[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] ATM Digest, Vol 45, Issue 32
Tom,
You're braver than I figuring with a full sized 10" lap at F5.3. To get to a parabola your going to work hard, probably with accented pressure, to get past the ellipse. Your correction is nearly 6mm from edge to center. I prefer to use a subdiameter star lap as detailed in Bob Kesther's article TM #16 or republished in appendix B of "The Dobsonian Telescope" by David Kriege and Richard Berry. 3" Star lap works great without TDE on a recent 8"F3.5 project.
I'm looking at a graphical representation of the numbers you've provided. Your measures don't show a TDE. (It does show zones 4&5 lagging behind.) If you don't have one... great! Just keep following the steep curve of the mirror/tool while using your strokes. For parabolic correction your zone measures indicate you need reduction of your number 3(most) and 2 zones. With the long straight stroke(slightly off centered), with a subdiameter tool, will raise the edge zones by removing more glass towards the center of your mirror. This is what I think you are looking for.
If you're going to stay with the full sized lap I would go TOT and accented pressure, heavy hand, on edge of tool. This is done with short W stroke consentrated over #3 zone drifting thru #2. Since these strokes are very short approx 2" and therefore quicker I'm always scared this action will roughen up the surface. If you scalloped the tool's edges you will be amazed how smooth the mirror's surface stays and gets. Always a great suprise/ relief.
Hope this helps some. The resistance to make another tool is always something most of us don't want to do but it does seem to make the job easier especially with larger mirrors at short F#s.
Dan Bartlett
atm-request@atmlist.net wrote:
Send ATM mailing list submissions to
atm@atmlist.net
To subscribe or unsubscribe via the World Wide Web, visit
http://www.atmlist.net/mailman/listinfo.cgi/atm
or, via email, send a message with subject or body 'help' to
atm-request@atmlist.net
You can reach the person managing the list at
atm-owner@atmlist.net
When replying, please edit your Subject line so it is more specific
than "Re: Contents of ATM digest..."
Today's Topics:
1. figure stroke ten inch (Tom Fredrickson)
----------------------------------------------------------------------
Message: 1
Date: Fri, 28 Sep 2007 19:05:16 -0700
From: Tom Fredrickson
Subject: [ATM] figure stroke ten inch
To: atm@atmlist.net
Message-ID: <20070928190516.37605631@Abit1.my.domain>
Content-Type: text/plain; charset=US-ASCII
Hi all,
I'm working on a 10 inch mirror full size lap. I turned the edge and
went to work with short coc strokes to clean it up. Now I need to add
correction to the edge. I have been working the edge and it is going
the wrong way. I feel I need to work the center and make it deeper.
Here are my numbers in millimeters roc 2712 mm Moving source mirror D
253.5 mm
mask zones
1 0 56.684
2 56.84 80.164
3 80.164 98.18
4 98.18 113.37
5 113.37 126.75
Readings 0, 0.49, 0.84, 0.98, 0.98
I appreciate any help.
--
Tom
------------------------------
_______________________________________________
ATM mailing list http://www.atmlist.net/
End of ATM Digest, Vol 45, Issue 32
***********************************
_______________________________________________
ATM mailing list http://www.atmlist.net/