Understanding starting point for setting offsets, etc

I have been reading many posts on bed and probe settings. What is never clear is where I am measuring FROM. Example:
#define LEFT_PROBE_BED_POSITION 15
#define RIGHT_PROBE_BED_POSITION 145
#define FRONT_PROBE_BED_POSITION 20
#define BACK_PROBE_BED_POSITION 150
The above Positions are to be measured from where? And should the bed/nozzle be at a certain location prior to taking the measurements?
Thanks for any clarification.

In my understanding all measurements are made from the center of the Nozzle to the center of the detection area of what ever device you are using to detect the bed.

On my 3D Printer the proximity sensor has a small area on the front of the sensor (shape 30mm x 10mm x 6mm ) of which only a 4mm circle in the front can detect the bed.

(Sensor is a TL-W3C2 Omron )




To stay withing the bed boundaries I choose too use a 20mm side boundary and a 25mm front to back boundary from bed edge
As my proximity sensor is exactly 25mm directly behind the nozzle the following chart is used for a 220mm X 270 Bed.
location 0,0,0 the nozzle is touching the front left corner of the bed.

The probe is 25mm behind this so location 20, 25, 0 is 20mm right and 25mm back for the bed to the probe location
The location 200, 25, 0 is 200mm right and 25mm back from the bed to the probe location.
The location 20, 265, 0 is 20mm right and 265mm back from the bed to the probe location.
The location 200, 265, 0 is 200mm right and 265mm back from the bed to the probe location.

#define LEFT_PROBE_BED_POSITION 20
#define RIGHT_PROBE_BED_POSITION 200
#define FRONT_PROBE_BED_POSITION 25
#define BACK_PROBE_BED_POSITION 265

Edited 4 time(s). Last edit at 03/31/2018 11:04AM by Roberts_Clif.

Thanks, but what I think you are describing is the probe offset from the nozzle, which I have set correctly. I am referring to the points on the bed on which to probe.

I define Bilinear bed leveling using the same numbers defining a 4 by 5 grid

#define AUTO_BED_LEVELING_BILINEAR

#define GRID_MAX_POINTS_X 4
#define GRID_MAX_POINTS_Y 5

// Set the boundaries for probing (where the probe can reach).
#define LEFT_PROBE_BED_POSITION 20
#define RIGHT_PROBE_BED_POSITION 200
#define FRONT_PROBE_BED_POSITION 25
#define BACK_PROBE_BED_POSITION 265

I cheat and use the "Unified Bed Leveling" save feature that way I do not have to re-level bed every time
After leveling the bed I save data using M500 and to restore I simply turn the data on using "M420 S1 ; Bed Leveling On" after the last G92 in the startup G-Code

M420: Enable/Disable Bed Leveling and/or set the Z fade height.
S[bool] Turns leveling on or off
Z[height] Sets the Z fade height (0 or none to disable)
V[bool] Verbose - Print the leveling grid
Send M501 ; Load data
Send a M420 V ; Print the leveling grid

Z Offset can be changed by using the M851 Z-offset the input

Z-Offset
Z-Offset " M851 Z-0.44 " Sets the Z-offset the input

Now most "Unified Bed Leveling" commands do not function from Bilinear bed leveling but that is OK as I only use these

Edited 5 time(s). Last edit at 03/31/2018 11:18AM by Roberts_Clif.

Thanks, but from where are you measuring for the 20, 200, 25 and 265 position? 20mm from where, for instance?

Edited 1 time(s). Last edit at 03/31/2018 11:16AM by nkuck.

My 3D Printer location 0,0,0 is in the front left Corner of the bed, Edge of the Bed front and left. I have no area outside of the bed that the nozzle can travel.

My Printer nozzle cannot travel outside the bed area, there is no physical way without breaking the endstops. It was designed and adjusted this way

Edited 1 time(s). Last edit at 03/31/2018 11:26AM by Roberts_Clif.

The LEFT probe....is that lefr front or left rear? ETC.

Quote
nkuck
I have been reading many posts on bed and probe settings. What is never clear is where I am measuring FROM. Example:
#define LEFT_PROBE_BED_POSITION 15
#define RIGHT_PROBE_BED_POSITION 145
#define FRONT_PROBE_BED_POSITION 20
#define BACK_PROBE_BED_POSITION 150
The above Positions are to be measured from where? And should the bed/nozzle be at a certain location prior to taking the measurements?
Thanks for any clarification.

Most firmwares allow you to define where X=0 Y=0 is on the bed, then you tell the firmware what the coordinate is when the homing switch triggers. So choose whatever position is most convenient for you. For Cartesian printers it is common to define X=0 Y=0 as the front left corner of the bed when looking in the +Y direction; but it's more logical to define X=0 Y=0 as bed centre.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

As stated from first post

Quote
Roberts_Clif

To stay withing the bed boundaries I choose too use a 20mm side boundary and a 25mm front to back boundary from bed edge
As my proximity sensor is exactly 25mm directly behind the nozzle the following chart is used for a 220mm X 270 Bed.
Location 0,0,0 the nozzle is touching the front left corner of the bed.

Quote
dc42

Cartesian printers it is common to define X=0 Y=0 as the front left corner of the bed when looking in the +Y direction; but it's more logical to define X=0 Y=0 as bed center.

Did not design the printer, Only followed the assembly Instructions, then when upgrading the Marlin firmware I used existing working configurations, saw no reason the reinvent a perfectly working wheel.

So my logical 0,0,0 is the left hand front corner. as I have never used anything else.

Edited 3 time(s). Last edit at 03/31/2018 12:08PM by Roberts_Clif.

Thanks.