Lathe motors + electrical witchcraft

[hotrodder]

Got a phone call from a mate last night...

You've just bought a new lathe... it's a Colchester, owners moving and needs it gone. It'll be dropped off on Fri Spent most of last night and half of today trying to make room (and failing), going to be fun tomorrow!

Anyway popped over to have a look, it's a Mk1 student 3 phase not had a look at the motor but from lathes.co.uk should be a 3hp jobbie.

Zero experience of phase convertors and VFD's. Bearing in mind it's got 8 speed gearbox is it worth going for a VFD? Assuming the origional motor (and that it's servicable) anyone know if it'd be compatible with a VFD or were they 3 phase only?

FWIW found a manual for colchester students here

 

[bigbadbugga]

search for 'electric motor man' on ebay, he just sold me a 1hp 240V motor and forward/reverse switch for my boxford for a very good price.

Just email him and he is very helpful and can advise what you need.

I'm assuming you want to run it on single phase of course

 

[hotrodder]

Yep, single phase supply.

Just bookmarked his shop, cheers. Reminded me of something i left out of the origional post though. The lathes.co.uk site mention of the single phase versions of the student... specifically weakness being the motor.

Been awake since Wed morning so may have it wrong but i the way i read it the weakness was not the specific 240V motor but the way lathe used the motor- the brake and/or clutch giving the windings a hard time or something. Have to read it again tomorrow. Comments?

 

[bigbadbugga]

I assume this is the bit you are talking about.....

taken from lathes.co.uk.

As standard, both Student and Master were fitted with a spindle brake, operated by a horizontal lever (on the headstock's front face) that also acted as a motor switch. To start the lathe the lever had first to be pulled out against a safety spring (designed to prevent accidental engagement then lifted up (this mechanism was later more fully developed with a proper external gate and called "Safti-lok" by the makers). The lathe was stopped by returning the lever to its central position and then pressed down further to operate what was, when the lathe was new, a powerful drum brake built into the headstock input pulley - though Colchester's assertion that this stopped the spindle "instantaneously" revealed that the handbook writer had either not used the lathe - or a dictionary. However, the brake was very useful, especially to those being paid on "piece-work" who would otherwise have had to watch the seconds tick away as 120 lbs of cast iron came slowly to rest from top speed. It's worth knowing that after many years of neglect the headstock brake first becomes ineffective and then (usually following ham-fisted attempts to improve it) may start to interfere with the free running of the spindle. If your Colchester shows signs of slowing down or even "seizing up" after a few minutes running, the brake assembly is the first place to look. If shoe linings are badly worn most industrial areas have a friction-materials specialist who can bond on new material. Unfortunately, unlike the competitor English Harrison lathes, a combined clutch and brake was not fitted as standard but a multi-plate clutch manufactured by "Matrix" used instead. This was a very well designed, easily adjusted and reliable device - and one that should still be working perfectly when any lathe fitted with it is otherwise worn out. Although a 3-phase motor is very robust, and will put up with a good deal of abuse, its 1-phase cousin is a relatively delicate thing and best run near its rated capacity all the time (i.e. worked nearly flat out); if such a motor is switched on and off frequently against "no load" the windings will be damaged and, if run through a cycle where it is started, worked briefly, stopped and started again, the capacitor will fail prematurely. To prevent this happening on 1-phase (and DC) equipped lathes Colchester fitted a Matrix clutch as standard - even though it meant sacrificing the benefits of a brake. On clutch-equipped lathes the stop/start handle was adapted to open and close the plates with a separate electrical switch on the front control panel. In normal use, once started, the motor was left running for as long as possible, the spindle being controlled by the clutch. If you come across one it is worth knowing that on early clutch-equipped lathes the safety-spring loading on the start handle was not fitted - and accidentally brushing against it can start the lathe running. If needed, a clutch can be retrofitted to a used machine - but make sure you acquire all the operating linkages as well. An electrical reversing switch was (at first) an optional extra and, if chosen, was neatly built onto the hub of the stop/start lever and worked concentrically with it.

I have no answer, but thought it might be worth posting on here to save other members searching about for it

 

[hotrodder]

That's the bit, nice one! Other reason for for sticking with 3 phase motor was smoothness, don't know if it makes a practical difference (or if a witchcraft box would negate it) but on paper it should result in a better finish (everything else being equal)?

