Variable speed motor.

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Variable speed motor.

This topic has 24 replies, 17 voices, and was last updated 12 November 2014 at 14:12 by Ian P.

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16 December 2013 at 13:37 #138006
James Hannabuss
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@jameshannabuss68871
Hey guys been a while since I last posted on here so I hope I'm putting it in the right section. My question is I have a Clarke cl500m lathe mill combo, ( I know don't shoot me haha) and I'm getting fed up with changing the belt every time I need to alter the speed. My idea is to make the motor variable speed so I can do it at the turn of a knob. Can I do this with the standard motor or have I got to look at getting a different motor? Also how do I wire it in? Electrics are not my strongest point being a mechanical engineer is haha .

Cheers in advance

All the best James.
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16 December 2013 at 13:37 #30472
James Hannabuss
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@jameshannabuss68871
16 December 2013 at 14:01 #138014
Carl Wilson 4
Participant
@carlwilson4
Hi James,

Yes you can do this. What you need to do is get a 3 phase motor and an inverter. The inverter is a device that takes the incoming 240 volts single phase mains power and converts it, electronically, to 3 phase 240 volts. This can then be used to drive a 3 phase motor. The beauty of this is that by varying the frequency of the power to the motor it's speed can be varied. The inverter is capable of this frequency variation as well.

I have got a Chester Mill that I have to shift the belts on to change speeds and I am in the process of converting it to 3 phase operation from an inverter. These units are not particularly expensive, you can get inverters for £80-£120 and a suitable motor for your lathe in the region of £60-£70. I am going to post my conversion on here.

I used to have a Chester lathe/mill combo similar to your Clarke one and I got tired of changing the belts too! My slightly more drastic solution was to buy a Harrison M250. If you PM me I'd be glad to email you and let you know suppliers etc.
20 December 2013 at 18:15 #138382
nigel jones 5
Participant
@nigeljones5
I too have fitted a variable speed motor to my clarke lathe since the electrics fried – its varies between flat out and stop. Piece of junk!
20 December 2013 at 19:30 #138387
Carl Wilson 4
Participant
@carlwilson4
Hi Fizzy,

Could you be a bit more specific? What sort of motor and what is driving it? Would be interested to hear if you have the time.
20 December 2013 at 19:45 #138389
nigel jones 5
Participant
@nigeljones5
I had a variable speed motor from a defunkt pillar drill. I fabricated a bracket, removed the screw cutting gears and added a belt drive.
26 December 2013 at 23:48 #138831
James Hannabuss
Participant
@jameshannabuss68871
Cheers for the replies guys. The 3 phase option has been considerd before. I could proberbly get hold of a three phase motor at work as there's one or two lying about ( depending if they work or not) haha. But how I wire it up I've not the foggyist haha. Is that really the only option or is there a way to do it with the single phase motor that's I've already got?

Cheers
27 December 2013 at 07:00 #138835
martin perman 1
Participant
@martinperman1
James,

I have the same lathe as you and have looked at the options, I have a Siemens inverter and when funds allow I have also done a web search for three phase motors and there is a direct dimensional motor type for the lathe of the same make, TYCO.

Martin P
27 December 2013 at 08:38 #138836
martin perman 1
Participant
@martinperman1
James,

Had a senior moment earlier, the motor is a TEC as found here **LINK** I've found my paperwork when I searched for it myself.

Martin P
27 December 2013 at 12:14 #138854
Lambton
Participant
@lambton
James,

I assume your lathe is fitted with a single phase induction motor. These motors require some method of starting them in the right direction after which they run OK on a single phase supply. This is normally done by using an out of phase starting winding or a capacitor that is cut out by a centrifugal switch as soon as the motor speeds up. These motors are synchronous and their speed is determined by the number of poles and the mains frequency.

Their speed cannot be changed simply by altering the supply voltage – only by changing the frequency. This is easily done by and inverter which is then used to power a 3 phase motor as Carl has explained.

I have fitted inverters and 3 phase motors to my lathe and mill (progressively as the money and opportunity came along )and I can assure you it is worth the trouble and expense .
27 December 2013 at 14:55 #138863
Gary Wooding
Participant
@garywooding25363
James,

I'll second what's been said about VFDs (the correct name for the inverters mentioned) and 3ph motors for variable speeds. I've fitted them to my mill, lathe and drilling machine. The lathe is a Chester 12×36 geared head and the difference it makes is amazing.

3ph motors are inherently smoother running than 1ph, and thus, potentially at least, can produce a better finish.

The 3ph motors I fitted to the drill and lathe were designed to be connected in star or delta format, as are most modern units, but those in the mill were not, and I had to break the star point in order to use them on a 220v household supply. If you use a discarded motor, check that it can be altered easily by means of jumpers in the connexion box. Breaking the star point is conceptually simple, but somewhat more difficult in practise.
27 December 2013 at 17:27 #138879
Muzzer
Participant
@muzzer
Make sure you buy a 3-phase motor that is rated for "220V 3-phase" (most probably in "delta" connection, for what it's worth). You only have 3 wires to connect up and it doesn't matter which way you connect them – if it spins the wrong way you can simply swap any 2 of the wires over. The motors originally fitted to these machines are Xmas cracker quality, so fitting a normal 3-phase motor may also bring the benefit of a quieter experience!

