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I watch quite a few youtube machining videos guys like doubleboost etc.
I fitted a new beefed-up motor and inverter with a speed controller etc to one of my metal lathes. The shaft on the new motor was a different size to the original. It's fitted with a Woodrow keyway.
I just bought an off the shelf V pulley and fitted it. I have noticed in all the lathe related videos the pully on the motor is smaller than the one on the spindle. The pulley I fitted is larger than the one on the lathe spindle. Do I need to change it?
What I have noticed when trying to take a large cut the lathe can slow down and in some instances actually stall. The V belt is the original it's not verry substantial I am thinking I maybe should change both pulleys for ones that will accommodate a beefier belt. A small one on the motor and a larger one on the spindle.

Any advice would be welcome.

Well I would suggest calculating your ratios first, then look for taperlock type pulleys and centres for a good solid job.

Usually with a vfd the range is good enough that a small pulley is fine. Plus at lower speed with a smaller pulley, it would rotate faster than a big one so you'd have better torque of the motor wouldn't you?
Plus you want the belt to be the bit that slips, rather than stall the motor.

I never thought of taper lock. Good idea. I will check them out.
The motor doesn't stall the belt slips. The new motor is a lot more powerful than the old one.

Yeah I'm saying you want it to, so don't go for a toothed belt

bradaz11 wrote:Yeah I'm saying you want it to, so don't go for a toothed belt

I get lt. I will stick with a v belt and look for some new taper lock pulleys.

Is the new motor a 2 pole or 4 pole and what speed at the secondary do you need? As an example a 3000 rev/min motor with a 2:1 ratio gives a final drive of 1500.

Slightly off topic but do you watch This Old Tony? He's very knowledgeable and even more funny!

Alpha1 wrote:The pulley I fitted is larger than the one on the lathe spindle. Do I need to change it?

If your new motor pulley is larger than the original, the spindle will turn faster (of course) for a given motor speed.
Now that you have a variable speed drive you can turn it down to a speed that's safe for your lathe / appropriate for the job - but that could reducing the torque and would (perhaps) explain the stalling.
A smaller pulley will give you more torque because you can use a higher motor speed (I think).
But in turn , a smaller pulley will limit your possible top speed.

Is there any guidance from the manufacturer regarding pulley size and max spindle rpm?

I've read that you also have to be careful as not all chucks and tooling are rated for the higher-speeds possible with modern motors and they can explode aaarggh

You can pick up a cheap RPM tester on fleabay, from memory they are about £10-£12 so you can check what speed you are getting at the spindle

I'm just about to go through this exercise with my aged Myford ML7 so it would be great to hear how you get on.

Do you have a link for the taper-lock pulley gizmos?

Taper lock pulleys are very common.

If you have a good bearing or motor place locally they will have them on the shelf.

Otherwise look on google.