lathe and mill motor control

[JACK SIDEBOTHAMParticipant @jacksidebotham67303]

Hi all,looking for some advice on powering my granville lathe and my dore-westbury mill,the lathe is running from a 3 pin plug,and the mill is not yet completed,l have some electrical knowledge,but very little electronic knowledge……l am considering using a pair of VFD,s but dont know much about them,can anyone recommend a suitable unit??,thanks,jack.

[noel shelleyParticipant @noelshelley55608]

Remember that mechanical speed reduction will increase the torque a VFD will not ! Noel.

[Harry WilkesParticipant @harrywilkes58467]

Your probably going to need two new motors and two VFD,s (you could get away with one VFD if you only run your machines one at a time. I think if your running of a 13Amp plug the motors are single phase for use with VFD you need 3 phase motors 415/230 volts. That’s  a brief outline

I run my Myford lathe with a Jaguar Cub with i purchased from Transwave there are other suppliers others will recommend or you can google

H

[Mike HurleyParticipant @mikehurley60381]

Have a look at Newton Tesla’s website. Plenty of info on VFDs & suitable kit. (Usual disclaimer)

As Noel comments VFDs give real variable speed ranges but that can cause an issue with torque when cutting heavy stuff! Like most things £ could be a major consideration.

Mike

[Robert Atkinson 2Participant @robertatkinson2]

Both machines will require 3 phase motors. If running from a 240V supply “13A plug” these should be rated for 240V this includes dual voltage 240V Dealta / 414V delta motors.
They should be at least 4 pole and ideally VFD or inverter “rated”. A totally enclosed fan cooled construction will prevent issues with mratallis dust or swarf getting inside.

The power rating does not need to be any higher than the existing single phase motor for the lathe at least. A 1/2 hp (0.375 kW) or 3/4 hp (0.5 kW) should be fine for the lathe. I use a 6 pole (910 RPM)  375W motor on my similar sized early ML7.
Using a 6 pole gives even smoother running and the lower speed provides more motor torque and allows a larger motor pulley.

The VFD should have the same or slightly higher power rating than the motor. With a quality VFD under-rating is not required and the parameters and dynamic range of the VFD will be better matched.

Don’t forget to buget for a proper enclosure for the VFD(s). It is not OK to run the VFD without a protective enclosure.

Robert.

[Pete RimmerParticipant @peterimmer30576]

I cannot imagine not using a VFD if there was a choice given. In almost any situation where a 3 phase motor (or even a single phase motor) was once an option, a VFD will improve the machine in terms of flexibility of use. You can usually keep the benefit of the original mechanical speed reduction but then add the flexibility of variable speed withing the speed ranges of the original pulley setup.

I say that if you have the option and the budget for fitting a VFD and 3 phase motor then don’t even hesitate.

 

[Nigel Graham 2Participant @nigelgraham2]

I have fitted my Harrison and Myford lathes, Myford mill and BCA jig-borer all with 3-phase conversion sets (not all at once – I hadn’t won the lottery!) from Newton-Tesla, and been very pleased with them.

The first and most obvious gain was very smooth running that removed the Myford cabinet’s loud resonance set up by the original 1-ph motor. The Harrison also runs much more sweetly, but the milling-machine is mechanically noisy anyway (well, mine is).

I told the company the application so they could supply the most suitable set for the machine.

To reiterate the above though – do keep the existing pulleys or gears transmission, for two reasons.

– Firstly, the torque multiplying effect while also giving a greater speed range.

– Secondly, the motors must not be run for long at low speeds, and the control knobs on my units do have green shading to red warning scales to remind you. This is to ensure the motor’s cooling fan runs fast but I don’t know if there is a more subtle reason too.

 

NB:

Unless the new motor is fully-enclosed, do ensure it can take in plenty of cooling air but is safe from the ingress of muck including swarf. A short-circuit in there might not hurt the motor, but could still wreck the electronics….. As I found to my expense!

[Nigel Graham 2]

On Nigel Graham 2 Said:

..

To reiterate the above though – do keep the existing pulleys or gears transmission, for two reasons.

– Firstly, the torque multiplying effect while also giving a greater speed range.

– Secondly, the motors must not be run for long at low speeds, and the control knobs on my units do have green shading to red warning scales to remind you. This is to ensure the motor’s cooling fan runs fast but I don’t know if there is a more subtle reason too.

 

To expand on this extract by Nigel – specifically point 2.

When I got mt Newton Tesla VFD package a couple of years back, i was a bit bemused by the asortments of Rec / Yellow / Green segments behind the controller knob. I assumed that this indicated (as Nigel suggests) these are for ‘preffered’ / ‘good’ / ‘not ideal’ speeds for expended running – so followed my own thoughts (note: there was no indication of the purposes in the user manual). However, more out of curiosity than anything else I contacted NT to see if understood things correctly.

I soon had a very detailed response from George Newton, the relevant section is as below:

Many thanks for your email.
You refer to the legend on our control pendants, the legend plate is due for updating like the AV750 which has smooth graduation from one colour to another. It used to be the case that running motors less than 20HZ could give rise to overheating with inverters running at a fixed voltage/ frequency ratio of 4V/HZ.
Today this is no longer the case as we operate inverters in ‘Flux Vector’ mode whereby the inverter automatically changes the V/F according to the torque demand.
Consequently full torque is available at slow speeds without danger of motor overheating. Also even though a lathe may be in use for long periods of time in the workshop the variation of cutting speeds and feeds, stoppages to check the job etc results in a duty cycle of about 40 – 60% compared to many industrial
applications having a duty cycle of 100% for 100% of the time.

Just thought this may be of interest to fellow forum participants. I will add that the VFD has worked without problems since getting it, and has proved a very useful feature. (usual disclaimer)

 

Mike

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