Bending Pryex Tubing

DrugPhreak · Working Bee

What's the best way to bend Pyrex tubing? SWIDP used wash bottles and pre-bent glass tubing for gassing in the past, but they would like to bend their own from now on. SWIDP has 24" 6mm pieces of tubing and a small blow torch, but the tubing never turns yellow and softens enough to bend it. Confused

Also, what's the best way to cut the tubing... a tubing cutter was purchased, which doesn't work too well in SWIDP opinion.

2spun · The Resistor

DP,

how hot is your gas? or what tpye are ya use'n.

score your glass where you want it to break hold with both hands, can use gloves.
swiy use's old rag or some pices of leather he has around. apply pressure,
snap
swiy belives he has a pic off this prosess. waite one he'll try to dig it up

DrugPhreak · Working Bee

Hey 2spun! Wink

The tubing SWIDP is currently bending will be used for gassing non-polar/freebase with dry hydrogen chloride. I think SWIDP jacked up the blade a little bit so it's not scoring too well anymore. Well... this is SWIDP first time trying this and they will probably have to get another blade already... lol. SWIDP is looking forward to that picture tutorial.

2spun · The Resistor

DP,

hey back!
swiy can not seem to find his pic's ect.. right now but this is off the web.
it's in MSword swiy really don't like that but it's what he has for now..
if DP don't have or use word. say so swiy maybe able to change it all around..

Techniques that are commonly used in simple glass-working operations

http://rapidshare.de/files/2764019/techniques_that_are_commonly_used_in_simple_glass-working_operations.doc.html

swiy has some small triangle file that he use's to score his tube before breaking

DrugPhreak · Working Bee

That's a nice document there... thanks a bunch! Wink

primathon · modified

To cut pyrex rod/tubing, follow these steps:

1) Score a groove at least 1/4 of the way around the rod/tube where you want your cut to be. I use a silicon-carbide edge, which is way better than those useless fucking glass cutters you'll find at Ace with the little wheel on the front. Those work OK for cutting flat glass, but they've got no place here. Cut hard and deep, make sure you make a straight cut, and don't breathe any glass dust that comes wafting up. If you make a deep cut, it doesn't have to be that long. I find it works best to hold the carbide edge in the pointer knuckle of my right hand, squeeze the tube tightly, and rotate the tube with my left hand to get an even cut.

2) Lick your thumb and wipe the cut with spit. From here you can go one of two ways: a) Hold the tube with your hands on either side of the cut, with your thumbs almost touching each other, about 1/8" from the cut. If you have a small piece of glass, you may try bracing the opposite side of the cut against the corner of a wooden desk or benchtop, press, and it should snap cleanly in half. If your piece of glass is larger, then you get to do it the easy way. With your thumbs in position, bring the tube up under your arms, so your elbows and forearms are resting on top of it. Then it's a simple matter of pushing your elbows down slightly, while raising your hands a bit. It takes far less force than you'd think it would, and it's a nice clean cut every time (with practice). Keep your face away from it when it snaps; sometimes it sends teeny glass shards airborne at great speeds. Bad for your eyes, y'know?

If you have access to a torch, you can opt for method b), which involves molten glass, and is therefore awesome. Start at 2) above, but this time, put a big-ass glob of spit on the cut. No, more than that. A little bit more. Okay, there. Looks gross, huh? Well, it is, I guess. Anyway, take a section of glass rod (6-9mm usually works best), and heat the tip until it's white hot. This next step you have to do fairly quickly, so pay attention. You're going to press the molten glob of white-hot glass into the center of your cut, which you've liberally covered in spit. While you're doing this, raise the far end of the tube a bit so that as you press down on the tube, you're countering it by raising the end, and therefore helping the glass create internal stresses and snap easier. You'll want to take the rod from the flame to your tube as fast as possible, and press fairly hard. It will probably squeal at you when you do this, due to the spit boiling off incredibly rapidly in between two glass pieces under pressure. I think it sounds neat. If after about a second, if the glass hasn't started cracking, feel free to move the hot rod around the circumference of the cut to help the fracture progress. As before, when it snaps, it will be quick, and if you've done it right, clean as well. This method takes a bit of practice to get to work right, as it is kind of finicky. The other method is usually preferrable, but this one works pretty well if you're cutting large diameter, thin-walled glass.

