Please help me choose a motor & VFD for a vintage Rivett lathe

cazclocker said:
Yes, I am positive that I need a motor rated at 3600 RPM or thereabouts. The lathe is a vintage precision bench lathe that was originally designed to run at a maximum of 3500 RPM. The lathe spindle runs a pair of size-matched V-belts which pass through a hole in the bench straight down under a headstock cover. I just found out that my friend who is selling the lathe to me will supply the SAME SIZE pulleys for mounting onto the motor shaft, so the drive ratio will be 1:1.

So far I now know that I want a 230/460 VAC motor, 1hp - 1.5hp, 3600 RPM (+/- a few RPM's) and (for reasons I don't understand) I don't want sleeve bearings.

Why are sleeve bearings not desireable?

I have yet to pick a VFD - thanks for suggesting dealerselectric.com.

...Doug
Click to expand...

But didn't that machine lathe have belt reduction to give a wide range of speed? (See link below). It says 150-3500 rpm. You will NOT get near that range with only a VFD for speed control. You are limited with a VFD at the low speed end by two things. #1 Motor cooling, the motor must run at a speed fast enough for the internal fan to cool it. #2 Power, at slow speed. You can go to a more powerful motor to help #2 but there isn't much you can do about #1. Personally I don't run any of my VFD driven motors below about 1/2 rated speed and no more than 1.5x rated speed. Using those seat of the pants numbers and a 1:1 belt ration with an 1800 rpm number you could go from 900 - 2700 rpm. Using a 3600 rpm and 1:1 it would be 1800-5400 rpm. With a different belt ratio you can move this speed range around but you will always have a limited range unless you provide for a way to change the belt ratio. I also like slower motors because are quieter and run smoother.

FWIW my Logan has it's original 1945 1800 rpm sleeve bearing 3 phase motor, I did put new bearings in it when I got it.

http://www.lathes.co.uk/rivett/page7.html
 
sleeve bearings are not as precise as roller bearings and can't hold up to high speeds.


as far as what you need for a motor given your specs is
230volt 3 phase, if you get a dual voltage 230/460 that's great but a single voltage motor(230 v 3 phase or even a 200v 3 phase motor) would suffice
1-5 hp, 3600 rpm

a 56 frame motor has a 5/8" keyed shaft with 1 exception the 56HZ which has a 7/8"(keyed 2" long) shaft
a 145t motor frame has a 7/8" shaft
a 182t has a 1 1/8" shaft
a 213t has a 1 3/8" shaft
a 215t has a 1 3/8" shaft

i hope the info helps
 
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cazclocker said:
Yes, I am positive that I need a motor rated at 3600 RPM or thereabouts. The lathe is a vintage precision bench lathe that was originally designed to run at a maximum of 3500 RPM. The lathe spindle runs a pair of size-matched V-belts which pass through a hole in the bench straight down under a headstock cover. I just found out that my friend who is selling the lathe to me will supply the SAME SIZE pulleys for mounting onto the motor shaft, so the drive ratio will be 1:1.

So far I now know that I want a 230/460 VAC motor, 1hp - 1.5hp, 3600 RPM (+/- a few RPM's) and (for reasons I don't understand) I don't want sleeve bearings.

Why are sleeve bearings not desireable?

...Doug
Click to expand...

CluelessNewB is correct. You will not have the speed range you need with the motor direct coupled to the spindle. I have never seen a belt drive lathe that didn't have step pulleys (or variable speed pulleys) for changing the speed ranges, even when using a VFD.

It is very unusual to have a lathe motor run the spindle directly at a 1:1 ratio. The exception would modern CNC equipment with big AC servos running the spindle.

The motor HP is a function of Torque x RPM, therefore, a 3600 RPM, 1.5 hp motor develops 0.75 HP at 1800 RPM. Also a 1.5 HP, 3600 RPM motor has 1/2 the torque of a 1.5 HP, 1800 RPM motor.

If I were going to run that lathe direct drive, I would be looking at about a 3 KW AC servo drive, and gear it down to about 1.5:1. This would give you the wide speed range, with reasonable torque throughout the speed range.

Sleeve bearings (bushings) are not good for side (radial) loading on the motor shaft, like a belt drive. If the motor is driving a load with no or very light radial load, like a fan, they have a reasonable service life. Ball bearings will hold up to the heavy radial loads for continuous belt drive duty.
 
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CluelessNewB said:
But didn't that machine lathe have belt reduction to give a wide range of speed? (See link below). It says 150-3500 rpm. You will NOT get near that range with only a VFD for speed control. You are limited with a VFD at the low speed end by two things. #1 Motor cooling, the motor must run at a speed fast enough for the internal fan to cool it. #2 Power, at slow speed. You can go to a more powerful motor to help #2 but there isn't much you can do about #1. Personally I don't run any of my VFD driven motors below about 1/2 rated speed and no more than 1.5x rated speed. Using those seat of the pants numbers and a 1:1 belt ration with an 1800 rpm number you could go from 900 - 2700 rpm. Using a 3600 rpm and 1:1 it would be 1800-5400 rpm. With a different belt ratio you can move this speed range around but you will always have a limited range unless you provide for a way to change the belt ratio. I also like slower motors because are quieter and run smoother.

