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Figuring a 6-in f/8

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#26 Pinbout

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Posted 25 August 2020 - 10:22 PM

Keep the channels clean

 

https://youtu.be/_81Mi3FfQo0

 

about the channels

 

https://youtu.be/T03b-5LyWGk
 

watchhow the cerox flows 

 

https://youtu.be/erF2jO34pgg


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#27 kcoles

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Posted 26 August 2020 - 12:50 PM

I did three 15-minute figuring sessions (each preceded by a cold press of 15 minutes). Washed it off and took a look in the tester, then back for the next session. I did do the variations on the 1/3 stroke, going a little side to side for one turn around, a little more or less length, a little more side to side or none at all (but the same way for a whole turn). I have the mirror marked so I can see how big my stroke is and when I've finished a full rotation. A typical turn is about 12 positions to make a full circle. I rotate the tool (all this is MOT) 1/4 turn after every few times around.

 

Since folks have been running models, I measured the real aperture and the numbers are diameter 5.94 inches, ROC 100.8 inches (gives me f/8.48), Ronchi screen is 100 lpi, on Foucault knife is entering from the right. After 45 minutes total I took pictures. Here are Ronchi inside and outside ROC by 0.4 inches, and a couple of Foucault knife edge shots (left is my attempt to null on outer zone, right null near center zone). I will use more exposure on future Foucault pictures so they aren't so dark.

 

f8_24Aug2020.jpg

 

The good news is that the Ronchi bars are a bit straighter than last time (post 10) so at least I'm headed toward less correction? The surface looks rough, however, and the next thing I planned to do (before I even saw Pinbout's posts) is clean up and widen the channels on the lap before the next pressing - they have narrowed a bit. I rotated the mirror and did more KE photos (not included here), which gave me an idea how the roughness varies.

 

[There are specks on the camera sensor - three of them appear in most of the pictures - so I've ordered some cleaning supplies to help me get rid of those.]


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#28 Pinbout

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Posted 26 August 2020 - 02:23 PM

so you have a shallow hole. still some edge too. I'd take care of the hole 1st, or both at the same time... 

 

I'd press a piece of wax paper into the lap and alt coc mot/tot

 

but smaller than this, and less pointy, have the points come out just to where the hole begins.

 

https://www.youtube....ZAqvzU_GA&t=68s


Edited by Pinbout, 26 August 2020 - 02:27 PM.


#29 dogbiscuit

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Posted 26 August 2020 - 05:48 PM

Make the channels uniform depth and width over the entire lap.

For a full trim open them up to about 8 mm  wide and deep. This should work good for this mirror working with Gugolz 64 at your working temperature.

 

If after each full work session it only takes a few minutes to look for and trim only parts of channels that have narrowed and gotten shallow be equal width and depth to the widest and deepest parts.

 

After a few of these light trims the channels will be getting narrower and not as deep.  If after a work session the channels have gotten down to less than 5 mm width and depth do a full trim to 8 mm depth and width again.

 

Doing it this way each time you trim only takes a few minutes and the channel quality is consistent.  I'm giving you a starting point that I think will work good for you on this mirror.  If you maintain consistent channels you can adjust the dimensions a little to find what works best for whatever you are working on.

 

Try to work pitch tiles to be same size, and try to keep narrow partial tiles at the edge of the lap from getting any smaller.  This can be done by choosing which side of a channel to trim to maintain channel width.  For that narrow row of partial tiles trim the side of the channel toward center.  Maybe you need to straighten the other side of the channel but minimize pitch removal on that side.  Across the lap on the other side is a row of exceptionally wide tiles.  Trimming of that channel should on the side of the channel of those oversize tiles to reduce there width.  Look over the lap and plan which side of channels if trimmed would result in more equal size for all the tiles.  Don't try to make it perfect all at once, just when you trim to make uniform channel width and depth try to work toward a more uniform tile size.

 

The edge is still turned, and a good uniform lap well pressed will probably help that.

 

I rarely ever alter a lap by pressing stars or other shapes, especially for something like a 6" f/8.5

The mirror has gotten more spherical. The area between about 55% and 90% is spherical. 

The central depression is not deep.  I would continue with the normal lap.

 

I'm not sure how much you press the mirror.  When you say you cold pressed 15 minutes before each 15 minute session I wonder how long you pressed before the first 15 minute session. 15 minutes is probably not enough before the start of teh session.  More like a few hours or more depending on how long the lap and mirror were apart. 

