Lathe wouldn't start

[Roger B]

After a longish period of milling on my Hobbymat lathe/mill combination I went back to lathe mode and found the lathe wouldn't start (Brian R's problem must be catching). I could hear a relay clicking in but no activity from the motor 

The first step was to unbolt the lathe from the bench and turn it round to remove the milling head (I'm sure it weighs more than it did 3 years ago  ).

I could then tip the lathe on it's back and remove the cover from the control part. I then found that the circuit diagram in the hand book was for the older style controls without the NVR (no volts release) so I had to trace it out and make my own sketch. There are two relays, one does the NVR latching and controls the second one which makes and breaks the live and neutral. The coil on the second relay was open circuit (vibration?). The chance of finding a similar 30 year old East German is slim so I need to redesign the circuit with a single modern 3 pole relay.

To get the lathe working again I removed the second relay and fed the live through the first relay. As the polarity of the sockets in Switzerland is defined this is a minimal risk until I can rebuild it properly.

[Admiral_dk]

I can't say that I like what I see - the Fuse connected to Neutral 

+ two resistors and five capacitors (beside the Relay) => do not make any sense in how it works too 

I hope that you have more success and a Safe, Reliable and Working Lathe again 

Per

[Michael S.]

Hello Roger,

I think a relay is to prevent restarting in the event of a power failure.
You can definitely build the circuit with new relays. I didn't know that in Switzerland you can only insert the plug in one direction.
(I didn't quite understand the thing about the East German relays. The blue relay in the picture?) 

Greetings Michael

[Roger B]

Thank you both.

Per, the diagram is drawn as relay logic so the resistors are the relay coils and the capacitors are the contacts. The wire colours are American with black for live (hot) and white for neutral.

Michael, The early versions of the lathe just had a rotary switch for on/off. Later ones like this had the no volt release to avoid restarting.

I installed a new three pole relay, modifying the wiring to suit and corrected the mains connection so the fuse is now in the live side. It all works, and will hopefully last another 30 years 

[Admiral_dk]

Thank you for explaining the Symbols Roger 

It still didn't make complete sense .... until I realized that the Stop Switch is a Break and not a Make Switch .... (they are drawn much different in Electronics).

Great to hear that it all works as i should again 

Per           

[Jo]

Pleased to see you have got our old lathe running again Roger 

Jo