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Author Topic: variable speed spindle  (Read 14513 times)

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Re: variable speed spindle
« Reply #10 on: July 30, 2007, 07:51:42 PM »
Sorry. USA.
any one else know where I might find a motor and driver
Re: variable speed spindle
« Reply #11 on: July 30, 2007, 08:57:37 PM »
Im looking on ebay and all the torque ratings for things are in newtons. anyone know the conversion for HP

Offline jimpinder

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Re: variable speed spindle
« Reply #12 on: July 31, 2007, 03:45:08 AM »
I can only recommend a three phase motor (240 volt) to replace your single phase, and an OMRON inverter to drive it. This gives very precise control of speed, because it works on frequency, and is programmable. My motor is about twice the size of the old one - about    1 3/4 HP instead of 1 HP to get over the loss of torque at low speed. I got mine second hand from my brother in law who is a factory electrician and most of these places have stuff that they don't use anymore. The Omron had apparently been in for repair, but was never used again.
My only problem is that it is not fully compatible with Mach3 - I have G3 G4 and G5 working (on, off, reverse) but the actual speed is controlled from the Omron panel which is next to the computer anyway. This is the fault of the Omron,(which is an old model)  not Mach3. It is possible to control speed on it directly, I just haven't got round to fixing it up yet!
Not me driving the engine - I'm better looking.
Re: variable speed spindle
« Reply #13 on: July 31, 2007, 10:34:16 AM »
would something like this work. It sais 1.75 HP
thats more than what Im working with now
Re: variable speed spindle
« Reply #14 on: July 31, 2007, 06:44:41 PM »
A big servo, like that Ebay item, would be overkill on a 9 X 20 lathe - you could not use the power, the lathe is not rigid enough and the bearings and slideways would be undersized. The power supply would be the size of a welding set and the driver would cost more than the lathe. As has been said, conventional wisdom is to go for a three phase motor with a VFD or a DC motor with a SCR type speed controller. With the VFD, use a polly-V or toothed belt and a 2:1 reduction will give you a good speed range. You don't need the low speeds with CNC as screwcutting (internal and external) is done at high speed and turning with carbide tooling if you need high metal removal rates.

Conversions :-

1 horse power = 550 ft.lbs/sec = 750watts
Torque 1 Newton metre= 141 0z.ins.

Hope this is helpful.

Re: variable speed spindle
« Reply #15 on: July 31, 2007, 10:34:45 PM »
alright i get it now so its a treadmill motor and a speed control or a 3 phase and a VFD. what are the plus's and minus's of each set up. Im of the understanding that if I go with the 3 phase and the VFD I will need a PWM to analog converter to be able to use it with Mach. Im not sure where to get one of those.
also Im not sure which speed controlers for DC motors is compatible with Mach.
Im looking at these controlers from KB
 but Im really unsure of which ones are compatible. can any one guide me from here.

This is the motor Im looking at
I think im getting closer any how.
Thanks guys :)


Re: variable speed spindle
« Reply #16 on: August 01, 2007, 02:29:32 AM »
I have a VFD on my Mill and it sucks for low revs unless I use the back gear so if you ever do any drilling with large drills on the lathe take it into consideration. The VFD I use is a Mitsubishi so its not that the VFD is crap, its just a fact of life with VFDs. On a small lathe it may not be a problem but I am jus making you aware that a VFD is not the perfect solution.
 Have a look at Peter Homanns site for  spindle speed controller  http://www.homanndesigns.com/ , also I think CNC4PC.com does similar.

Re: variable speed spindle
« Reply #17 on: August 01, 2007, 05:51:44 PM »
Also lok at :-
for BOB with speed controll.

DC or VFD - your choice based on availability and cost. I use iC5 series VFDs made by LG Industrial System at :-
they will have an agent in USA.
For 1/2 HP DC, I use SMC-00 from :-

Which is the best solution? No problems with either system. 3 phase is quieter and smoother.

KB have a good reputation on the net, talk to somebody there for a recommendation. If you need to reverse the spindle using a DC motor, be aware that it is not just a matter of revesing the polarity with big motors. You need to slow the motor to a stop before reversing because of the back EMF generated, otherwise you will damage either the controller or the motor. KB drives have a "-R" if they can do an almost instant reverse. All FVDs that I have seen have reverse built in which can be as simple as connecting in a low voltage switch.

I have not played with a treadmill motor. Wish we have a Suplus Center in the UK. Only problem with that motor is that it has open cooling slots, swarf can get in. If possible get a totally enclosed one.


Re: variable speed spindle
« Reply #18 on: August 02, 2007, 04:16:03 PM »
Yeah I hear what your saying about the open slots but it wouldnt be to hard to Isolate it on the back of the Lathe to keep the swarf out. I will be looking into finding an enclosed one anyway. I also read that the treadmill motors arent quite as strong as the HP ratings that are on them so you gotta get them bigger than you need. (dont know if there is anything to that or not)

I got in touch with the people at KB. In addition to recommending a speed controler they told me I would need a " signal Isolator"???

any one know why I would need that or what its for???

here is the one they recommended

Thanks for everyones input Im learning a good deal.
Re: variable speed spindle
« Reply #19 on: August 02, 2007, 06:24:17 PM »
Some BOBs have the speed control isolator buit in, look at CNC4PC C11G for example. You need to optically isolate the speed signal from Mach and change it into typically 0 to 10 volts for the DC motor control board (or the VFD) and at this point the 0 to 10 volts is referenced to the control board and not to your system ground.
If you look at Novamill in the "Show and Tell" section you will see why I know the problems!