Re: [CAD_CAM_EDM_DRO] Air assist on Series II knee?

Tim Goldstein wrote:

> Wife's away so I went out to play. Got an air line installed to replace the
> rotted hose. Hooked it up to the compressor and started playing with the
> pressure. Had the knee sitting about 1/2 way up with a wood block under it
> so I could work on putting the line in. Started cranking on the regulator
> and took it all the way to the 120 psi that my little compressor is capable
> of (Be putting a 6-1/2 hp unit in this week to replace this little 2 hp
> job). Nothing obvious happened. I then turned on the stepper driver and
> lifted the table off the block then switched off the driver. The table
> stayed in place. I then started reducing the pressure and at just under 40
> psi the table started to sink. So it appears that Bridgett's air assist is
> working fine. I looked underneath and I still don't see how it works, but
> know that it does work.
>
> Anyone know how you tell the proper pressure to run on one of these? It
> seems that anything from 40 - 120 psi will hold the table in place.

Well, 40 PSI equals the weight of the knee minus the drag of the stepper
and leadscrew. It is hard to guess the relative proportions of drag and
weight. You might try turning down the motor current and adjust air
pressure until the motor stalls evenly in both directions. Or, you
could disconnect the motor mechanically and find the balance pressure.

Jon