Originally Posted by
dwyersm
Thank you all, very informative answers.
So could you say that.... Because of the algorithms employed by decent CNC controllers, its safe enough to close the loop at the motor.
And because the motor takes care of the loop with decent algorithms within its own feedback loop, the encoder is safe enough on the motor or screw shaft, and no need for linear encoder on the slide to feedback to motor.
Only reason I asked the initial question is because I have for weeks been looking at aliexpress CNC controllers, and have not found one yet that has encoder feedback to the controller.
I have a little Australian made gear hobber Qualos #0, cuts 5" x 5" spur and helical gears.
I want to CNC it, but I need rotation feedback of hob tool shaft sent to the controller, then divide these pulses by a number, the result pulse train will be sent to drive the gear blank motor.
I cant CNC command the drive motor speed, its fixed, so therefore 2 axis G Code cant help, What I have to do is pick off at an appropriate shaft the rpm with an encoder, and use this as the starting point for gear blank rotation and feed motor rotation.
What a hobber needs is a whole number ratio of hob rpm to gear blank rpm. For example, a 40 T gear, the hob makes 40 rev, whilst the blank does 1 rev.
This is usually done with change gears. but to cut a prime number, you need the same prime on the change gears.
It also needs a feedrate that slightly "drags" (or advances) the hob rpm across the black, to give the helix of helicals.
CNC can do this for me, but I have to find controller with encoder input, I cant rely on closed loop at the motors.
The feed rate is important as it helps with cutting helicals.
So a 2 axis controller is needed.
And I have thought about an Arduino, There is code available to read quad encoders , all have to do is insert gear blank and feedrate divisor into code.
Shane,
AU