Sharing Limit Switches and Homing on a Single Input

Greetings All,

Apologies in advance as I know this topic has been posted many times but I haven't been able to piece together the info I need from the different searches I've read through.

I have a small 3 axis CNC mill currently running on Mach3 via a parallel port that I've been experimenting running with LinuxCNC. The purpose is to evaluate if we can convert the three CNC machines at our Makerspace to LCNC. I have successfully configured it using the StepConf utility to move all the axes and to recognize three temporary limit switches, use them to home the three axes, and, set the soft limits. This was accomplished by cabling and assigning each switch to three individual pins on the BOB and in the configuration and manually triggering them to act like the machine was hitting them. (Took some practice to get the timing right for the two-hit Homing sequence.)

However, the mill is currently wired up so that all the switches (X+, X-, Y+, Y-, and Z+) are in series and connected to a single input and in Mach3 and it's able to perform all of the functions mentioned above with just that one connection.

Sooo ,,, my questions are;

Can LCNC be setup to use a single input to perform limit switches & homing on all axes ?
- and -
Can this be configured using the StepConf utility and if so what is the correct selection ?

Thanks in advance for any help.

Social distancing here in Rochester, NY

Jay

Yes it can.
The principle is that you start with no switch active. Than you move only one axis. Home it an finish by going to its "home position = 0". Than next ais starts the same procedure. The order is defined by the home sequence parameter

Details are very good described in
linuxcnc.org/docs/2.8/html/config/ini-homing.html

Have fun

Thanks for the quick reply and the info and link Mike !

I have had some success in that I have all of my NC limit switches connected in series to a single pin on my BOB and can trigger Homing and limits switches.

However there are two significant problems I'm having that I haven't been able to figure out.

The first problem is that all axes are trying to home in the same, positive, direction. That's correct for the Z axis but X & Y have to move in the negative direction.

The second issue is that I haven't been able to get the homing to do the 'double-hit' where it moves into the limit switch and then backs off some distance, moves back into the switch at a slower speed, and then moves to the new Home position inside the Soft Limits.

Please remember, I'm trying to do all my configurations using the StepConf utility and can't figure out if it has all the necessary variables required to do these things. (I have trouble keeping track of details but I believe some of the terminology in the StepConf is different in the .INI file and I'm struggling to correlate the two.)

If it's possible to do all of this in the StepConf utility it would be very helpful if someone could guide me using that menu and terminology as it's my understanding that changes to the .INI won't update the StepConf, and, rerunning the utility will wipe out any changes that have been made to the .INI file.

Jay

The first problem is that all axes are trying to home in the same, positive, direction. That's correct for the Z axis but X & Y have to move in the negative direction.

I think you invert the home search velocity in the INI file. If its a positive direction switch it to negative. And you need a HOME_LATCH_VEL in the ini for the reversal I believe. It should be in the joint section in the ini file.

Thanks OT-CNC but I'm hoping to be able to stay within the StepConf utility if possible. I'm not ready to dive into that type of programming as it's a large and difficult learning curve for me.

In general, once you have a working config, you'll end up doing the fine adjustments in the INI file. It's where your parameters are stored and there is no programming involved. Just make a backup copy. The hal file is where things are more difficult to follow if you're not familiar with the hal connections. If you have working configuration, you can later add things like your pendant mpg connections to the hal file. You'll have to hand edit the ini for sure at some point.

Thanks again OT-CNC. I understand and appreciate that I'll eventually have to deal with the .INI files but I have four different machines and would like to go as far as I can in the StepConf utility for now.

Can you or anyone confirm if the settings I need are, or are not, available in the utility ?

Some of the people I would normally be working with to figure out these things are locked away due to the virus social distancing so we can't get together and pool our brainpower. I know quite a bit about CNCs and machining but have never been able to understand the vernacular programmers and Linux types speak in. Something in my brain. The others on the team struggle less with that but don't have much manufacturing experience so we can usually figure things out between us. Not sure when we'll be able to get together again though ...

Thanks again all for your help.

I worked in the .INI file as you've been suggesting and have things mostly working as I hoped. The only thing I haven't found is how to control the 'pull-off' distance after it initially finds the homing switch and comes off the switch some amount and then hits the switch a 2nd time at a slower feedrate. It currently pulls off a very small distance that would barely be perceptible if I didn't have tape on the end of the ballscrews.

This distance is adjustable in Mach3 and GRBL but I haven't found a setting for it in LCNC.

Can someone please confirm if what it's doing is expected behavior or point me to the settings where I can change the distance ?

Jay

Hi Jay
Good that it is basically running. And i could have only hellped you by modifying in INI.
The configurators are very good, but only to a certain level.
I never heard of an adjustment of the retract. This is in my eyes only a timing combination of your two speeds and your acceleration. I. Gues that your home_SEARCH velocity is (as you are careful) quite low for the machines possibilities and so you get minimal overshoot. Then home_LATCH velocity phase is very short. But that does not "damage" the precision of homing in my eyes. It is only faster, maybe better, than what you are used to .
Mike

I worked in the .INI file as you've been suggesting and have things mostly working as I hoped. The only thing I haven't found is how to control the 'pull-off' distance after it initially finds the homing switch and comes off the switch some amount and then hits the switch a 2nd time at a slower feedrate. It currently pulls off a very small distance that would barely be perceptible if I didn't have tape on the end of the ballscrews.

Can you post the ini file.

What do you have HOME = set to?