Which encoders?

[heathmanc]

I'm CNC'ing this mill http://www.harborfreight.com/cpi/cta...emnumber=33686 with some electrocraft E712 motors.

Reliance Electric DC Brushed Servo Motors, Model E712
37.51 Oz-In/A
25.0-30.5 V/KRpm
Motor Terminal Resistance .75-1.02 Ohms @ 4A.
Maximum Terminal Voltage 60V
Maximum Continuous Speed 2100 RPM (No Load)
Maximum Peak Torque 1500 Oz-In.
Maximum Peak Current 44.5A
Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In.
Maximum Continuous Current 8.9A

One of the renco encoders is busted up. First off, are these going to be worth using? I've got 3 gecko g320's to drive these. The shafts are 1/2 inch. For uniformity I am wanting to replace all 3 encoders. Would the E3's from usdigital.com be what I am looking for? Using roton ballscrew 5/8x.200 and preloaded antibacklash nuts. Good setup or not? Any other suggestions? Also what kind of reduction should I be looking for. Where would I come across a 60 volt 30 or 40 amp power supply for it. Would it be enough?

[JFettig]

Gecko drives read the encoder outputs in quadratecture, so basicly any CPR rating is gonna be quadroupled, if your running 1:1 ratio and want .0001" resolution, you would want 500cpr, if your running 1:2 ratio you would want 250cpr.

Jon

[heathmanc]

Now the question is do I need to reduce the gearing on the servos?

[JFettig]

I doubt you would, it sounds like some big servos for that machine, so it is likely that you wouldnt. This would give you some nice high speed rapids:not reducing the gearing.
Either way, 1000rpm at the screw is like 200+ipm on a 5tpi screw. You could go with the 500cpr encoders and attach them to the screw and decide the gearing later. This way you can change it up to your liking.

Jon

[heathmanc]

Thanks for the replies. Yes they are big. Just under 3/4hp. I want to set it up good the first time, don't want to mess with it later. Was trying to decide which one to build first, the cnc router or the mill, decided on the mill. The servo for the Z axis is too big to fit up in the head so have to figure something out about it still, and then the power supply.