I want to build a glass lathe

Specifically this glass lathe, a Bethlehem GL-50 although with a longer bed so really the GL-100 model. These lathes went out of production in the 80s and are hard to come by. I have the patent diagrams and a facebook owners group resource if I need anything measured.

The immediate problem I'm having is sourcing a fully splined driveshaft. It needs to be at least 3.5 feet long. Does anyone know of a common machine that would have a part like this I could repurpose? I've been unable to find one long enough and I'm thinking that even if I do it will be expensive.

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  1. 4 weeks ago
    Anonymous

    People on the FB group have been replacing the drive gears on these machines with 3D printed plastic ones with great success, its considered a upgrade since they are much quieter. This got me thinking that perhaps the driveshaft doesn't need to be steel either, maybe aluminum or even plastic would work? How would I go about getting a aluminum driveshaft made, I am unsure of how milling horizontal teeth is accomplished, a CNC machine perhaps? Could this part be sand cast or made through a process like that? I have the equipment on hand to build a small furnace if casting aluminum is possible but I expect that tight tolerances could not be achieved this way and milling is the only option let me know your opinion.

  2. 4 weeks ago
    Anonymous

    Glass lathes don't have external forces applied to them like metal lathes, there is no milling blades used. They do however need both head and tail stock to spin equally so that the hot glass doesn't twist and get ruined, this is why a large driveshaft that drives both stocks simultaneously is used.

    This lathe proves that most glass lathes are way over engineered as it weighs 220 lbs. for the benchtop model and most other glass lathes weigh over 1000 lbs. I think this is because way back when they were being designed someone told a engineer to make a metal lathe with both stocks spinning so the overbuilt aspect was copied from metal lathes which have a good reason to be built that way to avoid flex while machining.

    If I had a budget of say $1500 is it possible to get something like this built? Or am I way off on what parts and machining would cost? I know there would be lots of searching through McMasterCarr catalogs for appropriate bearings and such but it seems like other then the driveshaft many off the shelf pieces could be repurposed. The rails could be regular round stock or maybe even threaded pipe and the housings could be welded plate steel. The motor setup I will change as it is not necessary to do the cupped friction drive as in the original patent a variable speed DC motor is fine and many have done this changeover on their original lathes its considered a upgrade.

    I'm trying to get a handle on if this is even possible to build at home and if the tooling or machining expense would exceed the cost of buying a original Bethelhem. They are rare and don't pop up for sale often but when they do they are usually priced around $5-8k for the model I need.

    What sorts of hurdles am I facing here? Thanks.

  3. 4 weeks ago
    Anonymous

    what if you drove the headstock and tailstock individually with identical stepper motors via cog belt. feed the drive for each from the same pulse source so they more in unison. then you would need gears or shafts or anything of that bullshit with backlash that could frick your piece up
    these work really well for cheap vari speed stepper pulsing
    https://www.amazon.com/15-160V-Adjustable-Controller-Generator-Regulator

    • 4 weeks ago
      Anonymous

      fixed link
      https://www.amazon.com/15-160V-Adjustable-Controller-Generator-Regulator/dp/B07HNSVMVH

    • 4 weeks ago
      Anonymous

      I've seen a writeup on someone who did that but the lathe he built was tiny and could only make things smaller then a lightulb. He did make it work but had synch problems even going out of synch .1 degree per revolution will quickly compound into problems. I am not aware of stepper motors powerful enough to drive big metal gears and several pounds of glass at a time but I guess they probably exist.

  4. 4 weeks ago
    Anonymous

    You could call one of those companies who sell milled/unmilled blocks of 7075 aluminum. That might be your middle option between price/longevity

    • 4 weeks ago
      Anonymous

      I just looked up the mechanical properties of 7075 aluminum and I agree it looks like a good choice. I don't know exactly how to order or describe something like this to a machinist other then showing him the diagram. Would I need to submit a CAD file and if so could I outsource this work since I don't know CAD? I wouldn't mind learning it on a free version but I'm thinking the learning curve would be quite severe and outsourcing the work would be the smart move. How do I find someone to make this piece? Any idea what I should expect to pay?

      • 4 weeks ago
        Anonymous

        If you have a very accurate description that would be almost as good as having the real thing in your hand. You could call one of those places and ask them to make you a cylinder in the length and circumfrence dimensions you need, then take that piece to a local with a CNC and do all the finer work in person. You're going to have to go out and talk to machine shops in person. You could get one made out of plastic to start with then source all your other shit. If it seems like it might work then get one made out of aluminum. If that works get one made out of steel.

        • 4 weeks ago
          Anonymous

          I think rod stock aluminum is already available so I think I could use something off the shelf although it needs to be perfectly straight. Thats good advice though, thank you.

  5. 4 weeks ago
    Anonymous

    Here's a timelapse of a glassblower making a cup on a GL100 for those who might be interested:

  6. 4 weeks ago
    Anonymous

    What about hex stock instead of a splined shaft? A piece of 4140 hex wouldnt set you back too much.

    • 4 weeks ago
      Anonymous

      Dammit I opened this thread up a while back and didn't refresh it before posting

      Could you use hex shaft or keyed shaft instead of splined shaft? If you used hex shaft you could use a socket that slips over it as a center hub for a gear that would slide along the shaft to power your head and tail stocks...

      Great minds think alike.

  7. 4 weeks ago
    Anonymous

    Could you use hex shaft or keyed shaft instead of splined shaft? If you used hex shaft you could use a socket that slips over it as a center hub for a gear that would slide along the shaft to power your head and tail stocks...

