Topics

State of the art?


Rien
 

What is the current state of things in CMM?

I have been reading the posts in the yahoo-group, and there is imo little to no information in there that would help me in tackling this subject by myself.

Nor did I see any signs that a CMM project has been concluded with the production of an actual mirror.

Is there a ‘there’ there?

Background: I am in the process of returning to the ATM hobby after quite some time of inactivity. The things I want to do is making my own mirrors and scopes. I have (a long time ago) made my own 6” mirror in a mirror making class. And I wanted to mechanise that part. The obvious choice would be the MoM. But a week or 2 (3?) ago I stumbled across this group. Since I am a SW engineer with electronics background, a CNC-CMM machine has a certain appeal over the MoM.

In addition I have started the construction of a CNC for my other hobbies (mainly RC planes) so building a second one for mirror making should be no big problem once I get the first up and running.

So, what’s up?


 


Hi,

It is what it is, not very active, but a place to post about this topic.

For myself, I'm quite a ways down the building process and will be returning to that following a bathroom remodel I'm currently working on.

But this is not likely to be a "how to do it" resource, more like a "how I did it", or "how it might be done" sort of resource.  Everybody has their own ideas about how that works.

My particular approach is quite complex (on the machinery/coding side) and based on some years of development of the actual figuring techniques that will lend themselves to full x-y control with feedback for the figuring process drawn from automated testing.  The latter is absolutely necessary for what I'm building, but YMMV.  I'm not done with these machines and so there's no "there-there" there yet. ;)

I can see where people could gain a lot from automation of the polishing machine.  I know personally that Carl Zambuto is following this route, because we share notes and tech occasionally.  

So what would be excellent is sharing whatever you find works well that you feel like sharing.  The group exists mostly because James Mulherin mentioned to me once that he'd really like to see it online, so that's where it came from.

Mark



Rien
 

Ah, I see. Thanks for the explanation.

In fact I might enjoy some experimentation myself… but I currently lack the experience and want to complete at least one binewt before committing myself to another endeavour.
So a MoM it is then. Once I get tired of using that, I may return to CMM. Until then I will just follow the developments here from a distance.

Btw: have you documented your figuring experiences somewhere?

All the best,
Rien.

On 9 Nov 2019, at 22:02, Mark Cowan via Groups.Io <toolontop@...> wrote:


Hi,

It is what it is, not very active, but a place to post about this topic.

For myself, I'm quite a ways down the building process and will be returning to that following a bathroom remodel I'm currently working on.

But this is not likely to be a "how to do it" resource, more like a "how I did it", or "how it might be done" sort of resource.  Everybody has their own ideas about how that works.

My particular approach is quite complex (on the machinery/coding side) and based on some years of development of the actual figuring techniques that will lend themselves to full x-y control with feedback for the figuring process drawn from automated testing.  The latter is absolutely necessary for what I'm building, but YMMV.  I'm not done with these machines and so there's no "there-there" there yet. ;)

I can see where people could gain a lot from automation of the polishing machine.  I know personally that Carl Zambuto is following this route, because we share notes and tech occasionally.  

So what would be excellent is sharing whatever you find works well that you feel like sharing.  The group exists mostly because James Mulherin mentioned to me once that he'd really like to see it online, so that's where it came from.

Mark




Bill Thomas
 

this web site contains downloadable figuring spreadsheets for a various machines
http://www.astrosurf.com/gap47/T400/Machine/Utilisation_machines/utlisation_machines_eng.htm

instead of my modified 24" M-o-M perhaps i should have done a Zeiss machine which does not require an edged blank.


Rien
 

Thank you Bill, that was exactly the kind of information I was looking for!


