Re: Spindle crash



On Fri, 20 Aug 2010 22:03:59 -0700, pyotr filipivich
<phamp@xxxxxxxxxxxxxx> wrote:

Gunner Asch <gunnerasch@xxxxxxxxx> on Fri, 20 Aug 2010 21:20:42 -0700
typed in rec.crafts.metalworking the following:
On Fri, 20 Aug 2010 21:02:06 -0400, Ecnerwal
<MyNameForward@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

In article <GKudnfXuHLfrgPLRnZ2dnUVZ_uSdnZ2d@xxxxxxxxxxxx>,
Ignoramus11290 <ignoramus11290@xxxxxxxxxxxxxxxxxxxx> wrote:

No, nothing happened, I just want to know a little more.

What happens if I make a wrong instruction and, say, crash a spindle
into a vise. What would happen in reality? It is somewhere in the
range between "nothing special" and "explode in a giant fireball". So,
in reality, what happens if I crash a running spindle into a vise or
something of that sort. Would the mill be ruined permanently?

i

It depends. You will (almost) always kill the bit. You'll scar the vise
with the remains of the bit. At that point, either something breaks or
the drive system notices that things are not moving and hopefully goes
to a graceful error mode (ie, stop trying, shut down spindle if spindle
shut down is under program control), rather than making things worse.
Otherwise it becomes an "irresistible force .vs. immovable object" game
until one of them gives up.

In general, watch like a hawk (with a manual kill switch for the machine
- if you don't have one, make one or more) on any new program or
modification. With the router, I also like to "air cut" the whole
program with the machine zero raised an inch or more off the table,
looking for moves that don't belong. I don't always do this, but I've
had some nasty reminders when I don't (ie, trying a particular routine
thats supposed to do a circle cut which turns out to ignore z-axis
scaling - I was working about 25%, so the bit dropped 4 times deeper
than called for and took off smoking, while I grabbed for the kill
switch.)

This is one area where having super-fast, super-powerful axis drives can
become super-expensive when they crash in a superlative fashion and
damage things thought to be sturdy. If your drive logic/control allows
for it, setting some limits that are considerably lower than the drive
is capable of may help with damage control. You can also put mechanical
fuses (shear pins or slip clutches) into the drive train for a
non-computer-dependent limit on possible damages.


Indeed. Look in your software for a modal called "work shift"

Most ..not all ..many...software systems have a M or G code for work
shift..which means you say G10 Z3...which shifts ALL Z moves 3"
higher than your program tells it to. Use it at the beginning of the
program and it remains modal..active throughout the entire program.

Its like setting a universal offset and applying it to the quill. This
keeps you from sqewering bugs in your vise if you missed a decimal
point.

Every time I write a program for an OmniTurn 2 & 3 axis lathe..I use it
to keep the tools AWAY from the workpiece and run the program in single
block, then dead slow automatic before actually trying to run a part.

Single Block - "boring!"

But on some occasions, "bored is good".

"In my experience" the outcome from hitting the vise depends on
what else happens. Going fast, and hitting it with an end mill =
broken end mill. Going slow (as in single block, and feed rate
override turned down to 1%) - the collet hit the aluminum jaws, and
melted enough aluminum to wrap twice around the tool holder - before
it torques out of the spindle. Which is when it alarmed out. Even at
slow, that happens awful damn fast. Oh ... shit! I'm told that was
a "mere" $40,000 repair bill. Very expensive education.


pyotr


Ive never seen an Omni knocked out of alignment or busted that way.
There simply isn that kind of mass there...chuckle and the servos are
only 500 in/lb

I did see one cratered by forklift once though.....

that was a $34k bill.....


Gunner

--


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This is despite the thread you are in having not mentioned
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.