Boxford motor help

Hi Folks
I bought a Boxford Model C lathe but it has a knackered motor - a crompton parkinson 3 phase motor BS Frame no VMA544CM1A, 0.75BHP, 1425RPM
My question is this....

I've had a look at a few threads and the question I was going to ask - single or 3 phase - has been answered - (thanks so much for all of these informative posts), 3 phase seems to be the way to go.

so that moves me on to question 2.....

can you suggest a suitable direct replacement 3 phase motor that will fit and a cost effective 3 phase converter / VFD


My electrical knowledge is pretty basic but I'm happy to have a go at stuff with a bit of guidance.

should I look at a more powerful motor or am i runniung the danger of overpowering the machine and causing damage.

Thanks in advance for all the help.

cheers

You can use THIS to work out the existing frame size that you have from the bolt spacing. Then buy the same in 3phase as frame sizes are standardised.

My former Boxford A lathe tried different motors and the best by far was a good VFD and a 6 pole 1.1 kW.

Lathe is protected by the belt drive.If You do something stupid belt slips.

A short video showing same good VFD plus a four-pole .75kW motor.

Very nice but 6 pole 1.1kW was better but my space was limited in a new flat after change of home.

Boxford VFD

As Dave Halford says, first identify the frame (standard sizes for both Imperial and Metric), so the motor will physically fit. Then find a motor in that size, with the wanted volts, power output and RPM. It may be possible to find a VFD & Motor Package, which comes with instructions and simplifies installation - maybe Newton-Tesla. Otherwise the forum is good at answering motor questions.

A moderately more powerful motor wouldn't do much harm, (say 1HP rather than 0.85HP) but do you really know better than the bloke who designed the lathe? More power puts more stress on the machine all round. It also increases the amount of damage in the event of a crash and the risk of personal injury. Doubling the motor power, or more, is asking for trouble in my opinion, especially if the motor can be over-sped with a VFD as well. Lathes aren't like cars where improved acceleration is a benefit; on a lathe big motors can only do more work faster, which risks thrashing the machine. Big motors on small machines don't produce better finish or improve accuracy. Of course, it's your machine and you can do what you like with it! Chewing metal at high-speed, or delicate precision...

Have fun!

Dave

I have had a Southbend, then an AUD Boxford for 50 plus years 3/4Hp single phase. If you have the money, 3 phase seems to be the way to go, but its only 30 seconds for a belt speed change on mine. Also, there are several posts where the VFD has stopped working - Well its just a matter of more money, I would prefer to spend the money on making things!

If you were doing a lot of large face work using a powered cross feed, then variable speed would be handy...but how often?

On the basis that the model C doesn't have powered cross feed I would question the reason why you wanted a VFD ?

Is your lathe an underdrive or a bench model? I've got a bench type ME10. To go the VFD route, I found that the largest frame size motor I could fit without too much surgery of the mounting was a 71. I bought a TEC 0.75kW, 1440 rpm motor from Inverter Drive Supermarket. A 71 frame metric motor will have a 14mm dia. shaft, so the pulley needs to be sleeved You might find an imperial sized motor but prices seem to be higher.

If a CUD, can't really advise on motor dimensions.

A VFD makes lathe operation much more convenient IMO.

Edited By Clive Brown 1 on 20/06/2020 11:32:41

Dave

This is really handy - that was going to be my next question was how do I get a like for like fit

cheers

Thanks for this Dave - I was thinking about maybe going up to the 1hp to give it that wee bit more oomph but agree with your point about going silly with power being an accident waiting to happen.

thanks for the advice

Hi Speedy

to be totally honest - I don't really know. I'm a time served turner and am used to 3 phase but this is just a wee lathe for doing the odd bit of turning at home - mainly motorcycle related and the odd job for a few of my mates that are into steam engines etc. As i'm not looking to use it to earn income I don't really want to spend any more than I need to to get it running reliably - whats the rough price difference between 1 & 3 phase?

always good to have a variety of opinions from experienced users.

cheers

Hi Clive

it's an underdrive model so space is a bit limited. thanks for the heads up on Inverter drive supermarket

cheers

so - these replies have raised another question....

2 pole? 4 pole? 6 pole?

?????whats the difference / benefit

thanks again

Edited By Ewan Turnbull on 20/06/2020 21:29:41

remember too that if your VFD outputs 240v 3 phase you will need a motor that can be connected in Delta, but if you go for the VFD with 415 volt output the motor can be run in star. Some modern small motors do not bring the star point into the terminal box, and therefore they cannot be connected in delta.

Phil

Sorry Phil - I'm showing my woeful lack of knowledge on electrical matters - star / delta? i get your point about being careful to match the VFD output to the motor but is there a difference / benefit to delta over star or vice versa?

thanks

Ewan

Edited By Ewan Turnbull on 20/06/2020 21:32:40

Unless you happen to have 3 phase at your workshop, then the single phase motor installation is much cheaper. Going the VFD route, you need both the VFD and a 3 phase motor, and like I said, VFDs come with their own problems.

Roughly 2 pl 3000 4pl 1500 6pl 1000 RPM any new motor you buy should be marked 415/240 volts star is 415v delta is 240v

when using a 240v inverter the motor needs to be wired for 240v

If you buy from a supplier of inveter/motors you will get the correct motor but you will need to check it's wired in delta

Hope this helps

H

Hi Harry

ideal explanation - simple and to the point

informed is always better

cheers

E

If going the VFD route, then it is worth putting in a more powerful motor, if it will fit. The reason being that at lower RPM the torque available is reduced with a VFD.. Putting in a more powerful motor returns the torque to a higher figure.

Andrew.

Problems or not, my lathe and mills run on 3 phase motors controlled by VFDs. Much preferred to single phase.

That is currently four VFDs - and this is despite two machines already having (working) mechanical speed variators.

Personally, I’ve had only minor problems while setting up VFDs to control my machines. Improvements in operation, IMO, far outweigh the (fairly minimal) extra cost of a motor with VFD. Soft start, variable speed selection, easy reversal of direction (if required/permitted), reduced vibration, less risk of repairs (start/run capacitors, ‘centrifugal’ start winding switches, etc).

For machines with belt-position speed changes, that is much reduced as likely at least three positions can usually be accommodated with the belt in the middle position.

To be honest, I can’t think of any scenario where a single phase motor is actually better than a 3 phase installation with VFD.

Just an aside, if the Op doesn't know an awful lot about 3 phase, 440 volts etc etc, perhaps remind him that it CAN be a more lethal combination, more so than the standard 240 volts. Sure 3 phase VFD gives a smother ride and any variable speed can be selected, but for a casual user, the extra money for a 3 phase system would be better spent on tooling in my book. Its the old chestnut comparing a Myford to any other lathe - there isn't an answer. Its what fits your pocket and what is available when you go to purchase.

Ps,  Search This Site for VFD and look at all 96 entries - quite a few failures there !

Edited By Speedy Builder5 on 24/06/2020 11:22:13

Speedy,

I looked in and expected to see you posting an advantage (even If only just one) of a single phase motor.🙂

I expect most of those failures were of VFDs fitted where single phase motors had already given up the ghost (again).

VFDs are getting cheaper and cheaper. Some may fail but not many three phase motors are reported as failures. It will soon cost more for a decent start capacitor (for a single phase motor) than replacing a VFD.

If I were buying a second hand motor, I know which I would be more confident of it working satisfactorily.... particularly If the frame size was not an important factor.