Variable Speed 1917 South Bend Lathe

[Maui]

I have a century old 16" South Bend lathe that is in beautiful original condition. It did not come with the separate jack shaft for changing speeds, and I would like to convert it over to a variable speed lathe for this reason. I have never attempted to do this before, and would like to benefit from the knowledge of those of you who have done this type of conversion successfully. I have an 1150 rpm 1 1/2 hp 3-phase motor that I intend to use for this purpose. What I am trying to figure out is what brand and model of variable frequency drive (VFD) to buy to power the motor. I have several 110V outlets available, and would prefer to use one of those for powering up the VFD. But I can run a separate line for 220V power if that makes more sense to do. It would just add additional cost to run the new line.

What make and model of VFD would you recommend, and why? Will I likely run into issues regarding torque loss at low rpms? The motor that currently powers the lathe is a single phase 3/4 HP ac motor, and it has had no issues so I would think that a 1 1/2 hp three phase motor should not struggle at all. What do you think?

 

[Strouty]

You will still need to adjust the speed, a VFD is not a true way to vary your speed, it is more of a fine tune, or a way to soft start a motor.

 

[Maui]

According to this Wikipedia article, a VFD is what you would use to vary both your rotational speed and torque:

https://en.wikipedia.org/wiki/Variable-frequency_drive

Am I missing something here?

 

[Strouty]

So if you slow the motor down to 50 hertz, then load it up, the motor should be fine, but if you drop it to 20 hertz and load it, you may have issues. Does that make sense? Basically the lower the hertz the lower the speed and vice versa. If it is not a high power application, it may not matter. If you think you are going to set the lathe in one place and use the VFD to go from 200 RPMs to 1500 RPMs, you won't be happy.

 

[Maui]

Ok, got it. So I might be better off using a Direct current motor and a speed control.

 

[Strouty]

I don't have any experience with those, but I know people use them for belt sanders. I am sure some others will chime in.

 

[nsula_country]

A 3Ø inverter rated motor with a 3Ø VFD can go from 0hz (hold) to about 200hz (fast!) reliably. Non inverter rated motor, stay below 100hz.

CT

 

[brucey]

Maui can you post a link to an image of your style of machine please ?

If your lathe is still fitted with a back gear simply use the middle pulley of the speed range and fit any sort of VFD it will get you going to play with and gain experience with

I will not go back to any other sort of drive configuration now.

Use the back gear for screw cutting and enjoy the benefits of screw cutting at 30 - 100 rpm with a spin of a knob.

In my situation ( I simply used a matched motor and drive from WEG 3Kw -4hp) and gain almost full torque at 5hz latest models that's why I went with a matched motor and drive

Good luck with it Bruce

By the way is the lathe used as a hobby machine ?

 

[Showkey]

A 3Ø inverter rated motor with a 3Ø VFD can go from 0hz (hold) to about 200hz (fast!) reliably. Non inverter rated motor, stay below 100hz.

CT

Agree.........

 

[Strouty]

See, I am glad others are chiming in and that it looks like I am wrong. Sorry for the bad info, every motor with a VFD I have dealt with, I was told not to run the VFD too low or high. Apparently I have been given bad info or I didn't understand. I hate it when that happens, seems to happen a lot lately.

The worst part is that I thought I understood things, now I feel like I understand nothing.

 

[454ragtop]

That motor is probably a good choice, but you will still need some mechanical reduction. Does the lathe have a working back gear? Can you get 2 or 3 steps on the pulley on the spindle? Being an 1150 RPM motor, a VFD should be able to get you from about 500 to 2000 RPM speed at the motor with decent torque. How many amps does the motor draw? 115 volt VFD's are available to 1 HP, but if you have a reasonable amp draw you might just sneak by with one.

 

[brucey]

See, I am glad others are chiming in and that it looks like I am wrong. Sorry for the bad info, every motor with a VFD I have dealt with, I was told not to run the VFD too low or high. Apparently I have been given bad info or I didn't understand. I hate it when that happens, seems to happen a lot lately.

The worst part is that I thought I understood things, now I feel like I understand nothing.

Um no you are correct in what you said in layman's terms

Old Motor / Old Drive (old school electrics) don't vary speed to much

Old Motor / Modern Drive may give you grief with noise and over heating of windings cook the motor etc

New Motor with Matched Drive Welcome to the Digital Age all the bells and whistles

I am not an electrical person at all but in an effort to get my toolmakers lathe up and running at home that's what I found (240v single phase) etc

Bruce

 

[justanengineer]

It depends largely on your needs but I would suggest finding a larger 5'ish hp single phase motor and making yourself a countershaft with hardwood pulleys. 1.5 hp is pretty dinky for that size lathe and varying speed solely with a VFD will only decrease the power transmitted further. OTOH, 1.5 hp will get you up and making chips with a $100-odd VFD from Teco or others. Be aware that once you get over 2 hp VFDs get very expensive very quickly.

 

[Maui]

Bruce, you can see photos of the lathe in this link:

http://www.garagejournal.com/forum/showthread.php?t=246413&highlight=Maui+south+bend

There is a gear reduction box currently in place between the motor and lathe. I set this machine up exactly as the previous owner had it. I could still use the gear reduction with the replacement 1 1/2 hp 3-phase motor if I choose to, but I would prefer to remove it if it isn't needed any longer. And I can post up a photo of the motor tag if that would provide some useful information.

Maui

 

[DenisG]

When you use the back gear on a lathe you drop the RPM, but gain torque. You can drop the RPM on a motor using a VFD, but you won't gain torque. Instead, you will lose torque:
http://www.pumpsandsystems.com/topics/pumps/motor-horsepower-torque-versus-vfd-frequency
There are also risks of overheating (or burning out) some motors when they are run below their design RPMs for a significant time.

 

[brucey]

Maui that is a beautiful old lathe I can smell the cutting oil and the smooth tic tic of the link in the belt from the otherside of the world

I can see from you pictures you have a back gear so your all good for low range but the mass of weight in the spindle may give your smaller motor a hard time also as your machine has bronze head bearings you will not need to go faster than at most 700 rpm

your lathe was at the fore front of HSS technology so don't go trying to use cemented carbide tip tools and high surface speed

Even 3 HP 2.2 kw would be the minimum I would look for and stick the belt in the middle gear for most of your turning work say 300 to 550 rpm rev range for that style of machine size you pulleys so your motor rpm /Hz sits in the middle and dial up or down on the VFD

In my case in Oz I paid 600 for a new WEG motor and Drive 4HP my motor sits at 1450 RPM 50 HZ my Drive goes to 75 Hz so close enough 2200 rpm and down to 5 hz so one rev every 3 minutes

is it a hobby machine for home use then use what you got to play with but I would investigate the cost of a combined motor and drive good luck with it mate

Bruce

 

[American Locomotive]

I assume you want the VFD in order to be able to slow the lathe down?

As mentioned, one purpose of the gear-reduction, besides just slowing the thing down, is to increase torque, which might be helpful in certain machining operations.

You should keep the gear reduction in place, as some electric motors do not do well under high loads at low speed. They do not get adequate cooling of the windings. VFD-rated motors often have oversized cooling systems, or even a separate cooling fan that runs on a dedicated power feed.