Servo or Stepper

[Cartierusm]

I'm sure this has been asked a lot and I'm not sure if I'm in the right forum, but CNC Router didn't seem correct either. BTW I did an extensive search and couldn't find exactly what I was looking for. So here it goes.

I have a Bridgeport type mill and I'm going to convert it to CNC. I already have a CNC router I built so I already have all the electronics. I built it so all the cables coming out going to the cnc router use quick release plugs. So the question is should I just go with stepper so I can use the electronics I all ready have? Is servo all that much better? I will be using either stepper or servo with a pulley and belt system and probably 1200oz motors.

My understanding is the only real difference between stepper and servo is the encoder and the ability to go fast and keep the same amount of torque. I'm sure the speed of a stepper would be fine for my applications and as far as the encoder goes, it doesn't keep the motor from losing steps it just notifies you if you do lose steps, right? If I'm using these powerful of motors and a pulley system I should be fine, right? I'd rather stay with stepper and just use my current electronics, which would make this cnc retrofit super cheap.

[Cartierusm]

Addendum, I think I will be using the 906 oz. motors as I want to use my existing 5056 Micro Drivers and they can only handle 50V. So I'll be using a 48V powersupply and 1200 oz. motors need more power so I wouldn't be utilizing them so I'm going to go for a lower power motor so i'm not wasting money, but then again if I ever want to upgarde the drivers I wouldn't have to upgrage the motors and the price difference is only $15.

[DennisCNC]

I had a 36" table Bridgeport with 600oz steppers and that was the first machine I converted and used it for 2 years with the original lead screws it would break short 3/8" endmills like nothing and the max rapid was ~45 IPM. I would recommend start with the steppers and if work starts to pile up then get ballscrews and servos when the machine pays for them. There is nothing bad about steppers as long as you keep below the speed they can handle.

[ger21]

http://www.cnczone.com/forums/showthread.php?t=17419

[Cartierusm]

Thanks guys that's just the info I needed. I honestly don't care about speed, the speed I get from my steppers on CNC Router is more than enough, and usually when actually milling steel you have to go slow so you don't get bit deflection and/or breakage.

So next question: Bridgeport type mill with ballscrews with a 2:1 ratio. 12 tooth timing pulley on motor and 24 tooth timing pulley on screws. What would be the minimum you would run for a stepper motor. I think I'm going with the 1200 oz. motors and run them at 48V instead of the recommended 70-90V, so I can use the electronics/drivers I already have.

For the quill I will also use 1200 oz. and a 2:1 ratio, but I'm connecting the 24 tooth pulley to the actual quill handle post(where the quill handle usually goes) this way I won't have to use a screw and nut assembly. This seems like an ideal spot and it doesn't take too much force, plus the return spring will assist.