[signweld]

Just how far does a table go after hitting a limit switch in rapid (say,200ipm or so)? Do I need the kind with a little roller where it can go past the switch, a little,or can a push button type switch be used?

[ger21]

The laws of physics dictate how far it will go. It's bad practice to have the machine run into the switch. It should always be able to slide past the switch, or it's likely it'll get damaged at some point. I've seen several posts here talking about damaged switches.

[Claude Boudreau]

Ive use an estop right after the limit switches.
Also if using mach3 you might want to use soft limits.

Industrial CNC Router Tips: Setting Your Soft Limits in Mach 3

[tahustvedt]

If you activate "Charge Pump On in Estop" in the General Config menu it will hold if the steppers hit the Estop. It does kind of partially defeats the purpose of the Estop though.

[Khalid]

Ive use an estop right after the limit switches.
Also if using mach3 you might want to use soft limits.

Industrial CNC Router Tips: Setting Your Soft Limits in Mach 3

Sometime happens to me even keeping all the soft limit settings i accidentally turned off the soft limit button. When incident happen then i know i OVER RIDE the soft limit.. Don't do it in high speed machine

[Claude Boudreau]

I was talking about hard wired estop independent of software...usefull when joging the wrong side after a limit trip reset.

[Claude Boudreau]

a push button would work but i would activate it with a flexible arm that wouldnt break it if you jog the wrong way after the reset.

[wizard]

Just how far does a table go after hitting a limit switch in rapid (say,200ipm or so)? Do I need the kind with a little roller where it can go past the switch, a little,or can a push button type switch be used?

As has already been stated it depends upon the physics of the system. With the right motors in the wrong system you can break leadscrew nuts right off their mountings.

In any event I see hard limits as extremely important in these home brew systems because of the lack of advanced controls to do things like detect run away faults and properly handle them. Due to the fact that you can't tell for sure where the axis will stop, the hard limits must handle over travel of the axis. One of the preferred ways to do this is to make use of roller switches and cams. However I've seen just about everything else including whisker switches.

What you need to think about is; will the way you install your hardware result in a failure if the axis over travels. Also maybe just as important will the switch survive normal operations of the machine and the operator. This is one reason why people mount switches in protected parts of the machine or provide protection for the switch itself. A over travel does little good when jammed up with swarf or dust.

One other consideration, sometimes it is easier to design in a switch such that it rolls off a cam when the machine over travels.

[wizard]

a push button would work but i would activate it with a flexible arm that wouldnt break it if you jog the wrong way after the reset.

Depending upon the specifics of a machine, you can sometimes design the mechanics of the over travel into the end plate that mounts the axis leadscrew bearings. Buy a switch with reasonable over travel capacity and little extra is needed. A good manufacture will specify how much over travel a switch can handle. If you decide that you need lots of over travel capability it might become a more involved mechanical problem.

Work this out well and the same cover that shields the belt or couplings will also cover your switches.

[neilw20]

A big rubber donut on the ball screw is a nice crash stop.
I have seen older machines (pratt & whitney) with a wind up torsion spring on the ball screw. Very neat crash stop.