There are literally dozens of VFD manufacturers to choose from. It may be worth asking around to identify something that is very straightforward to set up and possibly even work out of the box if you aren't confident about configuring one of these.

Merry

Edited By Muzzer on 27/12/2013 17:28:23
27 December 2013 at 20:02 #138900
martin perman 1
Participant
@martinperman1
I have an original motor on my CL500M which I have owned for over ten years now and have no Xmas Cracker Quality noise or vibration in fact its a very quiet lathe.

Martin P
27 December 2013 at 21:09 #138908
Carl Wilson 4
Participant
@carlwilson4
Hello,

Yes, I'd agree, I have no less than three 1.5 HP Chinese single phase induction motors in my workshop, on my mill, bandsaw and compressor. They are decent enough units and well made. I am changing my mill motor for a 3 phase one to get variable speed. I should get smoother running and thus hypothetically a better finish too.
24 January 2014 at 21:56 #141590
Godfrey King
Participant
@godfreyking88452
I have been told that there is a problem with the cheaper ie £100 inverters with lack of torque and limited speed range and that you will still have to do some belt changing, is this right?
27 April 2014 at 15:49 #150837
Cedric Norman
Participant
@cedricnorman47847
I fitted a motor an control unit, pre-wired CL750 by Newton-Tesla in December 2012 to my Clark CL500M. It is much quieter than the original motor and I am delighted by the flexible speed range. The motor pulley fitted straight onto the shaft so all I had to make was a new motor mounting plate. Change belt ranges gives quite a choice of speeds. I generally run on the small motor pulley to the large spindle pulley which gives me 75 to 1000 rpm. I made some interchangeable speed dials that fit over the potentiometer shaft and are held in place by some small magnets so that I can change these if I change pulley ratios. It was an expensive Christmas present to myself, but I have no regrets and it would be high on my list of things to do on a new lathe. I chose the Newton-Tesla because all the wiring work is done for you. Working with Inverters, etc. was not an option that I wanted to mess around with. There is nothing wrong with the lathe and as improvements I fitted DR scales to the lead-screw and tailstock. Next I made a QC toolpost which is a boon. Then I made a new collar for the cross-slide to reduce backlash and a new collar with needle thrust bearings for the leadscrew. Finally I designed and built a reversing gearbox for the leadscrew so that I can power feed in and out of bores and cut LH threads if need be.

Edited By Cedric Norman on 27/04/2014 15:51:32
27 April 2014 at 18:58 #150853
Involute Curve
Participant
@involutecurve
Another useful source of variable speed motors are industrial sewing machines, and also some treadmills have a single phase motor with a vary drive uses belt and cones similar to a Bridgport.

HTH

Shaun
27 April 2014 at 20:38 #150867
WorkshopPete
Participant
@workshoppete
Hi Everyone

All the above is correct and I agree with it all but a couple of points generally the frequency from VFD's doubles at top speed i.e. – 50hz in 100Hz out – so the motor speed will at the top end double. The other thing to remember is that the motors we use are fan cooled so by reducing the speed and running the motor for an extended time it can overheat. The thing to do is select a speed range and set the pulleys to give the maximum speed when the VFD is set to maximum. I have two of these devices in my workshop one on a drilling machine and the other on my Myford I very very rarely change V belts an excellent investment.

Peter
28 April 2014 at 08:05 #150893
Gary Wooding
Participant
@garywooding25363
Posted by Godfrey King on 24/01/2014 21:56:15:

I have been told that there is a problem with the cheaper ie £100 inverters with lack of torque and limited speed range and that you will still have to do some belt changing, is this right?

VFDs are not torque multipliers. They don't work like gears, where halving the speed doubles the torque. In essence, a VFD driven motor will give constant torque at speeds at and below its rated speed (ie. its speed at 50hz in UK), and constant power at speeds above. This means that power is proportional to speed up to the rated speed, and then remains constant up to maximum speed.

There are VFDs that purport to give increased torque at slow speeds, but I don't think its significant (can anybody supply more information?)

I've fitted cheap VFDs (around £50-£70) to 3 mills, 3 lathes and a bench drill, all of them will work up to 120hz – that means that a 1425rpm motor will spin at 3420rpm.

I seldom change the gears or belts on my machines; I use the VFDs instead, but there are occasions when I need the extra torque that only gearing can provide.

Gary
29 April 2014 at 13:17 #151023
Andy Collins
Participant
@andycollins85655
There are VFDs that purport to give increased torque at slow speeds, but I don't think its significant (can anybody supply more information?)

