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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Source of small glass "tiles" for a mirror tool
      #1372109 - 01/20/07 12:13 AM

I want to make a grinding and polishing tool for a 6 inch rich field mirror.

The sagitta is not pregenerated so I will be starting from scratch.

Normally I'd make a conventional tool using dental plaster and ceramic bathroom tiles. This time I wish to do something different. I've heard some rather glowing reports of results obtained by pouring dental stone over glass squares.

If I remember correctly, the 1 inch square glass segments were each cut by hand from 1/4 inch plate glass. I'd sooner use round glass "coins" but can't find any.

Tried Googling the Internet. Tried craft stores like Michael's. No round glass.

Michael's does carry very nice glazed ceramic tiles, about 3/4 inches square. For making a small tool, these would work great. I suspect that a $3.oo bag of these small tiles will be sufficient to cover an 8" tool.

Still, I'd prefer round glass "coins".

Do any of you know where I can buy them?

Thanks

Art.

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Stefan Rostyne
Pooh-Bah


Reged: 10/19/04
Posts: 1026
Loc: Assenede, Belgium
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1372309 - 01/20/07 05:15 AM Attachment (38 downloads)

Art, you don't need to buy these. If you have a drill press, all you need is a cheap soft metal 'biscuit cutter', like an end of plumbing tubing from copper, brass or mild steel, some grit and a waste piece of plate glass. Now you can carefully cut as many glass coins as you need, on the free. With carbo 180, you get a fine cut with a soft surface. Use a cooling agent! petrol is fine, but water is just as good and makes a lot less hazard for the environment.

Here you see a 35mm coin, 9 mm thick :



Attachment

Edited by Stefan Rostyne (01/20/07 05:34 AM)


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Stefan Rostyne
Pooh-Bah


Reged: 10/19/04
Posts: 1026
Loc: Assenede, Belgium
Re: Source of small glass "tiles" for a mirror tool new [Re: Stefan Rostyne]
      #1372321 - 01/20/07 05:37 AM Attachment (38 downloads)

Actually, what you see is the blank for the secondary for my 12" f4/f30 cassegrain. But you can use these just as good for grinding tiles. A look at the edge :

Attachment

--------------------
Stefan Van de Rostijne

4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
22" f/3.5 dob project

Edited by Stefan Rostyne (01/20/07 05:37 AM)


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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Stefan Rostyne]
      #1372637 - 01/20/07 10:51 AM Attachment (29 downloads)

Hi Stefan!

I understand the principle completely. I did exactly what you suggested when trepanning the secondary mirror for my 6" Schiefspiegler. Funny, I never thought of trepanning the disks.

I will test it on some quarter and half inch thick plate glass. There is a glass shop near where I live with a dumpster filled with scrap. I'm sure they will give me some.

My concern is the amount of time it will take to make enough disk to cover the tool. I'll also have to throw away the hole saw afterward.


Thanks

Art

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--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1372660 - 01/20/07 11:00 AM Attachment (31 downloads)

In this effort, I machined away the Bi Metal teeth from the hole saw. (What a job THAT was!)

Since then I have found that the teeth in a hole saw actually accelerate the glass grounding process! The teeth serve a better purpose: they cut a slightly wider grove than the thickness of the cylinder does. This prevents the tool from sticking or grabbing the glass.

I don't remember how long it took to treppan the mirror (10 minutes?) but the disks for the tool should go much faster.

For one it's a much smaller cutting surface. 2 it's a much thinner material and 3. I don't need to be as careful so I can go faster, cut more aggressively.

Thanks!

Art

The

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Gregg Lobdell
sage


Reged: 01/20/06
Posts: 416
Loc: Covington, WA
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1373102 - 01/20/07 02:45 PM Attachment (32 downloads)

There are small glass blobs, usually used in vases for holding floral arrangements. They are probably soda lime glass, but I've never seen one etched, so they aren't the worst glass I've ever seen. Often called glass gems, they are flat on the bottom and rounded or domed on the top. They come in assorted colors, including clear. Michaels should have them, or other craft stores that sell floral arrangment supplies. I've also seen them at Pier 1. They are usually sold in a small bag or by the pound.

These blobs are also used as markers in the board game "Pente" (tm) by Parker Brothers.

