[Werdelin]

Hello,

I am a total newcomer in this CNC field; excuse me for my ignorance, feel free to laugh.

Anyway, this post is about limit switches. I bought sort of a prefab Steurung of a German supplier, I guess he put a lot of Chinese stuff together and sold it on to me. All the 4 cables are mounted and the limit switches, - of which there are 3 pairs and 1 single (look at picture), - does anyone know what this 4th switch is for, has it to do with that it eventually will be a 4 axis machine? - are soldered to the ends of cables.

But my logic is that there should be at least 7 cables : 3 pairs of switches for the home + limit for x-,y-,z-axis, and 3 single switches for the other end of x,y,z-axis, - and then 1 single for the 4th axis (if this in fact is assigned to the 4th axis)?

I have lost contact with the supplier temporarily, guess he receives tons of mails.

Can anyone help, it will be much appreciated. A diagram of how to put it up would be next to paradise.

Anders

[RicknBeachcrest]

Well my guess would be the H-Y is Home for the Y axis and so forth with the X and Z. I personally would not use these switches for homing due to their lack of repeat-ability (I use a Hall sensor type for the X and Y homing switch (there is a great thread on building your own on this forum)). But for limit switches, they should work just fine. If I were in your place, I would probably de-solder the switches and come up with my own wiring plan. It's really not that complicated, so don't overthink it.

As far as homing switches and limit switches, there are lots of threads on this forum that will describe how to wire and the logic as to why.

There are many ways that people will wire their homing and limit switches. It will depend a lot on your control program (I use Mach3) and your break-out board and drivers (I use the Gecko G540). I have all of my limit switches (2 on the X, 2 on the Y and 1 on the Z) wired in series and connected into one of the 4 inputs on the G540. I have 2 homing switches (1 on the X and 1 on the Y) each wired into a separate input on the G540. I don't home my Z.

Mach3 allows you to use the same switch as a limit and also as a homing switch (I don't use this option).

I know this is not exactly what were looking for, but building one of these machines will take some time and effort to educate yourself. And all the answers are in this forum. I know, cause that is how I learned to build my machine.

Good luck.
Rick

[Bartuss1]

What do you need so many switches? If you use Mach3, this is enough 3 recoiling limit switches. In the configuration of Mach you only have to turn off "Home switch safety".
But if you want to have two limit switches per axis - then you connect all common wires to the plus 5V. other cables assign pins : limit x +, limit x -, etc,

[A_Camera]

Limit switches, not for homing. 3 pair for X, Y and A ( slave ) and the single switch for the Z, which only needs one.

[Bartuss1]

I'm using a one switch on one axis - limit's and homing. Why complicate the solution?
What for limit switch on the slave axis?

[109jb]

I'm using a one switch on one axis - limit's and homing. Why complicate the solution?
What for limit switch on the slave axis?

That is YOUR choice, but others may want a switch at each end of the axis travel. Using only one switch you need to use the software limits, but this is not totally safe especially on a stepper machine. Software limits rely on an accurate home position and a accurate definition of the machine travel limits. Also, a stepper machine can lose steps, in which case the software doesn't really know where the machine is at and the software limits will not work correctly. True limit switches don't depend on any of this and are positioned at the end of travel and will trigger regardless of where the software thinks the machine is.

[A_Camera]

I'm using a one switch on one axis - limit's and homing. Why complicate the solution?
What for limit switch on the slave axis?

Using only one switch on each axis IS making it complicated. One switch at each end connected in series is super easy and extremely simple and safe.

[collibric]

Using only one switch on each axis IS making it complicated. One switch at each end connected in series is super easy and extremely simple and safe.

.. or using one switch can be more safe ..

when you will use just one limit switch which is turned on by force during whole path and disconnects circuit on the ends by force dissapearing you will be protected from
- switch fell off
- switch wire cut
- running out of rails (finally) - and in any direction

machine will work only when all the limit stuff will be in correct state, otherwise machine will stop ..

[A_Camera]

.. or using one switch can be more safe ..

One switch, two switches.... any number of switches is EQUALLY safe if you know how to connect them

when you will use just one limit switch which is turned on by force during whole path and disconnects circuit on the ends by force dissapearing you will be protected from

This sentence is not possible to understand. Please make a drawing or explain.

