"Gingery" glass working lathe

I doubt you need a machine *anywhere* near as stiff as a metalworking lathe. Just a slow turning, sealed spindle as far as I know. The only forces present are bearings, the flame and pressure (plus or minus) inside the glass, no? And the flame needn't be positioned within thousandths of the glass surface either.

Tim

-- "I have misplaced my pants." - Homer Simpson | Electronics,

I also saw your post on rec.crafts.glass.

Bear in mind that when the glass gets hot, unless both ends of the tubing are being driven at the same speed, the glass will twist (friction on the "free"end). A year or two ago, I saw a basic plan that used 2 identical servo (or was it stepper?) motors to drive the tubing - one at each end. Don't remember the web site, but a Google search should turn it up; try it on the Google Groups search first.

What do you want to accomplish that requires a lathe? Most glass work can be done by rotating the piece with your fingers. It probably would take less time to acquire that skill than to build a lathe. Of course, if I could get a glassworking lathe, I'd love to have it...

Joe

Allan Adler wrote:

I wouldn't say it was impossible, but the ones I've dealt with were a good deal larger, like about 2' swing or better. They also had two headstocks at the opposite ends with matching chucks and the rotation of each was synchronized with the other end. This last would be the hard part without using stepping motors or selsyns. Worm drive with some sort of speed-sensing control electronics, maybe. HP requirements would be pretty low, all you are doing is turning the chuck and workpiece, there's no cutting forces involved. It's been awhile, but IIRC, the through-holes in the spindles were pretty good sized. One suggestion for the bed would be to use large steel tubing, ala Shopsmith, and the same sort of locks for the sliding parts that are used on it. Except for the chucks and drive train, I don't think it would be too tough to make up a moderately-sized glass-blowing lathe.

Stan

The one's I've seen, some very old, just have the head stock and tailstock geared together with a shaft or with pulleys and shaft -- just keep the heat away from the belt. As said in other posts, there's very little force involved and speed is generally quite slow. There are lots and lots of burners, though; and plenty of steady rests and such.

Well I take if from all the comments that everyone is talking about taking a piece of fairly molten glass and chucking onto a lathe.

Curious question....... Could you put a cold piece of glass on a lathe and go from there.

Or am I totally reading this wrong.

How can you all tell I'm just an armchair lurker getting a free education.

Nope. Glass lathes are designed to allow pieces of glass tubing, etc, to be chucked up - sometimes from both ends - and worked with flame while they are spinning.

The 'chucks' are metal fingers that ride inwards, and have insulating fingers to hold the material when hot.

For example, one could chuck up two different size pieces of tubing, or tubing of two different materials, one in each chuck, and effectively weld them together with flame while they are spinning, so as to maintaine alignment.

Jim

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Thanks for clearing it up and making it as clear as glass.

Nope. I've used a couple of stepper motors duct-taped to a plank, for joining a couple of tubes. Worked just fine.

Joe, the only glass lathes I've seen were at RCA Sarnoff Labs when I worked there circa 1956. The characteristic that all of these glass lathes had in common was a headstock and a tailstock that were both powered an rotated in the same direction at the same speed. No metal lathe that I am aware of is capable of this trick.

I have no idea who manufactured these unique machines, but the work that came off them was truly remarkable and included some fantastic vacuum tubes, chemical apparatus, and even (under the counter) Christmas Tree decorations.

Now, 50 years later, I would like to learn about these unique machines, who made them, and maybe even how I could find one at a reasonable cost to put in my workshop.

Harry C.

In the 1960's and 70's when I worked as a scientific glassblower, we used glass lathes all of the time to make 3 stage diffusion pumps etc. The two most common brands were Litton (best) and Bethlehem (light weight and cheaper). There were a few other brands available - one nice one made in New Jersey and several from Germany.

The drive system was always variable speed accomplished by a variety of methods. This is necessary as the speed can be used to control wall thicknesses when sealing the tubing. The motor drove a splined shaft. The head and tail stocks were connected to this shaft by a timing chain (slack could be adjusted out by a snubber bar). There can be no slop (backlash) or the seal would devitrify or even break on cooling.

The tailstock must move in order to make a seal. There was always a crank on the tailstock to drive the movement and a gear rack under the bed. The bed was covered by a heat protective stainless steel sheet which passed through the bottom of the tailstock. For heat we used movable surface mix rack burners on the lathe bed, hand torches, or a Carlisle CC mounted on a movable stand. Fuel was high pressure natural gas, propane, and/or hydrogen depending upon the job. Oxygen was always used.

Most of the items we made utilized borosilicate glass with a relatively low coefficient of expansion. Sealed glass must always be annealed to remove stresses caused by the heating. There is much more to glass working than merely making the lathe. Larger tubing requires a glass saw for cutting. A wet belt grinder comes in handy. HF is often used to clean fresh cut tubing ends before sealing. Various graphite paddles and tapers will be needed. Heat resistant gloves are a plus!

A large part of glass lathe expense is the various chucks for holding the tubing. Some were even 6 jaw (2 separately operating 3 jaw chucks in one chuck) for holding a tubing in position within another piece of tubing. We used to shim everything with (dare I say it?) asbestos tape. The through hole was at least 4" on most of the lathes I used.

A good glass lathe is not cheap and would have very limited use without all of the required associated equipment. Jim

The best part is seeing one of those large 'strain-O-scopes' which are crossed polarizers. The part is placed between the two sheets, and any areas with strain still in them light up in all kinds of patterns.

Jim

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One of the things one sometimes has to do when glassblowing by hand is to force air into the tube. In my extremely limited experience, this was done with a cigar holder attached to one end of a rubber tube and the other end of the tube attached to the glass, with corks used to stop up other openings in the glass. You can use the air pressure to keep the glass from collapsing or to force it to expand outwards, depending on one's need. I think that arrangement would be a little awkward with a glass working lathe. Does the lathe chuck have a feature that allows air to be forced into the rotating glass tube?

A glassblowers' swivel is used - usually with plurostoppers (nesting multi sized rubber stoppers). Jim