Bill Thomas
 

U of Arizona and Perkin Elmer have closed loops systems - UofA interferometer (straight fringes - Reference, computer generated hologram) - Infamous Perkin Elmer interferometer (straight fringes - null Two Mirror Offner Compensator - spacing issues did the Hubble mirror in).

have found, for my mirrors (22" f/4) the Bath interferometer images has many, many densely spaced fringes which were not useful, and as a result developed what i call Slit Image Test SIT http://www.yubagold.com/tests/ a computer (no human judgment) fast (less than 30 minutes) repeatably accurate Foucault results which then input to FigureXp or Sixtests (which i prefer) gives the surface profile.?? i simply then work on the high spots.

the SIT is a derivative of the LWT (elegantly simple).?? but with the LWT could not get repeatable results which i attribute to room temperature changes while taken the measurements.?? as a result developed the SIT which takes an image of the returning zone rays and the process that image with free ImageJ which automatically determines the LATERAL position of each of the zone rays to a 3rd of a pixel or better - ImageJ computes the center of gravity of the recorded ray photons - ray image is bucketS of recorded photonS - the LWT in turn is a derivative of the Caustic, but being mask tests measuring a diameter strip and can't detect or deal with astigmatism.

when the image and light source are in the same plane the SIT equation is just a factor of 2 greater (just as the fixed Foucault is approximately 2 times greater than the moving Foucault) than the simple LWT equations.?? but when the image plane and source are not in the same plane (as with a digital camera) then need the SIT equations (non linear algebraic equations?? using Excels Solver for solution).???? the SIT equations are exact, not an approximation.

this paper i think might have the answer for us ATM'ers the Shark Hartmann http://ecee.colorado.edu/ecen5606/2014/Wavefront_SensingAOL2014.pdf
but instead of using a Shark Hartmann wave front sensor (same as used in adaptive optics) would use a Hartmann mask.?? but then instead of trying to numerically solve a 2d partial differential equations (which is the BIG draw back to the Hartmann) instead as this paper describes fit the the terms of the Zernike polynomial - doing a least squares fit instead of trying to numerically solve a 2d partial differential equations.

On 11/12/2019 11:58 PM, Rien wrote:
Thank you Bill, that was exactly the kind of information I was looking for!


Rien
 

Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.


Bill Thomas
 

from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.  i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.  the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of  the "quill" arc -  also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.  the toggle pad 5/8 NC female is then threaded on that stud.  the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.  also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).  it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?  also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes  - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.  stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.


Rien
 
Edited

What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?
 
Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))
 
Edit: I see now in the excel sheet that the lap is '15.5', which I suppose is the size in inches... (that would represent an undersized but fixed sized lap which is kind-of confirmed by the picture)

On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:
from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.  i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.  the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of  the "quill" arc -  also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.  the toggle pad 5/8 NC female is then threaded on that stud.  the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.  also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).  it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?  also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes  - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.  stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.
<StrokeSetup.pdf><log_22s.xlsx>


 


Hi,

Feel free to embed (paste) pictures in your post - this works for most people - or post them to the pictures section of the group and refer to them.  Pictures are very helpful.

I'm not quite sure what you're referring to with the "pivot position".

Mark

On Saturday, November 16, 2019, 11:11:36 AM PST, Rien <lugt@...> wrote:


[Edited Message Follows]

What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?
 
Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))
 
Edit: I see now in the excel sheet that the lap is '15.5', which I suppose is the size in inches... (that would represent an undersized but fixed sized lap which is kind-of confirmed by the picture)

On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:
from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.  i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.  the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of  the "quill" arc -  also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.  the toggle pad 5/8 NC female is then threaded on that stud.  the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.  also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).  it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?  also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes  - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.  stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.
<StrokeSetup.pdf><log_22s.xlsx>


Rien
 

With pivot position I meant the mounting of the tool/lap with the rod that drives it.
The MoM manual calls it the swivel or leveling pad.

Btw: I saw earlier that you wanted to actively rotate the lap. How do you then connect the lap to the drive-rod?
(I can think of some solutions, but are curious as to how you would do it)

Rien.

On 17 Nov 2019, at 04:49, Mark Cowan via Groups.Io <toolontop@...> wrote:


Hi,

Feel free to embed (paste) pictures in your post - this works for most people - or post them to the pictures section of the group and refer to them.  Pictures are very helpful.