- switch fell off
- switch wire cut
- running out of rails (finally) - and in any direction

machine will work only when all the limit stuff will be in correct state, otherwise machine will stop ..

A limit switch should be normally closed, not normally open. ANY number of NC switches can be connected in series and they are just as safe as one switch. I don't understand by what you mean, why would it be safer to use one switch, as opposed to two, or even six, like I have it connected.

If the circuit is broken for ANY reason (lose or broken wire, machine overrun, switch fell off... wire cut, running off the rail... whatever) the limit circuit will trip and the machine will stop even if you have more than one switch. Using only one switch on each axis is possible, but more complicated than using one on each end of the same axis. Of course, you MUST connect the switches in series and use normally closed type.

What you mean by "limit switch which is turned on by force during whole path"? If you turn ON a switch it means you make contact, that is very wrong, for safe function the switch must be on ALL the time and turned OFF by force, which should be detected by your circuit and stop the motion. It is important to use the right terms, otherwise it is easy to misinterpret and create confusion.

[collibric]

One switch, two switches.... any number of switches is EQUALLY safe if you know how to connect them



This sentence is not possible to understand. Please make a drawing or explain.



A limit switch should be normally closed, not normally open. ANY number of NC switches can be connected in series and they are just as safe as one switch. I don't understand by what you mean, why would it be safer to use one switch, as opposed to two, or even six, like I have it connected.

If the circuit is broken for ANY reason (lose or broken wire, machine overrun, switch fell off... wire cut, running off the rail... whatever) the limit circuit will trip and the machine will stop even if you have more than one switch. Using only one switch on each axis is possible, but more complicated than using one on each end of the same axis. Of course, you MUST connect the switches in series and use normally closed type.

What you mean by "limit switch which is turned on by force during whole path"? If you turn ON a switch it means you make contact, that is very wrong, for safe function the switch must be on ALL the time and turned OFF by force, which should be detected by your circuit and stop the motion. It is important to use the right terms, otherwise it is easy to misinterpret and create confusion.

I agree with your explanation as it is usual and mostly used ..
I did mean this:
Attachment 348218

it is just the second inversion of states by mechanical situation - next safe level ..

what can happen if your switch will be connected by wires, but not mounted (forget after maintenance, loose screw) ..

it is true, that i have to paint a picture as I've not found example like this on google .. but I have this on my first machine, and I'll have it on my second too .. and I feel safe on machine limts ..

[bevins]

I agree with your explanation as it is usual and mostly used ..
I did mean this:
Attachment 348218

it is just the second inversion of states by mechanical situation - next safe level ..

what can happen if your switch will be connected by wires, but not mounted (forget after maintenance, loose screw) ..

it is true, that i have to paint a picture as I've not found example like this on google .. but I have this on my first machine, and I'll have it on my second too .. and I feel safe on machine limts ..

This works yes but...... You are using the switch at all times only when you reach end of limit the switch releases. You are using it all the the time and it is a mechanical part so you dont know if it will release when you hit your limits. The other way around the switch is very rarely used and have a bigger chance that it will work when you hit your limits. I would never setup my limits like that.

But thats just me.

[A_Camera]

I agree with your explanation as it is usual and mostly used ..
I did mean this:
Attachment 348218

it is just the second inversion of states by mechanical situation - next safe level ..

what can happen if your switch will be connected by wires, but not mounted (forget after maintenance, loose screw) ..

it is true, that i have to paint a picture as I've not found example like this on google .. but I have this on my first machine, and I'll have it on my second too .. and I feel safe on machine limts ..

Yes... well... I don't think this is a good idea, and like I said it is indeed more complicated. As for the maintenance issues with installation... Use only qualified persons who can do a good job. Also, as been pointed out, this way you never know if the switch is working until it is too late. If you have a failure internally in the switch it might get stuck in the ON state, so when you actually expect it to release it may not release at all. The likelihood of that happening when it is used in the "normal" way is basically zero.

[collibric]

good point bevins, I agree with you - in case you are using mechanical switches, the spring can loose its force after some time ..

I believe in periodical maintenance schedule to verify basic functions and machine setup ..

[bevins]

good point bevins, I agree with you - in case you are using mechanical switches, the spring can loose its force after some time ..

