Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

We have an older NC lathe, "Sheldon Tape Lathe" that uses Moog proportioning
valves.

IIRC The valve needs a 0-20 mV signal to operate.
Our resident electronical guru made us a pair of boards that turns +/-10V
servo control signal into the signal that makes the Moog valve happy.

We retrofitted using a galil dmc740 motion controller.

This works great for really big iron.

Unless you NEED it, I'd try to avoid hydraulic servos.


"Denis G." wrote in message
...
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews.

Hydraulic duplicating (tracer) mills and lathes were once common. Last
I knew a customer of mine was still using a tracer mill to duplicate
molds for shoe counters for which there was no CAD data available.
Google True-Trace or Mimik and you may find some info.

Sinker EDM rams were often servo-hydraulic, but, I think, not so much
for coordinated motion as for smooth motion at very slow speeds

All the large planers I've seen were hydraulically driven, though
that's more for brute force rather than controlled motion.

--
Ned Simmons

"Ned Simmons" wrote in message
...
On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews.

Hydraulic duplicating (tracer) mills and lathes were once common. Last
I knew a customer of mine was still using a tracer mill to duplicate
molds for shoe counters for which there was no CAD data available.
Google True-Trace or Mimik and you may find some info.

Sinker EDM rams were often servo-hydraulic, but, I think, not so much
for coordinated motion as for smooth motion at very slow speeds

Small point, but the primary reason was that hydraulics could handle the
quick reversals -- often several times per second -- involved in the EDM
servo motion, and do it with relative simplicity. They just used a
voltage-sensitive valve switch. DC servos didn't have enough "first-pulse"
torque to do it until some advances came along in servo drive controllers.
The first ballscrew-driven servomechanisms for EDMs that were successful
used stepper motors.


All the large planers I've seen were hydraulically driven, though
that's more for brute force rather than controlled motion.

--
Ned Simmons

Production milling at one time was mostly a pass-through operation, a lot
like planers. Before CNC, production parts were, wherever possible, designed
so that you didn't have to precisely control the start and stop positions of
the axis traverse.

--
Ed Huntress

On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.


This is something we do all the time and is very common on spinning
machines because of the high forces required.

We can hold tolerances as well as if not better than a leadscrew
because of no mechanical influences.

http://s32.photobucket.com/albums/d1...nt=Spinvid.flv

Our website is www.debcomachinery.com.

If you need any further info let me know


Daveb

On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.
Over 30 years ago I ran Sheldon lathes that were hydraulicaly
controlled. We could hold .0001" easily with these lathes. They were
15 inch swing machines, I think. They had an adjustment called
"dither" which kept the valves always in motion. This was to avoid the
problem with "stiction". I don't remember if it was the valves, the
actuators, or both that needed the dithering. Interestingly, I have
two older CNC lathes with Fanuc controls that also use dithering. The
servos always move a little. The repair man had to adjust one of my
lathes when the dithering was out of whack, it would lose precise
position and the finish would suffer. He told me the dither was left
over from hydraulic systems. My newer CNC controls no longer have a
dither adjustment.
ERS

"Denis G." wrote in news:a4003630-b489-4b03-bd1e-
:


I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.


Hydraulic feed is an _old_old_ technology. Very inefficient also. Reliable
control can also be a significant issue.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Thu, 31 Jul 2008 22:50:45 GMT, Anthony
wrote:

"Denis G." wrote in news:a4003630-b489-4b03-bd1e-
:


I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.


Hydraulic feed is an _old_old_ technology. Very inefficient also. Reliable
control can also be a significant issue.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email


We do it all the time with applications that make leadscrews
impossible.

The last five machines we built have had zero follow-up calls.

This must be an area that you are unfamiliar with.
Daveb

I seen a special on Pro Baseball bat manufacture. Each player provides his
favorite blank. They are numbered and stored. A hydraulic tracer lathe turns
the bats with the master in the tracer.

Karl

Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html


We have built machines that free spin.......no tooling. This is how
most cng cylinders are made to eliminate welding.

The last one we built was 75 hp (spindle) and we were forming .375
material cold.

example:
http://www.leifeldspinning.com/necki...n_machines.htm

On our website the pnc 75 shown also has a turning holders as they do
2nd operation work.

