possible blown motor on 9x20 lathe

savarin

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