Tuesday, June 25, 2013


130625 SBAU Telescope Workshop, June 25, 2013
EdK, JerryW, TomW, TomT, DmitriiZ, TomK (~845p)

DZ- has put in 2 hrs since TW told him 6hrs more might be needed.  He will be polishing tonight with CeO2  http://www.ceroxid.com/html/cerium_oxide.html after settling in the tool on the mirror blank.  JW explained that during polishing glass is moved from one area to another, not removed.  Also, some of the CeO2 polishing compound will be embedded in the mirror.

DZ- TT email him for DropBox link to his downloaded YouTube videos of telescope making that TW will use for Westmont presentation & DZ will show at Tinker Fest.
JW- showing TW spreadsheet / MathCad for JW scope calculation for Foucault knife edge error.  Entered TW scope parameters / knife edge variables into JW form for calculation.
TW- showed JW upcoming presentation on mirror grinding and parabolizing with math for Westmont College Summer Science Institute students.

TK- plans on being at SBMNH Tinker Fest.  TW will bring 8” with Baader filter for sun viewing that day.
TK- discussed his solar scope plans (4”?)
TK- TT send him link to this blog http://sbautw.blogspot.com
JW- To correct aberration that causes coma use a ParaCorr by Televue http://www.televue.com/engine/TV3b_page.asp?id=61, maybe cheaper by Baader:   http://www.telescopes.com/telescope-accessories/photographic/baaderplanetariummpccmultipurposecomacorrector.cfm

Saturday, June 22, 2013

130622 Tim & mirror beveling

Greetings once again from the lab,
 I decided to try the beveling of the 8" down here at the lab. So that I didn't do a fancy "insert" of text in the pictures, I am including some notes you can follow for each slide. In the first image, note the soft stone I am using to soften the edge of the tool. Since we will use this at the upcoming event with the public, I wanted to soften the edge to rid ourselves of the chance of chipping the edge of our Pyrex. Second you can see this edge on the tool. On the third image, I wanted you to see the "rounded" edge of the mirror our donator has originally created. 

Now, I am not opposed to the idea of a rounded edge at all. In fact I'd like to discuss this a bit more in our workshop. There is strength to this round edge. When grinding the mirror, a hard edge will appear on the upper edge of the bevel or rounded edge. The lower  part of a rounded edge seems to me to be impervious to any chipping. Am I wrong on this? The fourth image shows me starting to cut a bevel on the edge. I am using a coarse diamond disc, that is actually quite flexible. I try to hold the handpiece at a 45° angle. With a 16" mirror this may be a bit more difficult. I can kind of move the mirror under the handpiece a bit with these smaller mirrors. Keeping this 45° is a little more difficult moving just the handpiece over the mirror, but do-able. The next picture shows the whole work top. I wanted to mention something Jerry told me that is important. When grinding these, it is advisable to use a wet grinding. For this, you can see the little dish of water behind. I can either wet the surface of the mirror, wet the diamond disc itself or both. In the old days, we had an attachment they made for dentistry to utilize compressed air and a water canister to draw the water up a small hose to the nosepiece of the handpiece. Today, they are more using this arrangement with high speeds. For this, I don't think it is a good tool. These turn at about 250,000 rpm and are for less "planing" stroke and more for spot grinding and facial contouring. I also think the incidence of chipping is increased, especially with pressure. I do want to add, you can see I have a hose in this picture.
It is a vacuum I use for grinding. Before I got this, I found myself coughing as i ground my porcelain crowns. As time passed over the years I realized I was actually working towards silicosis. With this vacuum right next to the work, it literally eliminates the danger. A wet grinding set up together with this vacuum would be better. Just get the sunlight to shine into the lab late in the afternoon and see what we are working in. the dust is silhouetted in the light. I am actually wondering why I have lasted all these years!The last two photos show our finished edge. In the first you can see it actually allows a fairly consistent bevel around the mirror. In the second I wanted to show you that small chips were noticeable to me. Look in the area that is most in focus and you will see them. I think this is within tolerance and acceptable.
 Hope you all enjoy this. I do not think anyone is using this exact technique out there. Maybe the Newport Glass Works do, but it may be a bigger machine doing the work. Next door to us is a glass company. I intend to talk to the owner a bit on this. I have used a tool they have in back of their shop to soften the edges of cut glass. Joe, it is a rather large wet belt sander on a stand. Kind of cool actually (literally). It has a place to rest the glass, but I wouldn't think holding a 16" against it would be as accurate as what I am doing. This is better.
 PS- Tom T. or Dmitrii,feel free to use this any way you wish.
 Tim the Tinkerer
see the photos attached to this email here: https://secure.flickr.com/photos/27241501@N03/sets/72157634222053744/

