Re: [CAD_CAM_EDM_DRO] Z axis- Knee or splindle?

dpresto3@... wrote:

> Hi all,
> I'm in the process of converting my Chevilier turret mill to cnc and
> I think I'll use the knee assembley as the z-axis, but before I
> commit to that I thought I'd ask a couple of questions first. I think
> what I'll need to do is use an air assist system rather than use a
> large and/or substantially geared down servo to lift the knee
> assembly, would I need a ballscrew with a system like this or would
> there be enough weight over the knee to take up the play? Would
> servos the same torque as that I would use for the x and y axies be
> siutable? Is there anything else I should know about this type of
> system, or would someone point out the pros and cons of each type
> (spindle v's knee)

I have a 1938 Bridgeport mill, that spent 95% of its life as a manual
mill. I will note that the knee (vertical) ways are the worst on the
machine. It seems that the knee gets more loading on the dovetail
than the other ways, as well as a LOT more weight on not much greater
surface area. Since it was a manual machine, I suspect the knee was
not moved up and down all that much. I know that I don't move
it any more than necessary.

Assuming the Chevalier is built to a similar design, I suspect your
plan might cause a lot of wear to the knee ways. The advantages
are the much longer travel. The disadvantage is that the Z motion
might not be quite parallel to the spindle axis, or that you can't
drill holes, etc. at special angles. If your machine has a non-tilting
head, then you can't do that easily, anyway, so it is not a disadvantage.

Jon