Rotary positioner

  1. Munkul

    Munkul Jack of many trades, Master of none

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    I got an old rotary milling table last year, it actually worked a little bit but then sized. So it got put to one side until now.

    It's a whopping great thing, probably 250kg?

    2019-09-03 18.53.18.jpg

    Stripped out the electrics, since they don't work, and I don't need them. There was a fwd/rev as well as an auto reverse toggle.

    2020-08-22 14.49.40.jpg 2020-08-22 14.49.49-1.jpg

    Started taking apart in earnest

    2020-08-22 16.11.54.jpg

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    Box of bits

    2020-08-22 19.13.23.jpg

    It then got pressure washed at 150 degC and lots of chem!

    IMG-20200822-WA0011.jpg

    It dried off nice and fast, being warm!
    2020-08-22 19.13.36.jpg 2020-08-22 19.37.34.jpg

    I wonder who made it? There's no clue as to the maker apart from this serial number and COM.

    It's nicely made. Plan is to clean up, replace the two bearings that were sized, convert the oilbath and contact oiler system all to grease nipples, and re-assemble.

    Then the fun will start...

    It has a few nice features for a welding positioner - it has the multiple changewheel setup in the gearbox for speeds. A dog clutch engagement and built in rapid travel on a lever. And the 3 phase motor will be inverter driven. Making the frame for it will be the challenge!
     
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  2. Robotstar5

    Robotstar5 Casanunda Staff Member

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    ESAB used to make welding positioners mainly for ASEA/ABB controlled as an external axis by the robot, the smallest I've seen could carry 160kg and the largest was 1600kg which manipulated tractor chassis at Terex.
     
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  3. daleyd

    daleyd Member

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    That looks like a proper beast! What size motor have you got to drive that? I’ve got a couple of small 3 phase motors with a 3:1 reduction gearbox on that I think would make a good power source for a positioner, but I think they might be a bit underpowered for that thing :laughing:
     
  4. Brad93

    Brad93 M J B Engineering

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    Could that not be a Hofmann from Germany. If so that’s too good for a welding positioner.
    Think they made them even bigger than that, Richard would know for sure. Not anymore though. China out priced them.
     
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  5. Munkul

    Munkul Jack of many trades, Master of none

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    Its a small 3phase motor :) the gearing within the table head will go wayy down to about 0.2 rpm and the inverter will go half that, so gearing won't be a problem. Getting it to go fast enough on small pieces might be!

    Brad, Ive had a look at hofmann this morning, but I can't see anything that looks like this... Its a shame cos you're right, it's too nice for welding on, but something this size is obselete anyway. No one apart from maybe @spencer 427 has a manual mill that would take it :D
     
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  6. Munkul

    Munkul Jack of many trades, Master of none

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    Cleaned some bits up last night.

    2020-08-24 19.01.52.jpg 2020-08-24 19.02.11.jpg 2020-08-24 19.02.38.jpg

    The changewheels are a nice design, you can swap and change them to get the gearing you want.
    The dog clutch and rapid travel friction drive are in good nick.
    The bearings on the drive shafts are all OK, so leaving them assembled.

    There are two sized bearings on the input shaft which caused the need for the stripdown in the first place - been ordered. I'm keen to clean it all up, reassemble, and then paint afterwards.
     
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  7. Munkul

    Munkul Jack of many trades, Master of none

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    20200825_171919.jpg 20200828_191302.jpg
     
  8. Munkul

    Munkul Jack of many trades, Master of none

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    Got it back together at the weekend, and fired it up... aside from one noisy bearing, it all worked nicely :) I've ordered a replacement bearing.
    Maximum speed the gearing gives me at 50hz (no VFD) is 0.3 rpm.
    Well... that's great for big diameters... not so great for smaller ones.
    Estimated smallest diameter usable on this table for TIG welding at 200mm/min is 212mm diameter. or 8" pipe...
    I could run the VFD at 100hz and get it down to 4" welding diameter... assuming the motor will take it. Or maybe higher.

    Thoughts?

    I was thinking I could use the rapid travel function for small diameters, it spins around 2rpm at 50hz, but it relies wholly on friction between two bevelled steel faces, and it's really a horrible way to drive something.

    Anyone want to make me an offer for this, and I'll buy a real one? :D
     
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  9. daleyd

    daleyd Member

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    Looks like the motors pretty old! I'd give it a whirl, probably be OK - I guess it's not having to provide a lot of torque?
     
  10. Agroshield Member

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    1,047
    Right now, the motor is going through a double worm reduction. The first is on the motor shaft, then the train of gears under the 135 cover, then the worm driving the table (where the dividing plate is). Put a motor directly on the dividing plate and it will go faster.

    There must be a good reduction in the 135 gear train. Pull them out and put a 1:1 timing belt and pulleys between input and output.

    Put a dog clutch on the first gear in the 135 train and extend its shaft for an external belt drive to the dividing plate shaft: slow speed using internal gears, fast speed using belt drive.
     