 

Not sure yet about the central depression.  I would expect that as you continue work the diameter of the depression would decrease.  It is still about the same diameter as before, but it might start shrinking as the spherical zone widens toward the center.  So that's what I would look for if you work another session same as before.  If it does not decrease in diameter I would think a lap fault to be the cause and most likely just not well pressed, or non uniformity of the central are of the  lap relative to the part that has made the spherical zone between 55 to 90%.

 

I say be sure the lap has uniform channels of suitable width and depth, well pressed before the start of the session.

Then do a session just like the last and see what the results are.

 

How much downward pressure do you apply during stroking?  I recommended between 3.5 and 7 pounds downward force applied by hand (not including weight of top disk).


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#30 Pinbout

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Posted 26 August 2020 - 06:25 PM

so you have a shallow hole. still some edge too. I'd take care of the hole 1st, or both at the same time... 

 

I'd press a piece of wax paper into the lap and alt coc mot/tot

 

but smaller than this, and less pointy, have the points come out just to where the hole begins.

 

https://www.youtube....ZAqvzU_GA&t=68s

Swayze  would tell you to press a star into it lol.gif


Edited by Pinbout, 26 August 2020 - 06:26 PM.


#31 dogbiscuit

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Posted 26 August 2020 - 09:43 PM

In the latest Foucault images what looks roughness might be artifacts from the camera such as the vertical dark streaks.  The streaks probably aren't really the mirror surface, and not likely watermarks.  I think I see some real roughness, not sure.

The border of the central depression is a hexagon.

 

Some suggestions that might reduce the tendency for that to occur:

Don't make exactly 12 equal increments of rotation to a full turn of the mirror.  If you do exactly 12 equal increments of rotation for a full turn,  after working increments 1 through 6 then 7 through 12 work the same diameters, just going across the other way. If you see polygons appearing on the mirror in Foucault testing, reduce the size of increments of rotation, just slightly.   In fact if you can learn to maintain a chosen size increment of mirror rotation, it helps to occasionally make a slight change (but always same for full rotation).

Less work at each step around and increments of mirror rotation will help spread work around more evenly.  I usually will work either 5 or 7 strokes across a W, maybe a couple more for larger mirrors.  Two trips around with 5 strokes at each position is better than one trip around with 10 strokes at each position.

 

 

 

Verify for me that your pitch is Gugolz 64.  You mentioned you also got some 73.  There are some things about your results that make me think the pitch could be hard, but I know 64 should work near perfectly for your shop temperature of 72° and you should be getting a very smooth surface. 

 

Forward and back = 1 stroke.  How many stokes per minute are you stroking? 



#32 dogbiscuit

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Posted 27 August 2020 - 06:20 AM

Same Foucault image one with hexagon shape drawn in. 

In a way there is also a triangular shape with 3 alternate sides of the hex being longer than the sides in between.

HexDepression.png

 

It looks like most of the hex is in the depression, little if any in the spherical zone outside the hex.

When the depression has been removed by working the spherical zone all the way to mirror's center the hex should be gone.

 

When I take Foucault images I open the lens aperture all the way because the camera iris leaves can sometimes get in the way.  I usually make a stop, hole about 1/2" diameter in black cardstock, to put on the front of the lens.  That's big enough to allow easy alignment of the lens with the knife and returning light cone and to block unwanted light coming in the lens.

Lens aperture full open, exposure is controlled by shutter speed.

 

Better Foucault images will show surface smoothness and edge better.



#33 kcoles

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Posted 27 August 2020 - 09:17 AM

Some initial thoughts as I work through your suggestions:

 

The hole looks sort of hexagonal (or like three smaller holes merged together) to me also, and in other photos I took. I did already wonder if my 12 steps around were too regular (easy pattern to fall into with a hexagonal work stand). The pitch is 100% Gugolz 64. I'm sure my channels aren't big enough right now and will work on those first (and work through all the other advice). Yes, the initial press can certainly be much longer than my 15 minutes.

 

I was commonly doing 5 back and forth, [edited:] same way dogbiscuit defines it. Pretty slow, perhaps 30-40/minute, as I still have to watch to see that the length is about right without being too regular. There certainly is an art to this! 55 to 90% does null all at once, so I guessed the sphere was appearing there and needs to grow, thank you for the confirmation of that. That's better than the raised, narrower zone I had near 50% when I started.

 

I recall at Delmarva there were those who pressed a star to fix a hole. We actually tried that near the start of my figuring there, but I now suspect the lap I had then was too soft for much to happen. I know there are several methods that work...but in any case I'll start with the channels. Thanks.


