Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: guynamedbathgate on July 30, 2007, 07:23:32 AM
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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? ???
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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
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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
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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
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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
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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
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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
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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?? ???
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dont think you want to know LOL will be in the thousands.
Nope dont think gecko will look at that size of motor.
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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
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Sorry. USA.
any one else know where I might find a motor and driver
Chris
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Im looking on ebay and all the torque ratings for things are in newtons. anyone know the conversion for HP
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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!
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would something like this work. It sais 1.75 HP
thats more than what Im working with now
http://cgi.ebay.com/BALDOR-SERVO-DRIVE-MOTOR-NEW_W0QQitemZ110152688092QQihZ001QQcategoryZ1267QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Chris
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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.
Ian
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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
http://www.solidstatedrives.com/index.cfm/act/catalog.cfm/subcategory/All%20Motor%20Controllers/category/KB%20Electronics%20Penta%20Power/browse/null/MenuGroup/Solid%2DState%20Drives%20Web.htm
but Im really unsure of which ones are compatible. can any one guide me from here.
This is the motor Im looking at
http://surpluscenter.com/item.asp?UID=2007073111330564&item=10-1688&catname=electric
I think im getting closer any how.
Thanks guys :)
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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.
Hood
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Also lok at :-
http://www.campbelldesigns.net
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 :-
http://www.lgis.com
they will have an agent in USA.
For 1/2 HP DC, I use SMC-00 from :-
http://www.beel.ca
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.
Ian
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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
http://www.solidstatedrives.com/index.cfm/act/Catalog.cfm/catalogid/92/description/KBSI%2D240D/browse/null/MenuGroup/Solid%2DState%20Drives%20Web/desc/KB%20Electronics%20%2D%20KBSI%2D240D.htm
Thanks for everyones input Im learning a good deal.
Chris
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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!
Ian
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Yeah that swhat I thought. I think Bob Campbells combo board is what Im gonna go with. since Ill need a BOB for my set up anyway. Thanks for all the help guys. I think I got everything I need.
Chris 8)
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wanted to ask another question that Im pretty sure I know the answer to along this topic.
Its the whole three phase to one phase and VFD's.
Do VFD's also convert single phase to 3phase power??? is there any problem with starting motors this way or will I need a rotary converter as well?
not really familiar with 3 phase power so I thought Id ask
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Yes but you need 220V single phase to run a 220v three phase motor, and no they work just as well as the three in/out ones. Just remember though a VFD loses torque as the motor slows so they are not perfect, still best to keep back gears if possible for low ranges.
Hood
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Guy (etc) - You seem to be getting a bit hung up on this.
I don't know if you have a machine yet or not, or are just fishing around.
Basically any machine you buy for the "hobby" type market will have a single phase motor - at whatever voltage is standard in your country. To have speed control of an Alternating Current motor, you must have a three phase motor - so you will have to change it.
To control the power to the motor you need a single to three phase inverter (forget rotary converters and all that ****). These are a simple electronic plug in unit, with no moving parts, that take in single phase from your mains and put out three phase to your motor. They come in several sizes to suit what motor you wish to power.The three phase is electronically controlled at different frequencies to give you speed control of your motor. The more modern inverters have a simple push button control panel to control speed manually, but also have the ability to be controlled from a computer (which is what we want).
On my Warco lathe I had a 1HP single phase motor running at 250 volts (UK standard). I changed this for a three phase 1 3/4HP motor. I took one off and put the other one on - as easy as that. The inverter was a second-hand Omron inverter which I plug into my 13 amp socket (UK standard) and this is wired via a 4 wire lead to the motor (three phases and earth).The motor is about twice as much output as the original to give better torque when running slowly.
The motor will turn freely at any speed from 10 hz (600 rpm) to 50 hz (UK standard) (3000rpm). I have a set of pulleys available to alter the final drive output on my lathe, but I have not had to use them.
My Omron inverter is quite old, and does not couple directly to the computer - however I have been able to link it (via relays) to turn on in either direction and stop - as per m3 m4 and m5 commands in the program. I set the speed manually via a push button control panel on the front of the inverter (which is next to the computer anyway), and I have recently rigged up a reflective sensor on the spindle (thanks to info from Dr Stein on this forum) which reads into Mach3 - to check the speed.
You can fix a potentiometer on the Omron inverter to control the speed by turning the pot, so I am trying to think up some way of connecting a servo to this - to be controlled by Mach3.
I have spent some £200 ($400) on the lathe, given in a good overhaul in the process and I am highly delighted with the result, and Mach3. I have just turned off my first batch of handrail stancions for a miniature railway locomotive - something I could never have done by hand. I must admit the look very good - my wife says so anyway - but then again - she would.