A Fusion 360 CAM post processor for hobby-class 3-axis CNC machines running GRBL, FluidNC, Marlin or RepRapFirmware — including the V1 Engineering MPCNC and LowRider, and similar builds.
Current release: v4.1.2 Beta 3, distributed as the single file MPCNC_v4.1.2_Beta3.cps.
Download the post · What changed · Release notes
This is a modified fork of guffy1234/mpcnc_posts_processor, originally forked from martindb/mpcnc_posts_processor.
- Supported firmware
- Installation
- Which guide is for you
- What this post does
- Notes and limitations
- Resources
Choose your firmware with CNC Firmware, the first setting in group 1 - Job.
| Your controller runs | Choose | Notes |
|---|---|---|
| GRBL 1.1 | Grbl | |
| FluidNC | Grbl | The g-code is GRBL's. Warnings that depend on a setting name both GRBL's and FluidNC's, and tool changes have a FluidNC option of their own |
| Marlin 2.x | Marlin | Read from source at 2.0.9.7 and 2.1.2.5. 2.0.9.7 is the oldest version these documents cover |
| RepRapFirmware (Duet3D) | RepRap | |
| Repetier 1.0.3 | Marlin | Untested; its g-code is Marlin's |
The post is a single file. Download MPCNC_v4.1.2_Beta3.cps from the
latest release, then:
- In Fusion, choose Manage → Post Library.
- Select My posts → Local in the sidebar.
- If an older copy is installed, select it and delete it with the trash-can icon. Every release has a different filename, so an old copy would sit beside the new one rather than being replaced, and the two are hard to tell apart in the picker.
- Use the Import icon to import
MPCNC_v4.1.2_Beta3.cps. - Close the dialog.
- When posting, choose Choose from library… and select this post.
- Review the properties — start with the guide for your kind of job, below.
Upgrading? Read the changelog entry for each release you are skipping. It says which settings, if any, reset to their defaults.
| Your job | Read this |
|---|---|
| One part, one tool, zeroed by hand. You jog to your corner, post, and cut. | Hobbyist guide — eight settings matter; the rest can stay as they ship |
| Several operations, more than one tool, or several parts on their own fixtures. | Pro guide — work offsets, the machine travel height, tool-change hand-over, the validation guards |
| Looking up one setting. | Property reference — all 57, in dialog order |
The post turns a Fusion CAM program into g-code for a hobby CNC. One idea shapes every other feature:
These machines work relative to the part, not to the machine. Most have no reliable machine-Z reference — no tool setter, no tool-length register, often no Z endstop, sometimes no endstops at all. So you establish a work zero, by jogging to it or probing a touch plate, and everything the post emits — cuts, retracts, traverses between parts — is measured from it. Where a machine can home, homing buys repeatability and one job-wide travel height, never the everyday Z reference.
Two consequences explain most of the dialog:
- The post selects a work offset but can never read one back. It always knows which register is active, because it selects it at job start. It never knows where that register points, because the contents live in the controller. So any mode that uses a stored origin trusts it, and the shipped defaults set an origin rather than trust one.
- The post changes no tool, on any firmware. A measured tool change needs a probe, a subtraction and a register to hold the result, and the post has none of the three. At a change it arrives safely, hands over to you or your sender, and resumes safely.
A one-part, one-tool job needs almost no setup: jog to your zero, accept the defaults, post, run. A larger job — many operations, several tools, several parts on separate fixtures — has the extra structure available and checked, without complicating the simple case.
Also included: 3-axis milling and jet (laser / plasma / waterjet) operations; drilling cycles expanded into plain moves; arcs; three laser power levels; two configurable coolant channels; four comment levels with every setting dumped at the head of the file; optional line numbers; include files for your own g-code.
Units: the post writes g-code in the units your Setup uses (mm or inch), but every dimension in the dialog is entered in millimetres. The head of each posted file echoes the values the post resolved, in output units, so you can check them before the machine moves.
What the post refuses
- 4- and 5-axis toolpaths. Only 3-axis is supported.
- Cutter compensation other than In computer. Control-side
G41/G42is a posting error. - A Setup built on a tilted face, with the tilt named. The tool only moves straight down, so a Setup whose Z is not the machine's Z would cut in the wrong plane.
- CAM probing operations. Fusion's WCS probing asks the controller to measure and store an offset, which none of these controllers can do. The post's own Z touch-off is unaffected.
How some things come out
- Arcs are on the XY plane on Marlin and RepRap, and on all planes on GRBL. Full circles post as two arcs; helical moves are broken into straight lines.
- Drilling cycles (drill, peck, bore, tap) are expanded into plain
G0/G1/G4moves. No supported firmware has canned cycles — and on RepRap those numbers mean bed probing instead. - Manual NC pass-through commands are emitted exactly as written.
M1(optional stop) is emitted asM0. No supported firmware givesM1a usable meaning: GRBL ignores it, RepRap treats it as end of job, and only Marlin waits.- Travel Speed X/Y and Travel Speed Z do nothing on GRBL or FluidNC. Those controllers take rapid speed from their own axis maximums, not from the g-code. Marlin and RepRap obey both.
- The end of the program differs by firmware. GRBL ends with
M30. Marlin and RepRap first getM84 S60, restoring the stepper idle timeout the post disables during the job. RepRap then getsM2, which runs yourstop.g. Marlin gets no end code: it has none, and itsM30means "delete SD file". - No
%line is written on any firmware — stock GRBL 1.1 answers it witherror:1. - GRBL laser jobs usually need laser mode turned on
(
$32=1).
How the claims here are checked
Firmware behaviour in these documents is read from each firmware's own source and changelog, with the file and version cited. This project has no controller to test against, so nothing here is proved by running it on a machine. The post itself is run, by an automated suite against Autodesk's own post engine — see what is verified, and what is not.
This is a beta. Review your g-code before you cut.