Re: [CAD_CAM_EDM_DRO] Crashing CNCs: what gives ?

On Tue, 2003-10-28 at 09:32, Vince Negrete wrote:

> Two methods I've seen Kim, maybe you already know about...

I'm all ears...

> But I'm sure
> they work
> First and best method was OverLimit Switches that switch a relay cutting
> power to the tool, much better than replacing fuses..

We've got limit switches on some of the axes. We omitted them on others
because it was obvious to us that the axis would hit something else
before it ran out of travel. None of this prevents the head from
hitting the table or the cross side from going into the chuck.
Thankfully neither of these have happened to us, but sooner or
later...

> The second and much older method was an absolute "Hardstop" setup along with
> cheap break-away parts such as Aluminum Pins.

That sounds like a good thing to do. The force these things generate is
incredible. One time we put the tool up against a stout workpiece and
then carefully moved it back and forth a couple of thou to watch things
flex. It is a real eye opener to put a dial gage on things.

On a lathe, with a turret type tool post, one could make the anti swivel
pin from aluminum. I'm worried it would lead to play or travel in the
tool though.

> On the 1500 pounds of force at (x) RPM, I dont know of any quick solution
> to stop its motion after power-off. I'd expect broken parts at that point..
> :)

That is why we fuse things. At least it stops at 5-600 pounds. Without
the fuse, current would go a lot higher and trouble would ensue. We've
got Geckos with current limiting, but we don't have it set really
precisely.

> Maybe the same or similar breakaway parts can be employed. In our Wafer
> Probers when something slams (if ever) the damage is always at the weakest
> point of course. This tends to be the coupler or dampeners. Other newer
> Japanese systems Ive seen used Magnetic Coupling. An intense shock would
> release it from the mount points undamaged.

I think there is some merit to using undersized motors or fusing them to
be undersized. We never need 5 or 600 lbs of cutting force, that I know
of, but yet these things will develop 1000+ pounds of force if you feed
them the current.

> Just throwing out ideas.

And I thank you for doing so.

> Vince
>
>
> ----- Original Message -----
> From: "Kim Lux" <lux@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Tuesday, October 28, 2003 6:24 AM
> Subject: [CAD_CAM_EDM_DRO] Crashing CNCs: what gives ?
>
>
> > I'd like to know what is supposed to "give" when one crashes a CNC
> > tool/slide into a chuck, tailstock, etc ?
> >
> > Lets say we've got a servo/ballscrew set up that generates 1000 to 1500
> > pounds of force when called on. Next, we accidentally command that axis
> > to run into something immovable: a chuck, tailstock, etc. On a
> > commercial machine, how is this handled without wrecking anything ?
> >
> > Right now we've got a quick blow fuse that pops in our equipment. It is
> > the only way that I can see to limit the damage. What is everyone else
> > doing ?
> >
> > BTW: now that we are experienced, we rarely crash our equipment. I'm
> > just curious/wondering how others and commercial equipment handle this.
> >
> > --
> > Kim Lux <lux@...>
> >
> >
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> OFF Topic POSTS: General Machining
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> http://www.metalworking.com/news_servers.html
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> 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........
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--
Kim Lux <lux@...>