How to set (relative?) home position?

Mostly Printed CNC - MPCNC Troubleshooting
1

We are messing with a new build. The rig is in order but we are running into a few problems.

One of them is the fact that we where not able to set X Y Z 0 relatively. But I’ll further explain what I mean by that, since it must be something I understood wrong, as it doesn’t work.
So what we are trying to do is to move the head manually to a 0,0,0 position, and let the piece mill/laser/whaterver from there.

We are using Repetier as our software, the latest RC8 Marlin drivers from this site.

Now firstly we are not able to set 0,0,0 in any way through the software.
If I initialize the machine by powering it on, it takes it’s current position as 0,0,0 (red). Then when I home it, it goes x amount to Z pos, X pos, Y pos, Z pos again. We’ve taken the exact config from the screenshots in the toturials from this site. But this happens every time we hit the general home button. It only keeps going positive. And once you’ve hit the home button, we are not able to go negative beyond that. That is a big problem.
To be clear, at this point we are using the source for the RC8 as is. Repetier configuration as showed on the site.

Now I’ve tried messing with different things. I first thought it was the endstops we don’t have, but after reading the forums I see that it’s better not to use them. I’ve tried with offsets, soft endstops, too much to sum up I guess. I also inverted the endstop parameters in the firmware, so they where open, with the expected result that homing just didn’t stop, and we still weren’t able to go negative from the point it initialized.

After messing around we put the normal RC8 firmware back, we even changed the Mega and RAMP, just to be sure, to brand new one’s. No releave.
Any help is greatly appreciated.

2

Sending G92 X0 Y0 Z0 to the machine will set the current position as 0. I placed that into one of the 4 script-slots, so I jut have to click the (1) icon to set the position to 0,0,0. (The Mac Version of Repetier Host had that as a button already).
BUT, I was not able to use the Home button yet. When ever I click that, the machine goes to somewhere but not to the 0, 0, 0.

3

A couple of things.

I do use z_min and y_min stops. Pressing the home button for X or Y will home the machine to the end stops and set the corresponding value to 0, regardless of where you are on the bed. Mine raises approx. 10mm of Z prior to pressing the X or Y home button, but only the first one I press. After that it doesn’t affect the Z.

You should be able to use Repetier (arrows or command line) to move the tool to where you want. Do not move it with your hands. This is so the software knows how much it has moved. Then you can set G92 X0 Y0 (must be in caps if you are using a Mac).

To set Z0, the same process can be used then issuing a G92 Z0. You could also create a touch plate and Home Z then set G92 Z(thickness of your plate here, some positive value).

You should be able to go +ve or -ve from that. I use G1 X?? Y?? Z?? F3600 to move around the work piece. I find typing in the codes is much quicker in most cases and resort to the arrows in Repetier for fine tuning.

On my version of the Mac Repetier, the scripts are on the GCode tab. There are 5 hidden in a drop down.

4

Supposedly, if we are still not able to move negative from the G92 code on, what would be the next step to try?

I don’t have access to the machine at the moment. And I’m not 100% sure anymore if G92 was one of the codes I tried out while messing around. Should’ve kept the log somewhere I suppose. I also suppose that once you initialize the G92 code, repetier will show all axis as black instead of red? The same as you would press the home button.

Because even when the numbers where black in Repetier we never where able to move negative in any way.

5

Keep this handy: GCode Cheat Sheet

Just to be clear, G92 “sets” coordinates. G1 “moves” to coordinates.

Also, I am still using RC7 so I don’t know if there is an issue related what you are experiencing as you are using RC8. Perhaps others can comment on this or you can switch to RC7.

You should have no issues moving -ve or +ve.

6

Just a guess here. Having the same problem but it just dawned on me that I haven’t checked that the end store are turned off in the Marlin firmware…
They should be and if not, it would explain the behavior…

I’ll check mine tomorrow…

7

The home button is actually “move in the negative direction until you hit and endstop”, it is not “move to 0,0,0”

Either use Jens method, or I just rest my arduino or have it pre programmed into my gcode through the fusion post processor.

RC8 is not available on the site at this time? Recheck your firmware.

You can move in the negative direction with my firmware.