Tony, if you have the machine you should be able to do it for $6K. I really need to add up all my costs so we have at least one bench mark. I think I'm at $8K including the purchase of the machine.
Um...I'm almost done with mine. I have the whole thing posted here in my conversion blog. Not saying that I have the way to go, just a way to go.
Servos -v- steppers. The debate rages on. Steppers seem to be the defacto standard for the hobby group and a lot of commercial machines. But a lot of commericial machines are using servos or steppers with encoders. The realy key here is not the motor, it's the closed loop feedback. People put encoders on steppers too.
Steppers can be made to behave more precisely in the first place. Thus no need for an encoder to ensure position. A servo is just a pretty normal DC motor with a shaft encoder on it. So it has to have drive electronics to complete the feed back loop.
Couple of recent developments.
Rogers Machine has worked with Jim Cullins to come up with an interface board to act as a DRO AND communicate with Mach3. Rogers wrote some software that allows Mach to be tripped into e-stop when the servos get behind. This is an improvement since the only way for that to happen now that is kinda of the shelf is to have the servo driver trip an e-stop. Then you are at the mercy of the servo driver. I am using Gecko G320s. They fault at 128 steps out. A circuit has to be built to trip the software e-stop via some kind of communication with the PC. Many of the break out boards have a pin or two for this kinda stuff.
Depending on you ratios and encoders, 128 steps could be a lot of distance. On my machine it's .004. I can live with that but I'd like it to be .001. Then I get into a higher drive ratio. Then I need a two stage belt drive and the complexity goes up.
So an electronic solution is really attractive.
Gecko has something called the GRex. It is a little computer really. It takes USB from the PC and hooks up to the servo motors and the encoders. Mach4 will have support for it later this year. It should, if I'm reading the tea leaves, allow some real feedback that will allow the servo motor speed to adjust as steps begin to get off. It will eventually fault out but this should make the servos darned near unstallable. I believe Grex also supports steppers and Gecko has been working on the unstallable stepper for a while. They do this by putting and encoder on the stepper.
This is really interesting to me because then the stepper is essentially a servo.
Then there is the whole EMC camp. This is the Linux based controller. Jon Elson, Pico-Systems, has some hardware that allows EMC to behave in a proportional manner as I described. EMC has a great following. It is free. It is a little harder to install.
In my opinion if you don't close the loop to the computer you are running open loop, so why bother with the servo? I didn't figure this out until recently. I'm waiting for Mach4 to make a decision. The Grex is additional cost.
Having said that, my motors are tuned such that I have not had this kind of a problem. I crashed a tool once and that screwed the datums up, but I'm not sure anything can prevent that. So, I could just as well be running steppers right now.
The smart thing to do now might be to get steppers that at least have the encoder shaft on them. Then you can upgrade to a closed loop system if you feel you need it.
That's my relatively non-technical explanation of what's going on.
Best,
-jd
John Delaney
www.rwicooking.com