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Author Topic: variable speed spindle  (Read 13161 times)

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variable speed spindle
« on: July 30, 2007, 07:23:32 AM »
Just in the planning stages of setting up a cnc lathe. Was curiouse if anyone could point me to some literature or other reading on what is needed, how to set up, parts suppliers etc for a variable speed spindle (probably not calling it the right thing) you know one that could be controlled by Mach in program. Im guessing I would need to also figure out what kind and where I would get a suitable raplacement motor for my lathe too.
Any help guys? ???

Hood

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Re: variable speed spindle
« Reply #1 on: July 30, 2007, 02:50:44 PM »
You could use a servo and a servo drive for a spindle. Other way is to use an Inverter (VFD) to control an ordinary 3 Phase motor but the drawback to that is lack of torque at lower revs.
Hood

Re: variable speed spindle
« Reply #2 on: July 30, 2007, 03:06:32 PM »
How big of a servo motor will I need. recommend any particular setup.
It is going to drive a relatively small 9x20 Lathe.
If I use a servo does that mean I can get rid of all the change pullys and just use one pully? and what is a resonable ratio for those pullys?
like I said Im just getting into the planning stage and I have a lot of questions. Ive already done a mill but I never rely messed with the spindle end of things.
Chris

Hood

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Re: variable speed spindle
« Reply #3 on: July 30, 2007, 05:30:05 PM »
No experience of this but most Industrial CNC have either AC or DC spindle motors. Suppose what you really need to do is work out the Max HP your lathe would have at the spindle with the standard motor then look for a similar sized servo. eBay is probaly a good source for servo motors, just keep your eye out and if you are not in a rush one will come along at the right sze and price ;)

Hood
Re: variable speed spindle
« Reply #4 on: July 30, 2007, 06:13:47 PM »
so wait.... no one on any of the linked sites, sells a motor that is big enough?
My lathe has a 3/4 HP motor on it now but it aint worth a darn at slow spindle speeds because the tiny little belt will slip or its got a built in clutch type mechanism in one of the pullys so as soon as you try and make any kind of a reasonable cut other than super skim it slips. not really the motors problem though, never had a problem with it slowing down. I want to get rid of this whole mess when I convert it to cnc. Not sure what 3/4 HP works out to be at the spindle but anything gotta be better than what I currently have.
Not really much for waiting around for Ebay to turn up a motor of questionable quality though. Would rather go to a supplier i can get some sort of recourse from if it doesnt work.
Chris
Re: variable speed spindle
« Reply #5 on: July 30, 2007, 06:15:00 PM »
Oh also. Im guessing that im gonna use a 3 to 1 ratio for the pully so tht I have a decent range if that helps figure out the size motor i might require
Chris

Hood

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Re: variable speed spindle
« Reply #6 on: July 30, 2007, 06:23:33 PM »
I have a 5 or 6 HP AC servo motor that I just put on the Z Axis of my lathe. Picked it up on eBay fairly cheap, same with the drive for it both cost me under $200 so well worth the risk IMO but I suppose eBays not to everyones tastes :)
Hood
Re: variable speed spindle
« Reply #7 on: July 30, 2007, 06:54:18 PM »
Whats a new one gonna run me anyway.
and will I need a special driver for such a large motor or will a ghecko drive it?? ???

Hood

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Re: variable speed spindle
« Reply #8 on: July 30, 2007, 06:59:33 PM »
dont think you want to know LOL will be in the thousands.
Nope dont think gecko will look at that size of motor.
Re: variable speed spindle
« Reply #9 on: July 30, 2007, 07:40:43 PM »
Chris,

If you are in the UK try Mark Butler at :-

www.drivesdirect.co.uk

He can supply a matched motor and VFD, which can be controlled from Mach and a breakout board like CNC4PC C11G, to give you speeds from zero to twice the motor's nominal speed. Torque, at low speed, will not be high but it depends what you want to do. My 12 x 36 lathe (not CNC) has a VFD and it is the best addition I could have made.

Ian Ralston