[CAD_CAM_EDM_DRO] Re: Rigid or flexable couplings plus limits

-- In CAD_CAM_EDM_DRO@yahoogroups.com, "callcbm2000" <callcbm@d...>
wrote:

> I built my router with rigid couplings and the encoder plug failed

so

> I found top speed of the machine .The ball screws that I used for

the

> X axis was turned down to 5mm and the coupling is a machined 2" od
> alum with removable caps to tighten to the shaft with friction fit.
> So when it crashed I was not worried I believed the coupling would
> slip. This has only minute's time. But it twisted the shaft clean

at

> the neck this was machined so it would not have stress or failure.
> Suggested on modifying the coupling and putting a new end on the
> shaft. I bored it out and put a dowel pin in but not sure of how to
> anchor so if it crashes again there will be some slip.
>
> Thanks Randy

Methinks you are trying to fix the wrong thing. Instead of trying to
design something that will let the motors slip when they crash,
engineer the machine so it won't crash. Put limit switches on all of
the axis that are tied to the motor DC source and will shut things
down before you get to a point where shafts get twisted. This is the
best argument I have seen to not rely on limit switches back to the
software to shut things down. Slip clutches are great but unless they
are tuned perfectly they will slip when they shouldn't.




No I was trying to test the limit switch when I hit the connector to
the encoder before I could hit e- stop it crashed. What I need to do
is fix the problem and if it so happens again not total everything
out with ball screw snapping. I don't trust the wire connector after
this one failed. I still have a problem with the limit switch the
lights on the interface board light up when a switch is trip but the
servos won't stop turning. I just would like to reuse the ball screw
again and if it runs away, have more than a switch for fail-safe.
Thanks Randy