Tandum Axis Shared Home/Limit Switches

I have a XYYZ gantry router setup. The X and Z axis are built and running, Homing etc. Next for me is setting up the tandem Y axis, dual motor, dual step drivers, home limit switches.

I'm using simple micro switches for the shared Home/limits.

Generally speaking what advice would you offer for mounting and setting up the switches on a tandem axis?

I'm running the MESA 7i96 and plan on 4 total limits for the tandem Y axis.

I guess what I'm wondering is how to physically setup the Home/Limits so when homing the gantry doesn't rack to much. Can you physically sync the two pair of home switches? Is it necessary?

Project_Hopeless wrote:

I'm running the MESA 7i96 and plan on 4 total limits for the tandem Y axis.

I guess what I'm wondering is how to physically setup the Home/Limits so when homing the gantry doesn't rack to much. Can you physically sync the two pair of home switches? Is it necessary?

When homing two tandem motors they home in sync with each other at the same time, this is achieved by making sure the the sequence No. in the ini file has a -ve sign before the sequence No.

i was thinking he means the _physical_ limit switches.
I bet he is wondering how important that the two switches be aligned to each other to stop racking.

IIRC linuxcnc moves both axis until one switch is tripped then that axis stops and the other continues till that ones stops, then they move together.

I don't see any description in the docs that thoroughly describe tandem homing.
Can anyone confirm what actually happens - for instance are back off a retrip moves done together or separately?

Chris

Ok, after setting my home switches to switch on at the same time as close as possible, can I use the HOME_OFFSET = with a different value to correct racking or squareness to the X axis. ? for both joints. ?
In other words for example:
Joint 1
HOME_OFFSET = 3.000
Joint 3
HOME_OFFSET = 3.054

That seems reasonable - easy to test.
If that works that means the final home move is when the synchronizing is complete.

keyboard wrote:

Ok, after setting my home switches to switch on at the same time as close as possible, can I use the HOME_OFFSET = with a different value to correct racking or squareness to the X axis. ? for both joints. ?
In other words for example:
Joint 1
HOME_OFFSET = 3.000
Joint 3
HOME_OFFSET = 3.054

Thats exactly what to do if your measurements are precise.

I did read a machine setup manual the other day that suggested you mark the corners of the largest square you can fit on your machine, measure the diagonals and do some maths to calculate the error. I was going to do it to mine one day..

can you confirm the complete homing sequence including latching for tandem axes?
ie after initial tripping of the switch of both joints, does it search the final trip point of both joints together, does each joint stop when the trip point is found etc.

Thinking about docs