Thread: 7 X 12 motor conversion???

Kryn have you considered replacing it with a 3phase motor and VFD?

That way it would be relatively inexpensive and you would still have variable speed.

I have done this on my 9x20 EVS lathe which also had a "poof" moment.

Originally Posted by Big Shed

Kryn have you considered replacing it with a 3phase motor and VFD?

That way it would be relatively inexpensive and you would still have variable speed.

I have done this on my 9x20 EVS lathe which also had a "poof" moment.

I had thought of that, but I think the motor will be bigger than the lathe, looking at going for a 240V 500W DC motor.
Just wondering if anyone had done something similar, that was all. Or is it just me that has crap motors!!!!
Kryn

Fred,
How well does the 3ph motor/VFD combination handle low speeds? It's understanding that the torque is much lower at slow speeds on 3ph motors.
I'm thinking of replacing the single phase 550 W motor on my lathe.

Originally Posted by snowyskiesau

Fred,
How well does the 3ph motor/VFD combination handle low speeds? It's understanding that the torque is much lower at slow speeds on 3ph motors.
I'm thinking of replacing the single phase 550 W motor on my lathe.

Iy depends how much you are prepared to spend.
On a generic VFD f you used a 2HP (1500W) motor you would have the same torque at 17Hz as you would with the 550W at 50Hz.
It also tails off at higher speeds but with a 2HP you could maintain at least the same torque or more torque from 17 to 120 Hz which would give you a range of ~7X

Even if you pay more for the VFD this may give you improved torque at slow speeds but it won't fix motor cooling issues at slow speeds.
This can be addressed with an independently powered motor fan like this one
https://www.woodworkforums.com/f65/3p-motor-192985

A 2hp motor wouldn't be too big for this lathe (9x20) considering it's supplied as standard with a 550W motor?
Later models of the Seig C6 have a 1KW, 230V DC brushless motor but a replacement motor costs about $470 + $$ for a controller.

I replaced my EVS motor (can't remember what size - I think 1hp) with a 1hp(.75Kw) 3 phase motor and VFD. I also replaced the driven pulley, was a twin belt (very small section) with a timing type belt and pulley.

The lathe headstock itself has a high and low setting via gear(s).

I have no low torque issues, can turn down to 75 RPM and up to 2000 RPM.

The motor and VFD came with the DRO I purchased some time and I kept it in reserve as I knew that one day I would release the smoke from either the circuit board or the original motor.

Yes the motor is way bigger than the original one and I had to re-jig the motor mounting quite a bit.

I can put up some pictures if anyone is interested.

Originally Posted by KBs PensNmore

Anyone with a 7 X 12 mini lathe done a motor conversion? I was taking off .075 mm, when poof the lights went out and the lathe stopped, reset the RCD and away I went 30 sec later did the same thing this time with a stinky motor smell.
This is the 3rd motor I've put in this unit, NOT HAPPY. At nearly $200 each, I'd have been well onto my way with a larger lathe. Toying with the idea of putting a larger motor without the variable speed, anyone done something like this.
Kryn

I assume you have the older brushed 400W DC motor, and not the newer (since 2009) bushless motor of 500W.

Power wise, a 1/2HP 3-phase motor with VFD would compare favourably with the 400W version. It would be a very much larger motor though and you would have to find another place to mount it. An alternative could be to upgrade to the Sieg brushless motor and controller. The VFD is likely to run without problems for 24h a day nonstop for 10 years (100,000hours). The Sieg brushless motor I would personally think is good for something like 2,000h. But it is much smaller. The original brushed motor and controller for comparison, are known for failing well before doing 500 running hours.

FYI, Sieg motor/controller prices can be found here.
These are for the SC2 which I think is a 7x14.

Originally Posted by snowyskiesau

FYI, Sieg motor/controller prices can be found here.
These are for the SC2 which I think is a 7x14.

motor $ 264.61
controller $217.35
total $481.96 plus postage

I would say this is crazy and makes no sense at all. A new C2 lathe is under $700 postage included.