Here's a couple of links I found by googling "craft supplies glass gem stones"

http://www.mcgillswarehouse.com/groupslist.aspx?CategoryID=125&selection=29
http://www.discountcandleshop.com/product_info.php/products_id/282

Attachment

--------------------
Clear skies,

Gregg


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kingjamez
scholastic sledgehammer


Reged: 10/03/06
Posts: 996
Loc: Washington D.C.
Re: Source of small glass "tiles" for a mirror too new [Re: Gregg Lobdell]
      #1373350 - 01/20/07 05:33 PM

Now that is a VERY interesting option Gregg. I think I'll give those a try on my next tool.

-Jim

--------------------
C8 on Atlas with EQMOD
ETX125 UHTC
Celestron Onyx 80mm
Meade Walmart 60mm guide scope
Canon Xsi Modified w/IDAS LPR
Gen 3 NightVision Eyepiece
Aspiring Optician
Watch my Wiimote control Atlas:
http://www.youtube.com/watch?v=PnmkygmGNiM


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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Gregg Lobdell]
      #1373459 - 01/20/07 06:33 PM

Hi Gregg!

Fantastic!

I will order some immediately! Two sizes. Would have gotten three but the 7/8th inch diameter glass gems were only available with a reflective coating.

I'm concerned that the coating could prevent proper adhesion to whatever substrate I am using (in this current case, clear casting resin).

Something to note.

Tumbling these gems in a motorized barrel will produce a satin finish thus providing a better grip for the substrate.

I don't have the kind that rock collectors use, but I do have a motorized tumbler used for cleaning brass pistol cartidges.

I'll report back on the results I get, with step by step images.

Thanks for the great tip!

Art

BTW: they also sell aluminum oxide in grades 24, 60, 80, 100, 120 and 180. I'd have bought some but the smallest bag they sell is 40 pounds!

Grinding materials


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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1373472 - 01/20/07 06:42 PM

While we are on the subject, would anyone care to offer an opinion as to why glass tooling is better for grinding a mirror than the more popular ceramic tiles?

Is it better?

Newport offers tooling blanks precurved to match the RC of the precurved mirror blank.

However, the only time I see these purchased is for the Mirror Making event hosted by the Del-Marva Star Gazers. It's a fast paced, get-it-done-in-3 days event so they haven't time to pour tools. No one else I know uses pregenerated glass tools.

Thanks

Art


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Stefan Rostyne
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Reged: 10/19/04
Posts: 1026
Loc: Assenede, Belgium
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1378233 - 01/23/07 05:13 AM

Quote:

Is it better?





It depends on what you define as better. I heard glass tiles give cleaner surfaces, less scrathes etc. But it's slooow, especially if the glass tile is of a softer glass than the mirror.

The advance of full ceramic tiles, iron tools and so on is speed : these are harder and bite faster through the glass.

I have made now 3 mirrors with full ceramic tiles and I don't see a reason to use anything else. -though I like the idea of glass tiles.

For our new mirrors we are even going to use copper 5-cent coins for smoothing.

--------------------
Stefan Van de Rostijne

4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
22" f/3.5 dob project


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Art Bianconi
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Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Stefan Rostyne]
      #1378544 - 01/23/07 10:51 AM

Last night I went to our bi-weekly mirror making session at Gordon Waite's optical lab and I discussed my intentions.

He reminded me that once-upon-a-time, when you ordered a mirror blank, two pieces of identical Pyrex would arrive. You chose which would be the mirror.

"The smart ones would make a seperate grinding and polishing tool instead and the remaining second blank would one day become another mirror."

Making sure the tool doesn't stick to the mirror was also discussed.

Tile tools can easily be grooved in between the squares with a Dremel or similar tool. This allows are to get in between the two.

This helps prevent vacuum from locking the two together, especially as the tool conforms fully to the mirror and when the grit get finer.

How easily I can cut groves between the circular gems will be tested.

I will make my Gem Stone-Casting Resin tool today. I will tumble the glass first in a drum with 80 grit to remove the polished surface, then proceed as usual. I'll take pictures.

Whether or not this tool will prove better or not, remains to be seen. It may turn out that the only advantage it has, if any, is the ability to see through the transparent resin to where the action is occurring. If Glass Coins were available off-the-shelf, I'd have gone with them instead. Trepanning is not a problem for me. However, right now my time is limited and I need to get cutting with glass sooner, not later.

