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[ATM] stubborn tde
David--
Try placing some weight on the polishing tool, and just slide the tool with the weight on top back and forth rather than pushing down with your hands .This is much like machine action with the pressure dispersed evenly.Let the lap ride the curve of the glass. Polishing temp around 70%?COC strokes. Maybe slight W. Slight.Vary the overhang ,25% of the tool diameter(1.5") down to 1". Keep the glass wet.Full sized tool , correct?? Cheers---JN
-----Original Message-----
>From: atm-request@atmlist.net
>Sent: Aug 29, 2006 9:00 PM
>To: atm@atmlist.net
>Subject: ATM Digest, Vol 32, Issue 28
>
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>Today's Topics:
>
> 1. Making a trepanning biscuit cutter (Christopher Dalla Piazza)
> 2. Re: 20" f/4 - f/23 spherical Mangin Cassegrain (Anthony Stillman)
> 3. Re: my first RONCHI test, with video of it (Arjan te Marvelde)
> 4. Re: my first RONCHI test, with video of it (Mitch)
> 5. Re: Thermal mirror deformation -fan on both sides (Ric Rokosz)
> 6. Re: Thermal mirror deformation -fan on both sides (tony gondola)
> 7. Re: Thermal mirror deformation -fan on both sides (Mitch)
> 8. Re: Making a trepanning biscuit cutter (Bob May)
> 9. Stubborn TDE (David Steinhauer)
> 10. Re: Stubborn TDE (Jerry)
> 11. Re: Stubborn TDE (Mitch)
> 12. Re: Stubborn TDE (Mitch)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Mon, 28 Aug 2006 23:03:12 -0400
>From: "Christopher Dalla Piazza" <dalchri@hotmail.com>
>Subject: [ATM] Making a trepanning biscuit cutter
>To: atm@atmlist.net
>Message-ID: <BAY118-F25B05B055D1EC6C4B5E67DB6390@phx.gbl>
>Content-Type: text/plain; format=flowed
>
>Does anyone have any advice on where to get or how to make a trepanning
>biscuit cutter?
>
>In every text that I've seen there is a picture of a sort of metal tube that
>has ½" triangular pieces taken out of it around its perimeter.
>
>The closest thing that I can think of to buy would be a hole saw for a drill
>at Lowe's but that would have pointy teeth and lots of them. Would that be
>too aggressive and cause too much stress on the glass?
>
>I've also heard of using a soup can but that sounds a little rickety if not
>painful to the nerves.
>
>The last thing that I could think of would be to use some sort of metal tube
>with an end cap. Then you would cut the teeth into the tube and attach a
>screw to the end cap for use with a drill press.
>
>A concern of mine with all of these methods is shooting for an exact hole
>diameter. This will be for a meniscus lens on a Newtonian so it will
>support a secondary holder. My understanding is that you would design your
>secondary holder diameter according to hole diameter that you can trepan
>because it is easier to machine metal than shave glass.
>
>Any additional ideas?
>
>
>
>
>------------------------------
>
>Message: 2
>Date: Mon, 28 Aug 2006 22:04:23 -0700 (PDT)
>From: Anthony Stillman <atmer@flash.net>
>Subject: Re: [ATM] 20" f/4 - f/23 spherical Mangin Cassegrain
>To: Jean Fejes <JsFejes@Swva.net>
>Cc: atm@atmlist.net
>Message-ID: <20060829050423.18663.qmail@web82003.mail.mud.yahoo.com>
>Content-Type: text/plain; charset=iso-8859-1
>
>Jean,
>
>I plugged the BK7 prescription into OSLO and toy
>around with it. The corrector is pretty insensitive
>to changes in TH and ROC as well as TEM. There is one
>huge problem however. The design has effectively no
>useful field.
>
>I also plugged in the prescription for a like sized
>Pressmann-Carmichel (Spherical primary, ridiculously
>oblate ellipsoidal secondary). This design is known
>for its effectively non-existent useful field. The
>two designs were fairly comparable. The Pressmann is
>a very little better.
>
>The sub-aperture catadioptricly corrected spherical
>primary cassegrain would work for on-axis photometry.
