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Lathe motor size and drive upgrade options?

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DerryUK02/03/2012 12:19:34
120 forum posts

I am currently stripping a Conect Cadet cnc lathe for cleaning and refurbishment. Looking at the spindle motor I have been thinking about what might be a suitable replacement. The current motor is a GEC DC 370W driven by a Eurotherm 506 supply. The motor drives the spindle via a 3:1 speed reduction toothed belt direct drive, no gearbox.

One problem I have discovered with this setup is that the motor is full of swarf. Conect have fitted a blanking plate over the motor main ventilation holes and subsequent owners have seemingly fitted bits of insulation tape over the rest!

The first question. Is this setup (no motor ventilation) safe? Is the motor likely to burst into flames?

I have been reading a bit on the web looking for a possible replacement. The current setup only allows for manual speed control and I would like software controlled (probably via EMC2). The obvious solution is to go for a 3-phase motor with an inverter. Are there any other options? I couldn’t seem to find any DC motor solutions.

With my current setup I would loosely seem to have a 1000rpm 1.5HP drive so was thinking in terms of a 1.1kW 2800rpm 1:1 drive motor as a replacement. But on reading http://www.lathes.co.uk/page27.html thoughts on the matter especially regarding having some form of drive ‘slippage’ as a safety feature (when the tool is driven into the chuck in error) perhaps I would be better with a with a non-toothed 1:1 belt with a no more than 370W motor?

Derry.

David Littlewood02/03/2012 12:31:06
531 forum posts

Derry,

Since the lathe you are working on is almost certainly unfamiliar to most of us - and I couldn't even find it on lathes.co.uk - then some details of its size and rigidity would help to suggest a suitable drive. In the absence of this all I can say is that I fitted a 1 hp 3-phase motor and VFD to my Super 7 a few years ago in place of a 0.5 hp single phase job, and t he improvement was dramatic.

David

Bazyle02/03/2012 12:41:31
1329 forum posts
42 photos

At that size for DC motors look around the robots and robot wars type stuff. Also wheelchairs. There is a place something like 4QD that does DC drive speed controls as used on electric locos. And the electric loco motors from Compass or Maxitrack might fit your bill.

DerryUK02/03/2012 17:32:22
120 forum posts

Thanks for the input, the 4QD site looks interetsing. Here are some images

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet002-1.jpg

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet003.jpg

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet005.jpg

The current motor is 130mm x 210mm.

DerryUK02/03/2012 21:18:27
120 forum posts

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet002-1.jpg

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet003.jpg

http://i692.photobucket.com/albums/vv286/Derryuk/Conect%20Cadet%20CNC%20lathe/ConectCadet005.jpg

I don't post here very often...

John Haine03/03/2012 09:55:59
423 forum posts
10 photos

Derry, looking at those photos I suspect that your lathe is based on the Hobbymat platform - it appears to have the cylindrical bed with a flat on the top. Also the locking screw on the tailstock barrel and the view into the headstock casing are suggestive. A 370 watt / .5 hp motor would surely be fine for this? The 1.1 kw you mention is drastic overkill!

If the Eurotherm controller is still OK I would stick with a DC motor. As there are 4 leads emerging from the present motor it is probably a wound-field type, but a modern PM motor would be perfectly fine. For example my Denford Novamill has a 375 W 5000 rpm PM motorwhich runs very quietly and has very smooth speed control. Modern controllers such as the Eurotherm have "IR compensation" which means that they give good speed control and high torque at low speeds. I found a data sheet for the type mentioned on the web which suggests that it does have an input for controlling externally from the CNC controller, even though that may not be connected at the moment. You would probably need a motor rated 375 watt with a running voltage of 180V max - this is what the Novamill motor has.

A few years ago I bought a DC servo motor and KB Electronics controller from Mr. Graham at Model Motors Direct - the controller now runs my Novamill but I have the motor which I have no plans for. It is rated 2A 110V - i.e. 220W or about 1/3 HP - as it is compatible with the KB controller it will run off the Eurotherm (though the latter would need a little adjustment, and you wouldn't need to use the field supply). PM or email me if you're interested - john.haine@ieee.org.

I used to have a Hobbymat, and I've converted my Super 7 to CNC and got my Novamill back from death's door which meant building all the electronics, happy to help if I can.

John.