  11. Munkul

    Munkul Jack of many trades, Master of none

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    The 135 gear train can go anywhere from between 3:1 reduction, up to 1:3 increase. (guesstimate looking at the 3 pairs of swappable gears and their speeds)

    at 0.3rpm, all 3 changegears are swapped around to provide the biggest speed increase around 1:3.

    You're right, it's the double worm reduction that kills it. But if you chop out the gear train and motor direct to the main worm shaft, then you'll not get the bottom end speeds - probably bottom out at around 1rpm around 25hz, which is still too fast.

    A low speed motor on the input gear to the geartrain, cutting out the first worm reduction would probably give the most flexibility for my speed needs... but will need some careful thought and some machining.
     
  12. Agroshield Member

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    1,047
    I am struggling to see the 1:3 reduction. If we look at:

    https://www.mig-welding.co.uk/forum/attachments/20200825_171919-jpg.248839/

    and use some educated guesses that the big ones are twice the teeth of the small ones, we have 1/2 x 1/2 x 1/2 x two more reduction ratios, so at least 1:8.

    How easy is it in practice to swap the gears? The centres are fixed and it is a PITA to remove the cover and fight the grease if you want to change the ratio.

    If you make the first gear slideable on its shaft (extend the keyway) and put the dog on it, as it comes forward towards the cover, it will disengage its mate and engage the external belt drive. Then the gear train can remain unmolested.

    Maybe make a new 135 cover out of 1/2" or 5/8" aluminium, thick enough to carry the belt mounting stuff. That and a new input shaft would nearly do it.

    Your idea is good. Make the first gear slideable so it disengages the worm. Put the motor on the second gear for higher speed.

    The real difficulty in this is making the gear re-engage after you have disengaged it. You will not be able to backdrive the gear train through the table nor backdrive the first worm through the gear itself. It might need an external handwheel on the first worm motor so you can rotate it to jiggle the gear back into mesh.
     
  13. Munkul

    Munkul Jack of many trades, Master of none

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    Ignore the first pair and the last pair, they are fixed. Also ignore the worm drives.

    The pictures don't show it all that well, but the central 6 gears are all swappable, and with a few teeth either way, the 3 pairs are roughly in a 3:2 ratio each pair. They can all go in any position on the brass keyed bushes, and a little sliding clip secures them in position. So 3:2 x 3:2 x 3:2 = 27:8 which is 3.3:1.
    Again, this is a guesstimate. I think it's closer to 3:1, and I haven't calculated it at all. And each pair is a slightly different ratio, so you can fine tune the speed if needed.

    Anyway, you can have 3:2 x 3:2 x 3:2, or 2:3 x 2:3 x 2:3, or any swap in between. Hence 3:1 and 1:3. It's less than a minute to swap all the gears around.

    My point is, it's very easy to make the drive turn slower, but the very fastest it will ever go with the current design is 0.3rpm.

    Cutting out the first worm drive will probably cut out at least a 20:1 reduction... again, at a guess... possibly up to 30-40:1 so increase speed up to 6rpm, swap the 135 gearing around brings it back down to 0.6rpm, and that's before a VFD.
    So, I'll have a look at that 1st stage worm, and if it's anywhere near a 20:1 reduction, then cutting that out will give me the full range of speeds that i want.

    If I do this sort of mod, I won't be bothering with a disengage, I don't really see the point.
     
  14. Brad93

    Brad93 M J B Engineering

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    Don’t chop the gears out it’s far too nice for that.

    I’ve still got the kit I had from Shox. All the motor is wired to the VFD and switch pedal.
    Maybe could do a trade.
     
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  15. Agroshield Member

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    1,047
    If that is all it will take, then maybe replacing the worm-wheel with a set of bevel gears might work. Allows the original motor to be used and there may be a limited choice of bevel ratios to further tune things.
     
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  16. Munkul

    Munkul Jack of many trades, Master of none

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    The more I think about it, the more I'm shying away from doing anything else with this.

    I like the bevel gears idea though, that would give me the speeds I want no problem, but getting the right sizes to fit on existing shaft centres might be tricky. It's a metric design though, so maybe not impossible.

    At this point I'm almost ready to sell it and put towards a "proper" 50-100kg machine... getting a few prices now so I can see whether it's worthwhile or not...
     
  17. Brad93

    Brad93 M J B Engineering

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    Worth asking Matt if Lorch have anything. @matt1978

    They make some lovely positioners.
     
  18. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

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    I’d forgotten you had bought one of those motor/wormdrives. How long ago was that:scared:.
     
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  19. Munkul

    Munkul Jack of many trades, Master of none

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    Probably too expensive for me :D I'm only asking for used prices.

    I've only got one firm job I actually want a positioner for, and last time I just spun them by hand :laughing: so atm it's an investment without much return.
     
  20. Brad93

    Brad93 M J B Engineering

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    Too long mate. Probably 3-4 years ago.
     
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