Edited by kcoles, 27 August 2020 - 09:27 AM.


#34 dogbiscuit

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Posted 27 August 2020 - 01:43 PM

The number of steps around the tool or lap when MOT doesn't need to be the same as the increments of mirror rotation.

 

The number of increments to a full turn of the mirror could be much different than the "about 12" that I recommend.  I've helped a few people make mirrors and I remember some of the funny stuff I saw when I was learning.  I've found that many first time mirror makers tend to do 8 increments to a full rotation and also 8 steps to a full trip around the tools.  Almost every time I've seen someone doing this they a squared figure and ripple.   I've seen pentagons and triangle probably from 5 or 10 steps, and 3, 6 or 9 steps.

 

The reason I recommend about 12 is that I see less trouble with 12 and if there is trouble a very small change in the step will smooth things out.  Much more than 12 might take too long to complete a trip around.  If whole number increments to a full turn of the mirror were to be use prime numbers are better than even numbers, worked diameter doesn't repeat on the way around.  I've known of tm's who mark the table and mirror, usually 12 positions on each as a reference for stepping and rotating.  If you feel you need to mark things out on the mirror or table don't do 12.  Do 11, 13, or 17.


A mark on the back edge of the mirror can help as a reference for when a full turn has been completed.  I think it is best not to start every work session with the mark at the some clock position.  Change the start orientation for each start and either write it down or remember so you know when a full turn is finished.

 

Pressing stars or other shapes into the lap can work.  I've done it.   I don't like using this method for most mirrors because I haven't had trouble doing things with a normal lap,  and if some shape pressed into the lap works faster to remove some defect, I then need to press the lap back into full contact before continuing.  The condition of the lap is a very high priority for me and I don't like intentionally taking away full contact.   Just a personal preference.

 

40 strokes per minute, a little more or less is ok.  Your 30 to 40 is ok.


Edited by dogbiscuit, 27 August 2020 - 01:46 PM.

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#35 kcoles

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Posted 28 August 2020 - 08:24 PM

Did a long (several hours) press, then 45 minutes of strokes similar to last time (checked on tester and repressed partway through), washed, and after dark took photos. There are some surficial smudges that I confirmed by looking at the mirror afterwards. The Ronchi bands look straighter, but there is still a hole in the middle and TDE is still there. Nevertheless, it feels like some progress. I am now going around in a prime number of steps (today I used 13), and will retrim and press the lap before doing any more. If I should modify any of what I am doing I am happy to hear about it. Thanks!

 

f8_sixth_test.jpg


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#36 Pinbout

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Posted 28 August 2020 - 09:57 PM

a star would take care of the hole and short fast strokes take care of the tde... just saying.

 

you keep the strokes fast to keep the lap from conforming to the glass. 

 

figuring with pitch is like figuring  with melting ice... that's why by the time the hole is gone so is the star.

 

and you can actually watch it happen if you did all MoT.



#37 dogbiscuit

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Posted 28 August 2020 - 10:46 PM

Looks only slightly better sphere.  I would expect faster change.

kcoles27-35.png

 

Seems the lap is not very effective.

Check things that could cause that.

 

Take a couple of pictures of the lap from straight overhead. 

One with the mirror centered on top of the lap with slurry on the lap after stroking about 1/2 D back and forth and left and right.  I'll look for things on the lap that could result in the depression.  It may be there is something about the lap that is making that depression as you work. Might be one or more pitch squares is not flowing as fast as the rest of the lap creating higher pressure on that tile.  That could be from a closing channel (narrow and or shallow).

 

Temperature in the workspace still 72° give or take a degree or two?

 

Downward  pressure?  For figuring I apply about .2 to .25 psi of lap area. The 3.5 to 7 pounds hand pressure plus mirror weight should come close enough to desired psi.  I'm sure other people use different pressure and do ok, but some pressure is necessary.  If you are not pressing down as you stroke things will go slow and maybe not so well for surface smoothness and edge.  Pressure should be steady.

 

Hands something like this. 

Hands6inch.jpg

Thumb tips or knuckles touching at mirror center can be reference for stroking pattern over the lap.

 

Surface of the pitch could be glazed, surface hardened from work, but I don't think you've been working with that lap long enough to have much trouble there.  If it were glazed brushing with wire brush (brass) can restore the surface.  After brushing apply relatively thick slurry and press well. 