FWIW my Logan has it's original 1945 1800 rpm sleeve bearing 3 phase motor, I did put new bearings in it when I got it.

http://www.lathes.co.uk/rivett/page7.html
Click to expand...

Clueless, you're right - the Rivett 715 came stock with a motor of unknown-to-me specs, and an intermediate countershaft between the motor and the lathe's spindle. Hence the 150 - 3500 RPM's both forward and backward.

OK, I'm starting to see that this is more involved than I was hoping for. I think I need to slow down and find out what the heck I need!

Ulma Doctor said:
sleeve bearings are not as precise as roller bearings and can't hold up to high speeds.


as far as what you need for a motor given your specs is
230volt 3 phase, if you get a dual voltage 230/460 that's great but a single voltage motor(230 v 3 phase or even a 200v 3 phase motor) would suffice
1-5 hp, 3600 rpm

a 56 frame motor has a 5/8" keyed shaft with 1 exception the 56HZ which has a 7/8"(keyed 2" long) shaft
a 145t motor frame has a 7/8" shaft
a 182t has a 1 1/8" shaft
a 213t has a 1 3/8" shaft
a 215t has a 1 3/8" shaft

i hope the info helps
Click to expand...

Thanks that's very useful.

JimDawson said:
CluelessNewB is correct. You will not have the speed range you need with the motor direct coupled to the spindle. I have never seen a belt drive lathe that didn't have step pulleys (or variable speed pulleys) for changing the speed ranges, even when using a VFD.

It is very unusual to have a lathe motor run the spindle directly at a 1:1 ratio. The exception would modern CNC equipment with big AC servos running the spindle.

The motor HP is a function of Torque x RPM, therefore, a 3600 RPM, 1.5 hp motor develops 0.75 HP at 1800 RPM. Also a 1.5 HP, 3600 RPM motor has 1/2 the torque of a 1.5 HP, 1800 RPM motor.

If I were going to run that lathe direct drive, I would be looking at about a 3 KW AC servo drive, and gear it down to about 1.5:1. This would give you the wide speed range, with reasonable torque throughout the speed range.

Sleeve bearings (bushings) are not good for side (radial) loading on the motor shaft, like a belt drive. If the motor is driving a load with no or very light radial load, like a fan, they have a reasonable service life. Ball bearings will hold up to the heavy radial loads for continuous belt drive duty.
Click to expand...

Thanks for that - I may have to change my goals - maybe I need to build a countershaft like the OEM had.
...Doug
 
I'm still trying to decide on a motor - I'll choose a VFD once I've settled on the motor for my soon-arriving Rivett 715 bench lathe. I've decided against the motors from Surplus Center. Instead, I've decided to choose a better quality motor. Can anyone here help me decide if the one I'm looking at is a wise choice or not? I'm looking at THIS ONE from MSC. I've been trying to study up on AC motors and I think I've learned a bit, but maybe not enough to make an informed decision. A few days ago I received the first box of bits & bobs from the seller (30 4C collets were included!), and the motor pulley was one of the items included. The pulley has a 5/8" keyed shaft opening, so right there it narrows down my motor frame search to the 56 series...am I correct in that?

One spec on the above-referenced motor is the frequency Hz....it says 60/50. What does that mean? Again, my power source will be the 220VAC dryer outlet in my workshop.

By the way, I was also looking at part #6136K77 from McMaster Carr, but I have a long history with MSC.
Thanks,
...Doug
 
50/60 Hertz means it will run on either USA or European power at rated HP. It will run fine on your dryer outlet. In the North America our power is 60 Hz.

The price looks good, and the brand is well known. With a 5/8 pulley, you will want a 56 frame motor.
 
JimDawson said:
50/60 Hertz means it will run on either USA or European power at rated HP. It will run fine on your dryer outlet. In the North America our power is 60 Hz.

The price looks good, and the brand is well known. With a 5/8 pulley, you will want a 56 frame motor.
Click to expand...

Jim, do you really think the price ($303.10) is a good price? My friend who's selling the lathe to me that it's outlandishly expensive; I can do better elsewhere.
...Doug
 
Here is an alternative.

About 1/3 the price, and a good vendor. Doesn't have the external cooling fins, and is not inverter duty, but I have used this motor with VFDs without problems. Extended running at low RPM might require an external cooling fan.
 
JimDawson said:
Here is an alternative.

About 1/3 the price, and a good vendor. Doesn't have the external cooling fins, and is not inverter duty, but I have used this motor with VFDs without problems. Extended running at low RPM might require an external cooling fan.
Click to expand...

Jim, thanks so much for that recommendation. At $101.00, it appears to be an unbeatable deal and for $13.00 more I can step up one notch to a 1.5HP motor. I especially appreciate the fact that you seem to have had personal experience with the 1HP version.

OK....now to pick out a VFD.
...Doug
 
Glad I could help. I buy a lot of stuff from those guys.

Take a look at the same vendor under Drives
 
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