I believe in periodical maintenance schedule to verify basic functions and machine setup ..

Yes well not only that but the switch is traveling so that means the wire is also. At least if it is connected N/C then if wire breaks, then it will halt motion. But why take chance. Limit switches are stationary for a reason.

[collibric]

Yes well not only that but the switch is traveling so that means the wire is also. At least if it is connected N/C then if wire breaks, then it will halt motion. But why take chance. Limit switches are stationary for a reason.

in any case of at least 3 axis machine - at least one of your limit switch wire is moving .. and not only this one ..

and when limit switch wire breaks - both designs will stop the machine ..

as I've mentioned before - it is not usual setup, but it has it's advantages ..

[Werdelin]

Limit switches, not for homing. 3 pair for X, Y and A ( slave ) and the single switch for the Z, which only needs one.

Thanks for your answer. But if you look closely at the photo at the beginning of this thread, my supplier has indicated the 3 axis' letters h - x, h - y and h - z (I guess that must be home -x etc) on the three paired limit switches, so the single limit switch apparently cannot belong to the z- axis (unless he has written the wrong thing on them...)

[Werdelin]

What do you need so many switches? If you use Mach3, this is enough 3 recoiling limit switches. In the configuration of Mach you only have to turn off "Home switch safety".
But if you want to have two limit switches per axis - then you connect all common wires to the plus 5V. other cables assign pins : limit x +, limit x -, etc,

Thank you for your reply. Reading the instruction manual for MAch3, I begin to understand want you mean. Apparently there's only 5 pins assigned for the limit and home switches. However, I am wondering what exact solution of the limit switches these pre-soldered limit switches point to, without me having to rearrange the cables; as I said everything is prefab and neatly put in a box?!

[Werdelin]

I agree with your explanation as it is usual and mostly used ..
I did mean this:
Attachment 348218

it is just the second inversion of states by mechanical situation - next safe level ..

what can happen if your switch will be connected by wires, but not mounted (forget after maintenance, loose screw) ..

it is true, that i have to paint a picture as I've not found example like this on google .. but I have this on my first machine, and I'll have it on my second too .. and I feel safe on machine limts ..

Thanks for your reply and the drawing and the time you have invested in this. I have to understand that drawing: The black part is the mechanical functioning, and it shows that the limit switch sort of drops to OFF state when not supported by the surface of the rail or frame or whatever that is not moving on the table? But then, can I ask you to elaborate on your drawing and indicate where you'd put the home switch (the second switch in the paired switches depicted in the initial photo in this thread) and repost it. THAT would be of some help... although I am not at all sure that my supplier is using your setup of ON / OFF state, or the other way around.

[Werdelin]

Well my guess would be the H-Y is Home for the Y axis and so forth with the X and Z. I personally would not use these switches for homing due to their lack of repeat-ability (I use a Hall sensor type for the X and Y homing switch (there is a great thread on building your own on this forum)). But for limit switches, they should work just fine. If I were in your place, I would probably de-solder the switches and come up with my own wiring plan. It's really not that complicated, so don't overthink it.

As far as homing switches and limit switches, there are lots of threads on this forum that will describe how to wire and the logic as to why.

There are many ways that people will wire their homing and limit switches. It will depend a lot on your control program (I use Mach3) and your break-out board and drivers (I use the Gecko G540). I have all of my limit switches (2 on the X, 2 on the Y and 1 on the Z) wired in series and connected into one of the 4 inputs on the G540. I have 2 homing switches (1 on the X and 1 on the Y) each wired into a separate input on the G540. I don't home my Z.

Mach3 allows you to use the same switch as a limit and also as a homing switch (I don't use this option).

I know this is not exactly what were looking for, but building one of these machines will take some time and effort to educate yourself. And all the answers are in this forum. I know, cause that is how I learned to build my machine.

Good luck.
Rick

Thank for your reply. I was looking for the wiring plan that my supplier had in mind, eventually I'd change it into my own wiring plan later. I have to add that my supplier mysteriously added an extra 10 metres of wire similar to the wire of the home / limit switches, but no extra switches, so I guess the extra wire is just for extension of the presents cables and not for additional cables and rewiring. But at this instance impossible to say.