 

There is some surface roughness, and I know Gugolz 64 will make a nice smooth surface and good edge with a full size lap if channels are good, pressing is good,  stroke rate is about like what you are doing, pressure is in the range I stated, and work room temperature is 72°.  With all that stuff right  it should not take long to rub out that shallow depression.  The shape is very close to a sphere and the faults are shallow.

 


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#38 dogbiscuit

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Posted 29 August 2020 - 04:30 AM

I trim channels with a single edge razor.  I've always done it this way and with a little practice I find it very easy to do.

Holding the blade at correct angles relative to the channels and pitch surface is important for reducing chipping.

 

 

Obviously the blade will be stroked in a straight line along the edge of and parallel to the channels.

Being right handed I lean the blade to the right at about a 60° or 70° angle.

As viewed from above I rotate the blade a few degrees counter clockwise to turn the blade into the channel wall so as to shave the wall of the channel.

kcolesRazorTrim.png

 

The rotation on the vertical axis is important. If the blade is stroked straight in line with the blade edge the blade stick to the pitch and pulls out chips. Turning the edge into the channel wall will shave the wall and there will be less sticking and chipping.

Pitch chips and powder will build up on the blade and that increases the chance of grabbing a chip out of the lap.  I use two blades when trimming.  One for trimming and the other to occasionally scrape pitch buildup off the sides of the trimming razor (not the edge).

 

Typical stroke length is something like 1 or 2 inches, width of the pitch squares, sometimes maybe longer but be careful when crossing other channels.  Depends on how well you can control a straight cut where you want it and that depends on how deep channels are at the moment.  When first cutting channels use very very light cuts to establish the channels.  Rotate the lap 180 degrees to cut the other side of the channel and continue doing this, going a little deeper each time until the full depth is reached.  As they are made deeper it gets easier.

 

I understand there will be some who might not like to do it this way, or just unable to get the hang of it.  In that case I would suggest looking at one of Pinbout's videos that shows using a soldering iron to make the channels.

 



#39 dogbiscuit

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Posted 29 August 2020 - 05:19 AM

Broad spherical outer zone, shallow central depression, your mirror is probably 1/8 wave on the wavefront now, but it's ugly.  I know ways it could be rounded into a better parabola, but the surface would probably still be rough and the edge likely no better than it is now.

So you know the strategy of my suggestions, my method depends on getting the lap in good shape. The lap makes the figure.  With a good lap the edge will get good as you use a few relatively normal strokes that make a sphere.  Hold near a sphere while the edge improves and surface smooths. When the edge quits getting better, parabolize. Pictures of the lap can be as important to me as the pictures of the figure, at least until it is established that the lap is good and being maintained good.

I think I understand your description of strokes you are using.  If what you are doing is what I think, you should have a better result than seen so far.  Your Gugolz 64 should be, most likely is good and you are working at a good temperature for that pitch. Don't know if you are using suitable pressure.  If you are I think something is wrong with the lap, most likely non-uniform depth and width of channels, or incomplete pressing, some chance pitch surface has glazed.

 

 Think positive. You are close. Work on getting the lap right.  When it is right figuring will be easy.  Send some pictures of the lap looking straight down from directly overhead.  And from side looking down the length of a channel. 



#40 kcoles

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Posted 29 August 2020 - 11:27 AM

I am going to work on the lap now but a couple of thoughts. Before yesterday's session I checked my hands on a scale, and it jumped to 10 or 15 pounds as soon as I touched it. But I was leaning over when I did that. The weight I press with is a 10 pound disk-shaped counterweight 6 inches in diameter, and hefting it I can now see I'm not close to 3.5 to 7 pounds with my hands. I was touching just enough not to lose the grip on the mirror. So that may well be part of the explanation. It's good to hear it should go faster than this - one wonders how many weeks or months it could take at my current rate.

 

I pressed nylon window screen into the lap yesterday before any figuring, so I wouldn't think the lap is glazed yet.

 

The channels have closed somewhat so I will open them up again.



#41 dogbiscuit

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Posted 29 August 2020 - 01:49 PM

For rough grinding it is good to get a lot of weight on the top disk, so  having the work table low so you can lean over and apply body weight is good.

 

For polishing and figuring it is better to have the work table higher so the mirror is at about mid torso height.  With arms t extended in front of you elbows straight and hands palms down on the back of the mirror apply downward pressure.

Stroking can be done by rocking body back and forth on your feet without arm motion.  Stroking this way it is less likely you would shift pressure on the disk during the stroke.  Arm stroking is ok if you can do it without shifting pressure.  Rocking the body makes it easier.

