4th Axis & LinuxCNC 2.7.15 RTAI i386

Hi All,

recently I made the 4th axis my home made CNC machine. To run it I use arch i386 RTAI kernel and Wheezy platform.

The machine has two step motors on X axis (gentry), and single motors for Y and Z axis respectively. The BoB used to operate machine is 5axis LinuxCNC/Mach3 (see enclosed link LinuxCNC Mach3 Breakout Board ) and in XYZ setup everything works like a charm. In configuration file P2 & P3 is used for X master motor and P8 & P9 is used for X follower motor. P4 & P5 for Y motor, P6 & P7 for Y motor.

Now with rotary axis I use P16 & P17 for A motor and set Axis performance later in config file as following: Steps 200, micro-stepping 64, gear ration 1:3, pitch 120 degree/rev, velocity 100 deg/s and acc 500 deg/s2. Home at 0, table travel -99999 to 99999.

When machine is fired-on, all motors are activated ready to go. All axis, double X, Y and Z works as before, however very slow move of A axis. Checking wiring, connections, cables nothing was found wrong. When I change connection and settings (swap) Z and A axis, A motor speeds up, Z is rarely rotating.

Is there anyone who could help me, give some advise, what I did wrong, what to do to get A axis running as good as other three?

Thank you!

At 100 deg/s, it takes 3.6 seconds for one revolution of the 4th axis, even longer if you did not raise the jog velocity in Axis GUI.
Now you should have 2 jog velocity sliders on the GUI, one for linear axis and the other for rotational axis.
You can set the velocity at 1000 deg/s, but as you are using parallel port and have 64 microstepping, it might not be able to output that high of a step rate, so you can lower the microstepping to 8 or even 4 if there are not to much vibrations. Do not forget to change the scale if you change microstepping.

Thank you Tommy for support. The microstepping was changed to 5 (all other axis set to 5 -- metric ball screws in all three linear axis), and max speed set to 1500 deg/s. Worked well. However, during the time it happened motor was speeding in one direction and in opposite started to jerk. Driver was checked - CW5054, wiring, connections, par port cable, everything was OK. The only thing not checked is BoB. Tomorrow I'll get new one and check if that is issue for my joy.

Though I would have fine tuning and accuracy setting of the rotary axis, for pulley - gear reduction 3:1, should I set 120 or to leave 360 deg/rev as pitch, what is your proposal?

3 turns of the motor is 1 turn of the chuck/spindle/main shaft, right ?
Then 120 should be set.
You can try to set the step time and step space a bit longer, like 5000, and see if the jerk stops.

Once again, Tommy thanks a lot. I set step time to 5000, step space 8000, machine started. Today I rounded the first piece of wood. Max speed revolution I could get is 90'000 which is not as fast as I thought.

In 4axis, I kept X, Y and Z axis alive. Present post-processor X values wraps around Y, outputs as A, ,which is Ok in my setup.

Cheers!

You are welcomed, always, or in your native language, Nema na cemu, uvek si dobro dosao.

Hvala