“Rapids” means rapid movements which are typically non-cutting movements to reposition the router. Because MPCNC uses a leadscrew for Z and belts for the X and Y, the maximum feedrate for the Z axis is significantly smaller than for X and Y. That is why the Ryan indicates that the Rapids need to be broken out separately. You could limit X and Y feedrates to the same limit as Z to get around the problem, but your cutting will take longer.
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Got it, like typically G00 (fast travel) and G01 (slower extrusion travel) in 3D printing.
Makes sense! How would that be defined in gcode?
G00 X75.2682 Y15.5365 Z5.0000 F2100
G00 X75.2682 Y15.5365 Z0.5000 F500 ;like this?
G01 X75.2682 Y15.5365 Z-1.0000 F210 S20000 ;and this?
G01 X77.4366 Y15.4952 Z-1.0000 F720
G01 X79.6043 Y15.4295 Z-1.0000 F720
G01 X81.7712 Y15.3396 Z-1.0000 F720
G01 X83.9370 Y15.2253 Z-1.0000 F720
This is an excerpt from @Ryan’s crown gcode. I had no other example that specifically works with the mpcnc.
I know that F refers to the feedrate, but what is S?
Estlcam uses it to define spindle speed. Likely that’s a default speed that was left behind when the pen tool that he used was defined. If you don’t give your machine direct control of the spindle, it doesn’t do anything in Marlin. (Well, it probably sets a pin somewhere, but if it’s not connected, it doesn’t matter.)
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I heard back from GRZ Software, the creators of MeshCAM.
Concerning Marlin compatibility, they wrote that I could try the Grbl post-processor, since it “outputs very basic gcode”.
Generally, they recommend to use Grbl instead, because “people have a hard time using ‘normal’ gcode meant for CNC machines with Marlin”. Whatever that means?
There was no talk of adapting a post-processor to my needs or similar.
Concering the 2D contour toolpath and 2D pocket toolpath being only available to pro version users, I seem to have been right. This only concerns gcode generation from two-dimensional CAD files. If you load a three-dimensional object with pockets and holes everything should work fine! They recommend to simply do a “roughing and unified finshing toolpath”.
What do you guys think of running the mpcnc (with dual endstops) with Grbl? Is this even possible?
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There are certainly GRBL releases that support things like the dual endstops, though we’ll be limited in how much support we can give you for it here.
Honestly, I’d stick with the V1 supported Marlin release, until or unless you are familiar enough with the software chain and firmware to make your own modifications. I know that there are people here using Fusion360 for CAM and exporting that to MPCNC machines. Less certain about MeshCAM, but it doesn’t sound like they want to “go there.” I’d bet on it not being too difficult to convert though.
If it absolutely has to be GRBL, I’d probably look at something like Bart Dring’s 6-pack controller which can manage 6 motors (2x X, 2x Y, 1x Z) though you’ll need a couple of the 4x input modules. 4x endstops + touch plate, so minimum 5 inputs) and maybe the relay module for spindle control.
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You could hedge your bets and go with a Rambo board instead of an SKR Pro. According to this topic, there is a GRBL version that runs on a Rambo board and supports dual endstops. So you could start with Marlin, and if you needed to go to GRBL, you would have that option without buying a new board.
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This, is a popular mantra when you talk to experienced Cnc folks about getting in to it. I heard it a few times myself… still curiosity prevailed and I gave both a try. I stuck with grbl, but I bet more than half the folks who try the same would not. It is what it is… folks made decisions a while back about supporting Marlin vs grbl, and Marlin was chosen since most folks entering Cnc here have printer experience… not because Marlin is better at Cnc, grbl is hands down. In fact I think the mpcnc project alone is responsible for making Marlin jump through Cnc hoops (the major proportion of the new Cnc related Marlin changes of late are there due to Ryan and the gang doing their thing).
Edit… bottom line it certainly would not be a dumb idea to get a board supported by Ryan… they can all run grbl if you wanted to try that sometime… but if you start off with a non supported board, even if it is the best for grbl… you could make your baptism into Cnc more painful that it is already going to be.
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Yeah, that’s a big fear. I for instance have some C++ and general coding experience, as well as advanced CAD and 3D modelling skills, however I’m pretty inexperienced when it comes to homebrew CNC stuff and electronics. I’ve done some small Arduino and ESP32 projects but that’s it. I’ve done lots of 3D printing over the last 5 or 6 years though.
Thanks for another reply, Dan! Especially for recommending the 6-pack controller.
True, thanks. Although the Rambo boards seem to be disliked for some reason.
I’m curious, why did you stick with it and why do you think most people would not?
Yeah, seems like sound advice! Thanks for your input.
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From my reading of this this forum, I have a different perception. The Rambo is viewed at the tried and true, very robust workhorse of a board, vs the SKR Pro as the flashy newcomer. I’ve see people on this forum make hardware mistakes with the Rambo that would fry other boards, and it comes out unscathed. The SKR Pro with its 32-bit processor and hardware math support edges out the Rambo on fast(er) laser burning, but I’ve never seen any indication that that the SKR Pro is better at CNC Router speeds.
You are now choosing a board and an ecosystem because of a piece of software you have not tried, and honestly has not shown up around here very much at all over the years. What about kiri:moto?