>
>
>Anthony
>
>
>difficile factu
>hard to do
>
>
>
>------------------------------
>
>Message: 3
>Date: Tue, 29 Aug 2006 09:48:36 +0200
>From: "Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>
>Subject: Re: [ATM] my first RONCHI test, with video of it
>To: <atm@atmlist.net>
>Cc: rtoledo2002@yahoo.com
>Message-ID: <000501c6cb3f$88df6dc0$0301a8c0@Acer>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Roman,
>
>> let me know what you think of the mirror and what it may need ;)
>
>Assuming inside ROC, it looks like an oblate ellipsoid (i.e. edge zones
>focus shorter than center).
>If the mirror indeed is polished out, I'd lengthen my strokes and work TOT
>mostly.
>
> Arjan
>
>
>
>------------------------------
>
>Message: 4
>Date: Tue, 29 Aug 2006 08:53:12 -0400
>From: "Mitch" <funnybone101@earthlink.net>
>Subject: Re: [ATM] my first RONCHI test, with video of it
>To: "'Arjan te Marvelde'" <arjan.te.marvelde@hetnet.nl>
>Cc: atm@atmlist.net
>Message-ID: <000601c6cb6a$165eeed0$6601a8c0@dmp>
>Content-Type: text/plain; charset="us-ascii"
>
>
>Assuming inside ROC, it looks like an oblate ellipsoid (i.e. edge zones
>focus shorter than center).
>If the mirror indeed is polished out, I'd lengthen my strokes and work TOT
>mostly.
>
> Arjan
>
>Watch the ronchi carefully though. A TDE MUST, I REPEAT must be avoided or
>it will be a real pain later. Look for any little "hooks" at the edge in
>either direction indicates your edge is turning one way or the other.
>Remember to press good and often. Cold presses are easy to do and can help
>greatly.
>
>Mitch
>
>
>
>------------------------------
>
>Message: 5
>Date: Tue, 29 Aug 2006 06:55:07 -0700 (PDT)
>From: Ric Rokosz <radicell2@yahoo.com>
>Subject: Re: [ATM] Thermal mirror deformation -fan on both sides
>To: Jan van Gastel <jhm.vangastel@wanadoo.nl>, atm@atmlist.net,
> atm_free@yahoo.com
>Message-ID: <20060829135507.55912.qmail@web34509.mail.mud.yahoo.com>
>Content-Type: text/plain; charset=iso-8859-1
>
>
>
>--- Jan van Gastel <jhm.vangastel@wanadoo.nl> wrote:
>
>
>> >
>> > Inspired by the recent thread on under/over
>> correction of a mirror due to
>> > radiative cooling, I have done some simulations
>> with a PDE solver and
>> > written an article about it. Please have a look at
>> >
>>
>http://home.hetnet.nl/~artm/atm/articles/cooling.html
>> > Iwould very much appreciate any comments: there
>> might be wrong assumptions
>> > or errors.
>
>I'm somewhat surprised more comments haven't been
>advanced on this specific example of the effects of
>mirror cooling,especially the fact that using a fan on
>just the backside of the mirror induces more
>distortion than no fan at all!Kinda sets a new
>standard for atm's that pro's knew about for quite a
>while.
>
>The best solution is to use a fan on both sides.This
>reminds me of the work done by a French optician that
>used a heater wires around the circumference of the
>mirror to both equalize the mirror temp in the blank
>and to distort the mirror's shape to an aspheric
>shape.
>
>Thanks Jan for this important work.
>
>Ric
>
>__________________________________________________
>Do You Yahoo!?
>Tired of spam? Yahoo! Mail has the best spam protection around
>http://mail.yahoo.com
>
>
>------------------------------
>
>Message: 6
>Date: Tue, 29 Aug 2006 07:27:42 -0700
>From: "tony gondola" <acgna@comcast.net>
>Subject: Re: [ATM] Thermal mirror deformation -fan on both sides
>To: <atm@atmlist.net>
>Message-ID: <00a601c6cb77$503d28d0$6501a8c0@HPLAPTOP>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
>I don't think it's a matter of how important the work is but is it a useful,
>validated tool? It's interesting but I don't think anyone really knows what
>to do with it. Everyone knows that performance will be degraded while the
>mirror is equalizing to ambient. My personal feeling is that actual field
>measurements would be more useful.
