Homemade Mini Glassworking Lathe
(Design notes appear at the bottom of this page.)
A glassworking lathe is a specialized lathe for manipulating glass. A torch is used instead of a cutting tool for shaping the glass. The glass, usually in the form of a tube, is held by two rotating chucks. The chucks face each other and rotate in sync. One chuck is mounted on a stationary headstock while the other is mounted on a moving one. The chucks and headstock shafts are hollow so that the glass and/or a blowhose may be passed through them.
The glassworking lathe described here is designed around TAIG metalworking lathe kit components.
The design goals were: 1) Low cost. 2) Simplicity. 3) Optional headstock de-synchronization.
This site describes but one approach to building a glassworking lathe and is not intended to be a "how-to". Your metalworking skills, electronics experience, and pocketbook may dictate an entirely different design. Please note that there are no plans or kits for this lathe.
Two headstocks and two scroll chucks were ordered instead of the normal one of each, and no tailstock was purchased as that was replaced by the second, moving headstock.
The TAIG 3-jaw scroll chucks were essential to the design. At only $44/chuck there was no way I could make anything that good and that cheap even though I have my own full-size metalworking mill and lathe. The jaws are easily replaceable so one could make new ones out of more appropriate materials (lower thermal conductivity, etc.) but so far I've just put a bit of hi temp tape on each aluminum jaw and that has worked just fine.
The headstocks can pass small diameter (~0.344") tubing through their centers, the chucks can pass about twice that. This makes connection of the blowhose easy via a stopper in the end of the glass tube, or, smaller diameters of glass tubing can just be passed through the chuck/headstock to the blowhose & blowhose swivel outside of the lathe.
In the present setup, the lathe will turn something 7-inches in diameter with 12 1/2 inches between the faces of the 3-jaw chucks. The lathe components are mounted on a length of heavy aluminum channel.
Two 130 oz-in surplus steppers are used - one for each headstock. This _greatly_ simplifies the mechanics allowing for synchronization & easily variable speed. The steppers were only $9.95 each from Herbach & Rademan. I was surprised that the 130 oz-in steppers barely have enough torque for the job, and they turned so slowly that I had to "gear" the setup as shown to get a good range of speed. The final setup with timing belt drive achieves a speed range of 6 RPM to 240 RPM (half-stepping the steppers.) This is on par with what "real" Litton glassblowing do.
The stepper driver was built around two Allegro UCN5804 stepper driver chips. International Rectifier IRLZ44N logic-level-drive HEXFETS power the stepper coils. The two separate stepper chips (<$4 each) will provide the capability in the future of doing any CNC trick twisting of the work. The UCN5804 has very limited drive, so the 55V 47A(!) HEXFETS should be able to handle any stepper imaginable.
I first made O-ring drive pulleys - but not quite well enough. There was a slight difference in diameters between the pulleys on each stepper which caused loss of synchronization. There was enough slip in the belts and in the grip of the chucks on the tubing that it wasn't an immediate problem. Timing belt drive is a better solution but I couldn't find any suppliers of these (or gears) that took orders over the 'net so I got impatient and machined the pulleys and made O-ring drive belts. I next installed a timing belt drive system using pulleys from McMaster-Carr (small selection - but at least their on-line ordering works.) But, these were steel and presented too much mass for the steppers to reliably start. I finally replaced the larger steel timing belt pulleys with plastic ones - that fixed the problem. The two chucks turn perfectly in sync. (BTW: I'd just as soon as avoid a chain drive - ever get something caught in a chain?)
I believe that some of the "real" glassworking lathes use a single motor driving a long splined shaft with moving return guides to sync their chucks. This is great, but is also _very_ expensive. One splined shaft and one return guide costs as much as I spent on my entire glassworking lathe! ($400) Plus, the splined shaft design requires a _lot_ more mechanics and doesn't allow de-synchronization when you want it without even more mechanics. An alternative to a splined shaft - just use a simple square shaft. Square stock is cheap and is available in long lengths. The ends could be turned round for the needed end bearings. The follower could be easily made from a block of Delrin with a square hold in it (make a square hole by milling a notch in a block, then close off the opening ("C") with a bar of material to end up with a square hole.) Still - this is more work & mechanics, and the headstocks can't be de- synchronized if one wants.
An idea for another inexpensive approach to the headstocks and chucks - lathe collet spin index fixtures. Did you know that Litton sells redwood collets for their glassworking lathes?
The TAIG lathe components were purchased from Nicholas Carter: http://www.cartertools.com
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(Please note that there are no plans or kits for this lathe.)
Okay, here's a schematic - but, you're on your own!