Typical values for Extruder/Probe offset

[old man emu]

This question relates to about Step 2 of Auto-leveling, but what is a typical extrude/probe offset along the X-axis?

I know that there is no single answer to this as there are a host of manufacturing variables in the sizes of servo and probe components, but I feel sure that there must be a typical ball-park figure.

I got my measurement by adding together a number of distances (extruder to probe arm; width of probe arm, and distance between edge of micro-switch and centre of its button)

I got values ranging from 30.65 mm to 30.71 mm. There is some lateral play in the arm. Looks like 30.7 would be a reasonable value for my machine.

When I enter a value for this offset, how accurate should the value be - to the nearest 100th; nearest 10th, or nearest unit?

Old Man Emu

[Roxy]

Mostly, the reason for knowing this number precisely is because after the angle of the bed is known, this information is used to correct the height of the Nozzle. The further the probe is from the Nozzle, the more the height will have to be corrected. In practice, what people do is look at the first layer going down and decide if the nozzle is too high or too low and adjust the Z-Probe-Offset to make the right thing happen. You numbers are accurate enough to get good results.

My current numbers are:
#define X_PROBE_OFFSET_FROM_EXTRUDER 18
#define Y_PROBE_OFFSET_FROM_EXTRUDER 17
#define Z_PROBE_OFFSET_FROM_EXTRUDER -3.85 //-4.20 prior to declogging nozzle on 07-07-2014

And notice the comment on the Z Axis. After taking apart and reassembling my extruder the number moved .5 mm. That number was not determined by measuring things. It got to where it is by watching the first layer and moving that number up and down until I liked how it was going down.

[old man emu]

This is what my probe set-up looks like:

Lights Off - flashlit.jpg

This is the file for it. I think it was created by Zennmaster:
Servo_mount.scad

My X-axis off-set is 66% greater than yours. Is here any problem here?

OME

[Roxy]

This is what my probe set-up looks like:

Lights Off - flashlit.jpg

This is the file for it. I think it was created by Zennmaster:
Servo_mount.scad

My X-axis off-set is 66% greater than yours. Is here any problem here?

OME

You want the probe to be as close to the nozzle as practical, but your numbers are going to be fine. Think of it this way. You used to be able to print just fine without Auto Bed Leveling. You might have to adjust the bed once in a while, but it worked. Once you get the Z height dialed in correctly, you won't have to mess with the bed any more.