Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic cylinder

Well, if you think so my buddy has a Moog Hydrapoint like the one i used to
run, spent more time fixing than running it. I also spent 4 years in the
USNavy as a hydraulic/electronic specialist machinist mate....be glad to
comfirm all the bad habits of hydraulics already brought up on previous
lists. I also spent 3 years in the Navy rebuilding servo control valves,
pilot assemblies in a clean room on our ship. Cheap servo's are $3000.00 and
the really good ones you need to control volume are 6 to 8,000 bucks a
piece, and you will need two for each axis and a dual remote control
equalizer for each pair, about $2000 each. so we are at 18,000 already just
for good hydraulics valves 3 axis, havent even got a machine yet.
Buy $800 dollar set of ballscrews, a $2500 Bridgeport type knee mill and
pay $500 to get it rigged, and $2500 for scraping, then you can make real
nice chips,quietly. $6,300 with some care will last for 20 years. cul brian
f.

----- Original Message -----
From: "alex" <telecomt@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, November 06, 2002 1:03 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
cylinder


> I really don't think that low reliability which requires high
> maintenance is an issue with the hydraulics. Some others - may be
> high costs, weight, ?
> We found it to be extremely reliable in machinery applications.
> Alex
> ----- Original Message -----
> From: Jon Elson <elson@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Wednesday, November 06, 2002 12:21 PM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
> cylinder
>
>
> >
> >
> > Van Der Sandt Coert wrote:
> >
> > >What if you had one big pump to keep up the pressure and some kind of a
> > >rotary valve on each axis that just lets a metered amount of fluid
> through
> > >every time its activated.
> > >
> > >Alternatively you could have a pump on every axis and calculate the
pump
> > >speed so that every axis reaches its goal at the same time.
> > >
> > >
> > And, what is going to drive those pumps? Electric motors? Clutches?
> > How can this be better
> > than just driving the machine directly with the motor? If you are going
> > to hook a servo motor
> > to a reversible hydraulic pump, then drive the table with a cylinder,
> > that has to be the
> > Rube Goldberg method of replacing a leadscrew!
> >
> > Just as a reference point, hydraulic systems, especially hydraulic
> > motors driving a leadscrew,
> > was a VERY common system on larger CNC machines, in the 1970s. I
> > believe it was the
> > most common axis drive system on the larger ones, in fact. Direct
> > electric drive cam in
> > VERY quickly after larger power transistors became available. The
> > makers of big machines
> > never looked back, and you'll be VERY hard pressed to find any larger
> > CNC machine with
> > hydraulic drive today. The only machines still using hydraulic drive
> > that I can think of are
> > surface grinders, where they just have a steady back and forth feed
> > between limit switches.
> >
> > The buyers of these machines must have a REAL good reason for making
> > this choice.
> > The reason, of course, is they had HORRIBLE experiences with the high
> > maintenance
> > costs of hydraulic systems! Another side light, the commercial aircraft
> > industry is trying
> > to desing their way away from hydraulics, for the same reason - high,
> > VERY high, maintenace
> > costs.
> >
> > Jon
> >
> >
> > Addresses:
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> > OFF Topic POSTS: General Machining
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> >
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> Addresses:
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> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
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>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>