I'd need help with my lathe v-belt drive

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I'd need help with my lathe v-belt drive

Post by Steam Captain » Sun Jul 07, 2019 7:45 am

Hey,

I am having a repeating issue with the v-belt of my lathe. After installing the pulleys with taper locks and mounting the v-belt, I realized the electric motor isn't moving. It is struggling and if I turn the shaft of the lathe by hand, it just moves a little until coming to a halt with a strong humming. All signals imply all the energy is wasted in the belt drive ven though the motor is definitely working and very strong without the belt.

I tried out several steps of loosening the belt until it became clear a belt drive wouldn't be used in such a loose state.

The lathe shaft is moving freely also.

Does anyone have any idea? I am using a 4 1/2" and 3" pulley with an SPA v-belt.
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Re: I'd need help with my lathe v-belt drive

Post by TriangleTom » Sun Jul 07, 2019 10:06 am

Are there any rough spots when you turn the motor by hand? What comes to my mind is that when loaded with a sideways pulling force on the motor shaft, a bearing that may already be going bad is stopping the whole motor from turning.
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Re: I'd need help with my lathe v-belt drive

Post by Steam Captain » Sun Jul 07, 2019 11:12 am

Thank you for the reply. It seams, that the bearings are ok. And it is the second electric motor I used. Originally, the lathe was stuffed out with a 0.37 kW motor and was running well with the old headstock with its completely worn out bearings. The first motor I bought for the new headstock had somewhat of the same power officially, but somehow, the motor was so weak, that I could stop the axle with my hand - something you can't do if the full power really applied. And the motor now has 0.8 kW and runs smoothly, has power and everything, but putting the belt on and nothing but a laborous humming comes out of the motor. The new belt seems very strong and the smaller pulley almost seems too small, though that is definitely not the problem here, because this would mean the belt would at least slip. The grip is good, the length is good, though the belt could be more flexible, I tried out lots of settings for the tension - even ridiculously loose settings and even than it wouldn't turn, but it turned more easily while helping turn it by hand also.
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Re: I'd need help with my lathe v-belt drive

Post by Steam Captain » Sun Jul 07, 2019 11:13 am

Thank you for the reply. It seams, that the bearings are ok. And it is the second electric motor I used. Originally, the lathe was stuffed out with a 0.37 kW motor and was running well with the old headstock with its completely worn out bearings. The first motor I bought for the new headstock had somewhat of the same power officially, but somehow, the motor was so weak, that I could stop the axle with my hand - something you can't do if the full power really applied. And the motor now has 0.8 kW and runs smoothly, has power and everything, but putting the belt on and nothing but a laborous humming comes out of the motor. The new belt seems very strong and the smaller pulley almost seems too small, though that is definitely not the problem here, because this would mean the belt would at least slip. The grip is good, the length is good, though the belt could be more flexible, I tried out lots of settings for the tension - even ridiculously loose settings and even than it wouldn't turn, but it turned more easily while helping turn it by hand also.

It can not be possible, that a belt swallows up all 1.2 HP!
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Re: I'd need help with my lathe v-belt drive

Post by fredrosse » Tue Jul 09, 2019 4:02 am

Ordinary V-belts work very well with low friction. My Atlas lathe, 12 x 36, built about 70 years ago uses a typical 1/2 inch wide V-belt with a 3/4 horsepower motor. I have been using this lathe for 25 years without any belt problems, and have never changed the belt. Maybe there is heavy friction in the headstock?
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Re: I'd need help with my lathe v-belt drive

Post by Mike Rometer » Tue Jul 09, 2019 8:09 am

By pressing in the middle of the longest belt run there should be about 15mm deflection without undue effort. Any less and the belt is too tight. A new belt should need re-adjusting after a little use and can then be a little tighter (12mm). Poly-vee belts and flat belts should be under mild tension.
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Re: I'd need help with my lathe v-belt drive

Post by Steam Captain » Tue Jul 09, 2019 10:27 am

Thanks Mike and Fred,

The headstock can be turned by hand, but it is hard to estimate how easily it should turn. But I am suspecting now, that it at least should do some turns on its own when spun by hand, what it doesn't. After half a revolution, it stops.

At least it seems like an attack point for me to solve this. It's the first mechanical machine I built the transmission for.

I will check if I can allign the two large flange bearings today and will let you know. (Actually IF it works, it'll immediately make me upload photos of the then just turned parts for the opposed-piston steam engine;)

Ok, step by step.
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Re: I'd need help with my lathe v-belt drive

Post by Steam Captain » Tue Jul 09, 2019 3:49 pm

Hello Fred and Mike,

I just came back from my workshop and got the lathe running. I am so relieved, because all the time I already wanted to machine pieces for my steam engine.

To explain what it was: The belt seemed alligned well, but actually wasn't. And the belt is very, very stiff and the electric motor seems to be unable to start under load - what surprises me to be honest. I also originally set the tension with the general rule for belts and chain gear, as you, Mike also explained. But since the belt is so stiff, I couldn't follow the rule.

Now, it runs very loosely. It runs and has power, yes. This is already a win for me. Now, I'll just try to get closer to the rule and hope the belt will also lose its strange stiffnes after a few hours. I thought about idlers, as the belt follows an unhealthy oval path.

And I just remember I DID allign the spindle until it was spinning freely for quite some time. So this might be the reason for the motor to be bately able to start.I think working through all these small issues should get me started finally.

I thank you a lot so far. Those are simple issues, but it does happen, that we get a tunnel sight.

I am happy my lathe soon will spit out steam engine parts.
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Re: I'd need help with my lathe v-belt drive

Post by Mike Rometer » Tue Jul 09, 2019 5:36 pm

You might need to check that the start capacitor/circuit on your motor is working. This will give more power to for the first few seconds of switch on to enable it to overcome the inertia of the start.
Last edited by Mike Rometer on Tue Jul 09, 2019 9:19 pm, edited 1 time in total.
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Re: I'd need help with my lathe v-belt drive

Post by Steam Captain » Tue Jul 09, 2019 7:44 pm

I just knew a capacitor removes the inductive phase angle of the virtual inductive resistance (there probably is a proper english term for that, but you'll know what I mean) but I didn't know of the initial power plus.

Indeed that motor originally came from a lawn mower and I got it without any capacitor. So, this might help also. Luckily, I kept the original motor-capacitor.

I will fiddle around with the more than anticipated options, which we scratched together now.

By the way, I already turned my first surface with the present, sub-optimal setting. So, it can only get better.

I am really thankful, that you take the effort to respond to such a rather boring subject, because it will be the start of a lot of fun projects.
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