Art


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waynet
professor emeritus


Reged: 04/20/05
Posts: 666
Loc: Oklahoma, USA
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1378570 - 01/23/07 11:00 AM

Maybe once upon a time isn't so long ago. I bought a 10 inch kit from Will-Bell last year which came with 2 identical pyrex blanks. I am currently working on the second one.

Wayne


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Moki
super member


Reged: 11/06/05
Posts: 474
Loc: Under the Clouds
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1378737 - 01/23/07 12:42 PM

Art, you may want to consider glass tiles. I don't know if you've looked at these before but I remember seeing some in a tile shop when I bought the hex ceramic tiles I normally use. I wondered then how they would work for grinding tools, especially fine grinding.

The glass tiles shown in the link appear to be mounted to a flex substrate which would make it easy to cast a Hydrostone or dental plaster tool. Unfortunately the price isn't listed.

http://www.mglasstile.com/catalog/item/360022/494685.htm

I also saw numerous other suppliers of glass tiles in the 1" round and square size on the web.

--------------------
"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." Galileo

12.5" F5.3 Dob on EQ platform
8" F7 planetary Dob / EQ Platform

Current ATM projects:

10" F5.5 Verylight PushTo - Finally done!
Lightweight computer-controlled EQ platform for the 10".

...and a 16" F4.5, eventually (I've got the blank!)


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Art Bianconi
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Reged: 03/06/06
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Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror tool new [Re: Moki]
      #1378817 - 01/23/07 01:36 PM

Great site Moki!

Thanks.

Arrived just in time too. I was about to go downstairs into the shop and start pouring!

I'll call, get pricing and then decide. A one dollar bag for the round gems at Michael's, will cover a tool for a six inch mirror with some left over. I doubt the squares will be as inexpensive but if not too much more costly, I'll likely go for them instead.

Thanks for the support!

Art


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Art Bianconi
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Reged: 03/06/06
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Re: Source of small glass "tiles" for a mirror tool new [Re: Moki]
      #1381965 - 01/25/07 01:35 AM

Moki, I called that resource you suggested after looking at their web site. I'd actually ordered two square feet of glass tiles and was about hang up when I remembered to ask "How much will that come to?"

I almost fell off the chair when he responded "about $56.00"!

Normally those glass tiles go for $30 a square foot. He was giving me a break but still I had to cancel the order.

I completed the 6.5" tool Tuesday evening using those glass gems. Worked out fine. I did the first pour of casting resin to cover the glass gems. Allowed it to cure some. Placed a pipe flange in the middle and then did a second pour of casting resin to cover the flange and lock it in place.

I will do perhaps an hour of grinding on the motorized bench with 80 grit tonight (Thursday) and report back.

I did take lots of pictures while making the tool. Except for the materials used (Glass gems embedded in clear casting resin) there's nothing novel about the device.

Expect a show and tell soon.

Art

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Moki
super member


Reged: 11/06/05
Posts: 474
Loc: Under the Clouds
Re: Source of small glass "tiles" for a mirror tool new [Re: Art Bianconi]
      #1382240 - 01/25/07 08:28 AM

Quote:

Moki, I called that resource you suggested after looking at their web site. I'd actually ordered two square feet of glass tiles and was about hang up when I remembered to ask "How much will that come to?"

I almost fell off the chair when he responded "about $56.00"!

Art




Ouch! Yeah, that's a bit much for something you're going to grind away anyhow. Guess I'll stick with the hex tiles for now.

One issue with glass tiles that I didn't think of until later is cutting the edge tiles to fit the tool. With ceramic tiles nippers work great and you get clean cuts. I don't think that would work with glass tiles, though. With the small gems you're using I bet trimming isn't necessary.

Good luck with the glass gem tool. It'll be interesting to see how it works out.

--------------------
"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." Galileo

12.5" F5.3 Dob on EQ platform
8" F7 planetary Dob / EQ Platform

Current ATM projects:

10" F5.5 Verylight PushTo - Finally done!
Lightweight computer-controlled EQ platform for the 10".

...and a 16" F4.5, eventually (I've got the blank!)


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jgraham
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Reged: 12/02/04
Posts: 11575
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Re: Source of small glass "tiles" for a mirror tool new [Re: Moki]
      #1382418 - 01/25/07 10:37 AM

For my 16.5" (ground, polished, and figured by hand) I roughed out the curve with a 9" tool, then made a full-face tool using ceramic floor tile set in blocking pitch over a couple of layers of plate glass foundation. It gave all of the illusion of working pretty well.

