Rambling hydraulic post that was: Multiple syncronized spindle question.

[Ray Henry <rehenry-at-up.net>]

Hi Fred

If using hydraulic rams is an experiment, go for it and report back.  I 
do know there is a fellow that has some plans to build a hexapod test 
machine using hydraulic rams.  My short answer for a production machine 
is I wouldn't.  Read on if you're interested in the details of why I say 
this.

I've had some experience with four different kinds of hydraulic 
controlled machines.  In each case, the control devices used were made 
was quite a while ago.  

The first was a Sheldon Lathe that used hydraulic motors to turn axis 
ball screws and spindle.  This machine turned out great parts when it was 
tuned properly.  The control was an AB-7360 that had analog I/O cards 
made specifically for the hydraulic valves that Sheldon used.   When we 
started up the machine in the morning we had to run the hydraulic pump 
for a half hour to warm the fluid.  When fluid was up to temp, we loaded 
a test program that ran until the positioning and palsey got within a 
specified value.  At that point we loaded and ran a spindle speed program 
that set adjustments to the analog out so the speed you got was near the 
commanded speed.  Then we could cut threads and accurate compound motions.

All of this hydraulic startup noise usually happened about five in the 
morning and drove the nearby residents nuts.  The operator had ear plugs 
or a muffling headset.  About once a week they called me in to tweak on 
the dozens of control points for each axis.  I Lost a lot of steady 
income when that machine went away.

The second machines were Moog Hydrapoint mills.  These were easier to 
maintain because there was very little tuning.  They used hydraulic rams 
that moved each axis and probably come closer to what you are thinking 
with the tracer.  These rams had a sliding steel plate attached with 
little holes that air passed through.  The whole positioning thing was 
done by balancing the air through this plate with the air through the 
position read head which took its values from a big block of punched 
tape.  When it worked it worked well.  I took the last one out of service 
about four years ago.  It had run three shifts for 30 years.

The biggest problem it had was wear on the sliding internal parts but it 
wasn't trying to use electrical signals to control hydraulic position.

I still service a bunch of Hardinge Automatics that use rams for cutting 
but not positioning.  These just turn on and off valves that run the rams 
back and forth.  Feedrate is done with rotary needle valves.  Positioning 
is done with micro switches and long screws that are set to trip the next 
action.  The machine is programmed by a drum switch with cams.

I also recently installed a lumber edger that used hydraulic 
proportioning valves to drive the position of several saws.  This works 
fairly well as long as the oil is clean and kept at constant temperature. 
This system does not require the kind of accuracy that you are thinking 
of.  Plus or minus a 64th (0.015625) keeps them happy.

In all of these, the fluid must be kept clean and near a constant 
temperature/viscosity.  All of them require a person who is patient and 
willing to fiddle to get the expected results.  I would guess that these 
hydraulic machines require 10 to 20 times the maintenence that I put into 
the average Mazak, even those from about the same age and use.   

Hope this helps

Ray


>  To: Multiple recipients of list <emc-at-nist.gov>
>  Date: Fri, 27 Sep 2002 03:41:13 -0400 (EDT)
>
> 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.
>
> 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.
>
> Any feedback or ideas would be welcomed
>
> Fred Harmon