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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 372
Loc: UK
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I have been making telescopes since William the Conk invaded Saxon England and in that time have learned a few tricks and wrinkles. I developed a method of cracking out slabs of glass from a large sheet. The method is good for thicknesses from about a 1/4 TO 1/2 inch thickness. You need a small hand held butane gas cylinder fitted with a needle jet burner. Mark out the line of the crack with a felt tip merker and light the jet then adjust the flame to the smallest needle you can get. Play the jet up and down the line until the plate cracks; it goes with a gentle click. You must try the technique with scraps of glass first until you have developed the skill. Do not use old glass as this becomes crystalline with age, and it with not break well. 
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Montana_Nights
member
Reged: 04/19/09
Posts: 78
Loc: Ennis,Montana
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Huh, interesting. I'd like to try that. Do you have any pics of one of the cutouts?
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Southwest Montana Astronomical Society, Bozeman Montana
My Kit:
A "new to me" Celestron Celestar 8
25mm and 10mm widefield EP
2x barlow
Various filters and accessories
Many, many books
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 2271
Loc: Kent, UK
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Hi John, how do you guide the 'vent' once it starts to run? doesn't it try to take the shortest route to the edge?
I've run a hot iron behind a cut (wheel or diamond) when restoring stained glass but never tried a naked flame.
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
PST
DSI 1
and a curious mind
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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Interesting technique - thanks.
How long a cut have you made that way? And no need to score with a glass cutter first?
Gary
Edited by Gary Fuchs (10/07/09 10:27 AM)
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 372
Loc: UK
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Hi John, the vent is straight, I have never tried to guide it in a curve. The impingment of the flame is very local, and the glass expands to the point of breaking along the heated portion as this becomes a stress raiser. I use the technik to cut glass into slabs before trepanning the disk out of it. Sometimes the glass will break awkwardly, so it is not a 100% cert. Gary, I have broken lengths up to 18 inches long, recently I cut up a 22 inch diameter disc, 1/2 inch thick along chords to produce sectors for further break up. You can score with a diamond, but I have recently found that there is no need to do this. If the glass is stubborn then scoring and heating with a squirt of water will crack it.
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Crayfordjon
Inventor
Reged: 06/17/09
Posts: 372
Loc: UK
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Montana nights. HI, I have not taken any pics of the process but it might be a good idea.
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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Thanks John
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 666
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Did not JAMES BOND use that to break in someware?? ha ha
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