Re: [CAD_CAM_EDM_DRO] hydralic bed control

> Hi,
> I have an old horizontal mill with a hydralic bed. Has anyone tried
> control of anything hydralic using a automotive power steering unit?
>
> Dave
>

Many of the earlier CNC machines were hydraulic, notably the Moog Hydrapoint
and some large Brown and Sharpe stuff. This technique went out of fashion
as larger servo motor drives became practical. Hydraulic systems were
reliable but messy and they generated a lot of heat. The biggest pain is
when you get air in the cylinders and movement becomes erratic.

A power steering pump would work but you might not get much table speed due
to lack of volume flow rate (depends on cylinder size). You may also need a
pilot acting unloading valve if you intend to run the pump continuously.

Servo valves are expensive, though not any more so than servo motor drives.
At any rate, they would cost more than your machine is worth. If you just
want manual control then you could possibly cobble something together with
flow control valves for speed adjustment. Just don't try moving two axis'
at once unless you have a cheap source for tooling.

Doug