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Biff
Carpal Tunnel
Reged: 09/04/05
Posts: 2257
Loc: Courtice, Ontario
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I'm going to be starting again on my 10" f/7.25 after a very long time. I still have at least a few hours left to get it fully polished out before I can start figuring.
This is maybe a stupid question but one that I haven't seen any info on. During grinding/polishing I'm making MANY strokes rotating the mirror and the tool often so it turns out spherical, yada, yada. But this obviously can't be the case during figuring since I won't be doing thousands of strokes. I've read about and seen the diagrams many times describing the 'W' stroke but after doing a 'W' stroke approximately how much do I turn myself 'around the barrel' and how much do I turn the mirror (assuming MOT) that I can have a good approximation of average for say only one time around the barrel? I'd hate to work the same area twice and not work another area at all.
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Ryan
Antares 200mm f/6 Dob & 130mm f/5 Travel Dob.
Projects on the go...
- a couple 80mm SS refractors on the back burner.
- a few small mirrors awaiting polishing
- 260mm f/7.15 mirror... still polishing
Member of DRAA
 My house.
 DRAACO
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Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2505
Loc: Northeast
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Well you could do something like this-
Once around, make 8 stops around the barrel. Next time, pick 11. 3rd time go back to maybe 7. Then rotate the mirror or tool a twitch on the stand/barrel. Pick other numbers you like.
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I'm assuming you're going to do most of the work TOT? (small polisher)
The trick with that F/7.3 -10" mirror is getting the initial sphere, or ellipse where you can then proceed. To me, those are 'slow' mirrors. With slow mirrors, a nice sphere, no zones and a proper clean edge is going to be the main job. If you can get that far, parabolizing should be relatively straightforward.
Mark
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Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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Biff
Carpal Tunnel
Reged: 09/04/05
Posts: 2257
Loc: Courtice, Ontario
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Quote:
Well you could do something like this-
Once around, make 8 stops around the barrel. Next time, pick 11. 3rd time go back to maybe 7. Then rotate the mirror or tool a twitch on the stand/barrel. Pick other numbers you like.
By that it sounds to me that for the first three times around the barrel in your example that the mirror doesn't rotate relative to the tool. Am I understanding that correctly?
I was going to do figuring MOT with the full size lap. Should I reconsider?
I'm oblate right now but I need to get the outer regions polished out and was going to proceed TOT for now. I'll try to post a pic tonight of the Foucaultgram but its shaky at best using a handheld camera. Planning on rigging something up to hold the camera solid for better pics.
Thanks,
Ryan
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Ryan
Antares 200mm f/6 Dob & 130mm f/5 Travel Dob.
Projects on the go...
- a couple 80mm SS refractors on the back burner.
- a few small mirrors awaiting polishing
- 260mm f/7.15 mirror... still polishing
Member of DRAA
My house.
DRAACO
|
Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2505
Loc: Northeast
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At this point, I'd concentrate on finishing the polishing task first.
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If you're doing MOT, and the edge is lagging behind, swap the tool and mirror positions to concentrate more action at the edge.
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" that the mirror doesn't rotate relative to the tool. Am I understanding that correctly?"
Don't ever hold the mirror in one position with MOT! Your mirror will -NOT- come out rotationally symmetric under those circumstances, regardless what you do around the barrel!
I was assuming you were doing TOT, with mirror sitting on the barrel. An error on my part.
Mark
--------------------
Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2505
Loc: Northeast
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I figured it would be a good idea for anyone polishing& figuring mirrors and wanting help, or advice, to give a glance at the following recommendations for providing necessary information. It will make communication of ideas and methods far easier. It's not very long, but just including these few items along with the question will make issues much easier to solve.
1. Machine polishing, or manual.
2. MOT or TOT
3. Polishing is completed.
4. Tool size
5. Pitch medium and compound used.
6. Mirror size- F/D
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For testing, I'm going to assume most folks won't have an interferometer, or have a high proficiency in interpreting Ronchi tests. Therefore, it would be a good idea to include zonal centers and present measurements along with test questions using a KE or Foucault test, which everyone can make for a few dollars. This will come later under more advanced stages of figuring.
Thought this might be helpful to all you glasspushers out there!
Regards, Mark
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Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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