myford stopping

my Myford super 7 keeps suddenly stopping then starting again

anybody out there any ideas have taken a video of it doing it so if anyone thinks of anything happy to send them the video

How is it driven mains, VFD, 3 phase ? Bad switch, connection, lead, motor faulty. More info required please.

Put the video on Youtube and add a link to post.

regards

Edited By Oldiron on 31/01/2023 18:00:20

Headstock bearings too tight?

It sounds as if the clearance of the bearings needs adjustng .If you follow the instructions in the manual for spindle adjustment you will be able to correct it .When you get the bearings right give the rear adjusting collar with the c spanner on a clout with a rubber mallet.

Frank

Sounds a bit like an electrical intermittent fault possibly vibration induced

Single phase motor with a large metal casing on the side (contains capacitor) ? or could it be a slack belt drive which doesn't as soon as you start turning.

First thing you need to do is determine whether the problem lies at the headstock spindle end of the drivetrain or at the motor end.

Next time it stops, shut off the power, release the belt tension and see if the chuck rotates freely by hand. If it is stuck solid, see Bricky's post above about adjusting the S7 tapered bronze bearing which could grab like a morse taper if not enough clearance and it gets hot and expands.

If the chuck is free to turn, problem is most likely in the motor or wiring. Check if the motor spindle can be turned by hand. If it can be turned, problem is not motor bearings b ut something in the wiring, most likely.

(All assuming of course that belt tensions are correctly set and not slipping.)

Edited By Hopper on 31/01/2023 23:08:14

Being able to watch the video would help. Maybe Garry could host it on one of the streaming services, like this example, and post the link on the forum?

Sounds electrical to me: loose wire, Dewhurst contact failure, fracture break inside a cable.

Check everything between mains and motor.

• With the motor running
  • waggle the plug in the mains socket (bad plug, loose wire in plug, damaged socket)
  • flex cable to lathe (intermittent break)
• With lathe unplugged from mains:
  • check wiring from input terminals to motor via switches (NVR), Dewhurst, etc. first visually, then confirm continuity with with a multimeter.
  • Look for loose connections at terminals; with luck vibration has undone a screw and it just needs tightening. Loose connections often show signs of heat or sparking: insulation changes colour at the terminal, and terminal is pitted

Switch contacts are prone to wear and tear. If the lathe is fitted with an elderly Dewhurst, it would be my chief suspect. The design isn't particularly good, and owners abuse them by using the switch to turn the lathe on/off. The contacts wear rapidly if used for hot switching because they weren't made for it. Have a look inside: any damaged contacts should be obvious.

Dave

Take the primary belt off and run to motor on it's own. Rattle the cables about a bit and see if you can get it to fail.

If it does you have a motor or supply fault.

regards Martin

Hi George,

You will feel the heat if you touch the headstock bearing area, luke warm is OK.

Likewise put your hand on the motor casing after it stops it's self. If it's as hot as your CH radiators it may be that a temperature cut-out in the motor end casing operating trying to protect the windings. If it does this off load it's usually the field coils shorting making the motor draw more current than it should. This means you need a new motor

Lots of ideas for solutions but far too little information on symptoms!! Please post your video on YouTube, I don't think anyone is going to want to ask you to send it then view it then puzzle out what might be wrong.