-John

--------------------
-John

The best advice on imaging I've ever been given... don't forget to look!


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Art Bianconi
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Reged: 03/06/06
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Re: Source of small glass "tiles" for a mirror tool new [Re: Moki]
      #1382568 - 01/25/07 12:05 PM Attachment (29 downloads)

The glass tool is done and initial tests suggest it will work just fine. I didn't do anything novel as far as I can see. The tool is made just like countless others before it.

1. I cleaned the blank, covered it with aluminum foil and smoothed the foil down a little.

2. Then I wrapped it with a long strip of aluminum flashing, tightened a large hose-clamp around it and sprayed some 3M adhesive onto the foil.

3. I distributed the glass gems around the interior in a random fashion and did what I could to fill all the voids. The gems are, of course, flat side down and once in position, I simply pressed them down to make sure the adhesive held it in place.

Then I poured the first level of catalyzed casting resin sufficient to cover the gems plus about 3/8th inch more.

I placed a prepared pipe flange in the center as close as I could using dividers and then continued with a second pour sufficient to covert the flanged area but not the center post. I waited about 20 minutes before pouring the second lap.

4. Shows the finished result with the clamp and aluminum flashing removed and the part waiting for separation from the blank. A light punch with the palm of my hand was all that was needed.

The use of two seperate laps was deliberate. I know from past experience that mixing too much of any resin can cause a "run-a-way" or exotherm whereby the resin temperatures get out of control. The stuff can get so hot it can burn you!

Epoxies and resin systems that cure too quickly cause a rapid and uncontrolled shrinkage. This often causes fractures like those you see in the surface of ice glaciers. Splitting the two pours helps prevent that.

After the second pour had started to harden, I placed the entire assembly under an Infra-Red heat lamp about 20 inches above the unit and cooked it some more. This was more to hurry up the process than anything else as it would have cured well without the added heat.

You can tell when resin systems are properly cured with a scratch test. A sharp object (an awl or machinist scribe) dragged across the surface will make a distinct scratching sound and produce white dust or chips. An improperly cured resin will produce no sound to speak of and produce a gummy build up.

4. Here the aluminum flashing has been removed and the tooling is ready for separation from the glass blank.

Cured casting resin will tolerate extreme heat. I've been making custom position lights for aircraft for decades from this material. During a test, the phone rang while I was conducting a heat test. I got distracted and didn't look at what was going on until I smelled something burning. I looked over at my bench and saw plumes of smoke rising from the lens.

When I hung up and intervened, I noticed that the lens was fine. It was the wood topped bench that was burning from the heat of the 60 watt tungsten-halogen bulb inside the lens.

One of the reasons I built such a broad speed range into my polishing bench was so I can one day spin cast a mirror from this same casting resin. It's extremely hard and while it may not have the same expansion rate of Pyrex and other substrates. it takes a polish well.

There will be questions to be answered like what happens it if gasses under vacuum. As for the tooling, it will be nice to see the action taking place at the surfaces under the tool, without having to place the mirror on top.

Clear Skies!

Art

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kingjamez
scholastic sledgehammer


Reged: 10/03/06
Posts: 996
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Re: Source of small glass "tiles" for a mirror too new [Re: Art Bianconi]
      #1382614 - 01/25/07 12:29 PM

Looks cool. So no MOT for you?

-Jim

--------------------
C8 on Atlas with EQMOD
ETX125 UHTC
Celestron Onyx 80mm
Meade Walmart 60mm guide scope
Canon Xsi Modified w/IDAS LPR
Gen 3 NightVision Eyepiece
Aspiring Optician
Watch my Wiimote control Atlas:
http://www.youtube.com/watch?v=PnmkygmGNiM


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Art Bianconi
Post Laureate


Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
Re: Source of small glass "tiles" for a mirror too new [Re: kingjamez]
      #1382659 - 01/25/07 12:49 PM Attachment (24 downloads)

Jim wrote: "Looks cool. So no MOT for you?"

I try to avoid MOT whenever possible. Sometimes it simply can't be avoided, like when making a pair of matched mirrors on a Schief or when correcting a curve.

My discomfort stems from having seen too many mirrors slip from the hands and go crashing to the floor. The tool can always be replaced. Not so easy the mirror.

Art

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--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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