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Author Topic: Hoping to retrofit a CNC mill with Mach3. Where do I start?  (Read 7372 times)
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Hood
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« Reply #10 on: June 04, 2009, 06:44:16 PM »

Knowing what you have will make it easier to advise what you will need to get, keeping the old drives may or may not be the sensible route, all depends on the drives.

Hood
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Jeff_Birt
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« Reply #11 on: June 05, 2009, 07:57:48 AM »

I would not be in a big hurry to trash all the drives unless they just don't work. I refitted an older Bridgeport 308 and left all the drives in place. A Galil card noes nicely to control them.
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Happy machining , Jeff Birt
 
ions82
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« Reply #12 on: June 05, 2009, 11:44:12 AM »

I would not be in a big hurry to trash all the drives unless they just don't work. I refitted an older Bridgeport 308 and left all the drives in place. A Galil card noes nicely to control them.

The reason I figured I would get rid of the drives is because they are so old.  I would rather have the reliability of something newer.  If I did the retrofit and kept the drives in place, I would be worried that one of them would fail at some point.  Are servo drives usually quite reliable?  Basically, I just want to end up with a machine that is reliable.  Right now, I've got a 4500-pound paperweight.  I will get getting all the specifics on the drives later today.  Hopefully, it will help figure out what exactly I need to do with this machine.
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Hood
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« Reply #13 on: June 05, 2009, 11:51:32 AM »

Industrial servo drives tend to be extremely reliable, but like everything they can go wrong. You could always swap out at a later stage if that was the case.
Hood
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ions82
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« Reply #14 on: June 06, 2009, 12:21:55 AM »

Here is some of the information I've managed to gather from the literature.  The maintenance manual for the machine gives a pretty good description of the various components.  I'll include any information that seems pertinent (even if I have no clue what it denotes).

Axes servo drives - Gettys N360 SCR   They are 3-phase half-wave drives.  I have the factory manual for the drives.  It includes diagrams and schematics, but some of it is tough to read because an obvious printing error jumbled up some of the text and placed some of it on the schematics.

The axes servo motors are Gettys permanent magnet motors.  The tachometer produces 9.5 VDC for every 1000 RPM, and the armature voltage at 1000 RPM is 34.2V +/- 10%.

The encoders are 500-line optical incremental encoders.  The literature gives a bunch of specs for them, but I have no idea what most of them mean.  For example, the outputs are described as quasi-sinusoid or square wave single channel or dual channels in quadrature.  I sure hope I don't have to understand such concepts if I am to be successful with this retrofit!

The spindle uses a size 3 Fanuc AC spindle drive and motor.  If I understand correctly, it is a servo-type motor.  It is rated at 3.7 kW (5 HP) continuous and 5.5 kW (7.5 HP) for 30 minutes.  The base speed is 1500 RPM and the max is 6000.  The input command voltage goes between +10V DC (max speed) and 0V (halt).  Power supply is 200/220V +10% / -15% at 50/60 Hz +/- 1 Hz.  Velocity feedback is provided by a pulse generator.  The Fanuc part numbers for the spindle motor and drive are listed, but I assume those are not necessary.

Anyway, I hope that some of this information will be able to help move me in the right direction.  As I said, I just assumed that it would be best to replace the servo drives.  This is mainly because they are so old (from the early 80s).  There is a factory-installed 4th axis on this machine.  So, there is a spare drive on hand.  The original rapid speed was 200 IPM (with feeds topping out at 100 IPM), so changing out the drives probably wouldn't turn a fast machine into a slow one.  If more detailed information is needed, please let me know.  The literature I have seems quite detailed, so there is a good chance it will have any info that might help.  Thank you to all for taking time to read my posts and help me with this project!  I'll be damned if I'm going to end up like these guys.

http://www.youtube.com/watch?v=x3RgyZRgshA
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Hood
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« Reply #15 on: June 06, 2009, 10:59:30 AM »

These axis drives are I think old style, I was expecting it to have PWM drives, afraid I know nothing about these drives but from what I hear they are relatively eay to repair.

The motors would get you 2000rpm on Geckos but it will depend on what the current is whether Geckos will do, any info on that?


Spindle sounds like it should be good, 0 to 10v is an easy thing to control and there are quite a few boards that will do that.
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ions82
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« Reply #16 on: June 06, 2009, 11:26:25 AM »

The data chart for the servo motors has quite a bit of information on it.  However, I'm not sure how much of it pertains to the current drawn by the motors.  The "Continuous Rated RMS at Stall" is shown as being 12.5 amps.  From what I've been told, old DC motors aren't the most efficient.  Is it a common issue for new drives being unable to support enough current for old servo motors?
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Hood
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« Reply #17 on: June 06, 2009, 11:30:32 AM »

That should be fine for Geckos, think they are 20Amp if I remember correctly, not sure if thats continuous or peak though.

Older DC Servos tended to be higher volt lower current and more modern ones I think tend to be lower volt higher current, then again I know very little about DC servos as it is AC that I use.

What pitch are the ballscrews and do you have any gearing between motor and ballscrew?

Hood
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ions82
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« Reply #18 on: June 06, 2009, 12:54:17 PM »

Hm.  I'll have the research the ballscrew pitch/size.  As chance would have it, that is one thing that isn't specified in the literature I have.  I can probably take some crude measurements with a caliper and figure it out.  The servo motors are geared down (via belts and pulleys).  I imagine this information is rather important when it comes to setting up a retrofit.
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ions82
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« Reply #19 on: June 13, 2009, 02:09:58 PM »

I've been busy with other projects for a few days, so I haven't been able to stay on top of this.  Are ballscrews typically made in even increments?  Do I just measure OD of the screw and get an estimate of the pitch?  I figured that most screws are fairly even measurements.  My only question is whether or not the dimensions of this old machine will be metric or standard.  Will I need precise measurements and specs for the retrofit process?
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