Homing Position and Axis Direction

[msbealo]

Hello,

This is my first post. I've just finished contructing my first CNC Router and have largly managed up until now. I'm now getting everything working and I'm a little confused with homing positions and axis directions.

I note that this has been discussed recently:

https://www.makerfr.com/forum/viewtopic ... 41&t=7390

However I'm not sure it's the same issue.

What I would like is some clarification. The limit switches have been mounted as per the instruction. Y axis limit is at the front, X axis is on the left and the Z limit switch is at the top most position.

I originally wired up the steppers as per the A-/A+ & B-/B+ labels on the motors but these were sending the X and Y motors in the wrong direction when using the nunchuk. I swapped the four wires for X and Y around and this now agrees with the direction I'm trying to move it.

Now, the machine homes when I press the home button, all X, Y and Z move to their home switches. The trouble is that when I then move the axis again using the nunchuks, the position readouts go negative. Is this correct?

So, what read out position should the axis home at (zero?) and what value should I read when the spindle is roughly in the middle of the bed? What direction does the Z axis move?

I notice that there was talk in the above topic about sending grbl a code to correct the orientation but I'm reluctant to do that just yet as I have a belief that the grbl build I'm using (downloaded and flashed as per the instructions) should be correct off of the bat.

I'm in the process of building a laptop which will hopfully help me with debugging.

Kind regards,

Mark

[mstrens]

There is a convention in CNC that says that 0 position is with Y backward, X right and Z up. So working positions are always negative.
Switch positions being with Y front and X left, when a homing is performed, GRBL set the Y and X position at homing equal to the (negative) size of the machine. So when it is moved to the back right, it will be at 0,0 as foreseen by the convention.

Please note that this is just a convention and some user does not follow it.

[msbealo]

mstrens,

Thank you for your reply.

That sounds like a wierd convension and I'd be interested to understand why. Coming from a 3D printer background it seems a little, well, backwards. I imagine that from a milling background it makes more sense.

Out of interest, where would i need to make the changes to move zero to the front left?

Regards,

Mark

[mstrens]

Here an extract from the official GRBL documentation (part of config.h file)

// After homing, Grbl will set by default the entire machine space into negative space, as is typical
// for professional CNC machines, regardless of where the limit switches are located. Uncomment this
// define to force Grbl to always set the machine origin at the homed location despite switch orientation.
// #define HOMING_FORCE_SET_ORIGIN // Uncomment to enable.

[msbealo]

Thank you