are travel stops required? or are limit switches enough

[Greolt]

One way to do it is to have the switch travel with the axis and have actuators at each end of travel. That way you only need three switches.

They can all be wired in series as Mach can distinguish between switches when homing. And limits don't matter which one tripped. So long as it stops motion.

Greg

[springlakecnc]

Hi,
One thing on limit switches: you need proper rated contacts for the amperage of your limit switch circuit. No, I’m not in reference to having heavy enough contacts, but the opposite! Yes, high amperage switches, like the ones on new iron from Taiwan. The problem is, if you are into these "step and direction" controls, your limit switch circuit may be logic level current, and if you have high rated contacts in the switch, you may get false limit switch tripping from vibration of the machine when cutting. Example: if your limit switch is rated at carrying a 20 amp circuit, and you are using logic level current, your switch will be tripping all the time, and your axis may not be anywhere near the switch. If I have a logic level circuit, I use a 1-amp contact. I do service work, and I get calls of “my z axis keeps tripping the switch, and I’m no where near it!” that’s usually the problem, the switch checks out ok with a meter, BUT, I have to replace it with one with lower amperage contacts. A prox switch won't have this problem, although i have had a tool changer that a prox switch was doing the counting, and wouldn't count correctly, I had to put in a schielded wire to the prox, then, like magic, it started counting correctly! moral: don't run unschielded control wire by high power wires. This was on a factory built machine, so i called the manufacture and explained the problem so they could correct it for the future.
Good Luck,
Buck,
Spring Lake cnc llc

[BobF]

Use NC switches and wire them all in series. If any switch triggers it will break the loop and trigger the limit. The machine won't care which switch triggered.
This is also a safety thing, since it will show if you break/cut a limit switch wire.

[flyon]

I'm going to be wiring my CNC machine up in the next few days. I'm thinking of running each home (x,y,z) to its own input, then the max limit (x,y,z) in series to another input. So a total of 4 inputs(1-Home x, 2-Home y, 3-Home z, 4-Limit x,y,z).

The reason is I heard that when homing, and sharing multible homes on one input, Mach will only home one axis at a time. It assumes home on whatever one axis it is moving at that time when it hits the switch. I'm thinking if I branch the homes out, it should be able to home all axis at the same time..? Have I overlooked something?

[acondit]

Originally Posted by flyon I'm going to be wiring my CNC machine up in the next few days. I'm thinking of running each home (x,y,z) to its own input, then the max limit (x,y,z) in series to another input. So a total of 4 inputs(1-Home x, 2-Home y, 3-Home z, 4-Limit x,y,z). The reason is I heard that when homing, and sharing multible homes on one input, Mach will only home one axis at a time. It assumes home on whatever one axis it is moving at that time when it hits the switch. I'm thinking if I branch the homes out, it should be able to home all axis at the same time..? Have I overlooked something?

Flyon,

As you know, I am using emc2. It allows me to share home and limit switches. On my router the xneg limit is also xhome, the yneg is also yhome and the zpos is zhome. So when you are homing, you can home multiple axii at one time. The effect is that when homing if a particular axis hits a switch, it is treated as a home switch rather than a limit switch.

The following is for emc2 but it gives you the picture.

### I created 3 loops, one loop for each axis that combines home and limits for that axis ### # create a signal for the x home and x limit switches combined net XLimits parport.0.pin-11-in => axis.0.neg-lim-sw-in axis.0.pos-lim-sw-in axis.0.home-sw-in # create a signal for the y home and y limit switches combined net YLimits parport.0.pin-12-in => axis.1.neg-lim-sw-in axis.1.pos-lim-sw-in axis.1.home-sw-in # create a signal for the z home and z limit switches combined net ZLimits parport.0.pin-13-in => axis.2.neg-lim-sw-in axis.2.pos-lim-sw-in axis.2.home-sw-in

Alan

[Greolt]

Originally Posted by flyon The reason is I heard that when homing, and sharing multible homes on one input, Mach will only home one axis at a time. It assumes home on whatever one axis it is moving at that time when it hits the switch. I'm thinking if I branch the homes out, it should be able to home all axis at the same time..? Have I overlooked something?

Mach in standard configuration homes one axis at a time.

If you want to home all axis simultaneous you will have to enter a new script. Easy to do.

Best practice to let the Z axis home first, then X and Y together if you wish. Less crashes.

Greg

[acondit]

Originally Posted by Greolt Mach in standard configuration homes one axis at a time. If you want to home all axis simultaneous you will have to enter a new script. Easy to do. Best practice to let the Z axis home first, then X and Y together if you wish. Less crashes. Greg

I agree with Greg. I home z first and then x and y together. If you forget to retract sufficiently and try to home all three at the same time you can break bits, machine into clamps or other little nasties.

Alan

[vroemm]

Originally Posted by acondit Flyon, The effect is that when homing if a particular axis hits a switch, it is treated as a home switch rather than a limit switch. The following is for emc2 but it gives you the picture. ### I created 3 loops, one loop for each axis that combines home and limits for that axis ### # create a signal for the x home and x limit switches combined net XLimits parport.0.pin-11-in => axis.0.neg-lim-sw-in axis.0.pos-lim-sw-in axis.0.home-sw-in # create a signal for the y home and y limit switches combined net YLimits parport.0.pin-12-in => axis.1.neg-lim-sw-in axis.1.pos-lim-sw-in axis.1.home-sw-in # create a signal for the z home and z limit switches combined net ZLimits parport.0.pin-13-in => axis.2.neg-lim-sw-in axis.2.pos-lim-sw-in axis.2.home-sw-in

This does not work for me.

I am using it with only a Y axis.
I have added this to the axis 1 section of stepper_mm.ini
HOME_IS_SHARED 1
HOME_SEQUENCE 1

When homing i get this:

AXIS error: hit limit in home state 8
AXIS error: joint 1 on limit switch error.

Any idea how to solve this ?

Thanks.

[Madclicker]

Steppers don't need limit switches. They stall happily. I have a 1300 oz/in on my main axis driven by a wide open gecko and stalls have never caused any damage.

If you run servo's you better have limit switches that are idiot proof or it's gonna cost you big one day.