Bazyle03/03/2012 10:33:24
1329 forum posts
42 photos

Yes, John is right it is based on the Hobbymat MD65 chassis. I think I have read that the original company went on to specialise in CNC but probably not common in UK as it was an eastern European company.

An exposed motor is amzingly common. On my hobbymat I just put a cardboard half tube over the end with the away side open. No problem then but 400W will get too hot is unventillated.

You haven't said if it is still working and what the voltage is. Is there a separate power supply? If it is all working but the control voltage is not isolated it might be easier to just connect an RC servo motor up to the control knob. You can't change the speed in miliseconds anyway so this would be plenty fast enough.

Ian S C03/03/2012 11:54:37
avatar
3583 forum posts
128 photos

If it were my lathe, I would like to take the motor out of where it is, and turn it around, block up the hole behind the chuck, and if you change motors that might be what you have to do, but I don't think I'd use much more than 3/4hp, and 1450 rpm/ 4 pole motor, the 2800 rpm motor has much less torque (you might need 1 hp). Ian S C

DerryUK03/03/2012 12:07:11
120 forum posts

John and Bazyle thank you for your replies.

You are right, it is based on the Hobbymat, in fact now I have it apart there is still some bright yellow paint remaining of the original.

The Eurotherm controller is U/S and before I buy a replacement I thought I would review my options. I have not run the motor

The current motor spec is:

GEC DC Machine

Size = MD7175

Ins Cl = F

No = MG26625601/08

Wdg = Shunt

RPM = 3000

Kw = 0.37

V = 180

A = 2.5

Size = 130mm x 210mm

Controller = RS237-3170

Eurotherm 506

If I keep the current set-up the I have been considering http://www.diycnc.co.uk/html/spindle_boards.html as an interface between the Eurotherm and PC.

Derry.

John Haine03/03/2012 15:04:04
423 forum posts
10 photos

As I thought a 180v motor. For a KBE controller see:

http://www.axiscontrols.co.uk/product/kbwm-240-dc-motor-speed-controller/42_238.aspx

...which is the one I use. Thought I use a PM motor it will support wound (i.e. shunt) field.

I see the web price is £72 which is less than a VFD. However I'm not sure if you can control this from an external voltage as the internal electronics I think are floating, so something opto-coupled would be needed. I don't think Roy's spindle board supports that easily though I'm sure he could say quickly.

If you need a new DC motor then hunt around for Bodine or Baldor.

By the way I don't think the CNC version is by Hobbymat, Connect CNC seem to have been a Northern Irish firm supplying machines for educational use. They probably bought a basic chassis from Prazimat without motor, leadscrew etc and built their product around that. There was also a mill but I haven't seen any pictures.

John.

Tony Jeffree03/03/2012 15:30:40
avatar
302 forum posts
5 photos
Posted by John Haine on 03/03/2012 15:04:04:

By the way I don't think the CNC version is by Hobbymat, Connect CNC seem to have been a Northern Irish firm supplying machines for educational use. They probably bought a basic chassis from Prazimat without motor, leadscrew etc and built their product around that. There was also a mill but I haven't seen any pictures.

John.


The only Connect CNC lathes I have come across wrere based on the Myford ML10 - see:

http://www.youtube.com/watch?v=FGiiUPj5DdE

Regards,

Tony

DerryUK03/03/2012 15:53:59
120 forum posts

I have sent you an email John.

There are several utube videos, I noted the following address on one of them:

Cadet Plus

Conect Numerical Control Limited

Hawthorn Road

Castle Donnington

Leicestershire

DB74 2QR

01332 853332

john fletcher 103/05/2012 13:51:11
110 forum posts

I hope I'm in the correct area.

Has any one any experience of using a 3 phase 415 volt inverter to power a 415 volt motor to just to obtain speed control of, 1. A .5hp. 2. A 1.5hp motor

DerryUK03/05/2012 15:08:16
120 forum posts

I suspect you'll get a better response if you start your own thread John.

Put 3 phase and 415v inverters and motors in the title.

Derry.

Peter G. Shaw03/05/2012 17:07:20
avatar
600 forum posts
29 photos

A long time ago I had a Hobbymat lathe and I recall from somewhere that this question of swarf etc inside the motor came up then. A suggested solution, which I think I did, was to use a piece of old nylon stocking over the inlet end of the motor. You will need to make sure that the girlfriend is no longer wearing them first.

Regards,

Peter G. Shaw

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