Air Assisted Knee Backlash on Series 2

[kewl_cat]

I have a Series 2 with air assisted knee. The knee is controlled by CNC and has quite a bit of backlash in the range of .100. Does anyone know if there is a way to tighten the backlash? I looked from the bottom and from the side inspection cover but don't see anything. Thanks

[machintek]

The knee has a air cylinder assist. What ia your pressure set to? The manual says to set at 40 PSI and adjusting the pressure up 5 PSI for every 100 pounds you put on the table.
I do not remember any adjustment for backlash. Are you certain the backlash is in the ball nut?

George

[polaraligned]

If you look from the bottom you should be able to see if the backlash is in the bevel gears or the ACME screw. Be REAL careful servicing these as the knee, saddle and table are super heavy. You may be able to shim if it is the bevel gears. There is not going to be an adjustment for the ACME screw. Everything OK with the motor driving the knee? Is this a factory setup or did someone add this on?

Backlash on the knee is generally not a problem because of the weight of the knee, provided your software can compensate for it.

[kewl_cat]

I had unregulated shop air into the machine. I put a regulator on it yesterday and set it to 65psi due to the weight on the table. We will see what it does today. Thanks for the info George


The machine is still running the original steppers but driven with Mach 3 and Geckos which means it does have compensation.

[machintek]

Many. many years ago I was called in on one of these machines because it was stalling in the Z down direction! Turned out he had shop pressure going to the knee with no regulator. The stepper could not overcome this force. Lesson learned.
With the correct air pressure and correct gib setting, I wonder: You have a mechanical counter (if it still works) on the Z. If you put a travel dial on the z and watch the counter, you should get a good idea of how well the Z is moving.

George

[kewl_cat]

Thanks George. I had problems with inconsistent Z depths although the counter always indicated everything was where it was supposed to be. I regulated the air and the Z depths are correct and the same each time.