Probe Offset, rectangular grid help

[Matt Mikula]

Been using BLTOUCH for a while, but not really set up right. 

Here's the setup:

- X endstop toggles when nozzle is at x=0
- Z probe (BLTOUCH) is 55mm to the RIGHT of the nozzle (55,0,0) offset

I've been running with 0 offset because if I use the 55mm, the calibration wants to drive past the Xstop to measure X0 with the probe, which is -55mm from the nozzle.  So I think I'm getting a good grid but the nozzle is being compensated for the point 55mm away if I understand things correctly.   See the dilemma?  I can't easily move the Xstop, is that the only option?  Or is there some way to limit the starting position of a rectangular grid to start at +55?  Seems all you can do is make the Xgrid size 55 less which prevents the probe from moving past the bed. 

Thanks...

[Johan Jakobsson]

Which printer design do you have? (I'm guessing cartesian I3 style?)
Which probing routine are you using?

If you do aahve a cartesian you could try the 3 point leveling which lets you specify where to probe; http://smoothieware.org/zprobe#probing-for-cartesian-machines

[Matt Mikula]

Cartesian and it's using Rectangular Grid.

[Matt Mikula]

So the requirement to use rectangular grid is the nozzle must be able to move off the bed at least the same distance as the X offset if the probe is on the right of nozzle? Doesn't seem that's practical. Looks like I have to redesign my mount to put the probe left of nozzle and limit bed probing size while giving up bed size???. What a pain... There should be a offset for either side.

[Johan Jakobsson]

It's all in the wiki; http://smoothieware.org/zprobe#rectangular-grid-compensation 

Optionally probe offsets from the nozzle or tool head can be defined with…

leveling-strategy.rectangular-grid.probe_offsets  0,0,0  # probe offsets x,y,z  (Z should always be 0)

Probe offsets may also be set with M565 X0 Y0 Z0.

The head of your printer will be moved to the X and Y bed sizes set above, PLUS any X and/or Y offset.

Make sure your printer's mechanism will allow moves to these locations. 

For example, if your probe is 60mm down from your nozzle in the Y direction (M565 X0 Y-60 Z0), and you bed is set to 200x200mm, the top row of probes will be done with the nozzle at Y=260 mm

What you've in effect done by having the probe 55mm right of the nozzle is to make the bed 55mm smaller in X when probing as your printer cant move the head 55mm to right of the bed to probe the edge.
They way around that i can think of is to set leveling-strategy.rectangular-grid.probe_offsets (55,0,0) and change the size of the bed by the same amount in the probe settings; leveling-strategy.rectangular-grid.x_size (bed size -55mm)

[Matt Mikula]

You've touched on it all, thanks for the time.  I've been up and down the WIKI, and the last paragraph you wrote is really what I was asking.  I'm ok to define a smaller bed for probe, but not have to limit the print bed size.  Not probing the first 55mm of X isn't that big a deal compared to limiting bed size. 

So seems I must either try 3 point, which is more limited. Or define a smaller bed size.  Or do some mechanical redesign. The best option for me (just exclude the first 55mm of X probe) is not possible unless I go back to Marlin.  Not the best news. 

[Matt Mikula]

Or maybe I junk the BLTOUCH and go to Piezo

[Arthur Wolf]

On Sat, Feb 17, 2018 at 6:02 AM, Matt Mikula <mattm...@gmail.com> wrote:

You've touched on it all, thanks for the time.  I've been up and down the WIKI, and the last paragraph you wrote is really what I was asking.  I'm ok to define a smaller bed for probe, but not have to limit the print bed size. 

I'm not sure I understand the logic here ...

If the probe can't go somewhere, you can't probe there, so you can't have the information to compensate there ...

You can still print there, you just won't know what the exact bed height is since the probe can't go there.

This isn't really a problem with Smoothie, it's just a physical limitation of the machine itself ...
 

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[Matt Mikula]

Thanks for the response.  You are correct, I'm fine to give up the first 55mm probing since the probe can't go there on the X axis.  That is indeed a limitation of the hardware. 

My question was how to configure smoothie to start at X=55mm without limiting the bed size.  The X offset impacts the max X position, not the min.