 

take some pictures of the lap after channeling and pressing.



#42 dogbiscuit

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Posted 29 August 2020 - 03:55 PM

Here is something to think about for how overhang pressure and stroke direction effect changes to the figure.

For MOT work...

As overhang increases pressure build at the edge of the lap where there is most overhang.  What this pressure does to the mirror depends somewhat on the direction of the stroke relative to this area high pressure at the edge of the lap.  Think of the edge of the lap as a blade. If stroke direction is tangent to the high pressure edge of the lap the blade slices.  If the stroke direction is in a radial direction to or from the center of the lap across the high pressure edge of the lap the blade planes.

Some strokes will have components of both.

SlicePlane.jpg

 

Slicing cuts a narrower path on the mirror, planing a wider cut

Some times on relatively large overhang strokes like a wide W stroke I will make the stroke at the extreme sides of the W where overhang is greatest with more left right motion.

templateDisk.png

Normal forward back stroke at the sides of the W will slice the surface near the center of the mirror and can make some ugly stuff, dimples or trenches around the center or just a sharply defined zone at the extent of overhang.

Making that stroke with more sideways motion make wider planing cut. This sideways motion at each side of the W will get some work near the mirror's center with a smoother transition between the work outside and work inside the overhang.

 

If I recommend a stroke with those somewhat sideways motions, it is meant to be done that way.

 

Don't do that parabolizing stroke now.


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#43 kcoles

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Posted 29 August 2020 - 05:48 PM

I trimmed the channels first. I've used a blade and had already discovered a stroke very like what dogbiscuit illustrates. In my hands it generates more chips than I like. It also wasn't uniform enough, so I got out my old stained-glass soldering iron. It has a variable control, and I found at 50% is just right. It melts the pitch without smoke or smell. Then I pressed for an hour, and some of the channels had narrowed, so I did it all (blade and soldering iron) a second time and pressed for two hours. I still need to trim the edge vertical, but I took these photos.

 

Lap_oblique.JPG Lap_vert.JPG


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#44 kcoles

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Posted 29 August 2020 - 05:52 PM

And then I wet the lap and mirror, did one stroke as suggested, and took this photo. Sorry for all the marks on the mirror, they help me keep track of what I'm doing.

 

mirror_lap2.JPG


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#45 dogbiscuit

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Posted 29 August 2020 - 08:19 PM

That looks pretty good and I think it's going to work good, but I'm going to nitpick.

 

See the light shade of the cerium and the darker surface of the pitch.

There is some cerium between the pitch and glass in the darker area, but it's very thin. These dark areas are in good contact, lighter shaded areas less so. If you look around the circumference of the lap if you see light shade on the pitch surface, good contact doesn't extend all the way to the edge.  This is probably why your tde is not going away and is worse than your first images.

 


 

Sometimes after pressing MOT  I have seen that pitch spills out over the edge and falls away from the mirror. Of course it's slow motion and its a microscopic fall and I didn't stand there watching it happen. I see that it has happened by looking at the light and dark shades of slurry between lap and mirror showing outer couple of mm not in full contact.  Pressing TOT I have seen better contact at the edge.

 

When pressing the full size lap and contact is good all the way to the edge some pitch may squeeze out and curl around the mirror's edge.  I rarely ever actually trim the edge of the lap.  With Gugolz pitch I just stroke the mirror forward and back left and right and the edge of the mirror either shaves the curl off or it fractures off vertically in relatively fine flakes at the edge leaving a surface as large as the mirror diameter and sometimes a mm or two larger.  I wipe the chips off the edge of the mirror and lap and go to work.

 

Now look at all the pitch squares.  There are some light area on some of the squares. I've marked some of the lighter shade areas indicating less than ideal contact.

PoorContact.png

The little bb size ones don't matter much if not too many.  A few finger or thumb tip size depressions won't have much effect.  A couple of corners chipped off pitch tiles usually won't cause trouble.  But don't want to many of them.  It is hard to say how much is allowable, but when you get really good contact the top surface of the lap will be much the same shade all over.  Your surface roughness is probably from the irregular contact across the lap surface

 

Ok, that's the bad news, and it isn't so bad.

The good news is most of that poor contact has persisted this long most likely because the channels were not good.

Channels look good now, pitch has room to flow and the depressions in tile surfaces will go away quickly with pressing and working. 

Things should be working well soon.

