RE: [atm_free] Re: Need help with figuring
- Hi Waldo,
I was doing completely random movements till very recently without counting rounds and set increments. It was mainly based on time and/or total number of strokes. So it was either 10 minutes of large-W strokes or 20 sets of 5 to 6 large W strokes in one position.
But some of the recipes that I read were in terms of number of rounds around the barrel. For example, if it is TOT, then I suppose the Mirror is fixed on the barrel. You will polish a bit in one position and then walk to a different position around the barrel and so on. You would probably walk a fixed number of steps (give or take one) around the barrel. In my case (of having no barrel to walk around) this will translate to "polish a bit, rotate the mirror a bit" such that 10-13 rotations will bring the mirror back to starting orientation.
If I need to stop counting the increments and rounds, then how do I interpret the steps provided by Jerry and others? Probably just convert it in to number of strokes or time from number of rounds?
I have one more question. It appeared to me as if you and others having three motions involved here. After every 4-5 strokes in one configuration, you
- Move around the barrel
- Rotate the mirror in one direction
- Rotate the tool in the other direction.
But that does not make sense to me because in the end you are re-orienting only two items. Whether I do it by just moving those two items directly or by a combination of 10 factors, should not make any difference.
Am I missing something? Is there any advantage of doing these three things? If so, I will need to figure out a way to translate to my case where I work on a large table and cannot move around it.
From: waldo kitty [mailto:wkitty42@...]
Sent: Wednesday, February 01, 2012 12:36 PM
Subject: Re: [atm_free] Re: Need help with figuring
On 2/1/2012 01:14, madhukar wrote:
> Hi Jerry,
> This is just to ensure that I have understood you correctly. Since I don't have the barrel or similar stand as yet, I have translated it to my context.
> The meaning of one round is:
> - Do 4-6 strokes
while i understand the task at hand, i cannot agree... there is no set count for a "round of the barrel"... in fact, there is no set number of rotations for any round of anything... this is /important/ because randomization is the key to gaining a smooth surface...
i need to get my MMM#11 movies online... i simply spun my mirror and tool with not care as to the rotation degree... seriously! i grabbed one and spun it one way based on the flotation and then spun the other based on flotation and simply grabbed them at some point...
> - Rotate the mirror and tool in opposite directions. Mirror rotation
> should be in 25 to 35 degree range
> - Keep going back to first step till the mirror orientation is back to where we started from.
do NOT try to do anything based on a set number of rotations! it /will/ impart some form of astigmatism or "fold"...
> This will involve around 55-65 strokes to complete one round. And if my stroking rate is in the range of one per minute, the round should get over in 2-3 minutes including the time it takes to rotate the mirror and tool.
counting movements for one round is a great hazard! all my moves were made without counting _anything_! to count rotations or movements is to grind or polish in "circuits" and this is what you do NOT want to do... get FREE, my friend! move and stroke a bit and spin your tool freely and then grab it and go... do not step any set amount at all! grab the spinning tool and move some random distance around the barrel...
> Please do let me know if my understanding is not correct. I do one
> session tonight and upload the results
see above... the /KEY/ is being *RANDOM* in your spins and revolutions...
- Vladimir, I don't know the answer to that question but the admonishment read many times on the Zambuto group rings true. Select a glass that is worthy of one's efforts.Personally, if the glass is sufficiently thick, I don't believe a few millimeters of eccentricity over a mirror of that diameter will prevent Madhukar from completing a usable mirror.Perhaps if I compare a few hundred more star tests against OF results I'll change my tune, but it appears that OF residual astigmatism is often more pessimistic than what appears at the eyepiece. I suspect that is because of the many variables and difficulties of trying to measure a fraction of a wavelength taken from a igram generated by a webcam, surplus glass, cheap laser, fabricated by an ATM who is all thumbs in a dusty garage.Still, it is remarkable that we can do this at all.Mark
From: vladimir galogaza <email@example.com>
Sent: Thursday, February 23, 2012 2:10 PM
Subject: Re: [atm_free] Re: Madhukar's igrams
Madhukar,>We might need to do one more round of igram analysis with more accurate>information about mirror dimension, beam separation and ROC.I will not expect much from this because the all aberrations in this moment are so big.You should do your own analysis via OpenFringe as soon as possible. Than you canquickly try with different input parameters and see what-if results will be.It will take you couple of minutes to become familiar with this wonderful tool.I have followed Dale's idea and excluded cca 3 mm TDE from the interferogramto see what will be with results. Difference is very small in this stage of affairs.This is question for Jerry and Mark.If the mirror is elliptic (not circular) with 2.5 mm difference in axes, can we be sure thatastigmatism or "ears" are not merely a consequence of this fact and usual grinding and figuringmethod which puts equal effort on every radial direction on the blank which is not same inevery direction.Perhaps now when Madhukar knows where the ears are, accentuated work on this areawill be better strategy.RegardsVladimir.