I'm not quite sure what you're referring to with the "pivot position".

Mark
On Saturday, November 16, 2019, 11:11:36 AM PST, Rien <lugt@...> wrote:


[Edited Message Follows]

What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?
 
Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))
 
Edit: I see now in the excel sheet that the lap is '15.5', which I suppose is the size in inches... (that would represent an undersized but fixed sized lap which is kind-of confirmed by the picture)

On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:
from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.  i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.  the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of  the "quill" arc -  also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.  the toggle pad 5/8 NC female is then threaded on that stud.  the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.  also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).  it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?  also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes  - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.  stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.
<StrokeSetup.pdf><log_22s.xlsx>


 

On Sunday, November 17, 2019, 04:06:52 AM PST, Rien <lugt@...> wrote:


With pivot position I meant the mounting of the tool/lap with the rod that drives it.
The MoM manual calls it the swivel or leveling pad.

Btw: I saw earlier that you wanted to actively rotate the lap. How do you then connect the lap to the drive-rod?
(I can think of some solutions, but are curious as to how you would do it)

Rien.

For non-driven (free spinning) tools I've used cast iron pipe plugs embedded in the tool with the free area (opposite the threads) at the top, receiving a stainless rod.  For the CNC work though it changes to a threaded insert that the driving arm locks into.  Then the polisher can be rotated under control clockwise.  I don't have pics currently but I'll take some to post.

Mark


Bill Thomas
 

for polishing i use a lap slightly larger than 70% with a max overhang of 25%,? table at high speed (just short of spraying fine mist) and slow eccentric? -? which strange as it may seem does not produce a TDE - some times is an antidote for a TDE.?

then beginning figure (slow table 4 RPM, faster eccentric) Zambuto's smoothing (Zambuto's log - figuring a 12.5"
http://www.astrosurf.com/gap47/T400/Machine/Utilisation_machines/Methode_Zambuto_12,5_Eng.pdf? - NOTE: M-o-M are not all the same) with that 70% instead of a sphere the outer zones are nearly a parabola with a hump in the center.? then the problem is dealing with the center hill with a 45% lap without having the next to outer zone going below to hyperbola hell - the antidote for hyperbola is high table speed, 50% lap working the 70% zone for a short period - if too long and then nearly a sphere the result is a big TDE.

my mental picture of the figuring is a glide slope as with landing a plane and not crashing.? but actually figuring is what i enjoy the rest of the process grinding polishing is just what i have to do to get to the fun part - figuring.

but with the M-o-M type the blank should have little run out i.e., it should be edged.? i try for having the optical center over the table shaft center less than 0.005" (M-o-M manual states 0.032" - seems large to me)? to avoid astigmatism.? i mark the edge at three 120 degrees points.? then take the average dial readings at those points and then nudge the mirror to get each point to the average.? then set the 4 cleats against the edge of the mirror with a 0.002" feeler gauge in between - with outdoor carpet under, a circular blank will auto rotate - but if not circular, the mirror will hangup on a high spot - and that is a BIG PROBLEM.

my understanding from a well respected mirror maker, his Zeiss does not need an edged blank - as is by hand over a barrel.
?
the SIT can't detect astigmatism - let alone fix it - do get a hint all is not well when getting different results at different mirror orientations - but its just a hint!? then its back to fine grinding and a lot of hope.

thankfully i have not had to deal with astigmatism - others using the SIT and doing what was suppose to be just refiguring (of large mirrors) turn out to be astigmatic and then its back to 80 grit!?

so being able to fix an astigmatic mirror without having to going back to grinding is a BIG DEAL!

the book, "A Manual for Amateur Telescope Makers",? by Karine and Jean-Marc Lecleire describes a "wire" apparatus for detecting and correcting astigmatism - the key to the apparatus is the wire can be rotated without ANY lateral displacement to some small portion of a wavelength of light - in that an astigmatic mirror has multiple focal points which are nearly identical to a few wavelengths of light.

that is why i think Shark Hartmann http://ecee.colorado.edu/ecen5606/2014/Wavefront_SensingAOL2014.pdf is significant.

and for the professionals there is the $10K Shack Hartmann? http://www.alcor-system.com/new/SH/Shackscope40x40.html fits into the focuser - same concept as with medically measuring eyes http://www.cvs.rochester.edu/yoonlab/research/ows.html

On 11/16/2019 4:33 AM, Rien wrote:
What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?

Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))



On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:

from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.? i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.? the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of? the "quill" arc -? also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.? the toggle pad 5/8 NC female is then threaded on that stud.? the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.? also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).? it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?? also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes? - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.? stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.

<StrokeSetup.pdf><log_22s.xlsx>



Bill Thomas
 

besides the low pivot point - controlling the downward force is important which the Zambuto's balanced type "Arm" provides i.e., the other end of the balanced arm has counter weights which then controls the downward force on the toggle pad attached to the lap (like the high end arm of LP record players of old).

With pivot position I meant the mounting of the tool/lap with the rod that drives it.
The MoM manual calls it the swivel or leveling pad.

Btw: I saw earlier that you wanted to actively rotate the lap. How do you then connect the lap to the drive-rod?
(I can think of some solutions, but are curious as to how you would do it)

Rien.

On 17 Nov 2019, at 04:49, Mark Cowan via Groups.Io <toolontop@...> wrote:


Hi,

Feel free to embed (paste) pictures in your post - this works for most people - or post them to the pictures section of the group and refer to them.� Pictures are very helpful.

I'm not quite sure what you're referring to with the "pivot position".

Mark
On Saturday, November 16, 2019, 11:11:36 AM PST, Rien <lugt@...> wrote:


[Edited Message Follows]

What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?
�
Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))
�
Edit: I see now in the excel sheet that the lap is '15.5', which I suppose is the size in inches... (that would represent an undersized but fixed sized lap which is kind-of confirmed by the picture)

On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:
from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.� i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.� the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of� the "quill" arc -� also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.� the toggle pad 5/8 NC female is then threaded on that stud.� the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.� also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).� it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?� also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes� - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.� stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.
<StrokeSetup.pdf><log_22s.xlsx>



Bill Thomas
 

http://www.sandsmachine.com/alumweb.htm
aluminum discs at a good price and they will ship.

https://www.mcmaster.com/toggle-pads

curious to see if these two images get through if not will send another email with these attached.









On 11/17/2019 4:06 AM, Rien wrote:
With pivot position I meant the mounting of the tool/lap with the rod that drives it.
The MoM manual calls it the swivel or leveling pad.

Btw: I saw earlier that you wanted to actively rotate the lap. How do you then connect the lap to the drive-rod?
(I can think of some solutions, but are curious as to how you would do it)

Rien.

On 17 Nov 2019, at 04:49, Mark Cowan via Groups.Io <toolontop@...> wrote:


Hi,

Feel free to embed (paste) pictures in your post - this works for most people - or post them to the pictures section of the group and refer to them.? Pictures are very helpful.

I'm not quite sure what you're referring to with the "pivot position".

Mark
On Saturday, November 16, 2019, 11:11:36 AM PST, Rien <lugt@...> wrote:


[Edited Message Follows]

What kind of lap diameter do you use for polishing? Same as mirror?, or undersized but fixed, or variable sized depending on the correction you need to make?
?
Thanks for mentioning the pivot point position, it makes sense to choose that as low as possible. (This will also place a minimum on the lap size, i.e. of the kind: the minimum lap diameter should be N times the height of the pivot point above the mirror))
?
Edit: I see now in the excel sheet that the lap is '15.5', which I suppose is the size in inches... (that would represent an undersized but fixed sized lap which is kind-of confirmed by the picture)