There are plenty of turret type machines that do both turning and
spinning.

www.debcomachinery.com
Daveb

On Fri, 01 Aug 2008 02:05:02 GMT, (DaveB) wrote:

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html


We have built machines that free spin.......no tooling. This is how
most cng cylinders are made to eliminate welding.

The last one we built was 75 hp (spindle) and we were forming .375
material cold.

example:
http://www.leifeldspinning.com/necki...n_machines.htm

On our website the pnc 75 shown also has a turning holders as they do
2nd operation work.

There are plenty of turret type machines that do both turning and
spinning.

www.debcomachinery.com
Daveb


BTW Tim, if you can afford my rates I may show you how its done.
If your at ITMS would like to show you what we have (for free)
Daveb

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.


On the tracers the hydraulic fluid transmits the cutting force to the
tool. I don't follow what you mean by "some fixture provided the
rigidity." A properly sized leadscrew is certainly stiffer than a
column of hydraulic fluid, but the stiffness of the rest of the
machine structure is a bigger factor than the stiffness of either a
leadscrew or a hydraulic actuator of reasonable length acting in
compression.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

Eric attested to the feasibility by virtue of the fact that the
machines he ran were able to hold tenths in production.

--
Ned Simmons

Ned Simmons wrote:
On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.


On the tracers the hydraulic fluid transmits the cutting force to the
tool. I don't follow what you mean by "some fixture provided the
rigidity." A properly sized leadscrew is certainly stiffer than a
column of hydraulic fluid, but the stiffness of the rest of the
machine structure is a bigger factor than the stiffness of either a
leadscrew or a hydraulic actuator of reasonable length acting in
compression.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

Eric attested to the feasibility by virtue of the fact that the
machines he ran were able to hold tenths in production.

I missed that post -- hmm. Having read it I'll count it as 'seeing',
though.

I know that the hydraulic fluid itself isn't very springy, but even with
all-solid lines you'd expect there to be spring as a consequence of the
valving. I'd be interested in seeing just how the hydro-mechanical
system is put together so that it's errors are correctable by the servo
system.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

DaveB wrote:
On Fri, 01 Aug 2008 02:05:02 GMT, (DaveB) wrote:

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.
I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.


We have built machines that free spin.......no tooling. This is how
most cng cylinders are made to eliminate welding.

The last one we built was 75 hp (spindle) and we were forming .375
material cold.

example:
http://www.leifeldspinning.com/necki...n_machines.htm

On our website the pnc 75 shown also has a turning holders as they do
2nd operation work.

There are plenty of turret type machines that do both turning and
spinning.

www.debcomachinery.com
Daveb


BTW Tim, if you can afford my rates I may show you how its done.
If your at ITMS would like to show you what we have (for free)
Daveb

What sorts of precision do you achieve? Is there anything special done
in the hydraulic system to make its action more positive, or is just
long rubber hoses and spool valves?

I'm glad I put weasel-words in my assertions, it looks like I'd have to
stand corrected otherwise.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tracers are a bit different technology than servo control. We used two
true-trace tracer units in production for years.

I have one available for sale, by the way.


"Karl Townsend" wrote in message
...
I seen a special on Pro Baseball bat manufacture. Each player provides his
favorite blank. They are numbered and stored. A hydraulic tracer lathe
turns the bats with the master in the tracer.

Karl

"Jon" wrote in message
news:hhpkk.500$aA5.361@trnddc05...
We have an older NC lathe, "Sheldon Tape Lathe" that uses Moog
proportioning valves.

IIRC The valve needs a 0-20 mV signal to operate.
Our resident electronical guru made us a pair of boards that turns +/-10V
servo control signal into the signal that makes the Moog valve happy.

We retrofitted using a galil dmc740 motion controller.

This works great for really big iron.

Unless you NEED it, I'd try to avoid hydraulic servos.

Oops, I missed a detail in the original post, the sheldon tape lathes use
hydraulic motors to drive ballscrews.
However, as later posts have described, technology marches on, and high
precision is feasable using cylinders now.
But still, it usually is saved for applications requiring high forces



"Denis G." wrote in message
...
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.

On Thu, 31 Jul 2008 23:11:52 -0400, Ned Simmons
wrote:

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.