Thursday, June 20, 2013

130619 TimC work donated 8 inch mirror new tool

Greetings all,
     Well, in spite of being under the weather, I took a little time this afternoon to make a new tool for the donated 8" mirror. I have a few photos I think Tom T. will appreciate. But, let me get a little more into what I did (beyond what the photos show.) First, we decided to grind this mirror ( now an f/8) to a faster mirror. We are targeting f/5 but I hope we can get a little feedback from Javier as to what f/ratio he would like this to be. I want to just say this now. I am hoping that this will be Javier's scope one day. There I said it. We can discuss this all later. For now, let me tell you what we have. We have a almost polished 8"  mirror, a tool covered with pitch and lots of ugly rouge that covered everything. Today, I went down to the lab with the idea in mind of preparing the tiles to cover the new tool.
     Now, this is interesting- we usually grind the edge of the mirror-to-be with a sharpening stone. I takes forever to do this, but it turns out really nice. We want to achieve a 2-3mm bevel. (I removed pitch last night from the tool). Today, I decided to try an experiment using a diamond disc in the lab to grind this bevel. I used our tool to see how it would work. It worked magnificently! Actually, I'd like to try this technique in the future on Pyrex. Next, I have a lttle kit in the lab to acid etch crowns and veneers. I thought , " what the heck, let's give it a try." So, before I applied the etching liquid, I sandblasted the surface ot the tool and all the ugly stuff around the edges. You will see this in the photos I hope. I trimmed up the piece of ceramic tile I set aside for this tool. You have to score it with a disc and then use nippers to trim it to size. Then using another fine stone in the hand piece, I trimmed to my liking the outer edges.

     Getting home, I had all the stuff ready to go. I used a two part epoxy to attach the tile. The idea was to get the epoxy mixed up and coat the tool then stick the tile to the surface. But before I did this, I was "clever C..." and leveled the work table. This is so the tile and epoxy wouldn't all fall to the low side. Tom W. who is one of my mentors in all things scopes and mirrors, told me to set the mirror on top of the tile to marry the couple together as close to the "dish" as possible. I used wax paper (all I had) to place between the new tool and mirror so they wouldn't accidentally bond themselves together. All things went well actually and I even took some masking tape and applied it to the edges of the two discs so they wouldn't slip. I do believe though I got too much epoxy in some places and not as much in other places. So I took the equivalent of a toothpick and moved it around to my liking. You can see some of the residual epoxy on the surface of the tiles.
     Hope you all enjoyed this. It was really intended to inform those that wan to use this either to understand the process, comment on the actual process, or even to use it in the upcoming July event.
     One last comment. I am actually thinking of using this mirror and tool in the upcoming Tinkerer's Fest. It will make those hours of mating the surfaces together much shorter (how about that Jerry?).
P.S. The photos are not labeled, so if you have questions on which is which, just ask me. [more photos posted at
https://secure.flickr.com/photos/27241501@N03/sets/72157634222053744/ ]

130619 JerryW 14.5 inch back coring of mirror blank disk

Here's a photo of drilling a central hole in my 14.5 inch disk in progress.  This the back of the blank.  The coring will come within 3/16 of an inch of the front side.  The front side is ground to #120.  You can see a dam of oil based clay holding a water/grit mix while the coring tool turns at the drill press' slowest rate.  This is in Joe D's garage.  The blank is clamped in a custom wooden jig to prevent any motion.  The jig is clamped to the drill press' horizontal platform.

