Help with lathe speed potential motor problem.

[jimbo84]

When I've got my boxford set to the highest speed it runs really slow. The motor/pulley shaft seems to be running very fast but the chuck is turning very slow and is easy to slow down/almost stall. The chuck turns quicker in the lower gear settings.

When I first got it the lathe it took a while to spin the chuck up to speed in top gear but it got there.

Strange thing the motor seems to be running at full speed. I can hear the centrifugal switch clicking in on start up and hear it dropping out after turning off when the motor is running down.

Speed plate, settings are set for the 1300 RPM.

I thought it was maybe a running capacitor fault not getting the motor to full speed but the centrifugal switch can be heard clicking in and with the belts off and the motor running idle it seems to running at full speed to the eye anyway, I've no tachometer.

I've meggered the windings to earth and getting 7Mohm.

Would you just slap a new running capacitor on and see what it's like? Any other tips?

Motors have always been a dark art to me

It runs faster at the 250RPM setting than the 1300 setting which suggests a struggling motor but the motor seems to run at the same speed no matter what which doesn't add up.

Speed plate.


Current capacitors



Edit: further info.

Disconnecting the white cap the motor doesn't start so I'm guessing that's the start cap and the blue the run cap.

Blue says intermittent does that suggest the wrong cap is fitted?



Start Cap.



Very helpfully the motor plate is missing so zero data on the motor type/speed to work out and check the right replacement capacitor size.

 

[daedalusminos]

Belts slipping?

 

[daleyd]

Do the boxfords have 2 belts? On mine (denford) there is one belt to an intermediate pulley then a second up to the headstock. If either of those are loose then you can get a speed diff between motor and chuck - I don’t know if boxford have same arrangement but I know there are some similarities…

 

[carbon]

The blue cap is the start cap and the white one is the run one. It will still need the run cap in circuit when starting

 

[jimbo84]

Belts slipping?

I didn't think they were but I've just tensioned them and it really struggles to run and doesn't get up to speed at all, slackened them off started it and then tensioned whilst running and the chuck is turning a lot lot faster.

Do the boxfords have 2 belts? On mine (denford) there is one belt to an intermediate pulley then a second up to the headstock. If either of those are loose then you can get a speed diff between motor and chuck - I don’t know if boxford have same arrangement but I know there are some similarities…

Yeah it has the motor and twin pulley assembly on the bench behind.

The blue cap is the start cap and the white one is the run one. It will still need the run cap in circuit when starting

That makes a lot more sense. With the belts tight and under load it really struggles to start, wonder if the start cap is bad.

 

[carbon]

You need to check the capacitance to make sure, some multimeters can. If you can hear the centrifugal switch operate that doesn't necessary mean that its switching the capacitor it could be a bad connection on the switch

 

[jimbo84]

My multimeter only measures up to 20uf. Seems the start capacitor fitted is an unusual size too, not commonly available.

 

[carbon]

Just had a quick look on ebay

Start capacitor

 

[jimbo84]

Just had a quick look on ebay

Start capacitor

Thank you

Didn't even think of ebay, D'OH. Had found some from electronics suppliers but north of £50.

Next question is current rating being 220/275uf would it be best to go for 200/250 or 250/315uf?

 

[hunter27]

I have a Boxford Bud running on 3 phase from an inverter. I replaced the inverter an (IMO 1 or1.5kw) and the 3 phase motor a couple of years ago. With the motor I slightly upsized to .9HP from the old .75hp one. My lathes data badge says max rpm 1400rpm but it is only comfortably achieves up to around 850rpm, I don't have the pulleys set up for top speed because it seems to struggle above that. speed and stalls easily. On the first use of the day I turn the chuck by hand half a turn because if I don't it can be reluctant to initially turn with the motor. The chuck can be turned reasonably easy by hand but there is the resistance of 3 belts and 4 spindles to rotate. I haven't looked into it as it has never been a problem but it would be interesting to know what was causing this to happen.
Don't know if any of this is relevant to your problem though.

 

[jimbo84]

I have a Boxford Bud running on 3 phase from an inverter. I replaced the inverter an (IMO 1 or1.5kw) and the 3 phase motor a couple of years ago. With the motor I slightly upsized to .9HP from the old .75hp one. My lathes data badge says max rpm 1400rpm but it is only comfortably achieves up to around 850rpm, I don't have the pulleys set up for top speed because it seems to struggle above that. speed and stalls easily. On the first use of the day I turn the chuck by hand half a turn because if I don't it can be reluctant to initially turn with the motor. The chuck can be turned reasonably easy by hand but there is the resistance of 3 belts and 4 spindles to rotate. I haven't looked into it as it has never been a problem but it would be interesting to know what was causing this to happen.
Don't know if any of this is relevant to your problem though.

Sounds like similar symptoms to mine although you're on 3 phase and this one is single phase. I got this one second hand and it's never been comfortable on top speed but it did used to get there but now doesn't seem to be and won't start in high speed with good tension on the belts.

Going to put a start capacitor on it and see what happens with that.

 

[123hotchef]

are you sure the belt aint slipping?

 

[jimbo84]

are you sure the belt aint slipping?

That was definitely an issue, spins faster with some more tension on the belt but the motor won't start or run at speed with that tension on in higher gears. Going with a new start cap and see where that gets me.

 

[carbon]

Has it always been like this or only recently started doing this?

 

[Kram]

Something is quite wrong if its struggling to get to speed unloaded.
Do you have a current clamp power meter? That would tell you if the motor is trying - no and its the start cap. Yes and it might be bad bearings.

 

[jimbo84]

Awaiting the new start cap but came across this on another forum which originated elsewhere, mine has the two step pulleys but sounds like it may have neglected to have had the motor upgraded.

By paying £3 : 10s : 0d extra the motor and countershaft could be fitted with 2-step pulleys when the speeds became: 38, 55, 75, 87, 110, 125, 175, 200, 250, 285, 400, 450, 570, 650, 900 and 1300 r.p.m. Unfortunately the makers neglected to mention the fact that in order to run on top speed a more powerful and expensive motor was required.

 

[jimbo84]

Something is quite wrong if its struggling to get to speed unloaded.
Do you have a current clamp power meter? That would tell you if the motor is trying - no and its the start cap. Yes and it might be bad bearings.

Unloaded the motor gets up to speed ok, it's when it's under load it's struggling.

 

[carbon]

Is the motor big enough to drive the lathe?

 

[jimbo84]

Bit of an update.

Finally had some time to fit the new cap.

Motor is still the same. Highest speed it will comfortably start and run in is 600 RPM.

I suspect the motor is under powered for it's use as per this I found.

By paying £3 : 10s : 0d extra the motor and countershaft could be fitted with 2-step pulleys when the speeds became: 38, 55, 75, 87, 110, 125, 175, 200, 250, 285, 400, 450, 570, 650, 900 and 1300 r.p.m. Unfortunately the makers neglected to mention the fact that in order to run on top speed a more powerful and expensive motor was required.

With the data plate missing there's not a lot of info available.

For the little use it'll get 600RPM will most likely be fine for what I need.