Grbl HotWire for CNC Foam Cutters
This guide walks you through exactly how to set up the GRBL HotWire system I’ve developed since 2020. It’s designed for hobbyists, not engineers, and it works with several affordable controller boards.
Whether you’re building your first cutter or upgrading an old one, follow the steps below and you’ll be cutting accurate wing cores and fuselage shapes in no time.
The latest release, issued in December 2025, includes every feature from the previous versions along with a range of new enhancements and full FluidNC firmware support.
Software Details
This Windows software was originally based on a program called GRBL Panel created in 2014. Daniel Rasico modified it to work with his foam cutter using GRBL 0.9. Since 2020, I have extensively developed it to work with GRBL 1.1 on Arduino Mega 2560 microcontrollers, as well as with grblHAL and FluidNC.
Here’s a summary of the new features, which are also explained in the supporting videos linked at the end of the post.
Runtime Controls
- Override settings while the job is running
- Override feed rate during run
- Restore GRBL settings from Export
Controllers & Firmware
- Supports FluidNC (ESP32)
- Supports grblHAL (32-bit)
- SKR Pico (RP2040 + TMC2209) — quiet & reliable
- Still supports Arduino Mega 2560
- FluidNC config via
config.yaml
Hardware & Motion
- Axes changed to XYZA
- SKR Pico drivers initialised on startup
- Wire paths scaled relative to each other (Dec 2025)
- Hotwire control shows current %
Detailed Electronics Build Guides
Each supported board now has its step-by-step build guide. Use the links below to select your chosen microcontroller. The BTT SKR Pico is a 32-bit microcontroller.
- Electronics Build Guide Arduino Mega 2560 RAMPS 1.4
- Electronics Build Guide MKS Gen L V1 and V2
- Electronics Build Guide BTT SKR Pico
Firmware and Software Download
GRBL Hot Wire Firmware and Software V2.51 1.77 MB 8571 downloads
This is the latest software and firmware for the CNC Foam Cutter version v2.51,…Axes Letters now XYZA
In the previous version (5.13) of the software/firmware, the axes letters were XYZU, which originated from the original grbl firmware. However, to simplify the implementation of further developments on grblHAL firmware and 32-bit controller boards, I decided to switch to the more conventional XYZA axes letters.
G-code generators can configure their axes for different axes letters. If you’ve got some g-code that you want to convert to the new axis letters, use the Windows utility below to convert to the new format.
Change Axes Letter from XYZU to XYZA 617.93 KB 1497 downloads
This small Windows utility changes the axis letters from XYZU to XYZA. This will…User Requested Features
The two most requested features since the release of the original software have been:-
- Adjust the current to the wire while the job is running
- Adjust the feed rate while the job is running
In the older software version, the hot wire current couldn’t be adjusted once a job had started. Now, you can modify the current during a job by increasing or decreasing it in increments of 10% or 1% using the Override Current Settings. The slider can’t be adjusted when the job is running and is only used to set the initial current setting. The video demonstrates this new feature, where I initially set the current too high, then adjusted it using the override buttons to achieve a clean cut without the wire dragging.
The feed rate can be easily adjusted for g-code that doesn’t contain the G93 instruction. DevCad software, by default, utilises G93. This is very useful for projects where the root and tip are different sizes. Other g-code generators use G94. This is a fixed feed rate. The new feature allows you to adjust the feed rate while the job is in progress.
Upgrading from version 5.13
To upgrade your setup, install the latest firmware and software updates. You can download both, as they’re included in the software package, from this link
GRBL Hot Wire Firmware and Software V2.51 1.77 MB 8571 downloads
This is the latest software and firmware for the CNC Foam Cutter version v2.51,…- Back up your current settings with the export option
- Install the new firmware using Xloader from the folder that matches your board. Xloader is for Arduino Mega 2560 boards, e.g. RAMPS, MKS Gen L V1.0 and V2 ( See the next section for the SKR Pico Board, this uses a different method.)
- Install the new software
- Restore your settings
- Disconnect and unplug the board.
- Reconnect and check that your settings are the same as the export file.
- Check your axis direction and calibration. These should not have changed, but it’s worth checking.
Videos to accompany this new firmware and software
Any Questions?
I hope this works well for you. If you have questions, drop me a line through the contact page. Please check the website FAQ and the troubleshooting article, as chances are I’ve already answered your question.
Happy foam cutting