 

I recommend pressing TOT over night without adding weight.  Check channels again after pressing, trim again if necessary and press another 30 minutes before working.  Using 3.5 to 7 pounds of pressure as you work will also help bring the lap into good contact all over

You could do another session like before except adding some downward pressure, or maybe a little later I'll send you a few strokes to do

 

 

 



#46 dogbiscuit

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Posted 30 August 2020 - 10:57 AM

Red zig-zag shows path of the mirror's center over the lap.

 

7 strokes across the W for the top strokes.

5 strokes across the W for the bottom stroke.

 

Do the top strokes 1 turn each.

Do top strokes again 1 turn each.

Do bottom stroke 1 turn.

 

Repeat all that for 30 or 45 minutes.  Let how many times you did the entire series and how long you worked.

 

kcoles46.png

 


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#47 dogbiscuit

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Posted 30 August 2020 - 04:34 PM

The intention of the suggested strokes is to put some work on the rim of the crater (depression) which is near the 55% radius.

The 1/2 and 2/3 D parts of the strokes will take the edge of the lap near that radius.  Local pressure between mirror and edge of the lap will be across the rim.   The 2/3 D part of the last stroke will have the most overhang and so will work faster than the other strokes so that stroke is not done as much.

kcolesFourcault35.png

 

This might add some correction in that spherical area,  but the goal here is to rub out some of that ugly crater and make the surface more regular.  Let's and to see how the lap works now. Maintain the channels and press well, the lap will get into better contact each work session.

 



#48 kcoles

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Posted 30 August 2020 - 06:12 PM

I had already done one 20-minute session of my old strokes before post #46. Pressed for 20 minutes and did one of these new cycles (I call the steps ABABC), about 20 minutes. Did a quick check on the tester, it was having a perceptible effect. It was also time to rechannel the lap and press it again. I also had to reballast the table as it needed some more weight. Then three more cycles of the ABABC strokes (rotating lap every cycle, odd number of steps around the table). That was about an hour (but all of this took all afternoon, as I always seem to). So four cycles of the new strokes altogether. Then took these images:

 

f8_seventh_test.jpg

 

Some correction is appearing, and the middle looks much smoother. Turned edge is still there, but I'm patient. Sad part is two tiny scratches on the mirror (you can see the larger one near the bottom). I will clean up and toss all the old materials around the work area and be as careful as I can to avoid any more of that.


  • Jeff B likes this

#49 dogbiscuit

dogbiscuit

    Apollo

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  • Loc: Barksdale

Posted 30 August 2020 - 07:59 PM

That looks better.  Smoother.  Edge has improved a little.  Note the diffraction ring is more visible on the right a little thinner on the left.  Not as sharp a hook of Ronchi bands.

See this one session has made significant improvement.

It looks like the lap is looking better now. 

 

 

It looks a little overcorrected.  That correction was there before as the ROC difference of the central area and the outer area. There is a lesson there.  By using strokes that with overhang that put the rim of the crater at the edge of the lap put pressure on the rim and pushed it down.  That smoothed the kink there making the change of ROC more gradual from center to edge.  There is still a little bit of the kink there but not much.

 

Probably best to work to reduce correction and let the edge continue to improve.

 

I think it is close enough that you should take some knife readings.  Get some practice taking knife readings and see that you are really very close now.

Do you have a Couder screen?

 

I'm going to think a little about what strokes to use next and post them later.

 

Take some knife readings.

 

 



#50 Pinbout

Pinbout

    ISS

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  • Joined: 22 Feb 2010

Posted 30 August 2020 - 08:49 PM

I had already done one 20-minute session of my old strokes before post #46. Pressed for 20 minutes and did one of these new cycles (I call the steps ABABC), about 20 minutes. Did a quick check on the tester, it was having a perceptible effect. It was also time to rechannel the lap and press it again. I also had to reballast the table as it needed some more weight. Then three more cycles of the ABABC strokes (rotating lap every cycle, odd number of steps around the table). That was about an hour (but all of this took all afternoon, as I always seem to). So four cycles of the new strokes altogether. Then took these images:

 

attachicon.giff8_seventh_test.jpg

 

Some correction is appearing, and the middle looks much smoother. Turned edge is still there, but I'm patient. Sad part is two tiny scratches on the mirror (you can see the larger one near the bottom). I will clean up and toss all the old materials around the work area and be as careful as I can to avoid any more of that.

When you have a hole and you don’t format the lap with a star, you always wind up pushing the hole out and become overcorrected 




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