Myford super 7

Hello all! I am an artist, broad based practise, everything from turning to covering carved forms in leather, to vac forming…so, to my question:

my Myford lathe worked one day, the next, it just made a loud buzzing noise when i turned the direction switch to run position, it buzzed in either direction….any thoughts? Is the motor buggered?!!

Hi Mark

If yours is a single phase machine it sounds like it could be a fault with the centrifugal switch in the motor or the start capacitor which that switch puts in and out of circuit on starting. As a rough check try taking of the primary belt, from the motor pulley to the clutch and quickly spinning the motor pulley by hand while switching on to see if the motor will run once it has been given a bump start so to speak. Worth checking that the lathe itself is running freely, I know someone who forgot about the spindle lock pin at the rear of the headstock. Give that a try for a start and if you post your findings more help can be given.

The start capacitors are fairly robust but do have a finite life, fortunately a cheap repair, if you do spin the motor up, turn the motor off and listen for a gentle click as it slows down,this will tell if the centrifugal switch is working mechanically, testing electrically will be more involved but fairly simple, see how you get on and report back.

Good Luck!

Edited By Dave Wootton on 23/09/2023 07:47:44

Hi Again Mark

Just realised that you said the motor just buzzes in either direction, which I assume means you have a Dewhurst type or similar reversing switch fitted to the machine. These reverse the connection to the start winding to change the direction of rotation, if the contacts on these are excessively burnt or pitted, which can happen, it could also affect the connection to the start winding and cause your problem. Still worth carrying out the above tests, but it does complicate the electrical fault finding somewhat. Depends if you have and are comfortable with using a multimeter.

Dave

Mark The forward / reverse switch should not be used for stopping and starting

Roy

This type of fault has been covered many times, several occaisons recently, Look in the archive for motor issues. Since you mention a direction switch it could be a Santon or the Dewhurst and the contacts could have failed. Strip the switch and inspect the contacts, which will almost certainly show signs of burning, it may be posible to clean them. THEN rewire with an ON/OFF switch BEFORE the reverser, select direction then turn on ! As Roy has said they should NEVER be used to stop or start the motor ! The motor may not yet be spoilt but DO NOT leave it buzzing for long or it will be ! If you are not OK with working with electrics then you will need help. Could be the start capacitor has failed, quite common on old equipment. Not to expensive and would need to be replaced. NOTE VOLTAGE and it must be a motor start capacitor ! Could be the centrifugal switch. If you take the belt off, spin the motor by hand and turn on it MAY spin up to running speed ! Turn off and listen for a CLICK as it slows, this is the switch operating, though the contacts may be burnt, they can be cleaned but this requires the motor to be stripped. A wiring fault may have developed - find and fix, or it could be that the start windings have gone - terminal ! Noel.

I have had this fault before and it's easily fixed if you have the same problem. If you have a dewhirst switch take the front off and examine the contacts. You will probably find that they are burnt due arcing but salvageable. Simply clean them up with an emery stick and retension them with some rat nose pliers. I had been stopping and starting my single phase motor for thirty years before I fitted a clutch so all the scare stories about doing this are almost nonsense to me. Of course, I only go by personal experience not what it says in the books or what Inspector Meticulous has to say about it.

Not all single phase motors have start capacitors, the one on my ML7 didn't.