Run a stepper from 2 DM542 drive

[A_Camera]

I keep asking about the relay because DM542 has - Pul+, Pul-, Dir+, Dir-, Ena +, Ena-, Gnd and+24VDC. According to your diagram I should have a relay with 7 inputs. Where I can find something like that? Or I got this wrong....
You use Arduino for the operation you want to be executed by your lathe. I don't need this. I only need to use safely 2 stepper motors (alternatively) with a one stepper driver.

No. All you need is a 4-pole relay. Pul -, Dir - and Ena - are all connected together to GND. You are controlling only Step, Dir and Ena.

I know you don't need the Arduino. The Arduino is generating the pulses I need for the lathe operation, but that's just for your information on my use. All you need is what my drawing shows, i.e. a 4 pole relay and a switch. The one I am using is DS4E-M-DC5V made by SDS. It is a low power signal relay, fast and requires very little current, but it is obsolete so maybe hard to find. Anyway, there are plenty small signal relays which can be used, and it is not critical that all the contacts are in the same casing, so you can use 4, 2 or 1 relay depending on what you find. Here is an example which works also, but you need to wire it:

https://www.amazon.se/Yizhet-kanal-r...03086861&psc=1

[gabi68]

No. All you need is a 4-pole relay. Pul -, Dir - and Ena - are all connected together to GND. You are controlling only Step, Dir and Ena.

I know you don't need the Arduino. The Arduino is generating the pulses I need for the lathe operation, but that's just for your information on my use. All you need is what my drawing shows, i.e. a 4 pole relay and a switch. The one I am using is DS4E-M-DC5V made by SDS. It is a low power signal relay, fast and requires very little current, but it is obsolete so maybe hard to find. Anyway, there are plenty small signal relays which can be used, and it is not critical that all the contacts are in the same casing, so you can use 4, 2 or 1 relay depending on what you find. Here is an example which works also, but you need to wire it:

https://www.amazon.se/Yizhet-kanal-r...03086861&psc=1

Sorry to be a pain. I have 4 inputs which need to be changed between. You said I will need Pul+, Dir+ and Ena (unconnected in my case). What should I do with the rest of the wires (Pul-, Dir- and Ena).

Thank you

[A_Camera]

Sorry to be a pain. I have 4 inputs which need to be changed between. You said I will need Pul+, Dir+ and Ena (unconnected in my case). What should I do with the rest of the wires (Pul-, Dir- and Ena).

Thank you

It is getting difficult to help because I don't know your background and don't have a clue about your wiring or who did the original work, but I'll make a new effort.

1. If you are sure you NEVER will use the enable signal then you don't have to care about that, so just ignore as it is ignored in your picture.
2. Check PUL - and DIR - with a DMM, I think those are connected to the same source, so basically you could have only the blue wire connected and from that bridge to PUL -.
3. In theory, if both your controlling devices share a common signal ground then you don't need to switch that signal, but it is a good engineering practice to do it, so I would definitely switch that also.
4. This leaves you with three signals to switch and these are the same as PUL + , DIR + and DIR -. Remember that DIR - is bridged to PUL - otherwise it will not work.

In the end, according to the above, you will need a relay which can switch three signals, but you won't find such relay. They are always made as 1, 2 or 4 (or more) pole relays.