On the tracers the hydraulic fluid transmits the cutting force to the
tool. I don't follow what you mean by "some fixture provided the
rigidity." A properly sized leadscrew is certainly stiffer than a
column of hydraulic fluid, but the stiffness of the rest of the
machine structure is a bigger factor than the stiffness of either a
leadscrew or a hydraulic actuator of reasonable length acting in
compression.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.

Eric attested to the feasibility by virtue of the fact that the
machines he ran were able to hold tenths in production.


If hydraulics cant handle precision..someone may wish to notify
Okuma.... And Mori Seiki....

Gunner

One disadvantage of replacing the leadscrew on a lathe with a
hydraulic cylinder would be that the length of the lathe would
probably need to be doubled (close). I tried to find details of how
the Sheldon tape lathes were made, but was unsucessful. Finding
details about how such machines are constructed is difficult, but I
was happy to find out that they exist.

As far as the criticism of stiffness between mechanical and hydraulic
systems, I believe that one only has to compare mechanical and
hydraulic presses. I think it's a matter of proper design to get what
you need.

Finally, I found a 2006 description of a CNC machine made by a German
company (Schutte) using electrohydraulic axes with a bed resolution of
0.1 microns (1 micron accuracy at the tool).

Here's a link:

http://www.productionmachining.com/a...lti-world.aspx

Here are excerpts:

... In 1996, Schütte made the decision to go with electro-hydraulic
axis drives for all end-slide and cross-slide actuation, replacing
cams. Speed, power and accuracy were the motives for this decision and
fit into the company’s multi-spindle philosophy.

As the name implies, electrohydraulic drives use a combination of
hydraulic fluid and electronic control to move an axis. Hydraulic
fluid provides the motive force, and electronics, in the form of valve
control and linear feedback, provide precision control of the
motion.....


A key to successful use of electro-hydraulic drives is precise control
of the valve that allows hydraulic fluid into and out of the cylinder.
It controls the force, speed and distance traveled.

The valve, in turn, is regulated by a processor. The valve and
processor system was created in conjunction with Bosch to give finite
measurement of fluid movement in the shortest period of time. In
addition to the hydraulics and electronic processor, each slide is
equipped with a linear scale to give actual position feedback to the
processor. The digital feedback loop operates at 800 Hz, feeding back
the slide position 800 times per second.....

“Multi-spindle applications have always been associated with high
cutting forces,” Jim says. “Form tools and drilling operations are two
prime examples of where feed power and cycle time intersect. The idea
is to rough out the part as fast as possible and then bring in the
semi-finishing and finishing operations. We believe the machine must
be capable of power for the roughing and finesse, such as single-point
turning for finishing. Electrohydraulic actuation gives us both.”

Also, the system is capable of delivering the close-tolerance
specifications necessary for shops to be competitive. “Our
electrohydraulic axes have a resolution of 0.1 micron. That resolution
delivers a usable repeatability of 1 micron at the tool,” Jim
explains. “That tolerance is necessary because of the changing nature
of the work being run across the multi-spindle. Close-tolerance
machining capability, along with processing flexibility, is in demand
to eliminate the need for secondary operations. Customers want to drop
parts off the machine complete, and that ability starts with
accuracy.”

On Thu, 31 Jul 2008 23:10:58 -0700, Tim Wescott
wrote:

DaveB wrote:
On Fri, 01 Aug 2008 02:05:02 GMT, (DaveB) wrote:

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott
wrote:

Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.
I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.

Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.

I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.


We have built machines that free spin.......no tooling. This is how
most cng cylinders are made to eliminate welding.

The last one we built was 75 hp (spindle) and we were forming .375
material cold.

example:
http://www.leifeldspinning.com/necki...n_machines.htm

On our website the pnc 75 shown also has a turning holders as they do
2nd operation work.

There are plenty of turret type machines that do both turning and
spinning.

www.debcomachinery.com
Daveb


BTW Tim, if you can afford my rates I may show you how its done.
If your at ITMS would like to show you what we have (for free)
Daveb

What sorts of precision do you achieve? Is there anything special done
in the hydraulic system to make its action more positive, or is just
long rubber hoses and spool valves?

