My Super-7 trips out

[John Wood1Participant @johnwood1]

I purchased a factory rebuilt Super-7 lathe on an industrial stand from Myford’s liquidators back in the summer but am having trouble with it cutting out.

 

I can use it for five minutes or so then the cut-out relay clunks but resets itself, so I carry on. A minute or so later it trips out completely. Press the start button and it comes on OK for a minute or so then does it again, this time often with a bit of relay chatter first, start it again and a minute later it stops and will not re-start until it has stood for five or ten minutes. I have tried it under load (being used) and just running free but no difference. The motor has only the chill taken off it, certainly not hot so I need to investigate further.

 

I have the usual industrial switch panel with the large red stop and smaller green start buttons. The overload relay is a Crabtree type BD. I have made sure the white adjusting wheel is set to maximum (it was when I got the lathe) and the relay looks to be in good condition and has been probably re-wired at Myfords. The relay contacts were dirty so these were cleaned but with no improvement.

 

Does anyone have any suggestions please?

 

Thanks, John

[John Wood1Participant @johnwood1]

Advice needed on a sensitive overload relay on my Myford

[Ed DuffnerParticipant @edduffner79357]

Hi John,

 

I don’t know anything about the Super-7 but have worked on a few relays and contactors in the past. I would have suggested cleaning the contacts but you say you’ve cleaned them already. The only other thing I can think of is, if the relay has a latching coil, the coil might not have secure connections (loose wire or solder joint) and is unable to maintain a solid latch. Or whatever is providing the latching current could be starting to fail.

 

ATB.

Ed.

[Ex contributorParticipant @mgnbuk]

Check that the current rating on the overload matches the motor full load curent on the motor rating plate. The overloads have a working current range that is adjustable, but setting to “maximum” may still trip if the overload maximum is less than the motor. The overload should be adjusted to the motor current & no more.

 

If that is OK, I would use a clamp-on current meter to check the current that the motor is drawing. If it is at or over the motor rating plate FLC, I would remove the input drive belt & check again. If still over current, have the motor checked out. If it is now under, how tight is the spindle drive line when rotated by hand ?

 

You don’t say what speed range you have the machine set to, but if it is one of the higher ranges it may be that your spindle front bearing is set a bit tight. I run my S7 from an older inverter – my front bearing is set close enough that it won’t start at the top couple of speeds (inverter trips) unless it has been “warmed up” for a while at a lower speed.

 

HTH

 

Nigel B.

[Les Jones 1Participant @lesjones1]

Hi John,

I would suggest eliminating the overload tripping because of a real overload first.

I would do this by disconnecting the motor and then seeing if the contactor drops out when there is no load. Before disconnecting the motor I would see if it still cuts out with the belt removed from the motor pulley.

 

Les.

[John Wood1Participant @johnwood1]

Thanks guys, I shall go away and check all the above out and I’m sure I shall be able to resolve the problem now. Of course I could just convert to three phase and use one of the proprietry speed controllers, I have done this to my larger Warco and it’s brillient.

 

First things first though…..

 

John

[S.D.L.Participant @s-d-l]

Have you got, or know someone who might have access to a clip on ammeter to measure the motor current?

 

Is the overload a 3 phase one used on single phase? If so are all 3 overload circuits wired in series to stop nuisance tripping due to unbalanced coil loads.

 

Steve Larner

[Author]

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