Respecting tool heights

[lukDev]

Hi,

I recently started working with your post-processor. First of all, thanks a lot for implementing it – works great!

There's one issue I noticed: The heights of tools that you set in the FreeCAD tool library are not respected, which means that if I set my work origin with a bit that is 38mm in length and then do an operation later in the job with a tool that is 40mm in length, the cut will be 2mm deeper than it should be.
I did some research and it turns out that the G43 command (which is supposed to make the machine compensate for the tool length) is not supported by Snapmaker, since it uses Marlin gcode (which doesn't keep a tool table).

So, in order to be able to work with tools of different lengths without having to reset the work origin after every tool change, I implemented a small fix that basically reads the tool heights as they were set in FreeCAD, computes the difference between the current and first tool (the one with which the work origin was set) and then corrects the Z values of all commands executed with the current tool by that offset.

Would you be interested in integrating this change into your repo?
Let me know :)

[clsergent]

Hi,

I didn't know about G43, but it seams very interesting indeed.

I would be happy to add your fix (rather an upgrade). Would you like to open a pull request?

Just notice that because of my current job I will not be able to merge it before two weeks, but as soon as I can I will work on it.

In addition, I will also add this enhancement to the Snapmaker postprocessor shipped in FreeCAD (along with another fix, I'm late, being busy at work...)

[clsergent]

Hi,

I'm finally able to work on G43! My ideas so far:

1. change Z home offset (M206/M428) : sadly it is unsupported and may be removed in the future (thank you Snapmaker...)
2. switch to relative mode, move along z axis then switch back to absolute mode: not sure if it would work
3. add the tool offset to any G0/G1 command : unpractical and ugly trick, I want to avoid this as much as possible

Indeed, option 1. or 2. would only lead to tweak tool change GCODE, which is already done by the postprocessor (only an M76 command so far).

Did you find any other solution?

[lukDev]

Hi,

actually, the fix I implemented is exactly your option 3 :D
I know it's a bit of a hack, but it was the only thing I could find that seemed to work. I've also searched quite a bit in forums and people seem to be having trouble making this work without manually resetting the Z origin after every tool change.
I have, however, not yet looked into your option 2. Perhaps this really is a good alternative.

If you give me the rights, I would be happy to submit a PR with my changes. I'll let you be the judge of whether you want such a hack in your repo :)

[clsergent]

Well if you don't mind, I would like to check option 2 this weekend. If it fails I will gladly receive your PR!

[clsergent]

I played with my machine this weekend and I came to the conclusion that the best way to implement TLO (learned this acronym in my journey inside FreeCAD CAM code) for Snapmaker is to use ˋG92 Zx`.

Indeed it doesn't require tweaking anything outside TLO operations. However it requires to know Z position before applying it.

Fortunately it seems that the toolhead always goes to a certain safe position before M6 is executed. I will look into how to get this position and change Z height accordingly.

I hope to implement this quickly as it seams reasonably achievable.

[lukDev]

Sounds cool!

I wrote some code to keep track of the latest Z position – maybe that helps here?

[clsergent]

It's always welcome!

Currently I calculate a safe height (max of every path safe heights), raise the toolhead to it and apply the coordinate change (based on delta between tool lengths).
I opened a discussion (FreeCAD #25637) to discuss implementation details. I´m ready to commit but I want to conduct several tests on an actual machine to test it in real conditions.

If you want I can create a new branch to release this enhancement for tests purposes.

[clsergent]

I have just pushed commit f3e75a6 with a custom TLO handling.

It can be enabled by adding --tlo and --tool_change (both are required).

As discussed earlier, it works by adding two additional GCODE command for each tool change:

• G0 Z{safe height + tool length}
• G92 Z{new height}

I haven't tested it so far on my machine, but it seems to work in CAMotics. Be cautious if you ever want to test it!

[clsergent]

I have just pushed yet another commit (81b2118) because TLO ops happened after HMI pause, while it is actually easier to pause the machine at the right height before swapping tools!

Once again, tested only in CAMotics, so be cautious. I will report when I will be able to test it on my machine.