I had the tool machined out of soft steel, but any circular metal object can be used.  One common tool is an empty "tin" can.  [also another wider photo here: https://secure.flickr.com/photos/27241501@N03/sets/72157634222053744/ ]

Wednesday, June 19, 2013


130618 Telescope Workshop June 18, 2013
attendees: TimC, TomW, JerryW, TomT, DmitriiZ (+J)

TW- 8” “richfield” scope reviewing w/ JW.  Knife edge error 4zone chart compared to theoretical, in cm, see photo of chart.  Someone in the Chabot group made this chart http://www.chabotspace.org/telescope-makers-workshop.htm
TW- then went over his parabolic vs. circular mirror making mathematics that he will be presenting at the Westmont College Summer Science Institute http://summerscience.org/home/index.php with JW as well.  TT was mostly baffled by it all.
TC- working on cleaning off old pitched tool glass for mirror that Javier gave him.  He plans on making the f8 glass into a faster mirror (f5?).  He will grind the existing 8” mirror deeper by making a new tool from the old, with new tiles adhered on it.  JW recommends using tool glass directly to grind with, but with good bevel.  No channels needed for grinding material.  Tiles may actually be dangerous due to each tile's sharp edge that can break off.  Some people cut tiles to fit tool, others only leave full tiles that fit on tool.  TimC continued to bevel the 8” tool and his 16” mirror, which is still at the grinding stage.
TT- showed Newport glass mirror kit cost list, and TW/JW commented on increasing cost http://www.newportglass.com/ngwkitp.htm.
DZ- dropped in to stay in touch with the group and while on babysitting duty.  TT noted that he had started to review DZ's mirror making blog going back to 2009 (see link).
More photos here: http://www.flickr.com/photos/27241501@N03/sets/72157634222053744/

Saturday, June 15, 2013


130611 SBAU Telescope Workshop June 11, 2013
attendees:  JerryW, EdK, TomT, DmitriiZ

JW- Newt for the Web (JW working on mirror 18” f3.9) from Stellafane http://stellafane.org/tm/newt-web/newt-web.html is used to predict 75%, 100% illumination.
JW- PHD software “press here dummy” star tracking, from stark labs software,  includes periodic error correction http://www.stark-labs.com/phdguiding.html .
JW- He has Vixen GPD Super Polaris mount, designed/made in Japan http://www.vixenoptics.com/ .
DZ-polishing his 12.5” w Cerium Oxide, setting pitch tool for a few minutes with gallon water bottle on top.  He is using center of tool over center of mirror strokes w/ random movement around the mirror and turning of the tool and mirror.  JW says Iron Oxide used to be used for polishing.  http://www.willbell.com/ATMSupplies/ATM_Supplies.htm does not list CeO.
TT- brought in TimC 38pg “Crafting a Mirror” (not finished) presentation for viewing.  Possibly will be used at Tinker Festival July 21.
JW- explained knife edge test and zones to TT using TC presentation pages.
JW- said that he took issue with Stellafane instructions on removing a raised edge, but Stellafane replied that they had to keep some steps to make it easier to understand for new users.

Wednesday, June 5, 2013


130604 SBAU Telescope Workshop June 4, 2013
TimC, TomT,TomW,JerryW,JoeD
-Javier gave TimC a donated 8” polished pyrex glass, with the requirement that someone reports on the final product telescope back to the donator.  TimC brought this in tonight and TomT took photos of the glass, Edmunds rouge, pitched tool for polishing, and some extra.  Mirror measured to be a f/8 with the Ronchi test showing a good pattern?

-JerryW patiently explained focal radius vs focal length to TomT.  Also mirror types for various types of cassegrain telescopes.
-JoeD 6” brought in his $300 astro-tech newtonian F/4 mirror, which measured to about F3.9 on TomW testing setup and surfaces were viewed with Ronchi and knife edge.
-TomW measuring his two 6” glasses, one is R-87” f/7, the other is f/4, and examining the surfaces with Ronchi testing, perhaps a tad high center on the second? with the pinched center of the Ronchi pattern.
-TimC grinding his 16” w 120 grit still, JerryW spherocity tester shows it very good already.
-Finally TomW 10” F3.3 was viewed and it was almost perfect for the Ronchi pattern.
-TomT took off at 9pm to go see the outreach at UCSB Ucen...it was very busy there with students.
Photos available soon here for both the TW and outreach:
Potluck this Friday.

