Re: [CAD_CAM_EDM_DRO] Crashing CNCs: what gives ?

Kim Lux wrote:

>I'd like to know what is supposed to "give" when one crashes a CNC
>tool/slide into a chuck, tailstock, etc ?
>

Many machines have no real provisions for surviving a crash, and
can have damage running into the tens of thousands of $. CNC
turning centers are the worst, as ramming the toolpost into chuck
jaws at 3000 RPM can completely destroy the machine.

>
>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 ?
>
>

You should have software limits that prevent a move that will cause a
crash from even being started. This gets real complicated when you have
complicated fixtures and clamps that need to be avoided, though.

A fuse is about as useless as an emergency stop button next to the door of
the shop. When the fuse blows, the machine has already crashed. Limit
switches are also pretty useless, as the switches would have to be
inches from
the real crash point to allow sufficient distance for deceleration.
That would
restrict the work envelope of the machine.

>BTW: now that we are experienced, we rarely crash our equipment. I'm
>just curious/wondering how others and commercial equipment handle this.
>
>
>

I don't have much experience with CNC turning. I have had a few small
crashes on my CNC'd Bridgeport. I have knocked the head out of tram
a couple of times, and made end mills fly across the room and ping off the
wall when I hit them with the vise or a clamp bolt. This was while
setting up with the spindle not turning. I now keep my jog speed down
to where I can watch everything and anticipate things hitting, and haven't
done this in years.

Jon