    • 4 weeks ago
      Anonymous

      I thought of that too but with a square shaft. I'm hesitant because there are dozens of lathe designs out there from several manufacturers and they all use splined shafts, all of them. It seems like a idea that could and should work but why has no one ever done it that way? I will think about it because I agree it *should* work but maybe there's accelerated wear or lash problems or something. Thanks.

  8. 4 weeks ago
    Anonymous

    I would guess that a splined shaft give the best combination of linear and rotary motion. I would be a hex or even square would work though.

    What kind of rpms and distances are we talking here?

    • 4 weeks ago
      Anonymous

      RPMs max 120 I think. They don't need to spin that fast. I would like 4 feet between chucks but I think 3.33 ft would be fine and would account for the offsets of the head/tail stock if a 4 foot driveshaft was acquired.

      I've been thinking hard about the points made here and diving deep into internet research. My mcmaster.com searches were dissapointing, not a whole lot of applicable parts and man they are expensive. Then I thought about the dual servo idea and researched servos and position sensors to keep them absolutely aligned. Turns out there are large servos with onboard sensors, the website claims accuracy to one nanometer (doubt) and they are also expensive at $500 each for the ones I looked at. I shot the company a exploratory email since they require a proprietary driver and asked about exactly syncing 2 motors. I'll see what response I get. They claimed 560 inch lbs. torque which I divided by 16 to get 37 ft.lbs. I am unsure if this is sufficient as I don't really have a handle on how much that is really combined with all the possible gearing that could happen. I understand there will be math but I don't know how to calculate it and it seems very early in the process to worry about it anyways.

      https://catalog.orientalmotor.com/viewitems/az-series-85-90mm-absolute-encoder-stepper-motors/az-series-85-mm-absolute-encoder-stepper-motors-dc

      I did a little more research and there is already a lathe manufacturer out there making the double servo style lathes. They look nice but only have 2.3 feet between chucks and at $18k each thats way beyond my budget anyways and at this point I want to do it myself if I decide its possible.

      https://sinctechlathes.com/

      • 4 weeks ago
        Anonymous

        oops when I said "servo" I really meant "stepper"

      • 4 weeks ago
        Anonymous

        >I divided by 16 to get 37 ft.lbs.

        frick I'm fricking up tonight and should probably go to bed. Theres 16 oz. in a pound but 12 inches in a foot I should have divided by 12. Derp.

  9. 4 weeks ago
    Anonymous

    Just now I found this website and its exciting. Turns out there are aluminum driveshaft and gears available from the company linked below that may fit the bill. The best part is they are CHEAP. I think this company is marketing to the robotics industry but definitely mentioned their products being used as driveshafts and they have a 4 ft. section of what they call the "SplineXL" series for like $20! I looked into the specs and it could work. I am worried about the driveshaft only being available in 6065-T6 aluminum and the wall thickness (its a tube not a bar) being under 3mm. I am unsure if it can handle the torque and also if it as enough inertial mass. I was wondering if it could maybe be filled with concrete or something to get the weight up if that is necessary. They have hex bar in steel but only up to .5 inch and only 3 feet long. The exciting part is theres lots of gears in aluminum steel and plastic and they are cheap. If the materials are suitable this seems like the way to go I can adapt the Bethlehem patent to this system perhaps.

    • 4 weeks ago
      Anonymous

      oops forgot link:

      https://docs.wcproducts.com/frc-build-system/spline-and-motionx-system

    • 4 weeks ago
      Anonymous

      Good work op, some good info here
      wonder if one could use a small aluminum extrusion as a shaft with a rolling carriage to set up a poor-mans ball spline.

    • 3 weeks ago
      Anonymous

      >wall thickness (its a tube not a bar) being under 3mm.
      The round ridges of the star profile should give it enough stiffness for spinning glass, I'd be more worried about gear backlash

      I thought of that too but with a square shaft. I'm hesitant because there are dozens of lathe designs out there from several manufacturers and they all use splined shafts, all of them. It seems like a idea that could and should work but why has no one ever done it that way? I will think about it because I agree it *should* work but maybe there's accelerated wear or lash problems or something. Thanks.

      Looking at the picture in

      https://i.imgur.com/gQdeLf4.jpeg

      People on the FB group have been replacing the drive gears on these machines with 3D printed plastic ones with great success, its considered a upgrade since they are much quieter. This got me thinking that perhaps the driveshaft doesn't need to be steel either, maybe aluminum or even plastic would work? How would I go about getting a aluminum driveshaft made, I am unsure of how milling horizontal teeth is accomplished, a CNC machine perhaps? Could this part be sand cast or made through a process like that? I have the equipment on hand to build a small furnace if casting aluminum is possible but I expect that tight tolerances could not be achieved this way and milling is the only option let me know your opinion.

      it seems they used a splined shaft so that the chuck assembly gears could mesh directly with the shaft to allow for easy removal of the entire assembly from the top

      Looking at a few DIY glass lathes on youtube it seems most just use plain stepper motors without encoders.
      Servomotors will compensate some error but won't mantain perfect alignement unless they're largely oversized or geared down.

  10. 4 weeks ago
    Anonymous

    If it was me I would get 2 ebay linear shafts and 4 linear bearings. Use a piece of 4140 hex as the shaft with adapters to drive the chucks. The adapters would ride in dual rotary bearings on the chuck assemblies to allow rotary and linear motion. 90v dc motor with a gearbox to get you down to the appropriate range plus cheap or diy pwm control.

    If youre savvy I bet you could do it for under $500 depending on what you do for chucks. And if the hex doesnt work it was a cheap gamble, make friends with a machinist and have a splined shaft made.

    • 4 weeks ago
      Anonymous

      Excellent idea well worth trying. Otherwise OP will need to have the shaft turned to diameter then milled lengthwise on a rotary indexer which in the US will not be cheap.

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