Cass wrote:

Hi,

I am trying to get started into working glass.  I am going to build a
co2 laser and that requires scientific glassworking.  I could farm
this out but prefer to do it myself.
I already have a Smith Equipment "Little Torch" and am planning on
using that with oxygen and natural gas.  I will be working with Pyrex.

Has anyone ever used this torch before?  What about a National 3 a/b
or a Victor J-50?  Any suggestions would certainly be appreciated.

Before I offer you an opinion, let be relate some background.  I presently own a neon sign shop.  I've been blowing glass for years.  I'm trained in scientific glass blowing.  I build all the laser projects in the Scientific American's Amateur Scientist columns back when they were first published in the mid-late 60s.
*** End brag :-)

That said, the very worst thing you can do in trying to learn glassworking is to try to learn with inadequate tools.  With inadequate equipment, you can't know whether your problems are in your technique or in your equipment (or both.)

I have a Little Torch that I use for refrigeration work and occasionally for micro-welding in glass work.  In general, the flame is too small and too intense for glass work.  When the heat is too intense it causes the glass to devitrify (silicon separates out and reverts to crystalline state.  Crystals effectively won't melt.)  Devitrified glass cannot be welded and will likely fracture along the crystal boundaries as the glass cools.  Glass burners really are specialized!  The flame must be just right -not too hot and not too cold.

For soda and lead (neon) glass, a gas/air flame is needed.  For borosilicate, an oxygen-enriched flame is necessary.  Gas/air requires compressed air (abbot 2 psi) and gas.  My air supply is a bank of 3 smog pumps from cars (bought at the local junk yard for $10 ea) driven by a 3/4 horse motor.  This drives 3 large fires (the correct term for glass burners) and several small handheld fires.  One pump should do for you.  For my oxygen supply I use a medical oxygen concentrator.  These things continuously separate oxygen from air using molecular sieves and are prescribed for people with chronic oxygen needs.  You can usually get one used from a medical equipment company.  Medicaid pays many times what these things are worth so after the patient dies, the company will frequently sell the unit cheap.  the oxygen is not pure but you only need about 10% enrichment for glass work.  You'll also need a pressure regulator.  There was a recent (last couple of days) article on the neon mailing list (neon-l@lists.io.com) about how to make a regulator from PVC underground sprinkler pipe.  I made mine from a PVC plumbing check valve.  The one on the net is probably better so check the archive. (you really should be on that list -many world-renown glass blowers lurk there.)  I'm going to try to attach a gif drawing of the regulator if I can figure out this damn windoze mail program (I'm an old unix hack who is lost in the Microsloth world)  You'll still need to read the description from the archive.

You can make burners (I have done so successfully) but they are so cheap from the source that it isn't worth the effort.  The main US vendor is J&P machine & tool company.  This is an ancient, old-line manufacturer of glassworking burners.  Call them at 973 779 6158 and ask for their Industrial Burner Catalog.  Buying from them is a trip.  they don't have a price sheet.  They just kinda make it up as they go.  But they're so cheap it doesn't matter plus once you have bought from them one time, you can remind them of the old price (if it is cheaper) on subsequent purchases.  They don't do credit cards or anything so Snailmail is the thing.  They also make excellent needle valves and venturi mixers.

The most basic burner and the one you'll most likely want to use on the laser project is called the cross-fire.  This consists of 2 banks of 3 to 5 pencil burners arranged so that they point toward a single point.  The heat is very intense and very well defined.  The pencil burner looks just like the head of a simple propane torch.  They cost about $7 from J&P.  J&P sells crossfire manifolds but you can also make one out of a chunk of square steel tubing after you look at the pix in the catalog.  I made mine.  Maybe if I get my scanner working under Windoze98 I could send you a pix of mine.

You'll need a hand-held welding and tipping torch.  I recommend J&P's "V" torch.  This has 2 opposed fishtail burners on a handle.  The burners produce a ribbon of fire and are pointed at each other.  You use this for welding tubing together, fire polishing tubing and making "tee" joints.  You also want to get a hand-held pencil torch.  J&P's single head hand torch equipped with a pencil burner will do.  you use this for the intense heating of a spot on a tube to blow a hole in preparation to making a Tee joint.

You MUST have venturi mixers and accurate needle valves to control the gas and air flow.  J&P makes the best.  A lot of people try to get by without a venturi mixer and simply pipe the gas and air into a pipe tee.  This does not work.  you will chase the mixture every few minutes as conditions change.  The venturi mixer uses the air flow to drag the gas into the flow.  It is almost independent of gas pressure and keeps the ratio constant over a range of air pressure.  set it and forget it.  I've seen people try to use the little needle valves from Ace Hardware with great frustration.  The adjustment is so sensitive that you're fighting against the drag of the stem O-ring.  J&P's valves are wonderful.

Do whatever you have to do to get a copy of "Creative Glass Blowing" by James Hammesfahr & Clair L. Stong (known in the biz as the "stong book")  This is the bible of creative glassblowing.  they cover lampworking, neon, scientific and artistic blowing.  Indeed one of the practice projects is to blow the glass for the SciAm HeNe laser project.  I believe this book is out of print.  Check amazon.com or whatever.  If it is, you can try an inter-library loan (and xerox the book) or perhaps one of the rare book services on the net.  Also get "Neon, The Next Generation" by Dean & Michael Blazek of Northern Advertising (a sign shop).  Dean is a gray-beard in the neon biz and this book is the bible of setting up a neon shop.  Most will apply to what you're going to be doing.   You can buy this from ST Publications, the book division of Sign of the Times magazine.  They're on the net.  You can also buy it directly from Northern advertising and if you do, Dean will autograph it for you!  they're on the net and dean lurks on the mailing list.

When you get to the point that you're ready to think about filling your tube with gas, get back in contact with me.  Most of these projects suggest consulting with a neon shop for the vacuum processing but frankly, most neon benders don't have a clue about processing.  they put out tubes that are dirty and burn out quickly.  This would be vastly too contaminated for a laser.  I can tell you what you need for pumping and where to get the gases.

This should get you started (and my fingers are tired!)  Feel free to ask further questions.

Regards
John

---
John De Armond
Neon John's Custom Neon --- Bendin' Glass 'n Passin' Gas.....
johngd@bellsouth.net