Vintage Lathe + Variable Frequency Drive

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TDPurcell

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Are there any pitfalls in adding a motor controlled by a variable frequency drive to an antique lathe that operates from a countershaft set up such as the one in the attached pic? The lathe's motor currently runs a v-belt to the countershaft drive pulley which, in turn, runs the countershaft/spindle belt.

I'm wondering if I could swap the motor for one controlled with a VFD, such as the KBAC-24D, and control the lathe's spindle speed with the VFD instead of the step cone on the counter shaft (as well as have a forward and reverse option). I'm guessing there may be some problems in doing this that I am unaware of. Any input is appreciated.

image1.jpeg
 
It can be done, but I'm not sure there would be any advantage to doing it. Most line shaft machines have extremely low spindle speeds as compared to more modern lathes. My Seneca Falls Star #20 is supposed to operate at between 18 rpm and 340 rpm. The highest rpm of any of their line shaft machines were the 13" engine lathes. They had a top speed of 557 rpm. Running them much above the rated speed would quickly wear out the headstock bearing material. Unlike more modern machines the headstocks have plain bearings and an oil reservoir below each of the headstock bearings. The bearings are lubricated by an oil slinger that runs on the spindle shaft and brings oil up from the reservoirs.

The lead screw and other intermediate shafting is supposed to be lubricated every 4 to 8 hours of runtime using a squirt oil can at each of the oil ports. These lube points are a total loss system meaning there is no reservoir to hold oil against the bearings. They would quickly run dry and be damaged with speeds above their rated maximum.

DSCF8035.JPG

Note the size of the speed reduction pulley on the jack shaft my lathe and the one in your picture. I would think running the motor at the speeds needed to keep the machines from self destructing would be awfully hard on the motor.

As a side note my Sheldon lathe uses roller bearings with oil bath reservoirs in the headstock. Top speed on this machine is 2,200 rpm.
 
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projectnut,

Thank you for this feedback. This is very useful information.
 
Great information Projectnut. I've noticed that most older machinery that was converted to electric by the manufacturer usually used often a low power motor that were 4 or 6 pole so often it is quite cheap to repower them but sometimes extra speed reduction is needed and an eye has to kept open that they are not overpowered.
 
old motors (non-inverter rated motors) can safely operate in the 30 to 90 HZ envelope without problems.
a single phase to 3 phase VFD could be quite useful when all you have is single phase power to run a single machine on 3 phase.

you can use the belt reduction too and vary the speed in each belt ratio

here is an example of what i did to a near antique motor on a 1925 Superior Dual Spindle Milling machine
https://www.hobby-machinist.com/threads/superior-duplex-milling-machine.30196/#post-260125
 
you can also program/use the VFD to achieve a smaller operating envelope, if overspeed is of concern
say like 30 to 60Hz or 50 to 70Hz , or simply run it at 60Hz, but still run on single phase power as the added bonus.
on my Shenwai lathe i have the 10 to 85 Hz envelope programmed into the VFD, and a potentiometer for setting the speed control
i rarely change belt position anymore
 
Thanks,
I am aware of how to use VFD's but they are still very expensive here and I'm not rich. I have re-powered old 3~ machines by replacing the 3~ motor which is often in the 3/4 - 1 1/2 HP range rated at 750, 1250 or 1450 r.p.m. with a much smaller 1~ motor of a different speed suitably geared.
My comment was more related to overall power requirements as looking at old brochures there is often a warning that a motor should not exceed a stated power level and required r.p.m. is also clearly stated.
As Projectnut so clearly pointed out, while the old stuff works perfectly well in its original state there are pitfalls that have to be addressed if 'uprating' and those approaching an old machine may inadvertently overlook these constraints.

Regardless, any time I see some old iron saved from the scrapper I feel good no matter if it will be 'uprated' or not. We're engineers,(or at least pretend to be), so that is what we do.

I hope you all had an enjoyable Solstice so now back to work.
 
I have to confess to doing something similar to this to an ex-lineshaft milling machine (an early Burke #4). Being able to dial in the speed to tweak the cutter speed was a nice touch, and having done it with a treadmill motor and controller the cost was minimal.

I simply replaced the original (very tired) motor on the conversion with the DC motor and mounted the controller in a box on the stand. I DID retain the jackshaft and its drive - this let the motor spin at optimum speeds and still retain low speed at the cutter. A comfortablepackage to use, and not difficult to fit.

Just a thought - Alan
 
I replaced the motor on my 9" Seneca Falls Star lathe with a 1hp 3 phase unit and a VFD. Definitely a worthwhile upgrade though not cheap if you're buying new components.

I'm sure I could have done it with a treadmill motor too but I really wasn't patient enough to source the pieces. It's great to be able to dial in the correct speed for whatever operation by feel, and now since I installed a tachometer I can repeat speeds without much effort. I did gear it to where it's hard to overspeed the lathe too.

Cheers,

John
 
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