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Clarke CL430/500 - Fitting new motor and in verter

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Godfrey King26/01/2014 10:43:14
5 forum posts

Hi, as you can see I'm new to this forum and engineering.

I have bought a secondhand Clarke CL430 lathe and I find changing the belts a real faff.

Has anybody fitted a new motor and inverter with a remote speed control to this machine? If so how did you do it?

I was told at the ally pally last week by the man on the Transwave stand that only the top of the range package on their list was suitable, costing the best part of £500!!!

Any cheaper inverter would be unreliable (even their own) and not have good torque across a usable speed range, especially at low speeds and that I would still have to change belts.

Your thoughts please.



Edited By Godfrey King on 26/01/2014 10:46:37

Edited By Godfrey King on 26/01/2014 10:46:58

martin perman26/01/2014 11:05:36
2055 forum posts
86 photos


I have a CL500 that I intend to convert, I do know that there is a direct three phase equivilant for my lathe, same make, size etc which I need to purchase, I have a Seimens 420 inverter 2hp rated, acquired from work from a machine that was beyond repair when it fell off the forklift that was moving it, I have tested it and it works well.

I would say that as long as the motor and inverter are matched for horsepower or the inverter is rated higher you shouldnt have a problem, on mine you can dial in the motor characteristics to suit your motor i.e amps, revs, horse power etc

I like you want to get away from belt changing and I also want to be able to thread cut slower as the slowest at the moment is to fast.

Martin P



Edited By martin perman on 26/01/2014 11:07:28

John Rudd26/01/2014 11:13:54
1456 forum posts
12 photos

Depending on you particular inverter, many have a torque boost setting, whereby the torque can be increased at lower motor speeds.....

V8Eng26/01/2014 11:14:38
1730 forum posts
6 photos

I know nothing about Inverters or fitting them, but another supplier of drives I have seen advertising is Newton Tesla.

Hope this might help.


Edited By V8Eng on 26/01/2014 11:22:40

Bill Dawes26/01/2014 17:28:43
539 forum posts

Hi Godfrey, I bought the CL500M a few years ago brand new, despite the thought of others who urge Myford etc.

I decided I did not have sufficient experience to go used and would prefer a new machine, albeit with some disadvantages to a more expensive lathe.

I have been quite happy with the machine accepting its shortcomings and was thankful for the milling head. (I am now in a position to buy a proper milling machine)

Like you I got a bit fed up with the belt change business, not that it is particularly difficult, just not instant.

I acquired a WEG CFW10 inverter (through work so at a good price) like wise a 3 phase motor.

All for less than £100, you may not be able to get it that cheap but never quite understood the advantages of these costly packages. (Look around for a second hand 3 phase motor, not so sure about the inverter)

By studying the terminals of the lathe I worked out what went where, fitted it and it worked!

It makes life so easy. The only real problem I had was the single phase motor I took off was a different frame size but with a bit of juggling made the 3 phase fit.

My connections disabled the original reverse switch but have that ability on the inverter although you have to go through a menu of parameters to do it so a bit more time consuming although the only time I need reverse is to make the mill head rotate the correct way.

Bill D.

Bill Dawes26/01/2014 17:35:29
539 forum posts

PS. on this inverter there is a torque boost for lower revs which is needed as motor torque reduces with speed.

In reality you will need a similar torque to higher speeds so this is useful. I think there is a limit as it can cause a problem if you crank it up too high. Can't remember why without wading through the manual.

Bill D

Andrew Johnston26/01/2014 21:25:42
6668 forum posts
701 photos
Posted by Bill Dawes on 26/01/2014 17:35:29:

PS. on this inverter there is a torque boost for lower revs which is needed as motor torque reduces with speed.

In reality you will need a similar torque to higher speeds so this is useful. I think there is a limit as it can cause a problem if you crank it up too high. Can't remember why without wading through the manual.

Bill D

In simple terms an induction motor, below its base speed, is a constant torque device, for a given current. Let's say base speed is 1500rpm. So at 150rpm the torque, and current, are the same as at 1500rpm, but the speed has reduced by ten, so the power of the motor is only one tenth. A belt driven, or geared, headstock avoids this loss of power by keeping the motor running at 1500rpm, so although the speed at spindle has decreased, the torque has increased. So, ignoring losses in the belt or gears, the power at the spindle hasn't changed.

In order to increase power at lower speeds we can increase the current. As has been correctly stated some inverters allow an over-current. Let's say we double the current, and hence double the torque. We also double the power, so it is now one fifth of that at 1500rpm; certainly better. But, the heating in the motor coils is proportional to the square of the current. So while we've doubled the current, we've increased heating by four. If we keep increasing current the motor will overheat in short order.



