[FR] Increase the amount primed from 2mm to 15mm before drawing the Bed Mesh Validation pattern

[Thinkersbluff]

Is your feature request related to a problem? Please describe.

Currently, the Bed Mesh Validation pattern is programmed to drool at the left side and to prime 2mm before starting.

In my experience, that priming action is completed so quickly, and the head then moves into the pattern so quickly, that I do not have time to pick either the drool or the primed amount from the end of the nozzle before it is being carried into the print and deposited on the bed.

The larger priming amount gives even a user like me (old man, short-sighted, bad depth perception) sufficient time to get their tweezers in there & pull it all away, before the head starts to descend.

On my own system, I have also added a reminder to the "Starting..." message, to "Prepare tweezers..."
In the absence of a user manual, this prompt might help warn new users (at least for their 2nd attempt), that there will be a user action required, at the beginning of the pattern...

Are you looking for hardware support?

No. This change is valid for all configurations of CR6 hardware.

Describe the feature you want

I want the Bed Mesh Validation test pattern to prime for longer, so that I have time to grab the drool and primed amount from the end of the nozzle before the nozzle starts moving, at the start of the pattern.

This change can be made by changing P2 to P15 in line 72 of MeshValidationHandler.cpp.

As a kindness, it would also help to modify the message at line 80 in that same cpp file, to read something like:

SetStatusMessage("Starting. Prepare tweezers..."); // Add a friendly reminder to prepare tweezers to hook the drool off the nozzle just as the head starts to descend and start the pattern.

NOTE: If FR #301 is also approved, it would be helpful to address this issue at the same time.