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possible blown motor on 9x20 lathe

Discussion in 'MINI-LATHE & MINI-MILL INFORMATION' started by savarin, May 19, 2017.

  1. savarin

    savarin Active User H-M Supporter-Premium

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    Halfway through cutting a 12x1.25mm thread in some stainless last night all the magic smoke suddenly poured out of what I thought was the motor.

    Turned it off, turned it back on in forward and it worked, turned off then into reverse and nothing.

    But forward still worked.

    So, after removing the motor and dismantling it I couldnt find anything looking like a burnt patch or any discolouration.

    Reassembled but not installed I plugged it back in and it worked in forward and reverse, Hmmm. (no load on the motor) It could still be a burnt spot somewhere in the winding though I guess.

    Checking the change gears it looked as if at one point in the revolution the small 30 tooth on the leadscrew shaft stuck, ie, the backlash was too great and the teeth tops hit the teeth tops of the 120 gear.

    So, obviously my fault so I attempted to turn the lead screw by hand by just twisting the gears (no handle) and it was easy so thats all right.

    Engaged the half nuts and tried to turn by hand but no such luck.

    Disengaged the half nuts and engaged the apron drive, this worked but was not easy.

    Went back to the half nuts and tried them again. It worked but was incredibly stiff and difficult.

    Can anyone here try to move their saddle with the half nuts engaged and turning the gear by hand and report back how difficult it was?

    Many thanks.
     
  2. terrywerm

    terrywerm New Member Liaison Staff Member H-M Supporter-Premium

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    I just tried it on my Logan 200, no cutting tool, just moving the saddle using the lead screw and the half nut. I engaged the half nut, then turned the gear on the end of the lead screw by hand and it did not move all that hard.
     
  3. hman

    hman Active User H-M Supporter-Premium

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    My 9x20 is a Grizzly G4000

    • Disengaged the QCGB, engaged the half nuts. Leadscrew could be turned by hand without much effort, other than trying to get a finger grip on it.
    • Engaged the QCGB at position 5. Released the banjo to disengage the gear train from the spindle. Tried turning the 127 tooth gear against the 60 tooth gear. Easy.

    Hope this helps diagnose your problem. By the way, might it be a switch problem? Or maybe the centrifugal start winding switch not throwing out, causing the start winding to overheat? If you can you hear a click as the motor reaches full speed, it's probably OK. If not, that would be an item to check.
     
  4. savarin

    savarin Active User H-M Supporter-Premium

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    I dont like the sound of that, mine's quite difficult.
    However, I stuck the handle in the head stock spindle and moved the carriage up and down and it seems as roughly the same resistance when I first did this when the lathe was new.
    I think I will investigate slackening off the pressure in the half nuts.
    BUT, there didnt seem to be much difference between the half nuts engaged or the lead screw drive moving the carriage.
    I believe I have found the source of the smoke, there looks like a tiny pin hole in the starter cap with a weep of fluid so that needs changing out if nothing else.
     
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  5. markba633csi

    markba633csi United States Active Member Active Member

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    I was just thinking the cap might have smoked but it sounds like you found it. If the value is around 120 microfarad there was a guy with some NOS Mallory caps for 3.50$ on Ebay - I bought one for one of my motors. Worked like a champ.
    Mark S.
     
  6. savarin

    savarin Active User H-M Supporter-Premium

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    Some more searching, I dismantled the apron to check out the lead screw alignment and it looked like the half nuts were pushing to lead screw into the lathe bed.

    I fiddled and poked but couldnt find a reason. everything lined up ok but I noticed that the apron had a tiny bit of misalignment. I set this up straight and now the half nuts are easy to move. This was only a teeny bit of misalignment but seems to have caused a huge amount of friction.
    One down two to go.
    I will get a new cap tomorrow and see what happens but I'm not holding my breath.
    One new future problem may be the worm and worm bracket as they seem very loose with a heap of play. My brass shells I pressed in to repair a previous problem with slack here are now somewhat worn. It never ends.
     
  7. savarin

    savarin Active User H-M Supporter-Premium

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    I have searched but cannot find a drop in replacement motor.
    There are so many varieties that I cant work out what would work.
    Does any one know all the requirements of the motor that I need to know?
    Cheers
     
  8. savarin

    savarin Active User H-M Supporter-Premium

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    tried a new cap today, no go, the motor has karked it.
     
