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kempy's Lathe motor doesnt start.


kempy
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I haven't posted anything much apart from Random pictures for a long time, However realising that I'm in the company of other Myford Barry's and recently becoming a member of this exclusive sect, I thought I'd post up a few pictures for those that may come across this problem in future.

I recently picked up a sweet little Myford ML7 lathe in really good condition, the previous owner has stripped it down and replaced guides, bearings, bushes etc. and apart from one or

two things it's almost ready to go

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One of those things that needed attention was that the motor doesn't start by itself, instead it just meditates and hums.

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As you can see from the picture above, it's an old Brooks 1/3 HP single phase motor.

There's no starter capacitor on these, instead they have a centrifugal clutch which opens or closes a set of points/contacts.

This motor has two sets of windings, one set is the RUN winding that stays powered when ever the motor is running, the second winding is a START winding, this winding is energised when the motor

is first powered on and disconnects shortly after the motor reaches speed by means of a centrifugal clutch

 

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You can see from the L/H side arrow that the contact is open and sitting against a rest, it should be firmly against the contact which is shown by the R/H side arrow when the centrifugal clutch isn't engaged

 

 

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This picture shows the clutch disengaged and the contacts closed, which would engage the START winding.

The Start winding gives the motor an boosted magnetic field and kicks the motor in a direction determined by whether the phase/neutral are wired in forward or reversed.

 

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Here you can clearly see the two windings, The Red wires connect to the RUN windings, the black wires connect to the START windings. This of course may differ between motors, revisions. manufacturers etc. so don't trust this solely just by colour.

 

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The weights when spun, extend outwards and pull the clutch in (indicated by the direction of the Blue outlined arrow) and the contacts open, which disconnects the START winding.

 

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The issue here (as you may have already guessed) is that the Centrifugal Switch was jammed up by a little bit of corrosion and very old grease which had gone hard and by result permanently keeps the START winding open.

 

Picture of a dirty shaft...

 

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Gave the motor windings and rotor a quick clean and blew out decades of old dust.

Said shaft cleaned , lubricated,  and reinstated clutch, points lightly filed to remove pitting and fitted, bearings were mint so were pressed back on and wiring reinstated to the correct terminals this time.

 

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All reassembled, a quick check with the Multimeter and Fluke tester to check the windings, wiring of the reverse switch and earth leakage etc. and it's away.

It starts instantly in either direction, the only thing that really need some attention is the black plastic or Bakelite clutch plate has a crack and in time could possibly fly apart. it also make a ticking noise when the clutch disengages and presses the black plate against the contacts as the motor comes to a stop or is starting up.

Unsure if that's a part I will ever find so I'll cross that bridge when I come to it.

 

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49 minutes ago, datlow said:

Will it start if you spin it?

Try both directions

Yep, sure did.

 

I forgot to mention... Before embarking on totally dismantling the motor, it's advisable to check that both sets of windings are OK,  by memory the start winding was approx 8 ohms and the start winding approx 17 ohms. ( you'll need to take the terminal end of motor off to get to the winding side of the contacts to check this)

If either winding is open then you're screwed without a rewind.,

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