I would suggest selling the lathe with the broken motor on gumtree or ebay. That should fetch something like $2-300 as a spare parts carrier. Add to this the above $481.96. Together that should buy an old iron 9" lathe instead. It will last much longer, even if it was already 50 years old to begin with.

Thanks for that Snowy, some useful info there. Just got to consider spending $480 for motor and control board, then to work out wiring of it all?
This metalworking is becoming an expensive hobby, and still end up with a small machine. I wish I could get 50 hours out of it, let alone 2000!!!!!!!
Thanks CBA, something I'm having to consider.
Regards
Kryn (n)

I'd like to see some pictures Big Shed!

What about a Treadmill Motor and controller ?

I have swapped out motors on a lot of lathes.
On lathes the size of the Emco 5 usually a 1/4 hp (0.18 kW) with a vfd works perfectly.
Lathes of the size Emco 8 and similar will be happy with a 1/2 hp (0.37 kW) motor.
I have got a Fortis lathe myself (=Clausing 100) and I use a 1 hp motor.
Never had a problem with being underpowered.

People often read the given power of a lathe as output power, where the manufacturer always states the input power, so don't worry about the difference in power between the original factory motor and the "new" three phase motor.

Of course I am talking about three phase motors and standard vfd's.

Over here I buy the motors and vfd's second hand via Marktplaats (the Dutch Ebay)

The most expensive vfd-motor combination has cost me some € 150,=.

Look around for second hand and you can save a lot of cash.

Once used to a threephase motor + vfd you'll never look back!!
Jan

Originally Posted by KBs PensNmore

Anyone with a 7 X 12 mini lathe done a motor conversion? I was taking off .075 mm, when poof the lights went out and the lathe stopped, reset the RCD and away I went 30 sec later did the same thing this time with a stinky motor smell.
This is the 3rd motor I've put in this unit, NOT HAPPY. At nearly $200 each, I'd have been well onto my way with a larger lathe. Toying with the idea of putting a larger motor without the variable speed, anyone done something like this.
Kryn

Kryn,

of course, another option to consider would be to repair the existing motor and/or controller. What worries me, is that you already went through tree $200 brushed motors. They are very low quality, both the motors and the controllers.... but 3 motors is rather unusual unless you use that little minilathe as a production tool.

This is a link to a document "troubleshooting the Mini Lathe variable speed drive" from the US dealer LittleMachineShop:
http://littlemachineshop.com/Referen...leshooting.pdf
The fact that a Sieg dealer has to put up such a document speaks for itself WRT the quality and reliability of these Chinese drives. But it is relatively simple technology, and someone handy in electrics/electronics stands a good chance to troubleshoot. Be aware though that these drives works with line voltage and are unforgiving. Read the above .pdf, but only do the checks you feel confident doing safely. Also keep in mind this is an American document, where line voltage is only 110V. We use 240V, and our fuses are rated lower because at tyhe higher voltage it take a lower current for the same power. Also be aware that many spare parts sold in the USA will be for 110V version, especially important for the motor armature and speed controller.

If you google for "minilathe motor troubleshooting" you will find articles and videos that may help you. There are also people out there offering repair service like http://olduhfguy.com/#
But postage cost both ways may rule out this option.

If you google for "mini lathe circuit diagram" you will see other people have reverse engineered these Sieg speed controllers to assist with repair. You may find someone close to you that may try a repair if you give him motor and controller and circuit diagram. Can you see an obvious problem on the controller?

I agree with Jan, this minilathe is about the size of an EMCO Compact5. But, whilst the Compact 5 had 1/3HP single phase TEFC motor it also had a belt drive with pulleys for 6 speed settings. Whereas the Sieg minilathe is 350W DC variable speed with just only two speed ranges. It is going to need a much stronger motor to compete with the metal removing capacity of the Compact 5.