Unable to go negative coordinates

Mostly Printed CNC - MPCNC Troubleshooting
1

Hello,

I’ve been using a pen and laser on my MPCNC for the last week since I have had it assembled and it has been working great. I noticed that I wasn’t able to use the manual control on repetier to move the tool to negative values. The steppers are able to move both positive and negative directions they just don’t move past zero. And the zero point resets to the current position that it is in as soon as I connect to repetier host. So what I have been doing is homing X and Y and Z and since I don’t have end stops I just disconnect as soon as it gets to the position that I wan’t it to be and as long as I am starting on the bottom left corner for my origin I do not have any problems with negative values. And I have been having a lot of fun with the pen and laser. But now I would like to start using the router and that means I have to allow negative values since the origin will likely be the top of my work piece and I need to move downwards.

I bought my Mini-rambo though V1 shop. The other hardware/electrical I had/purchased locally.

I was having this problem before doing anything to the firmware, but I have since had to modify the firmware to reroute the fan pin so that it can control my laser. I did not do anything to it other that reassign the fan to the z min pin on the rambo board as has been suggested on the forum to allow for 0-5v PMW for my laser.

If anyone could give me some guidance, it would be much appreciated. Thanks!

Here’s an laser etching I put in some leather… going to make a book case. Fun stuff.

20180331_121551.jpg
20180331_121551.jpg3024×4032 1.45 MB

2

It should go negative with Gcode commands or with a LCD. Sounds like you have a setting in repetier preventing that without homing. Not sure what it is but try changing it to cnc instead of printer (normally not needed). Look for check boxes about homing and negative as well in the settings.

3

Yes Repetier Host prevents me from going negative in x and y as well, but z has always been fine. Just keep your part in xy positive area and it should be ok. If at some point you do not want to deconnect-reconnect, you can use G92 X 1000 Y1000, move your head where it should be, and G92 X0 Y0 before starting the cut.