Hi.  I have an Acu-rite 2-axis CNC that I would like to convert to 3-axis.  I have watched youtube videos of conversion, but I'm not sure where to start.

Has anyone ever done this?

I currently have servo motors and ballscrews on the X and Y axis.  Can I use these when I convert?  Do I have to get a servo motor for Z?  Can I use my current scales, or will all 3 scales need to be the same?

I have looked into kits, but have not found anyone that will let me use my current motors, ballscrews, or scales.  Going that route doesn't make financial sense to me.

It appears the most cost-effective route is to do this on my own.  I have an email in to Gecko drives to see what they have to say.  Any other options?  What about controllers?  I am using Bobcad/cam now for CAM.  Maybe that doesn't matter, but I would like to continue using it.  I want to find a controller/software that is easy to learn.

Any ideas?

Thanks!!


Scott

Lots of options and lots of routes you can take. The drives that are on the machine now will almost certainly be analogue input control, ie -10v to +10v signals. Mach uses Step/Dir natively so its unlikely you can get Mach to control the drives directly. You have a few options, first is to get a controller that can send out analogue signals, there are a few and the price varies quite a bit, here they are starting with most expensive
Galil
DSPMC
CSMIO-IP/A (soon to be released hopefully)
Kflop with Kanalog.

The other option is to get servo drives that can accept Step/Dir input but the choice is determined by the motor voltage/current. It is likely the Geckos will not be high enough voltage for your motors as they Max out at 80V and often the DC servos on that vintage machine are 100v upwards. There are drives from CNCdrives of Hungary that can handle up to 160v, they are reported to work well.

Depending on the route you take you may have to get a drive for the Z that is similar to the X and Y as the controls that can talk to analogue drives can only talk to them and not a mix of step/dir and analogue. The Galil can do both but dont think the others can but you would need to check to be sure.

Glass scales may be ok to use but the problem with them is the axis has the feedback rather than the motor so if you have any kind of backlash at all it can make tuning a nightmare as the motor is not directly coupled to the feedback and can tend to hunt. Most systems have encoders on the motors.

Hood

Thanks Hood!  Very good info.  My motors are rated at 140V.  So maybe I should look at replacing the motors so all 3 would be the same.  I contact the vendors you suggested to get their thoughts.

Just so I'm clear, to do what I want I'll need:
3 motors (probably)
3 drives (one for each motor?), or will one drive run all 3 motors (assuming their are the same brand/capacity)
1 controller/software to run the drives/motors (i.e, mach3, etc.)
1 ballscrew for the Z axis
Plus making my own adapters, etc to get the motors to run the ballscrews, etc.

Thanks,

Scott

Motors dont have to be the same and personally I would keep the ones that you already have. You may need to fit encoders to them although you may get away with using the glass scales if they are ttl output and the machine is tight.
Whether to go with one of the controllers that can do analogue out and get another analogue capable drive for the Z or go with new drives I dont know. I think I would see if anything could be found for the Z and make my decision then, often you can get deals on eBay.
 If you do go with step/dir capable drives then you may still want to look at using an external controller rather than the parallel port. The benefit of the parallel port is everything Mach has been designed to do will work from it where the external controller route may not support some of the more obscure function although I think most support nearly everything.
The benefit of a controller is you have external pulsing which is a lot cleaner that you will ever get from the parallel port and you will not be limited to the 100KHz (60KHz more likely) that you would from the parallel port. That means you can have higher resolution encoders which will give better resolution and likely make tuning easier.

Quite a few  Step/Dir controllers available,  have a look at the SmoothStepper, Ethernet being the version of that I would recommend, you would also need a breakout board to make connecting to the machine a safer experience and an easier one, PMDX would be my choice
 The other controllers that look good are the ones from CS-Lab of Poland, they are more industrial in design with differential step/dir, analogue I/O for spindle and FRO etc and also the digital I/O is 24v which is more in keeping with Industrial machines, no breakout needed for them.

Lots to think about I am afraid
Hood