>
>I'm also not sure that I agree with conclusion on fan placement. The most
>common configuration is to blow air out from the back of the tube or mirror
>box. The fan isn't blowing directly on to the glass but is rather setting up
>a flow of air that surrounds the mirror, front back and sides. The actual
>airflow is much more complicated then Jan's simple infinite diameter disk
>model suggests and is also subject to turbulence and dead areas induced by
>various structures in the flow path including the mirror's edge. Even a full
>CFD analysis wouldn't tell the whole story.
>
>Tony
>
>
>
>----- Original Message -----
>From: "Ric Rokosz" <radicell2@yahoo.com>
>To: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>; <atm@atmlist.net>;
><atm_free@yahoo.com>
>Sent: Tuesday, August 29, 2006 6:55 AM
>Subject: Re: [ATM] Thermal mirror deformation -fan on both sides
>
>
>>
>>
>> --- Jan van Gastel <jhm.vangastel@wanadoo.nl> wrote:
>>
>>
>>> >
>>> > Inspired by the recent thread on under/over
>>> correction of a mirror due to
>>> > radiative cooling, I have done some simulations
>>> with a PDE solver and
>>> > written an article about it. Please have a look at
>>> >
>>>
>> http://home.hetnet.nl/~artm/atm/articles/cooling.html
>>> > Iwould very much appreciate any comments: there
>>> might be wrong assumptions
>>> > or errors.
>>
>> I'm somewhat surprised more comments haven't been
>> advanced on this specific example of the effects of
>> mirror cooling,especially the fact that using a fan on
>> just the backside of the mirror induces more
>> distortion than no fan at all!Kinda sets a new
>> standard for atm's that pro's knew about for quite a
>> while.
>>
>> The best solution is to use a fan on both sides.This
>> reminds me of the work done by a French optician that
>> used a heater wires around the circumference of the
>> mirror to both equalize the mirror temp in the blank
>> and to distort the mirror's shape to an aspheric
>> shape.
>>
>> Thanks Jan for this important work.
>>
>> Ric
>>
>> __________________________________________________
>> Do You Yahoo!?
>> Tired of spam? Yahoo! Mail has the best spam protection around
>> http://mail.yahoo.com
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>
>
>
>------------------------------
>
>Message: 7
>Date: Tue, 29 Aug 2006 13:57:02 -0400
>From: "Mitch" <funnybone101@earthlink.net>
>Subject: Re: [ATM] Thermal mirror deformation -fan on both sides
>To: "'tony gondola'" <acgna@comcast.net>
>Cc: atm@atmlist.net
>Message-ID: <000001c6cb94$8b7cad40$6601a8c0@dmp>
>Content-Type: text/plain; charset="us-ascii"
>
> This doesn't directly relate but I thought this was a bit of a novel
>design, off of Mel Bartels site under the 2001 Oregon star party walkabout.
>
>Pictures 12 and 13
>
>http://www.bbastrodesigns.com/osp01/osp01.html
>
>I think it would be hard to align such a face on fan and might add unknown
>diffraction effects if you're not careful but with everyone talking about
>fan placement I figured I'd throw this in to hopefully stir more debate :)
>
>Mitch
>
>
>
>------------------------------
>
>Message: 8
>Date: Tue, 29 Aug 2006 15:44:31 -0700
>From: "Bob May" <bobmay@nethere.com>
>Subject: Re: [ATM] Making a trepanning biscuit cutter
>To: <atm@atmlist.net>
>Message-ID: <003901c6cbbc$b1dd5340$ddadfea9@amd>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Trepanning cutters are easy to make although a bit touchy.