Gary,

these are called 'Vector' drives- a massive (actually frightening) increase in torque at low speeds- but still quite expensive. ("frightening" because it's so unexpected that such a slow running motor has so much torque!)

Andy
29 April 2014 at 20:56 #151057
Mike Poole
Participant
@mikepoole82104
A simple inverter will rectify the incoming supply to provide a high voltage DC supply which can be used to create 3 phases. Torque will fall considerably at low output frequencies and although high frequncies can be created the power will be limited but a free running motor can be made to spin very fast. Specially made motors can be run at 25,000rpm. for applications like how power routing, no doubt much higher speeds are used with specialist equipment.

Various manufactures produce a more sophisticated inverter usually incorporating some or all of the words "sensorless flux vector". This type of inverter uses powerful processing to estimate the position of the rotor and thus time the phases to produce high torque at low frequencies. Sophisticated industrial inverters can accept an encoder input to give rotor position and can produce near servo system performance from a humble squirrel cage motor and produce full torque down to a standstill, this will cost serious pennies though.

I think the sensorless flux vector drives are worth paying the extra for as the improvment in performance is worth it, but it depends how deep your pockets are and how averse to belt changing you are.

Mike

Edited By Michael Poole on 29/04/2014 21:05:29
29 April 2014 at 23:06 #151066
duncan webster 1
Participant
@duncanwebster1
I've got three phase motors and drives from Newton Tesla on both of my lathe and my milling machine and wouldn't consider not having them The milling machine in particular went from very noisy due to motor induced vibration to eerily quiet. You can get cheaper than Newton Tesla, but you get what you pay for, and their after sales is top notch
11 November 2014 at 21:50 #169338
Nigel Brown 5
Participant
@nigelbrown5
HI I am new tonight so if I get it wrong sorry.

As an Development Engineer we use Invertek optidrive E2 Single phase inverters these ramp up to full speed and then slow to the set speed (amount depends on quality of motor), yes on single phase motors! I have reduced speed quite a lot, on several motors.

They are not cheap but do what they say on the box!

Nigel B
12 November 2014 at 09:46 #169352
john fletcher 1
Participant
@johnfletcher1
I'm not sure what size of motor you need but there are plenty on the market and an ad here or on Home Work page will I think get some response. Many motors have provision for reconnecting to Delta within the terminal box, usually there is a label under the terminal box lid explaining what to do. Locating the STAR point is not so difficult either, but it does need the motor to be dismantled. Scratch mark the stator and end shields so that it is easy to reassemble, two marks one end one mark the other. Be careful when with drawing the rotor, not to scratch the varnish off the copper windings. Look at the stator winding ends and you should find a lump, not a big one but a lump never the less. That is the STAR point where the three wires are connected together, they need separating and extending so that all three will extend into the terminal box, together with the other three,6 in all. Make sure that you insulate the new connections very well. Next you have to get the Delta connections correct, for this you will need some form of continuity tester, a multi meter, battery and bulb or battery and buzzer. There are three separate circuits, for every circuit there must be a one end and a two end of the winding. Identify and label all three using the meter and some coloured tape or masking tape with writing on. The original ends will all be the two ends, mark them U2, V2, and W2.Now connect together U1 to W2,W1 to V2 and V1 to U2 using a block connector. Job done. Sorry I don't know how to included a diagram. Regarding an inverter, there are plenty of used one advertised and I've never heard of anyone being ripped off. One of mine is more than 25 years old and it wasn't new at the time. Making a remote control box is easy as well. The control circuit is low voltage so cheap pushed and other switches are available from hobby shops. I suggest you do include a relay to give isolation from the main in the event of mains or other supply failure. give it a go, sorry about the protracted write up.Ted
12 November 2014 at 14:12 #169376
Ian P
Participant
@ianp
Posted by Nigel Brown 5 on 11/11/2014 21:50:15:

HI I am new tonight so if I get it wrong sorry.

As an Development Engineer we use Invertek optidrive E2 Single phase inverters these ramp up to full speed and then slow to the set speed (amount depends on quality of motor), yes on single phase motors! I have reduced speed quite a lot, on several motors.

They are not cheap but do what they say on the box!

Nigel B

I can imagine that being able to vary the speed of a standard single phase motor could be indispensable in some cases, ie cases where the motor of a lathe or mill is not amenable to being replaced with a 3 phase motor. My Emco mill has a very non standard motor with a long splined shaft so could be a candidate. I have not checked the inverter price but I expect it will be very expensive.

I think the fact that the motor starts up at full speed would rule out it being used on a lathe (unless it has a clutch). In my workshop I have mostly 3 phase motors with VFDs and I use the ability to start at just a few RPM every time mainly for safety reasons. Even if I had left the chuck key in the odds are it would just fall out rather than being flung across the workshop, same applies to fly cutters or something held in the four jaw. At very low RPM there is very little torque so its unlikely any damage will occur.

The consensus always seems to have been, that you cannot usefully vary the speed of single phase induction motors. Invertek have blown that myth out of the water.

Ian P
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