CNC Mill protection

[David G]

I think I might be ready to test out the CNC changes to the mill this weekend that I have been working on for a WHILE.

I will post pictures.

Is there any need to put a kill limit switch for over travel, or just let the stepper overurrent stop it?

 

[Oliver 500 Wa]

Since stepper driven machines are usually pretty slow moving, you could just let it run up hard and stall the stepper. If it were me, I'd at least put in some urethane bumpers rather than just go metal to metal.

 

[Janicholson]

Your driver software should have limit switch inputs for the XYZ movements. Letting the motors go into hard stops is poor design and can wear drive screws and "nuts". Micro switches are way cheap, and allow the homing to be repeatable. Our converted mill has had a limit switch fail and every time it ran into the physical limit, the Machine Zero (G53) was lost. Jim

 

[David G]

It is very easy for me to add these, I can wire them into the ESTOP circuit.

 

[Oliver 500 Wa]

If you wire limit switches to the E-stop circuit, it would be handy to have an E-stop "bypass" switch. That allows you to press it, reset the drives, and jog out of the overtravel condition.

Software or hardware limits are nice if your control system supports that.

Are you using a PC based CNC?

As far as running things up to hard stops, any wear or damage would be determined by component choices and your design. Homing to hard stops was common in early industrial NC machines. That means that every time the machine was started, you ran through a homing routine that hard stopped the motion system until torque limits were reached. Then the axes would reverse a set number of steps/encoder counts, stop and set home position at that point.

 

[David G]

I have wiring done for all the wire I brought up to the house, getting up the nerve to hike to the shop in the blizzard and drill the back panel.

Here is picture of components going in cabinet.

 

[Janicholson]

That works to keep over travel under control. but might not automatically index the G53 machine XYZ limits and "home". Jim

 

[David G]

Jim,

There will also be a separate home switch for each axis, I would just put the kill limit switches outboard just before the mechanical stops.

I have hand wheels, so can crank manually if needed.

 

[Janicholson]

Cool. Jim