Re: Multiple syncronized spindle question.

[Jon Elson <elson-at-pico-systems.com>]

Dncnorthwest1-at-aol.com wrote:

> Hi,
> has anyone worked with a multiple spindle machine with separate spindle
> offsets and a synchronized movement of the spindles? This would entail an
> offset for the tool length and the z axis of the fixture offsets, and then
> slaving the spindle motions to the common z motion. This could allow for
> things as simple (relatively) as mounting a pair or more of Bridgeport BOSS
> series heads to a TEE Ram and making a small multi spindle production machine
> with multiple tool capability, or to retrofitting a larger machine.

I'm not exactly clear on the terminology.  But, what it sounds like is rigidly
mounted
heads, and Z motion is on the knee (or the quills are all tied together,
somehow).

As far as I know, EMC, and most other controls that have tool length
compensation and
G54,G55, G56 etc. up to G59.3 work offsets would be able to do this.  Instead of
using
G54, etc. to produce the offsets between multiple workpieces, it would perform
the
offset between the heads.

>
> Along those same lines, has anyone played with using hydraulic servo valves
> to retrofit a tracer mill. Considering that tracers are almost unwanted in
> most shops, can still produce good finishes and come with one to six heads,
> they could be a great source for experimenters.  They usually can be found
> with two axis table cylinders and a knee lift cylinder. If the tracer valve
> goes out, the cost of repair often makes them unattractive if the shop has
> any CNC's.

It makes some sense, but in fact, is pretty difficult.  You need proportional
servo
valves (aka Moog valves).  These are really expensive units.  Possibly the
electronic eye tracers that would follow a pen on paper drawing used these
valves,
but the finger on the template mechanical tracers didn't use an
electrically-operated
proportional valve, at least.  They probably DO have proportional valves of good

quality, however, and a good tinkerer might be able to create an electrical
actuator
to drive the valve.  What these will most likely be is valves which produce a
velocity
of the machine proportional to the position of the valve.  Standard servo CNC
programs produce a voltage proportional to the velocity they need the machine to
move.
So, to go between this, you need a device that will move the valve plunger an
amount
proportional to the voltage applied to the input.  An ordinary solenoid won't do
it.
What you need is a closed-loop servo amp with a device (LVDT?) to measure valve
position, and then drive a solenoid or even a motor to work the plunger.  This
will need
to move the valve plunger in increments of thousandths of an inch, and
absolutely
supress the sticktion of the valve.  Not impossible, but definitely difficult.

If course, you'd need to add linear encoders to all the driven axes.

The commercial electric prop. valves move the solenoids inside the valve, so
that
they don't have to deal with the sticky valve seals.  They still add 'dither' to
the
electrical signal to keep the valve from settling in one spot.

The real reason why you probably don't want to do this is that hydraulic
controls
are VERY inefficient, power hungry, LOUD, and dangerous.  If something
electrical
on a DC motor drive shorts out, it causes an E-stop or a blown fuse.  If
something
goes wrong on a hydraulic drive, a hose can blow off under 1500 PSI, and kill
anyone standing too close.  Even if noone is hurt, the mess of having a gallon
or
5 of hydraulic fluid sprayed all OVER the shop would be a mess that you could
literally
NEVER clean up!  You'd be buying kitty litter by the truckload, and still
falling down
on the slippery spots.

Jon