>Start by taking a piece of wood (or metal or plastic if you wish)
>and cutting a nice round side on it along with a nice mounting
>hole in the middle. Use a router or the table saw (rounding jig
>setup) to get it good and round. Then take some steel flashing
>and screw it to the wood all the way around, making sure that the
>flashing is vertical to the wood and isn't bowed out at any
>point. The edge of the flashing should run true to the method
>that you're mounting it to the driver for it. A little bit of
>wobble won't hurt too much but you don't want to have a lot of
>wobble or you'll be cutting a really big slot in the glass. Cut
>the triangular slots in the edge so that they push the grit into
>the edge (reverse of what a cutting tooth is on a saw blade!) and
>you're ready to start.
>Bob May
>bobmay at nethere.com
>http: slash /nav.to slash bobmay
>http: slash /bobmay dot astronomy.net
>Replace the obvious words with the proper character.
>
>
>
>------------------------------
>
>Message: 9
>Date: Tue, 29 Aug 2006 17:50:21 -0700
>From: David Steinhauer <desteinhauer@verizon.net>
>Subject: [ATM] Stubborn TDE
>To: atm@atmlist.net
>Message-ID: <44F4E0CD.6010206@verizon.net>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>I've been trying to get rid of the TDE in my 6" f5 mirror, without success.
>
>Here's my original Ronchi photo, before I tried tackling the TDE. It is
>quite spherical, but has a
>narrow TDE. Note that all my Ronchigrams are outside of focus, and all
>my KE photos have the
>knife edge approaching from the right.
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060521-Ronchi1-sm.JPG
>
>First I tried using accented pressure just inside the edge, with TOT.
>All I did was increase the TDE
>and create a central hill:
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060529-Ronchi-sm.JPG
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060529-KE-sm.JPG
>
>Using Allyn Thompson's method, next I tried using short 1", narrow W
>strokes with TOT. I did short
>5 minute polishing sessions with 5 minutes of cold pressing in between.
>After quite a while I finally
>managed to get it to look close to how it looked at the start. However,
>the TDE is still there.
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060716-Ronchi-sm.JPG
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060716-KE-sm.JPG
>
>I tried using accented pressure again, making sure I cold pressed every
>5-6 minutes. But again the
>TDE increased instead of decreased.
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060812F-Ronchi-sm.JPG
>
>So I went back to the short 1" strokes with TOT. This time I tried COC
>rather than a W stroke.
>Again I'm getting closer to my original photo, but it's taking a long
>time (twenty-four 5-minute
>polishing sessions so far).
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060829-Ronchi-sm.JPG
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060829-KE-sm.JPG
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/060829-KE2-sm.JPG
>
>So, to summarize, my original Ronchi and KE photos look the best of
>all. Until I started working on
>the TDE, I would cold press for a while and then do long 1-hour
>polishing sessions with no cold
>pressing in the middle. I realize now that that was too long, but even
>so I still managed to get the best
>figure so far. With all of my efforts since then I've only managed to
>make it worse! I've never been
>able to see a diffraction ring all the way around - I've only seen it on
>just one side.
>
>Any ideas on what I could be doing wrong? How much downward pressure
>should I be applying? I
>tried doing MOT, but that also didn't get me anywhere at all.
>
>David Steinhauer
>
>
>------------------------------
>
>Message: 10
>Date: Tue, 29 Aug 2006 21:29:12 -0400
>From: "Jerry" <wa4guu@verizon.net>
>Subject: Re: [ATM] Stubborn TDE
>To: "'David Steinhauer'" <desteinhauer@verizon.net>, <atm@atmlist.net>
>Message-ID: <002a01c6cbd3$b4653f30$0100a8c0@D85SJB21>
>Content-Type: text/plain; charset=us-ascii
>
>Maybe you did not put the accented pressure in the right place. Closer to
>the edge might work. Or maybe just a bit on the other side of the edge.
>
>You put the pressure on the area just inside the turn down and made it
>worse. You probably thought that you would wear that area to a longer radius
>more like the edge. Sounds like it should work... but it went the other way.
>Accept what really happens when you do that and think about where you could
>apply the same action that would produce the same result it did before but
>in the right place.
>
>The zone you put the pressure on will shorten in radius compared to the zone
>outside the work. The correction from the zone inward to the one worked will
>be reduced.
