Z-Homing

[VRA (Ralf Vogelbacher)]

Troubles with z-homing

Hello everybody,
I‘m new, that’s why I’d like to tell you who I’m.
I‘m a Mechatronic-Design-Engineer from Germany.
Congrats to all developers who developed this really great hobby machine. Thanks for that!
But now my problem. I know, this topic is not new, but I think I‘m thinking the other way around. X/Y homing works well.
But, when I’d like to travel to the touch plate in Z-direction, the machine travels about 10mm to Z+ and stops.
There is nothing wrong with the touch plate, because when it‘s not touched, it says „open“, and if it‘s touched, it say‘s „triggered“
All steppers driving the right direction, because the machine works. As well as the Z-direction, because traveling to Z-, it’s traveling towards the table, so downwards.

I think there is a deeper problem. Could it be, that the machine is thinking, it‘s already in zero position and that’s the reason it travels to safety distance of 10mm upwards?

Crazy is, the position the machine reached after traveling the wrong way, is automatically set to zero.

I‘m using a arduino mega, a ramps 1.4.
I built the MPCNC primo, added a Ortur laser and a knife. The machine is also adjustable via Joystic, and later on, it will get a plasma gutter and a Makita spindle.

Hopefully anyone had the same problem and could help me, because I’m dancing in the dark.
Maybe important to know, I’m not a programmer, but sometimes I understand what you‘re talking about!
I’m working many day‘s regarding this problem and my wife and children call me crazy!

[Tokoloshe (Philipp)]

Welcome Ralf, we can always use another German.

And whoever has not been called crazy by his wife for fiddling with the CNC is doing something wrong…

Nevertheless: Has the error always occured? Is it a new one? I don’t know how Ramps works, but for my controller I have to tell the program in which direction it is supposed to home. Maybe there is a switch somewhere?

[Bartman]

@VRA

when I’d like to travel to the touch plate in Z-direction, the machine travels about 10mm to Z+ and stops

What is the exact Gcode command that you are using? What are the Z coordinates when you start the command?

The correct syntax is G38.2 Zn (where n = 0 or some other number)

In a Marlin setting, it means move the Z axis lower until either:
a) it touches the probe, or
b) it reaches the specified value.
(whichever occurs first)

Using the LR3 as an example, starting from the homed position of Z200, a G38.2 Z0 will move lower (Z-) until it sees the touch plate activate, or until it reaches the bottom of the travel and starts skipping steps ( as there is only about 80mm of available travel, so it will never reach Z0)

Note that if your starting position is less than the specified value, I think that it will move in the Z+ direction instead of the Z- direction (not 100% sure about that).