Hope this helps.

primathon · modified

Additional information on Pyrex [borosilicate] glass can be found here.

As for how hot your torch needs to be:

Working point = 1,252°C
Softening point = 821°C
Annealing point = 565°C
Strain point = 510°C

DrugPhreak · Working Bee

Thanks for all that excellent info Primathon! Wink

blurcraft · Fri Jul 15, 2005 5:04 am

When working w/ glass always remember:
A) Every time it is subjected to broad temp. change (eg: heated and cooled), it is weakened to some degree...that said, the usual amount of stress caused by everyday usage of pyrex on a hot plate, etc. is negligable(sp?). But anytime it reaches the stress point (like, ~>500c-- around 510c, I believe...Not sure tho. Swim's been working w/ Kymax lately and the specs are slightly different...) and especially breeches the annealing point (I wanna say 560c, cuz thats about it for Kymax, but double check that earlier post in this forum for the right specs, not that yer gonna have a thermo. in the flame or anything... Wink

), two things have to be considered. 1) any glass that seems to be touching other glass (it isn't really, unless it's a smooth flow str8 thru between em) as it begins to cool (eg: a fold or a crack)will have to be annealed BEFORE cooling. the easiest way to make sure it's safe is to turn the glass at an acute angle (not too close to the ol' face tho...unless you LIKE the smell of burning flesh) so that you're looking into the glass ~laterally along the the surface plane, rather than across it. this is much easier with tubing and other curved pieces. Now slowly move the glass around and view the troubled area very closely from different angles. look for a definitive line or "wall" as it would appear from the angle you're at. if its just a bit of a warp or looks wavy, give it a little heat to almost the softening point and you should be good to go, BUT...
B) anytime you make broad changes in the temp of glass, it needs to be done very S--L--O--W--L--Y. This is actually not usually true w/ heating if you know the technique, but ALWAYS for cooling. As glass cools, the outside does so faster than the inside, and therefor the different cross sections contract at different rates. If there is too much difference in the rate, it'll violently crack/ shatter on the spot, as cooling, HOWEVER no matter how slowly it cools, they still contract at different rates, no matter how infinitesimal, and therefor create tension between them. I have seen a piece of glass blown and then put carelessly aside to cool at whatever rate it pleased NUMEROUS times. It may be in an hour, it may be tomorrow, it may be a week or a month, but it is GONNA happen: the piece will shatter simply because the A/C kicks on or someone TOUCHES it. So if you have access to a kiln or annealing chamber- super. If not, and you have/can get a working crockpot, plug it in, fill most of the way (~1 inch from top) with vermiculite, turn it on high, wait for it to heat up and when yer done working the glass, give it a couple of secs to drop below the softening point, so it isnt impressionable, and plunge it into the crockpot, covering it all the way w/ the verm. and replacing the lid. After about an hour, turn the crock pot off and leavethe lid on for about another hour. then take the lid off and remove the glass.
I have to go to work right now, but I'll return l8er and tell you how to fix those stars as easily as you can do such things...hope this helps in any way.
~blur~craft~

primathon · modified

The technique you're describing in A) above is called flame annealing, and it takes quite a while (but it does work fairly well). I've had to use that on many occassions when the kiln wasn't ready yet.

The crock pot idea seems like it would be fairly viable, but I think just heating the piece to red heat and immersing it in vermiculite would work just as well. I've heard of numerous glassblowers using that method until they acquired a kiln. Also, refractory fiber blankets are available from various places, and supposedly work quite well. Look into Kaowool (I think that's the brand name...) for a start.

I've gotten good results every time by heating my piece to red heat (just under the point where you can shape it) and then immediately transferring it to your annealing chamber of choice (kiln, fiber blanket, vermiculite, gas range with a metal lid over the burner - in decreasing order of preference) and letting it sit until it's cool. Don't rush this part - I've had pieces explode violently after they were cooled too quickly. Having a very hot and sharp glass shard slam into your goggles, knock your head sideways because it hit so hard, and fly to the other side of the shop is a very sobering experience.