Servo control with printer port.. (Linuxcnc is cool or printer port isn't dead yet)

There has been the talk about how you can't get machines with printer ports and that they don't work well anyway.. Yadda yadda yadda.. Linuxcnc has always had really good printer port performance and allows you to do almost anything with it. (it is just another hardware interface)

So - I grabbed the last emco lathe we had on a shelf for my basement tinker area.. It is the compact 5 cnc version. It has had a life and was the one missing the most parts. (didn't come with steppers and such and maybe a ball screw?) I think we have scrounged enough parts now to create a working lathe.

Here is the twist. Linuxcnc works great using the printer port for step/dir interfaces.. I am not going to do that. The printer port is going to be used to output PWM+Dir and read back the A/B encoder signals.. Linuxcnc will close the loop and it will be a true closed loop setup. (Using PID)

There will be limits. Obviously the computer can only count so fast and output lower pwm frequency than dedicated interface hardware (like mesa)

so - what I have is
HP 8300 SFF i5 computer (3rd gen)
Pci-e printer port from newegg Approx $15
2 amc drives that take pwm/dir input. (they are bd15a8 - brushless servo drives but will work with brushed servos)
2 Pittman motors from a surplus outlet (bought years ago)

With the encoders I have - the resolution will be around .005mm (.00002"). This will limit the speed to about 50ish inches per minute. (know more when I get everything setup.)

The emco is currently apart as I clean it up..

Attachment 484550

https://youtu.be/sUz5ZZyf2LU