G3YNH.info Workshop

Glass lathe

I did a glass-working course in my final undergraduate year (1981-1982); and in the research lab where I did my final-year project there was a town-gas (mostly methane) and oxygen burner used for fixing-up vacuum lines, etc.. So, for practice, I took to raiding lab rubbish bins for broken Quickfit (ground-joint borosilicate) glassware; and during the long boring periods of waiting for spectroscopic scans to complete, I salvaged glassware parts and welded them together to make usable items. These were mostly things like separating funnels, still-heads and vacuum adapters. Hand annealing was the only option, and so some of it cracked where I had welded too close to cones, sockets and stopcocks; but a lot of it was fine, and I still have some perfectly serviceable pieces.
     More recently, I have become interested in vacuum systems again; this time for the purpose of using the ionisation of low-pressure gas to reveal the standing-wave patterns on helical transmission lines. This work is self-funded however, and I seem to have developed a powerful aversion to paying the prices that science equipment suppliers ask for vacuum system components. The solution, of course, is to revive the art of the glass vacuum line, which is cheap and cheerful, and has the advantage that it doesn't conduct electricity.
     There is however more to making a vacuum line than welding bits of glass tubing together. It is a collection of components that includes traps, gauges, valves, stopcocks, ports and receiving chambers. Thus a certain manufacturing capability is required beyond the possession of an oxy-propane torch, and this leads to the desire to own a glass lathe. Such machines are rare, fabulously expensive, and much sought-after; but they are not particularly complicated, and making one is not beyond the capabilities of a small workshop equipped with a lathe and a milling machine.
     Various descriptions of home-built glass lathes can be found on the web, but most designs seem to be based on the metal-working lathe. This is not a good approach. About the only thing that a glass lathe has in common with a metal lathe is that the workpiece is rotated about a horizontal axis. After that, there is no obvious similarity. A glass lathe is an anti-gravity machine, allowing molten glass to be worked without sagging. Its typical rate of rotation is about 1 revolution per second. There is no need to apply any torque to the workpiece, which is held lightly in a very-soft-jawed chuck. Large diameter tubes need to be able to pass through the chuck, which means a large spindle throat. Finally, the basic operation performed on the machine is that of joining co-axial glass tubes. This requires two chucks rotating in synchrony; one fixed horizontally (the headstock); and one moveable on a sliding bed, or on rails (the tailstock).

>>>> More when I get time . . . .

Web links:
Dual spindle glass lathe. Lindsay Wilson. Home built glass lathe + collected photographs of other examples + useful links.
Mini glassworking lathe. Using Taig (Peatol) lathe components and synchronised stepper motors.
Glass working lathe . Rail-based construction for tailstock transport.
Glass lathe. Tubecrafter. This design recognises the need for a large throat in both chucks.
Glass lathe chuck using worm gears - Dalibor Farny, Nixie tube maker.
Laboratory Glassworking for Scientists: A J B Robertson, D J Fabian, A J Crocker, J Dewing, Butterworth 1957. Chapter 6 (p97-101) gives a description of the Edwards G3 glass-working machine. Figs. 34 and 35 from the book are reproduced below.

Edwards G3 glass lathe

Edwards G3 glass lathe

Marble Factory
Making an ornamental vase. (Teign Valley Glass Works, 2014).  The glass billet, heated to a viscous state, has been attached to the end of a thick-walled steel tube.  The billet is initially rolled on a steel plate to form a bulb.  The bulb can be blown through the tube if a hollow item is required. The tube is then rolled backwards and forwards on a pair of steel rails, to give a lathe action, occasionally reheating it in a gas furnace to maintain viscosity, while the item is shaped using a heat-proof pad and various steel tools.  Once finished and cut from the tube, the item is subjected to a slow annealing process involving a series of progressively cooler ovens.