 

[stormin]

I've got a student mark one.
I run it on a variable frequency drive and the handy part is you can alter the motor speed to anything you want, not just the fixed speeds of the gearbox. The gear ratios leave some quite large gaps in speed range.
Mine came with the spindle brake dismantled and most others will be worn out or ineffective. The VFD allows for variable motor braking so you won't need the mechanical brake.

Both my main motor and the coolant motor needed re-jigging from star to delta so they could run on 240V 3 phase. You could leave them as they are but you'll need a more expensive phase converter that outputs 415V 3 phase.

Since getting my VFD I've now got a milling machine and pillar drill all with three phase motors that I run. Simply plug in the right machine as required.

 

[hotrodder]

Cheers, odds have just gone up a little that the motor might be dual voltage then. Not got to actually look at the thing as it's coming tomorrow now due to sellers work schedules changing (very handy as there'll be more bodies available tomorrow!)

Been googling vfd's tonight trying to learn more, from what i've gleaned the change from star to delta is for motor torque reasons? Completely forgot about the coolant pump yesterday. If the vfd is powering both what happens with speed changes to the main motor- drips to power showers or is it fine? Or do keep the vfd in a narrowish range to suppliment the gearbox?

 

[Pete.]

The VFD can only power one motor, so you'll either have to lose the pump, fit a 240v one or use a capacitor to try to run it from 240V. If you fit a single phase motor you might need to change your contactors or modify your existing ones to run on 240.

 

[stormin]

The VFD can only power one motor, so you'll either have to lose the pump, fit a 240v one or use a capacitor to try to run it from 240V. If you fit a single phase motor you might need to change your contactors or modify your existing ones to run on 240.

I'm using my 3hp rated vfd to drive the main motor and the 1/2 hp coolant pump without problems on my Student. Had to change from star to delta on both motors. I must admit I forgot the coolant pump at first and it wouldn't turn at all whilst still in star.

Easy enough to adjust the flow of coolant via the tap regardless of motor speed. If you've got it really slow for threading coolant isn't as important anyway.

The VFD's are rated for an overload of upto about 4.5hp to allow for motor starting loads. So the extra 1/2hp of coolant motor isn't really a problem unless you have something massive on the chuck and require the full 3hp of the main motor.

 

[hotrodder]

Tap to control coolant!

Still no lathe as he was stuck on site until todays job got done- was still working/swimming at 7!

When i was reading up last night some sellers were in Pete's camp others saying multiple motors per vfd fine (as long as sufficient capacity vfd was used). Aside from the obvious one of the motors can't be independantly controlled with 1 vfd didn't really find an explanation though

A mute point for me until i can confirm that the motors dual voltage...

 

[Pete.]

Most are, there should be a schematic for the connections somewhere on the electrical cover on the motor housing.

 

[stormin]

Most are, there should be a schematic for the connections somewhere on the electrical cover on the motor housing.

I assume the motors fitted to my student were original but can't be sure. When I opened the connection box, there were no instructions but I just looked at how the six wires were connected and deduced it was in star. Did a quick check on continuity on the leads (all the same colour) to get the poles and labelled them up then reconnected on terminals for delta. Can't explain more as it's a few years since I did it and don't mess with motors much so had a few nights reading up before taking the plunge.

When I got my milling machine that had a two speed main motor, which everyone I spoke to said couldn't be made to work with an inverter, so replaced with a standard 3 phase motor. The coolant pump and feed motor I had reworked internally to split the star point and wired to delta, only cost £30.

 

[brightspark]

this might help bit of a crap picture mind take no notice of wire colours just the markers on cables eg w1 u1 v1 then u2 v2 w2 look where the feeds go and the links. if it isnt a dual voltage motor transwave do a 415 v converter which i use £400 quid but use it on other machines as well or as stormin says take to local rewinders and they will alter it for u at a reasonable price to run on 240 v delta with inverter

 

[hotrodder]

Cheers guys, still no lathe (long and boring story) but it's now sat in the yard opposite his, oiled and wrapped up. Transport will sorted in the next day or so. Mate of mine says he has a phase converter that i can borrow to run it up once i get it home. Assuming it's alive i can then go inverter shopping

 

[Shox Dr]

Hotrodder you got mail