Homing And Four Corner Jogging

@chrismakesstuff @andy - Ok guys, I think this is something up your alley. I have the 30x30 MK1 from the kickstarter program. It has been running fine all of this time. Not too long ago I added the homing sensors. I followed the installation instructions as posted. All seems good until recently (currently on Ver 1.1.1). After homing I’m getting some weird numbers on the X and Y movements. On the Z there is something else weird. I am attaching several pictures below and putting what I’m seeing at the beginning of each picture. What I’m seeing does not affect any of the work I have done so far but distances to the corners are a little off. Keep in mind I operate in inches. Also the actual moves in the X and Y are not the same as the firmware Max Travel. X should be 29.53 inches but moved only 28.05 inches. Y should be 31.97 inches but moved only 30.37 inches.

Start and LM is homed. All locations set to zero as expected.

Selected icon for back left corner. LM moved to back left. X shows +.039 even though it did not appear to move and I saw it incrementing as it proceeded to the back left. Also noticed the Z axis dropped to -.037 almost immediately and I saw it move and it stayed there through all remaining moves.

Selected icon for back right corner. Even though X from previous move was at +.039 (I did not rezero). Only X value incremented. No other axis movement.

This was the same move to the back right corner but this time I zeroed out the X value (+.039). Notice the difference in the final X value. Difference of roughly .04.

Selected the front right icon. Carriage move smoothly. Now the X is still at the same location it was on the back right corner. But the Y instead of being .00 is +.039. Weird.

Selected the front left icon, not the home button, and got these numbers. Check the machine locations showing +.039.

And finally hit the home button and this was the final back home readings.

Firmware settings (again I use inches). Hard limits and soft limits disabled. Step resolutions are in the upper right corner and are based on gSender calibrations.

Hi Heyward,

This is working as implemented and expected for X and Y. The idea is to get you close to the corners but not exactly to the limit.

Moving away from the limit switches moves you 95% of the way to the limit which explains your numbers - for example, for your X movement, 0.95 * 750 is 720mm, or ~28 inches.

Moving towards the limit switches places you at $27 (switch pulloff EEPROM value) away from that axis. Our default value is 1 mm, which is ~0.039 inches This is because not everyone is running our configuration of the firmware which sets machine zero at current location after homing, and if we sent the carriage to exactly mpos 0, it would trigger the switch for those users.

Z is definitely something weird since rapid position doesn’t move that axis at all.

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Thanks Kevin for the explanation. I figured there was some reason but just couldn’t figure it out. I spent about an hour today recalculating my max movement numbers. I got both X and Y to move to within 1/2 inch of the corners. I’m satisfied with that and your information. Oh! and the X axis was moving as the carriage moved to the back left corner. I just couldn’t see it with the naked eye. I put a piece of tape on the X lead screw and watched it.

Now if you can figure out why the Z is dropping all will be good. It’s not really a problem since I set/reset Z for every run. And, of course, the other numbers don’t affect my projects either. Was just confusing to me since I wasn’t aware of the 95% limiting.