On 16 Nov 2019, at 07:19, Bill Thomas <bthomas32000@...> wrote:
from what i have experienced, polishing requires the greatest amount force - my 24" machine http://www.yubagold.com/mom/index.html
uses 1/2 hp and 1/4 hp - two stock M-o-M systems - using ball bearings - more than enough power.? i should replace the M-o-M system with 2 monster variable speed control motors which a friend gave me - would eliminate the belt hassle changing.? the other change i need to make is moving the arm pivot back further from the table axis so as to increase the radius of? the "quill" arc -? also on the website pictures the "arm" is counter balanced like the old high end LP record player - so as to control the downward force on the lap - which i have found necessary to stop chattering of smaller laps (noticed this in a picture of a Zambuto machine).

(need to send along a picture - worth a thousand of the following words) also to that end found i needed to get the pivot (toggle pad) attachment as low as possible to the back of the tool/lap - use a 5/8" short threaded stud into the back of the aluminum plate of the tool/lap.? the toggle pad 5/8 NC female is then threaded on that stud.? the 1" top of the toggle pad then fits into a machined adapter which on the other end is then threaded on to the 5/8" NC arms quill.

attached is a "strokeSetup.pdf" which i use to setup my modified M-o-M and record the settings.? also attached is a spreadsheet i use with my homemade sphereometer - the radius of the 3 legs from the center of the dial indicator was done with a bar of approximate 3" radius - then the actual radius was determined by measuring a mirror of known focal length (using excel solver).? it is vary accurate.

but i don't think a M-o-M type machine will be what you need for a closed loop system - would be more like a Zeiss machine?? also think you will need to know the exact RPM of the table and arm to avoid repatriation of strokes? - one crude method is to mark on the edge of the mirror where the tool/lap crosses the edge - those dots should be uniformly spread out.? stroboscope would be better?

On 11/15/2019 3:11 AM, Rien wrote:
Again, I have to thank you Bill. To me this is like opening another door of which I did not even know it existed.
I will study both the site (yubagold) and the pdf. I am however not yet in a knowledge state that would allow me to make sensible comments on it.

Btw, I have pretty much decided to make the CNC machine -that I was planning anythow- sturdy enough to also handle grinding/polishing forces. That does not impact my schedule too much and at least gives me the option to start experimenting with CNC grinding/polishing whenever I feel ready.
<StrokeSetup.pdf><log_22s.xlsx>



 

I think what I didn't add was the design goal to keep the effective point as low as possible to the mirror to reduce force loadings (torquing) from side to side.  This might be an obvious point but I notice a lot of people seem to overlook it.

Mark



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_._,_._,_


 

Unless there's wedge in the glass you do this by extended machine time with a large polisher.  You can always polish out what was polished in...

Mark

On Monday, November 18, 2019, 11:39:53 AM PST, Bill Thomas <bthomas32000@...> wrote:



so being able to fix an astigmatic mirror without having to going back to grinding is a BIG DEAL!


_._,_._,_


Bill Thomas
 

also the downward force - somewhere saw a posting that gave the pounds per square inch to avoid lap chattering.

On 11/18/2019 3:23 PM, Mark Cowan via Groups.Io wrote:
I think what I didn't add was the design goal to keep the effective point as low as possible to the mirror to reduce force loadings (torquing) from side to side.  This might be an obvious point but I notice a lot of people seem to overlook it.

Mark



 

My loading for polishing is around 1/4 lb per sq in.  If that's helpful.

Mark

On Tuesday, November 19, 2019, 02:28:55 PM PST, Bill Thomas <bthomas32000@...> wrote:


also the downward force - somewhere saw a posting that gave the pounds per square inch to avoid lap chattering.

On 11/18/2019 3:23 PM, Mark Cowan via Groups.Io wrote:
I think what I didn't add was the design goal to keep the effective point as low as possible to the mirror to reduce force loadings (torquing) from side to side.  This might be an obvious point but I notice a lot of people seem to overlook it.

Mark