I'm glad I put weasel-words in my assertions, it looks like I'd have to
stand corrected otherwise.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html


Tim, some machines we build have stainless tubing from the hydraulic
power supply and some use steel under and over braid hose.

The servo loop usally consist of just a standard cnc control +-10 volt
error signal and the position loop is normally 20 micron scales
(quadrature) with a zero reference mark.

We use moog servo valves and servo amps

In some cases we use a frequency to voltage converter driven by the
scale feedback and use this as velocity feedback.and of sum this with
the speed reference.

Some machines have rotary hydraulic motors with encoder feedback and
ballscrews.

Only downside of hydraulic loops is rapid traverse speeds, we try to
run 400 ipm in rapid and can repeat to .0001 all day long, due to
using scales.

If you walked in and watched a machine run you would be unable to tell
any difference.







Daveb

(DaveB) wrote in
:




We do it all the time with applications that make leadscrews
impossible.

The last five machines we built have had zero follow-up calls.

This must be an area that you are unfamiliar with.
Daveb


Dave,
We used to have a floor full of hydraulic fed machines. They work, but
can be troublesome. We still use hydraulics for one axis on one certain
CNC machine type (It is a CNC axis - X axis specifically). Works great,
adjustable in increments of 0.0002 microns _diameter_. Very stable.
But....when it has issues...it has serious issues and downtime and tuning
can be a lengthy and tedious process.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Sat, 02 Aug 2008 01:18:00 GMT, Anthony
wrote:

(DaveB) wrote in
:




We do it all the time with applications that make leadscrews
impossible.

The last five machines we built have had zero follow-up calls.

This must be an area that you are unfamiliar with.
Daveb


Dave,
We used to have a floor full of hydraulic fed machines. They work, but
can be troublesome. We still use hydraulics for one axis on one certain
CNC machine type (It is a CNC axis - X axis specifically). Works great,
adjustable in increments of 0.0002 microns _diameter_. Very stable.
But....when it has issues...it has serious issues and downtime and tuning
can be a lengthy and tedious process.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email


I agree Anthony, no one is more surprised how well the machines we
build run than me.

I went way out as far as warranty on this type machine ,not really
knowing how reliable they would be both from the software as well as
hardware aspect.

One advantage we have is we build it, so it makes it easier to
troubleshoot and tune.

Having good heat exchanger and well filtered oil is one important
issue.

Look forward to meeting you at ITMS.


Daveb

On Thu, 31 Jul 2008 21:44:22 GMT, (DaveB) wrote:

On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.


This is something we do all the time and is very common on spinning
machines because of the high forces required.

We can hold tolerances as well as if not better than a leadscrew
because of no mechanical influences.

http://s32.photobucket.com/albums/d1...nt=Spinvid.flv


Interesting industrial video, but wow!! the next pic is a keeper :-)
Care to share the details??? ED





Our website is www.debcomachinery.com.

If you need any further info let me know


Daveb

(DaveB) wrote in
:



Look forward to meeting you at ITMS.


Daveb

A mistake in my typing......... that should have been 0.0002 mm (not
microns) (0.2 microns)

I'll be at IMTS Monday and Tuesday. We all need to designate a place and
time to meet up.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Fri, 01 Aug 2008 22:31:09 -0600, ED
wrote:

On Thu, 31 Jul 2008 21:44:22 GMT, (DaveB) wrote:

On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.


This is something we do all the time and is very common on spinning
machines because of the high forces required.

We can hold tolerances as well as if not better than a leadscrew
because of no mechanical influences.

http://s32.photobucket.com/albums/d1...nt=Spinvid.flv


Interesting industrial video, but wow!! the next pic is a keeper :-)
Care to share the details??? ED





Our website is www.debcomachinery.com.

If you need any further info let me know


Daveb

snicker......

Daveb

On Sat, 02 Aug 2008 14:51:10 GMT, Anthony
wrote:

(DaveB) wrote in
:



Look forward to meeting you at ITMS.


Daveb

A mistake in my typing......... that should have been 0.0002 mm (not
microns) (0.2 microns)

I'll be at IMTS Monday and Tuesday. We all need to designate a place and
time to meet up.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email


I noticed the typo....at first I thought WOW !

Daveb