Z tool height setting probe and automation for MPCNC using machinekit and pymachinetalk

[Tom M]

My apologies in advance about this long brain-dump.
I've been making good progress and having a lot of fun auto-homing using Charles' HAL gantry component for my dual gantry MPCNC but now and now I'm ready to take it further. (A MPCNC is a Mostly Printed CNC is a low cost kit that you can make or buy which goes together fairly quick. Here's a link of one that we're putting together at workshop88: https://www.youtube.com/watch?v=N12Rk-Ss3aw )
I've been thinking about my next steps for my machine.

At this point, I want to focus on V-carve engraving using F-engrave for generating g-code 

Some of the issues that I've been running into are:

• Setting the Z-tool-offset
• Parallelism being the wood surface and x-y plan of the machine.

To that end I'm interested making some type of z-axis touch probe and start exploring pymachinetalk.
Starting out, I'm probably going to make something simple, along the lines of this:

http://www.mycncuk.com/threads/5057-another-tool-hight-setting-proble-%29

I like the idea of having some spring to the system that that I wont bury the tool into the tool height setter if I go too far.

One thing that I don't like is that I have a wired connection to the pre-setter.  It would be the cat's meow to have the switch wired to a pi-zero with wifi (I have a bunch of RPI's sitting unused) and have it talk to my beaglebone over wifi(or other wireless method)and tell the beaglebone  about its reference height or if it's been touched but I'm getting way ahead of myself here.


I really enjoy watching the Hal-gantry component derack to the switches.  It's pretty cool which is influencing my thinking here.

I want to have the z-offset work flow setting be something like this:

1. Manually rough set the z-height to the work
1.     (This would be less than the height z-offset probe and would be a safety to insure that I don't bury the tool when using the probe)
2. raise the z-height and insert the probe above the tool.
3. Press a custom button on the axis display, which would lower the z-axis till the switch on the probe is tripped. It would then raise lower to find the exact point.  If a rough distance has been defined and has been exceeded a fault estop would be generated.
4. Have parameters be automatically entered for tool offset.
   

I'm thinking I can use tool/system initially for setting the Z tool offset, but could be extended to calibration of the x-y plane.


My questions are:

• Does this sound reasonable?
• Is there a more established method for doing what I'm talking about.
• Similar things have been done, but has what I'm talking about been done already?
• If so does anyone have a links to recommended reading or the magic Google search terms to plug in?
  

[Masoun Mardini]

You mean something like this???

https://youtu.be/OmOqhB4CsJk

if so you need to write your own G code program and remap to custom M instruction ( note the video is done Linuxcnc but I think it will work on machine kit)

[Tom M]

Looks nice,Is that your machine?

Thats not exactly what I was thinking, but a custom Mcode has some appeal.

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[Masoun Mardini]

Then i think you refer to z leveling which used in reprap 3d printers, it takes several touch points on surface and then make a file to represent the heat map to z levels and use yhem during machining, but I didn’t see anything similar in machinekit nor linuxcnc.
Also i have read something about parallelism in the new version that gives you a perfect cube whatever skew your machine had.