John Rudd26/01/2014 21:58:27
1456 forum posts
12 photos

And some of the more up market motors have embedded thermistors that can be utilised to prevent overheating of the windings when incorporated with appropriate protection circuitry with a vfd.....

Steven Vine27/01/2014 09:03:38
340 forum posts
30 photos

I have got a Warco WMT300 which looks to be fairly equivalent to that Clark. I fitted a 0.75kw Teco motor and an inverter rated for 1HP. I got them from Drives Direct, for around £150 all in, about 5 years ago. I have had no problems with power output and torque and am very pleased with the set up.

I have run the motor for long periods at 20hz. I forget the rpms at this rating but it is very slow. It is slow enough to do finely controlled threading work up to shoulders, and reversing the carriage under vfd control after the cut is a pleasure. At these low frequencies I cool the motor using a small powerful fan from a microwave (any powerful localised fan will do). In normal operation (at 30hz to 50hz) I don't need the fan on. I get quite low useful speeds, with enough torque, at around 30hz, and things are very usable.

If you take aggressive cuts at low speed then the motor will stall. I have overcome this by then changing the belt arrangment for that particular job and/or taking lighter cuts. Slow speed and high torque; I dont think you can have your cake and eat it too, at least not at a cheap homeshop price. Do you really need tons of torque at low speed?

I moved my motor 180 degrees so it was outboard to the left of the machine, directly opposite to where it was factory fitted. This simplifies the fitting and also gets the motor away from the back of the bed which makes it so much easier to clean up. I made a mounting for the motor to slide and sit on, out of contiboard/melamine, so the pulley position and belt tension can be adjusted if needs be. I made a pulley to fit the shaft ot the new motor, which was a nice excercise. I removed the lathe end cover box. With the end cover box removed, the pulleys and gears are exposed but I have not had any trouble or disasters with this 'whatsoever'. You can also move the motor so that is underneath the bench and then keep the end cover box; you will have to make up some shafting and get longer belts, but this is no big deal and is very easy to do.

For a few pence, I bought a plastic box and components from Maplins for the remote control and sited the box next to my left hand directly in front of the lathe. A potentiometer for the speed controller, with a home made aluminium knob. Two momentary push to make switches for start and stop. I used a sliding switch from the back of a computer (the 110v/240v power supply selector switch) for the forward and reverse. This type of switch prevents inadvertently selecting reverse. I used normal twisted pair telephone wire to connect the control box to the inverter and have not had one problem.Some will tell you that it has to be top notch screened stuff, but it does not have to be; if the low voltage control cables are not run parallel to high power cables they will be fine.

Get a motor and an inverter for the price you are willing to pay, and give it a go. Once you jump in there and start dealing with it you will find your own way to get it all working. You can always ebay it and get your money back if it is a failure, but I very very much doubt it will come to that.


Steven Vine27/01/2014 09:27:05
340 forum posts
30 photos


I did away with the intermediate pulley and belted from the motor pulley straight onto the main shaft pulleys. For some situations you can easily reinstate the intermediate pulley if you have to.


Andrew Johnston27/01/2014 10:01:41
6668 forum posts
701 photos

Posted by Steven Vine on 27/01/2014 09:03:38:

............. Do you really need tons of torque at low speed? ...............

Yes: it would have taken a lot longer than it did to machine this 16" OD flywheel without a sizeable percentage of the motor power being available:


Cutting parameters were 58rpm, 0.05" DOC and 0.01"/rev feedrate. That's about 1.46 cubic inches per minute removal rate, requiring roughly 1.5hp.


Steven Vine27/01/2014 11:22:54
340 forum posts
30 photos

Nice set up, and I see your requirement. I once 'roughly' trued up a light thin 9 inch dia wheel, which is about on the limit for one of these machines in question. It was slow going, much slipping and stopping, but I got there in the end. I'm not turning that size all day everyday. I was really answering the original posters question and posing a consideration for him with the question about torque. Changing belt positions on these machines gets tedious after you have done it a hundred times, as the original poster has also pointed out. Fitting a vfd overcomes that tedium, and brings the pleasure back. Of course you trade off the power at low speed. What I am saying is, in my experience, the machine is still usable at low speed with a cheap vfd, so go ahead and do it. Of course it all depends on what you intend to turn.

Without getting too technical, a cheap vfd will (should) work.


Godfrey King27/01/2014 20:50:08
5 forum posts

Thanks everybody for all the info.

I have been talking to Inverter Drive Supermarket and they have a kit which will suit my lathe for £224.46. It includes inverter, motor and screened cable, the remote control I can make myself. When I have finished the present project I think I will give this a go.


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