130603 JerryW: Mel Bartels-oversized laps

---------- Forwarded message ----------
From: Jerry W
Date: Mon, Jun 3, 2013 at 10:20 AM
Subject: Mid course correction.
To: Tim C, Dmitrii Z, Tom T, Tom W, Chuck M, Ed K
It seems another ATM "rule" needs to be discarded.  Here's an interesting quote from Mel Bartels discussing the benefits of 1. Not keeping the channels of a pitch lap open, 2. Not pressing and 3. Using an oversize pitch lap, all to get a perfect mirror.
"...developed a new technique.
     Many years ago, back in the age of over the air TV and phones with cords that connected to walls, I decided to teach that 12 inch mirror a lesson and furiously keep polishing despite the pitch lap's channels gradually closing in and the pitch lap expanding beyond its normal size.
     You see I had partially burned off a tiny portion of my left eyebrow in a home chemistry experiment (I was in 6th grade at the time) that I conducted I never figured out if she was more curious about my eyebrow or about the smoke that had wafted upstairs.
     So when I say that I raised my eyebrows at the mirror's surprising figure - you know I mean it - a perfect edge and ultra-smooth surface. From that day forward I never channeled a lap again and I always made over sized laps.
     Being a student of history and a great admirer of elderly people with all their wisdom, I asked an old time pro optician about the oversized lap. I raised my eyebrows yet again when he didn't (where is Spock when I need him). It turns out that this was common knowledge - no big whoop (a phrase that ought to be making a comeback any day now thanks to the all-powerful and all giving INTERNET).
     Researching further, I found that Brashear mentioned oversized laps as a standard technique in the late 1800's. You see, during that era, there was an explosion of pamphlets and small books on how to do things. Telescope making was a 'big deal' back then. Holcombe had formed the first USA telescope company in the early 1800's (to the surprise of leading European intellectuals who maintained that Americans were not up to the task), followed by Fitz and Clark which was followed by Brashear and others.
      The reason that oversized laps were lost to amateur telescope making is because the ATM world fell into the trap of promoting glass tools as the same size as the mirrors.
     Centuries ago, right after the adoption of the Keplerian telescope, astronomers stalled out because the images were upside down. They didn't know what to make of it and shied away. It took a younger generation of astronomers to declare that it didn't matter that the Moon was upside down in the telescope.
     The same conceptual moat and lack of imagination exists today. Amateurs apparently cannot conceive of how an oversized lap would be made and how it would work. Maybe it is time to singe an eyebrow and get mad at a mirror that's not polishing out very quickly and 'get her done'.
      Believe me, there is no secret and this is not new.
Mel Bartels [ http://www.bbastrodesigns.com/tm.html ]"
Very interesting, eh?
Jerry W
Sent from my iPad

Tuesday, June 4, 2013

130602 TimC Tele Work email

From: Tim C Add to Addresses Block Sender
Date: Sunday, June 2, 2013 7:58 PM
To: Tim C Add to Addresses
Subject: workshop
Size: 5 KB
There will be a workshop this coming Tuesday, June4th. Bill, could we have the gate open please? Thank you!
I hope to be there this week with my 16" glass. I hope to get some grinding done this week and measure the sagitta.      [ http://stellafane.org/tm/atm/grind/measure.html  ]                                 

Also, we have inherited a 8" mirror that is almost or half way(?) complete. The donor only asks that we show him the finished scope some time. I am hoping to make this a "class" project we can all work on. I do not know yet if a tool comes with it or we may have to make one and break it in.  In the end we will pick a worthy person to own this scope. ( I do have someone in mind). I will get a consensus at our meeting this week.

Please come on over to the Broder if you get a chance. The class has been coming along nicely of late. I do hope you will join us. We start at 7:30 and go till 9 or a little later.


130528 Telescope Workshop meeting notes May, 28, 2013
TimC, TomW, EdK, TomT, JerryW

-TimC set for July 21 Tinker Festival.  Minimal handouts.
-EdK brought in knife edge mirror tester that he made back in high school

-TimC working 120 grit on his 16” mirror blank, with full size tile grinding tool, mirror glass on top.
-TomT asked TW and JW about field stop of eyepiece and field of view.  Televue.com has a webpage about choosing eyepieces and discusses various factors.  see: http://www.televue.com/engine/TV3b_page.asp?id=154
-TW, JW, TT went out to parking lot to try to see line up of Venus, Mercury, Jupiter.
-Dobson was a monk and had a masters in chemistry...but more here: http://en.wikipedia.org/wiki/John_Dobson_%28amateur_astronomer%29
-TW, JW discussing working, testing mirrors at home.
-final eye check for the evening of Tim's 16” mirror with flashlight beam up to 8x loupe and side view to bright light source to the side.
-More Photos here: http://www.flickr.com/photos/27241501@N03/sets/72157633972763979/with/8971554853/