  9. David S

    David S Canada Active User H-M Supporter-Premium

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    If it works in forward, I would think it should work in reverse. Do you think there is an open connection / contact in the reverse circuit?

    David
     
  10. savarin

    savarin Active User H-M Supporter-Premium

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    Its worth a look.
    Heres the full description of whats happening, just the motor, not driving the chuck or change gears.
    It makes no difference if I use the old cap or the new cap.
    In forward it works but it is noisy as if there is a sort of vibration.
    In reverse sometimes it starts and sometimes it just hums or starts turning very slowly humming loudly.
    If it does start in reverse it sounds just like when its going forwards ie. noisy
     
  11. hman

    hman Active User H-M Supporter-Premium

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    Switch? That's what I'd look at if one direction works differently than the other.
     
  12. savarin

    savarin Active User H-M Supporter-Premium

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    Motor definately cactus.
    Cannot find a new motor with a 14mm shaft. It seems the regs insist a 3/4hp motor hust have a 19mm shaft.
    Would a 1/2hp motor work ok? Would it have enough power?
     
  13. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    G'Day Sav,
    Ow yar goin mate?
    do you have enough meat in the pulley to bore it to 19mm? or have access to another lathe or mill to bore the pulley?

    i had to bore my 1236 1.5hp 19mm motor pulley to accept a 22mm shaft on the transplant 3hp motor.
    as a thought, maybe you could do the same or possibly fabricate a new pulley from other materials if need be, Bob's yer uncle :)
     
    Last edited: May 25, 2017 at 9:38 PM
  14. savarin

    savarin Active User H-M Supporter-Premium

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    G'day Mike, She's apples mate.
    unfortunately there is insufficient meat on the pulley.
    If I bore it to 19mm then the keyway required removes a section of teeth on the little toothed pulley.
    Without a keyway there is just enough meat left but no way to anchor the pulley.
    Hare and forbes who supplied the lathe can supply a replacement for $350 and a 3-4 month wait. W H A T ????????
    I would really like to use a VFD and a 3phase motor but I dont have the knowledge to do all that.
     
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  15. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    the VFD and 3 phase conversion sounds daunting, but don't let that stop you!
    the units are quite easy to set up for the most part.

    i heard that regular folk are not supposed to do their own electrical work Down Under, is that true?
     
  16. hman

    hman Active User H-M Supporter-Premium

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    I just checked my Grizzly G4000. It's also a 3/4HP. Depending on what you cut (size, material, depth of cut), you might get away with a ½ horse - but beware of Chinese hoses!

    I was going to suggest you try to see if Grizzly could help you. Their parts people pretty good (don't know if they'd ship to OZ). Unfortunately, the replacement motor for the G4000 is 110 volts only:

    http://www.grizzly.com/products/g4000/parts

    I guess you might still want to give them a call or email (techsupport@grizzly.com ... 570-546-9663). Maybe they have a dual voltage motor available. Wish I could offer more help, but I don't know what else to suggest.

    PS - I've converted both a 12x24 lathe and an RF-30 clone mill to 3 phase motors with VFDs (single phase 230 V AC input). It's actually pretty straightforward and easy to do. If you can find a dealer who sells both motors and VFDs, he can probably provide good phone support.
     
  17. savarin

    savarin Active User H-M Supporter-Premium

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    Correct, nor plumbing but I have a couple of tame leccys.
    I have also thought of getting the 3/4hp with a 19mm shaft and turning it down to 14mm on a mates lathe as being the easiest and cheapest option.
     
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  18. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    turning the motor shaft was going to be my next suggestion!:D
     
  19. savarin

    savarin Active User H-M Supporter-Premium

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    Just for kicks I filed and sanded the centrifugal switch points because I could see a bit of arcing on them.
    Put the motor back and blow me down it works. Now thats a cheap fix.
    Started making a pin spanner for the spindle for a test, heavy interrupted cut, no problems.
    Runs in reverse with half nuts engaged no problems.
    Although I'm certain its noisier than before so I think I will get the 3/4 Hp and turn the shaft down so I can have the replacement waiting.
    I would like to go the VFD with speed control but I really dont want all the hassle with sorting it out. (and the expense)
     
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  20. hman

    hman Active User H-M Supporter-Premium

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    Congratulations on your fix! And now you have a lathe you can use to repair the lathe ;)
     
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