.6(w/Paracorr) Reflector , 8" F11 Dall Relay Scope ,
6" F5 RFT Refractor w/Istar Obj , G11 Mount Gemini1 Level 4
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Old Dinosaur
Carpal Tunnel
Reged: 05/08/07
Posts: 2675
Loc: Down there on the river
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Yeah, you can't cut stainless with oxy/acet torches. A plasma cutter does a beautiful job, but I would go with aluminum too. BTW, a plasma torch is excellent on alum also.
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JMI NGT 12.5 SN21
coupla truck loads of other stuff
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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Acetylene torches make too crude a cut for what you are attempting. Even my Dillon torch, good as it is, leaves too rough an edge for this application.
Not sure why you chose stainless but if you must make your cell from stainless, I suggest you consider finding a shop with a plasma or water jet cutter.
Those machines cut like a hot knife through butter and will leave the edges smooth. No need for extensive secondary operations and, most important, all the pieces will be identical. That's important in a cell.
Art
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“Everything is on its way to somewhere. . . . . everything!"
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davidpitre
Post Laureate
Reged: 05/10/05
Posts: 3183
Loc: Central Texas
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Kriege suggests stainless.
My band saw and table saws will be borrowed for the woodworking in the scope.
I'm not sure I want to ask my friend who makes his living from cabinetry to use his tools to cut aluminum.
Hence, mild steel.
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David
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John Jarosz
Astro Gearhead
Reged: 04/25/04
Posts: 3026
Loc: Chicago area, IL
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That sure is a mystifying recommendation. Lotsa people have remarked how difficult it is to use SS for the triangles. I can't imagine why he recommends that. That is one serious flaw in the book.
Mild steel is fine.
john
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6" F4.6(w/Paracorr) Reflector , 8" F11 Dall Relay Scope ,
6" F5 RFT Refractor w/Istar Obj , G11 Mount Gemini1 Level 4
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JimMo
I'd Rather Do It Myself
Reged: 01/08/07
Posts: 3809
Loc: Under the SE Michigan lightdom...
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My cell triangles were made out of aluminum, too. Much easier than other metals to work and much lighter. Are you sure the book recommend SS?
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Jim M.
Ford Amateur Astronomy Club
Homemade 14.5" f4.3 Truss Dobsonian
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"I'd like to remind you at four in the morning my world is very still,
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LateViewer
Pooh-Bah
Reged: 11/17/05
Posts: 1009
Loc: Manhattan
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Here is a link, Mirror Cell Project, from a few years ago that is about just the questions you ask.
There was a lot of participation in this thread.
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Chance favors the prepared astronomer.
Yeah I have some stuff.
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jasonharris
sage
Reged: 09/16/06
Posts: 305
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If you are still thinking SS when I did my 18pt cell I used a jigsaw and some lubricant. With the right blade itisn't a problem just a bit time consuming, maybe an hour to do them all.
Thanks,
Jason
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davidpitre
Post Laureate
Reged: 05/10/05
Posts: 3183
Loc: Central Texas
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That's a great thread.
Jim. Yes Kriege does state several times that stainless is preferable.
It seems like the extra added weight of mild steel in the bottom of the mirror box might not be a bad thing to counter the weight of a large finder,Paracorr,...
As far as rust on mild steel, what is the fear? The cell frame will be steel and if improperly painted would be just as likely to rust.
I am a little concerned that cutting steel with a torch might warp it. But if the triangle is not perfectly flat, the flotation system should still work properly, no?
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David
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jasonharris
sage
Reged: 09/16/06
Posts: 305
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Yes David, the three points on the triangle will find their own plane regardless of how flat the triangle is.
I didn't even bother condiering how flat they would be as long they they are not to visibly warped.
Jason
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Houdini
professor emeritus
Reged: 07/13/07
Posts: 631
Loc: Europe
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Nearly any material will do for the triangles: aluminum, steel, plywood, carbon.
Use the material that you're most comfortable to work with. If you find SS steel too difficult to cut, simply switch to any other of the above.
FWIW, I'll be using 3/4" plywood triangles for the final stage of the 54-point mirror cell of the 1.1 meter telescope.
Robert
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16" f/4.9, 25" f/5 Dobson, 1100 mm f/3.6
Mirror Edge Support Calculator, Telescope Limiting Magnitude Calculator
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dave b
Post Laureate
Reged: 05/10/05
Posts: 4501
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i like aluminum because it looses its heat rapidly, steel takes forever to cool down.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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Dick Jacobson
professor emeritus
Reged: 12/22/06
Posts: 723
Loc: Plymouth, Minnesota, USA
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I used a horizontal bandsaw to cut stainless. I ran it at the lowest speed, about 80 feet/minute. It worked fine, though it took 2 or 3 times longer than cutting aluminum. These saws are sold by several retailers including Harbor Freight (see horizontal bandsaw ).
I suspect Kriege & Berry recommend stainless because it makes the mirror cell as thin as possible.
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Equatorial Newtonians, 20" and 14"
"The purpose of life is to be defeated by ever greater things." - Rielke
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dromedar
super member
Reged: 06/11/07
Posts: 142
Loc: Σουηδ...
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Have you tried an angle grinder with very thin disc?
Hacksaw is also and underrated tool.
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bbriggs
sage
Reged: 01/09/06
Posts: 217
Loc: Graham, Wa.
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I would also recommend aluminum for the triangles and bars. Save the stainless for the screws and nuts. I also found that McMaster Carr has acorn nuts with thru holes that make superb pivot points.
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18 f4.5 home made newt
14.5 f4.5 homemade newt w/Zambuto
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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So long as the part is reasonably stiff and doesn't flex under load, you will be fine.
The system should be as friction-free as possible which is one reason why I so enjoyed the design of a multipoint cell that made generous use of spherical rod ends.
It's worth looking for here at CN
Art
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Olivier Biot
Amused
Reged: 04/25/05
Posts: 24589
Loc: 51°N (Belgium)
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Quote:
i like aluminum because it looses its heat rapidly, steel takes forever to cool down.
This depends on the type of Aluminium. It appears that Aluminium is more a thermal "semiconductor" that can either provide great insulation or be an excellent thermal conductor, depending on other elements mixed with the pure Aluminium.
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I think you're worth a double serving of happiness!
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