Cutting glass tube problem

[tabbypurr]

I want a nice clean cut on glass tube. So I found the way to do it, apparen tly, is to use thread & fuel, light it, then dunk it in water. I've tried t hat over & over... and nothing happened whatever. Even 100 turns of sewing thread and a double burn with lighter fluid did absolutely nothing.

So next I tried an ad hoc lathe arrangement with gas flame. Got it good & h ot, plunged it in.... this is what happened!

Anyone know what/why/ how to moev forward? The cut does need to be clean re peatedly, so the methods that produce all over the place cuts are no good.

NT

[tabbypurr]

ently, is to use thread & fuel, light it, then dunk it in water. I've tried that over & over... and nothing happened whatever. Even 100 turns of sewin g thread and a double burn with lighter fluid did absolutely nothing.

hot, plunged it in.... this is what happened!

repeatedly, so the methods that produce all over the place cuts are no good .

It's thin walled 1" tube

NT

[newshound]

What's the tube diameter? For 6 mm or so the technique I would use would be to score a nick at one point with a triangular file. You then heat a glass rod up in a flame and hold it against the nick. If the temperature is right you will hear a "crack" sound, and generate a through-wall crack over perhaps 30 degrees. You then repeat the process "leading" the crack until it goes all the way round. At this point it will still hold together, but will snap easily along the crack if a bending moment is applied.

For much bigger tubes you can use more normal sheet glass cutting technique: mark all the way round with a glass cutter, then tap to generate the initial crack and propagate it by judicious tapping in the right place. You can also use the "hot rod" technique.

Ah, just looked at your picture. This is a fairly thin-walled tube. Cancel what I said above, the second won't work and the first is doubtful.

I suppose you might be able to cut it with a thin abrasive disk on a Dremel, but I would not expect a very high success rate.

[Adrian Caspersz]

Looks like a lamp bulb. Any difference releasing the vacuum before starting the cut?

[Fredxxx]

That may be quartz glass, which has a very low expansion coefficient, far less than borosilicate glass (Pyrex).

So thermal shock is less likely to work.

The usual technique, with conventional glass, is a loop of hot wire, heated by an electric current.

[tabbypurr]

I don't there's any likelihood of that, the thing's a good foot long and only 30w. The picture may not indicate scale.

Yes. I want to avoid putting that equipment together if I can. The less I can do it with the better - and I'm ready to push that as far as I can.

NT

[Syd Rumpo]

It's not quartz is it? You can tell with a blowtorch, it would get red hot but not soften. I guess not if it's 1" diameter, but it could be Borosilicate (Pyrex) glass which would also be problematic and wouldn't work with the thermal shock method.

I'd try turning it in the lathe while grinding with a Dremel.

Cheers

[tabbypurr]

arently, is to use thread & fuel, light it, then dunk it in water. I've tri ed that over & over... and nothing happened whatever. Even 100 turns of sew ing thread and a double burn with lighter fluid did absolutely nothing.

& hot, plunged it in.... this is what happened!

n repeatedly, so the methods that produce all over the place cuts are no go od.

The people that will end up doing this have no access to anything like drem els or lathes of any type. If it proves the only option I can use something rudimentary as a lathe, but a dremel is not possible. I guess I should hav e said that upfront, I just assumed there was a basic way to do it.

I've seen people cut fluorescent tubes with thread fire & water, I assumed a tubular filament lamp would be the same. Maybe not.

NT

[Syd Rumpo]

Just thinking out loud, but how about thread or string dunked in some sort of abrasive slurry then wrapped around the tube once and used with a sawing motion?

I've cut wine bottles with the thread and fire method, it does work, so I suspect your glass isn't ordinary. Another thing you can do with thin sheet glass is cut it with scissors underwater - can't see how that helps, but who knows.

Cheers

[RJH]

Or fine diamond wire in a wire saw? Not tried it mind, and not exactly the type of thing to have lying about.

[Malcolm Race]

Aeons ago when I was a student I was taught some basic glassblowing skills. I was taught two methods of cutting pyrex tube.

1 make a small nick in the tube and dampen it with spittle from your finger . Heat a piece of pyrex glass rod until the end is almost molten and touch it onto one end of the nick. A crack should propagate around the tube and it will then be easy to separate the two halves. 2 As 1 but instead of the hot glass rod grip the two halves firmly and apply a (considerable) sharp downward and outward pressure. I used this to break 2cm diam medium wall pyrex tube.

These methods work with pyrex and soda glass - anything harder & its worth a try

Malcolm

[tabbypurr]

pparently, is to use thread & fuel, light it, then dunk it in water. I've t ried that over & over... and nothing happened whatever. Even 100 turns of s ewing thread and a double burn with lighter fluid did absolutely nothing.

od & hot, plunged it in.... this is what happened!

ean repeatedly, so the methods that produce all over the place cuts are no good.

dremels or lathes of any type. If it proves the only option I can use somet hing rudimentary as a lathe, but a dremel is not possible. I guess I should have said that upfront, I just assumed there was a basic way to do it.

med a tubular filament lamp would be the same. Maybe not.

I'm beginning to wonder that too.

I'm liking that.

NT

[Capitol]

How about a diamond saw tile cutter?

[Dave Plowman (News)]

I'd have a go with a wet tile cutter. Check the blade is perfect and take it very gently.

[tabbypurr]

I have tried a wet tile cutter on glass before. It cuts but also tends to b reak lumps off.

But anything above £1 is pretty much out of the question. The people will not be able to afford it. I've made a lathe of sorts from a bit of bent me tal. I suspect at this point the way forward is a bit of grit to score it a ll round, and see if it'll break cleanly with the help of heat. I'm not fil led with optimism.

NT

[Dave Plowman (News)]

Yes. I suspect you'd need a very fine diamond coated blade. But any 'snap' isn't going to be perfect, either.

[tabbypurr]

no, but the closer I can get the better. The glass will then be hand sanded to finish.

NT

[Dave Liquorice]

I was wondering that with the vacuum in tact it has 15 lbs per square inch holding the tube in fairly hefty compression. It's an ordinary filament lamp I don't think there is anything particulary special aboout the glass.

[tabbypurr]

If there isn't, and I wouldn't expect there to be, how come 100 turns of thread soaked in lighter fluid & burnt twice followed by a dip in cold water doesn't affect it?

NT

[Brian Gaff]

Those awfully skilful glass blowers seem to have something like a tube cutter that just scores the tube, they then just tap it and it comes off clean. Very clever if you can do it.

Brian