Variable speed motor.

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.

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.

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!

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.

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.

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

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

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

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 .

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 12x36 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.

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

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

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.

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?

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

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

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

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

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

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