I hope this doesn’t come off poorly but most CAM software packages have a guide to making your own post processor and allow you to make changes. If they do not have that or basic Marlin PP then you might want to reconsider. I have written PP’s for CAM packages I have never even used. I am a amateur programmer at best but they are simple they only involve outputting numbers in a specific order. Marlin might not be the absolute best Firmware for CNC but it has to be the second most common in the non-pro space (it might even be the most common simply because of the number of boards supported).
Once the firmware is chosen and the board is picked, getting it working is a bit of a hurdle. After that though, you honestly never actually need to change it (unless you want some fancy new feature in the firmware) and the PP is behind the scenes. Every job you will interact with the CAM package so that is the most important choice. Most any board will work and will quickly become an after thought to your actual projects.
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I haven’t made my final choice yet, but understand that as a macOS user I came across MeshCAM and it seemed like a sound program and very beginner friendly, from what I’ve seen in videos, even more than the Windows-only EstlCAM, which I’ve also taken a look at. I’ve even tried to virtualize it with Crossover and Wine, but both attempts didn’t work.
What about it? Cura is my favorite slicer for 3D printing.
You’re right, but Fusion360 seems to be my only alternative and I’ve yet to test if their TurboCNC V3 post-processor does work with Marlin indeed. I’m currently busy building the table that the MPCNC will sit on, which might be more work than actually assembling the machine. 
I’m also an amateur programmer. 
Thanks.
Fully understood. We are all just trying to point out you are going down a path few here, if any have taken. If you choose that path, we won’t be the best place to get help.
It has CAM functionality.
It is not.
We have two fully functioning Fusion post processors available fully tested, linked on the milling basics page. I am not sure if that Turbo is one of them.
This was to point out I find it odd that they will not expand their PP’s to include a Marlin version, it is not complicated from my past experiences writing and editing a few of them.
The Guffy’s/Don’s post processor for Fusion 360 I pointed you to above should work on the Mac. Custom post processors for Fusion 360 are installed as plain text files, so I assume they are either dynamically compiled, or the code is interpreted. Either should work for the Mac environment.
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I also understand that. It’s not like I’d hold you guys accountable, if I stray too far from the side walk.
I maybe phrased that weirdly. I meant the MeshCAM TurboCNC post-processor that a user here and somewhere else on the web pointed out to work with Marlin.
Really what other options do you know of that run natively on macOS?
I didn’t ask for that and it wasn’t offered. I merely asked if any of the existing post-processors work with Marlin, and the answer was maybe Grbl - which I doubt - and that I should consider using Grbl board instead. 
About post-processors in general, they are basically only doing some structuring and text formatting, except maybe the Fusion one, which also seems to regulate z-axis speed, right?
The CAM software generates strategic toolpaths, which are basically polylines (lists of 3D points), and the post-processor takes that information and converts it to the right formatting?
Yes, I can confirm that it does.
I really appreciate you guys’ patience and willingness to discuss all of this!
Kiri:moto with Onshape should be a wonderful pair that I am fairly certain a few users around here run. I was pretty sure Esltcam worked fine under wine but I have no experience with that, if it didn’t work for you that is a bummer, but I think a few people around here could help with that.
Cam outputs raw coordinates and speed. Your firmware (grbl or marlin) will make sure not to exceed any axes max speed. The post processor is just a translator. In the most basic form it adds a move command before the coordinates (eg G0, G01, G28 vs $H). Some machines require one axis commands per line, others can handle multiple. Some machines want line numbers, some choke on them, how comments are handled, etc. Simple stuff like that, no math or anything that I can think of.
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Kiri:moto does cam for milling slicing for printers and I think some laser work too.
FreeCAD has a CAM package.
bCNC?
Fusion 360
Estlcam (I use it in linux under wine, but some mac users preferred to just run it in a VM. It is lightweight, mostly).
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Why “Kiri:moto with Onshape”? I don’t really need another CAD app. I’m satisfied with Rhino. I’d rather have a stand-alone CAM solution. Also Onshape seems to be basically the same as Fusion360, which already is my last resort.
At second glance, Kiri:moto seems interesting. I’ve explored it a little, however it doesn’t seem to have a Marlin post-processor by default either? It’s very customizable though.
I installed all the required dependencies into the wine bottle, like .NET and what not. It still didn’t work. Some other users have reported this, and only the 32-bit version seems work under Linux.
It would be ridiculous for me to virtualize a Linux distro, only to sub-virtualise EstlCam.
I’ve seen the laser option, but it doesn’t seem to have a Marlin post-processor either?
Isn’t that Grbl only? I believe to have read that somewhere and think that’s what’s used as a CAM sollution inside FreeCAD.
Too many hoops to jump through in my opinion.
Btw, there really is no reason why something like EstlCam couldn’t be ported to macOS and Linux. It seems to be written in C# (.NET) and that’s largely cross-platform nowadays.
Sorry I was offering onshape as a bonus package I knew to work on MAC. If you prefer Rhino, kiri:moto standalone is fine. OnShape & Kiri:Moto - Marlin unsupported: GCODE conversion or firmware flash? - #39 by stewart The creator of it helped work through a few issues.
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No need to apologize! Thanks for the link.
Curious why f360 is your last resort? I initially was scared of it not being fos abs cloud based, but it has fulfilled a lot of my obscure needs. There are not as many folks here using it, but there are plenty of resources to get you going with it.