>
>Some strange logic says to me that if your edge had been 1/2 inch closer to
>the center of the mirror, what you did would have improved the edge.
>
>Jerry
>
>
>
>
>-----Original Message-----
>From: David Steinhauer
>
>I've been trying to get rid of the TDE in my 6" f5 mirror, without success.
>
>Here's my original Ronchi photo, before I tried tackling the TDE. It is
>quite spherical, but has a
>narrow TDE. Note that all my Ronchigrams are outside of focus, and all
>my KE photos have the
>knife edge approaching from the right.
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/
>060521-Ronchi1-sm.JPG
>
>First I tried using accented pressure just inside the edge, with TOT.
>All I did was increase the TDE
>and create a central hill:
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/
>060529-Ronchi-sm.JPG
>http://www.atmlist.net/contrib/desteinhauer-at-verizon-dot-net/060829_6inch/
>060529-KE-sm.JPG
>
>
>
>
>
>------------------------------
>
>Message: 11
>Date: Tue, 29 Aug 2006 21:45:59 -0400
>From: "Mitch" <funnybone101@earthlink.net>
>Subject: Re: [ATM] Stubborn TDE
>To: "'David Steinhauer'" <desteinhauer@verizon.net>
>Cc: atm@atmlist.net
>Message-ID: <000001c6cbd6$0ca92790$6601a8c0@dmp>
>Content-Type: text/plain; charset="us-ascii"
>
>I struggled with TDE for 14 hours. I tried EVERYTHING. I ruled out
>everything except 2 things I did either of which could have made it better,
>both, or one more so than the other, not sure.
>
>The first was suggested to me by Ken Hunter. Working TOT use accented
>pressure at the edge furthest away from you and "pull" the raised glass zone
>just inside the TDE. I suppose you could do the same with pushing the glass
>with the edge closest to you but this is how I did it.
>
>Then I did 4.5 hours of 1/4 W's as I was oblate and it took me forever to
>lengthen my stroke enough to really move along faster. I pressed every 30
>minutes with 5 minutes of weight and 10 minutes just gravity (this doesn't
>matter; just make sure you have good contact.)
>
>Like I said, one or both of these helped. And reduced my 1/2 Wave TDE that
>had already been reduced from a full 1 wave of TDE just by spherizing.
>
>I can see why the inside TDE thing doesn't always work. After I beat my TDE
>now I'm struggling with TUE! I have been going at it for a few hours
>already. I tried a bit more of a drastic approach when nothing worked; it
>specifically says in books it can make a TDE. Working TOT with overhang and
>pressure on the over hanged lap.
>
>After 4X around I had a TUE with a tiny TDE on top of it. So I had a turned
>up edge whose edge was turned down! Not sure if the TDE extended deeper than
>the TUE.
>
>Edges are a pain, good luck and I hope this works for you. For a better
>description of that stroke ask Ken Hunter.
>
>I think the 4.5 hours of 1/4 W's did a lot but I'm not sure which did it,
>try both!
>
>Let us know how it progresses.
>
>Mitch
>
>
>
>------------------------------
>
>Message: 12
>Date: Tue, 29 Aug 2006 21:48:10 -0400
>From: "Mitch" <funnybone101@earthlink.net>
>Subject: Re: [ATM] Stubborn TDE
>To: "'David Steinhauer'" <desteinhauer@verizon.net>
>Cc: atm@atmlist.net
>Message-ID: <000101c6cbd6$59150ef0$6601a8c0@dmp>
>Content-Type: text/plain; charset="us-ascii"
>
>Make sure you check in Foucault too, after my TDE was gone I thought it was
>still there but on the ronchi it was just diffraction of the lines, Foucault
>will clearly show it if it is still there after a session.
>
>Don't worry, most of us have struggles with it at one time or another;
>you'll lick it and make a great mirror out of it.
>
>Mitch
>
>
>
>------------------------------
>
>_______________________________________________
>ATM mailing list http://www.atmlist.net/
>
>End of ATM Digest, Vol 32, Issue 28
>***********************************
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