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#1 GilATM

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Posted 21 April 2014 - 12:47 AM

I'm about to finish a slow spinning turntable for my grinding and polishing needs - primarily so I don't have to walk around. (interrupts my movie watching hobby). It is approximately the size and set up as Mike Lockwood's smaller machine.

I now read that a stationary tool of about 75% can bring it to a sphere. So now I'm thinking of adding that to my table. (I didn't want to make a M-O-M type machine with all the extra motors/gearing/etc.) but if it could grind and polish to a sphere, that would be great!

But I have a question:
some examples show a single arm on a vertical shaft (as in Mike L's example) that would seem to let the arm slide back and forth. But I don't get how the mirror stays in place on the tool - it seems like it would slide off the mirror. What am I missing?

Thanks,
Gil




I did

#2 kfrederick

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Posted 21 April 2014 - 09:08 AM

http://www.youtube.c...h?v=M9JsANO3kn4 Here is my setup not sure your question

#3 Pinbout

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Posted 21 April 2014 - 09:17 AM

that's so slooooooow


https://www.youtube....h?v=Oi8mH6904eQ


:lol:

#4 mark cowan

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Posted 21 April 2014 - 10:57 AM

42 is your answer. That and find the sweet spot for spin polishing.

And/or this thread from a few years back on that topic:

http://www.cloudynig...2534638/page...

Best,
Mark

#5 Pinbout

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Posted 21 April 2014 - 12:18 PM

42 is your answer.



Jackie Robinson? I live across the street from Larry Doby's house where his children still live. :grin:

#6 Pinbout

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Posted 21 April 2014 - 12:20 PM

But I have a question:
some examples show a single arm on a vertical shaft (as in Mike L's example) that would seem to let the arm slide back and forth. But I don't get how the mirror stays in place on the tool - it seems like it would slide off the mirror. What am I missing?



https://3dwarehouse....5-ac2c-ba557...

#7 mark cowan

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Posted 21 April 2014 - 02:59 PM

42 is your answer.



Jackie Robinson? I live across the street from Larry Doby's house where his children still live. :grin:


No, the other 42. My target turntable speed.

The amount of work it does is directly proportional to the speed.

Best,
Mark

#8 Pinbout

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Posted 21 April 2014 - 03:05 PM

42 is your answer.



Jackie Robinson? I live across the street from Larry Doby's house where his children still live. :grin:


No, the other 42. My target turntable speed.

The amount of work it does is directly proportional to the speed.

Best,
Mark


Steve Swayze saw my speed and said no wonder your ruffles have ridges... :grin:

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#9 GilATM

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Posted 21 April 2014 - 04:55 PM

I found this video:
https://www.youtube....h?v=ar1xgUeGTjY

with the polisher just held, apparently, by string - and decided I'm overthinking this thing!

I'll experiment and see what works.


Gil

#10 mark cowan

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Posted 21 April 2014 - 11:41 PM

Danny, turntable speed has no effect on the kind of problem you're showing. :shrug:

The polisher will create zoning if when it rotates on the mirror there are any areas lacking full contact. Razor blade scoring 3 ways across the surface of a non-channeled tool sets it up, wire brush scratching under hot water gets it ready for work. The tool has to spin just slightly less than the turntable, faster or much slower means poor contact and it leads to zoning and worse problems (like primary astigmatism if it gets into a resonance with the table).

Best,
Mark

#11 Pinbout

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Posted 22 April 2014 - 06:17 AM

This was polishing pads over penny tool. I've done pitch polisher and that was worse. I've tried the slanted lines as in your old thread, didnt help.

#12 kfrederick

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Posted 22 April 2014 - 07:07 AM

If using a machine I see no need to use pads . I like them for hand work . But on a machine the risk is more as they can come off .And you need to polish on pitch any way . Also pads turn the very edge some spin polishing .I think .

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#13 Mark Harry

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Posted 22 April 2014 - 07:29 AM

Spinning pitch polisher while used with a machine turntable:

Try to spin the polisher in reverse by hand.
If it spins easily, it is center-acting, and will drill a hole or make a zone if offset.
If it spins VERY hard, it's edge acting, and if offset, will rip the edge.
If it spins with moderate resistance, it's neutral. This is what you want.
*******
A channeled polisher's grooves will generally close up in the center first; and will gradually become center-acting. Check for this about every 20 minutes.
*******
Pad polishing on a machine- spraypaint the tool surface with krylon, or blue layout to prevent the pads from peeling off the ground surface. Been there, done that.
M.

#14 mark cowan

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Posted 22 April 2014 - 02:36 PM

I've tried the slanted lines as in your old thread, didnt help.


I don't use that anymore for machine polishing, as I found a better method - and it's quite possible to slant the faceting but still end up with something that has areas of different contact viewed while it's rotating, which gives you small zones on the mirror.

The better (and easier) method is, starting from 100% contact (no faceting) with an Aculap polisher, I score it with a razor blade at 120 degree angles, about 1/2" apart (and/or if it glazes). This yields a completely non-imprinting pattern to the work. I used to get a central zone that corresponds to the overlap of the tool regularly but that's vanished as well with the newer method - just a sphere, and nothing but a sphere, ready to figure. The wire-brushing is before each short session, BTW, and ensures even contact with a brief hot press.

If you went pads on anything you will get zonal irregularities. Pads that come off on a machine are extremely bad news.

Best,
Mark






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