Re: Hydraulic lathes?

On Thu, 31 Jul 2008 23:10:58 -0700, Tim Wescott <tim@xxxxxxxxxxxxxxxx>
wrote:

DaveB wrote:
On Fri, 01 Aug 2008 02:05:02 GMT, debco99@xxxxxx (DaveB) wrote:

On Thu, 31 Jul 2008 18:56:52 -0700, Tim Wescott <tim@xxxxxxxxxxxxxxxx>
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/necking_in_machines/necking_in_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
.

Relevant Pages

  • Re: Hydraulic lathes?
    ... I don't know if you could control hydraulics as precisely as ... I imagine that the big problem is in designing the ... Enerpac that control the balancing of bridge sections to keep them ... Notice that the cited examples (the mentioned tracer machines, ...
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  • Re: Hydraulic lathes?
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