Lathe motor stutters when running slowly

[Chris152]

I got my lathe back home after a year of no use, running fine at speed but stutters when slow (Variable speed control). I know it has a dodgy female to male connector in the switch but have crimped that down and it seems to be fitting tight.
Any thoughts/ advice?
Thanks, C

 

[Chris152]

Ran it for 30 mins at speed to get it all warmed up and dry, seems to have done the trick.

 

[Sideways]

Glad you fixed it.
Just a general comment for those who don't realise this ...
Running an induction motor on a variable speed control, power is pretty well directly related to speed. Half the speed and you're only getting half the power.
Run a 1500W / 3000 rpm motor at 300 rpm and it's only a 150W motor. At 100rpm it's 50Watts. The motor and drive will stutter and stall at slow speeds if they meet any great resistance.
There's no substitute for moving the belt to get decent torque at slow speed.
When I setup a VFD I tend to program a fairly high minimum speed : 25 to 30% of full speed so it's not possible to wind the VFD down to stupidly low speeds.
I'd make an exception for people wanting to copy Mick Hanbury who dries turned pieces slowly under zero load with a hair dryer fastened to his toolpost

 

[Chris152]

Thanks Sideways - that's really helpful, I didn't realise. I swapped the belt around a couple of times and noticed a difference, and it was only happening at really slow speeds. Seems fine now but one to remember.

 

[Sideways]

Spot on Chris. Well done
"Keep the revs up" I remember my driving instructor telling me after I'd stalled the car a time or three. It's a similar concept. You can't pull away in top gear with the engine just idling.
Cheers

 

[Spectric]

I have used lathes on and off over the years but always set the speed using the gearbox on the machine, I cannot see why you would need a VSD unless you are running a three phase motor. As sideways has said the torque is proportional to frequency so for max torque just set the frequency to 50Hz and leave it, then use the gearbox. Another issue with running a motor very slow is it can overheat due to lack of cooling, you can buy cooling fans that replace the end cowl on some motors but these low speeds are often only used on gantry cranes.

 

[Chris152]

I have used lathes on and off over the years but always set the speed using the gearbox on the machine, I cannot see why you would need a VSD unless you are running a three phase motor. As sideways has said the torque is proportional to frequency so for max torque just set the frequency to 50Hz and leave it, then use the gearbox. Another issue with running a motor very slow is it can overheat due to lack of cooling, you can buy cooling fans that replace the end cowl on some motors but these low speeds are often only used on gantry cranes.

I've no idea about frequency and assume 'gearbox' refers to the pulleys, but there's no question having variable speed is really helpful when trying to turn irregular/ off-balance wood and trying to minimise vibration; I find changing pulleys part way through turning a pita; quite often slight variations in speed feel better on the gouge for this or that piece of wood; and sometimes I turn the lathe slowly while banding with paint on a piece's surface.

 

[Spectric]

Hi Chris

Having spent all my career in various fields of engineering I just assumed lathes mean metal turning, wood turning lathes do not seem to register and I assume on these you have to change belts to alter speed like on a pillar drill whereas metalworking lathes have a gearbox as in a harrison or Colchester where you just select speeds using knobs and levers and also feed speed for screw cutting.

 

[Chris152]

Well, it still stutters but now when it's turning off-balance wood at speed! (I.e, when the lathe is vibrating a bit.) I've checked the connections on the switch that caused issues in the past and all seem tight, but reckon that's where the problem is. Can I get a replacement switch for this or is it now pre-historical? And is it likely to be the switch itself or am I just clutching at straws?
Thanks.

 

[Reginald]

I got my lathe back home after a year of no use, running fine at speed but stutters when slow (Variable speed control). I know it has a dodgy female to male connector in the switch but have crimped that down and it seems to be fitting tight.
Any thoughts/ advice?
Thanks, C

hit the connection with a resistance test it may be good when current is flowing hard but not so when trickiling through.

 

[Chris152]

hit the connection with a resistance test it may be good when current is flowing hard but not so when trickiling through.

It seems to be fine at slow speed now, the 'new' problem is when it's running at high speed. A friend who likes these things is coming around to bypass the switch to check whether or not it's the switch. We'll see...

 

[Chris152]

Definitely the switch - working fine when the switch is bypassed. I'll start another thread to see if anyone knows if/ where I can find a replacement.