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Old 09-27-2017, 12:42 PM
Scott Benefield Scott Benefield is offline
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Cracking off/fire polish

I'm trying to work out a line of mold-blown tumblers that are cracked off and fire-polished. The cracking off is pretty easy, followed by a quick wet grinding, but I'm having trouble getting the thin (2mm) lip fire-polished without shocking it.

I've seen it done in factories (ring burners) and I watched Dan Mirer do it with a very homemade set-up years ago, but I wasn't paying close enough attention to detail (apparently) and I've been breaking too many. Does anyone have experience with this--what kind of flame, tip, distance, etc. works for you?
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Old 09-27-2017, 04:58 PM
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Someone posted this video a while back, maybe it will help:


https://www.youtube.com/watch?v=Jqj1Q7w4EEE
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Old 09-27-2017, 05:07 PM
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Do they have cane/murrine work in them?
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Old 09-27-2017, 06:14 PM
Eben Horton Eben Horton is offline
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Scott - get 2 old record players. On one player set up a torch with a bushy flame that gently brings the lip up to temp. On the second player, have a more agressive flame.
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Old 09-27-2017, 07:38 PM
Marty Kremer Marty Kremer is offline
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33, 45 or 78?
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Old 09-27-2017, 09:54 PM
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I do it on my lap wheel with and old resin disk that is worn out. I used some playdo to crate a U shaped guide that lets me slide it in place while it is spinning with ease.

Then I set up a forked ribbon burner national. So two ribbon burner heads that are 6 pin sized jets. I have the burners on a swivel so I can put them in place.

I drop the glass on, hit it with a hand held bottle of map gas set a little from full tilt for about 10 seconds, then pull the ribbon burners down. Round that dog out, pull it off and set it on the table.

Then I slow ramp them up to annealing temp in the annealer when they are all done and let them soak for 2 hours then normal ramp down.

I have more breakage on the hop pop than the lip polish. I use the same set up for the hot pop but I use a single pin tip instead of the ribbon burner.

I think I can hot pop about one every 20 seconds and fire polish takes about 30 seconds so about a minute each to be safe. I think I lose 1 in 20. My personal best for not having one bust was 43. I bet I have done about 800 like this by now. Give or take 10.

Last edited by Scott Novota; 09-27-2017 at 09:56 PM.
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Old 09-28-2017, 12:39 AM
Scott Benefield Scott Benefield is offline
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Thanks everybody, I'll try a two-step process for flame polishing. It makes sense, although hitting a cold piece of glass directly with even a small flame still feels very wrong to me.

That was Dan Mirer working from the Corning shop in the video, Rich, and then doing the finishing in his off-campus studio. Dan is very, very good--a skilled glassblower, especially with the production of multiples, but he also makes inventive and unfussy tooling.
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Old 09-28-2017, 08:40 AM
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Quote:
Originally Posted by Marty Kremer View Post
33, 45 or 78?
*******
33. I even can turn mine on and off with the tone arm. It's really ancient.
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Old 09-28-2017, 01:41 PM
Eben Horton Eben Horton is offline
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Quote:
Originally Posted by Scott Benefield View Post
Thanks everybody, I'll try a two-step process for flame polishing. It makes sense, although hitting a cold piece of glass directly with even a small flame still feels very wrong to me.

That was Dan Mirer working from the Corning shop in the video, Rich, and then doing the finishing in his off-campus studio. Dan is very, very good--a skilled glassblower, especially with the production of multiples, but he also makes inventive and unfussy tooling.
Dan M's set up was 2 turn tables. Each turn table had a pipe that has a slide that could move up and down with a locking mechanism and another pipe on that with a locking mechanism
That would hold a national torch. He used the tips that looked like a fish tail.
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Old 09-28-2017, 06:01 PM
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I found that setting the torch for fire polish was not hard but small ones made it time consuming. Too Big? It makes the glass ball up. I don't think they need very long at annealing point at all, based on my polariscope readings. If they aren't thick, 20 minutes satisfied the strainoptics unit. Then bring them down. So far, I even have glasses that did not go through reannealing and have been used a lot that suffered no checking.
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Old 09-29-2017, 03:15 AM
Durk Valkema Durk Valkema is offline
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Scott,
You need to preheat the vessels and deheat them after the firepolish.
If you develop a thick ring you heat to much, not much heat is needed.
In industry they use a carousel of revolving tables. The top part covered to keep the heat. Opposite of where you place the cold glass and eventually remove the polished pieces you have a propane torch heating the rim. the cover directs the heat generated there to either side to preheat and deheat.
I got an old machine for the Hoglund studio in New Zealand years back. They might still be around if you search.
Otherwise make a hand operated inline one with a turntable/flame in the middle. Key is they need to be pre/de heated.
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Old 09-30-2017, 05:54 PM
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2mm thick lips are probably the maximum thickness I would want to fire polish after hot-popping. 1mm fire-polishes like a dream

Don't know if this video link will work but I spend a lot of time pre-heating my cups before I really fire-polish them. My hot-popping machine has 3 little burners that preheat before I come in with my hot-torch, then I flash it down (kind-of) with the hot-popping machine after I'm done.

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Old 09-30-2017, 06:05 PM
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The goblet polishing table we had had a big turntable that had 7 smaller turntables on it. Each turntable sat in a heated muffle (sheet metal tunnel that had a small flame) right before their turn to be polished. Maybe a min each... just enough to make the heat transition very wide, not just a tiny band on top
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Old 10-01-2017, 02:57 AM
Scott Benefield Scott Benefield is offline
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The Essemce machine is nice; you can still get them for about 2500 Euro. Is that a carbide scriber on the right turntable in the video, which isn't automated? And then the small burners on the automated turntable are for cracking off and pre-heating before the fire polish?
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Old 10-01-2017, 04:56 AM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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I can't see the video but no its just two popping off tables to make the job go faster.
The edge melting machine is what Durk is describing
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Old 10-04-2017, 09:22 AM
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Quote:
Originally Posted by Scott Benefield View Post
The Essemce machine is nice; you can still get them for about 2500 Euro. Is that a carbide scriber on the right turntable in the video, which isn't automated? And then the small burners on the automated turntable are for cracking off and pre-heating before the fire polish?
Hi Scott! Yes my Essemce machine has a non-motorized turntable on the right with a scribe and a motorized turntable on the left with the burners. You can get models with more turntables however I have the basic one which I bought used. The scribe looks to be a carbide steel rod or tungsten? ground to a point and press fitted into a mild steel rod. The left side has 3 fine burner tips. The adjustable arm is good because when you raise one you raise both so there is no messing around trying to get the torches lined up with the score mark and again for fire-polishing. I finish my cups in 4 stages, first hot-pop, then light linish on the belt-sander, fire-polish with the hot-torch and finally re-anneal in a kiln.
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File Type: jpg HotPopMachine.jpg (36.1 KB, 48 views)
File Type: jpg HotPopMachine_FirePolish.jpg (29.6 KB, 49 views)
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Old 10-04-2017, 02:06 PM
Scott Benefield Scott Benefield is offline
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Thanks, Jacqueline, that's very clear and seems to be a fairly simple approach, too. Simple is best until you get into big numbers.
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Old 10-04-2017, 07:48 PM
Art Freas Art Freas is online now
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The Essemce glory holes are definitely on my lottery list.
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