In the world of 3D printing, smoother motion means better prints.
One of the tools that can dramatically improve your printer’s motion, surface quality, and even print speed is Arc Welder—a powerful G-code optimization plugin.
If you’ve heard the name but don’t know exactly what Arc Welder does, or how to enable it for your own prints, this guide will walk you through everything you need to know.
We’ll explain what Arc Welder is, how it works, its benefits, and how to enable and use it properly to achieve smoother, faster, higher-quality 3D prints.
What Is Arc Welder in 3D Printing?
Arc Welder is a tool that optimizes G-code by converting short linear segments (G1 moves) into arc commands (G2/G3 moves) whenever possible.
In simple terms:
- Normal slicers generate lots of tiny straight lines to approximate curves.
- Arc Welder identifies these segments and replaces them with smooth arc movements.
- This results in simpler, smaller G-code files and smoother printer motion.
Arc Welder was developed by FormerLurker, best known for creating the OctoPrint Arc Welder Plugin.
Why Would You Use Arc Welder?
| Advantage | Description |
|---|---|
| Smoother Surfaces | Arcs eliminate tiny vibration-inducing straight-line moves, improving surface quality. |
| Reduced File Size | Fewer G-code lines = smaller files, faster uploads, and less processing load. |
| Faster Prints | Printers spend less time processing thousands of tiny movements. |
| Reduced Artifacts | Less ringing, ghosting, and small surface imperfections. |
| Efficient Motion Planning | Helps 32-bit boards and firmware process G-code faster and more accurately. |
By simplifying curves into true arcs, your printer can move more fluidly and create better visual and mechanical results.
How G-Code Normally Represents Curves
Without Arc Welder:
- Slicers output hundreds or thousands of short G1 moves to mimic a curve.
- Each tiny move needs to be processed individually.
- Small errors accumulate, causing slight deviations and visual defects.
With Arc Welder:
- Those G1 moves are replaced with a single G2 (clockwise arc) or G3 (counterclockwise arc) command.
- The printer moves in a perfect arc between two points.
Result: Cleaner motion, fewer pauses, better surface quality.
Does Arc Welder Work on Every Printer?
It depends on your firmware.
Your 3D printer firmware must support G2 and G3 arc moves for Arc Welder to work properly.
Supported Firmwares:
| Firmware | Support Status |
|---|---|
| Marlin | Yes (G2/G3 supported; enable ARC_SUPPORT) |
| Klipper | Partial (G2/G3 expanded, but direct arc motion still translated) |
| RepRapFirmware | Yes |
| Smoothieware | Yes |
| OctoPrint | Supported via plugin (Arc Welder Plugin) |
Important:
- Some cheap 8-bit boards may struggle with G2/G3 processing.
- 32-bit boards (SKR, Duet, BTT, etc.) handle arcs much better.
Make sure ARC_SUPPORT is enabled in your Marlin firmware configuration if you’re unsure.
How to Enable Arc Welder for Your Prints
You can use Arc Welder in two main ways:
1. Arc Welder Plugin for OctoPrint
Best for: Automating G-code optimization before printing.
How to Install:
- Open OctoPrint’s web interface.
- Go to Settings > Plugin Manager > Get More.
- Search for Arc Welder.
- Install and reboot OctoPrint.
How It Works:
- When you upload a G-code file, Arc Welder automatically optimizes it before sending it to the printer.
- No changes to your slicer are needed.
- You can configure arc tolerance and minimum segment length settings.
Recommended Settings:
| Setting | Recommended Value |
|---|---|
| Maximum Arc Error | 0.02 mm |
| Minimum Segments | 10 |
| Optimize External Perimeters | Enabled |
These provide a good balance between file size reduction and print accuracy.
2. Arc Welder Standalone Application
Best for: Optimizing G-code manually before printing.
How to Use:
- Download Arc Welder from the Arc Welder GitHub repository.
- Run it as a command-line tool or use the available GUI front-ends.
- Feed your G-code file into Arc Welder.
- Output optimized G-code to upload manually.
This method gives you more control over optimization but requires an extra step in your workflow.
Arc Welder and Slicer Integration
As of now, most slicers like Cura, PrusaSlicer, Bambu Studio, or OrcaSlicer do not natively generate G2/G3 commands.
They still export traditional G1 segmented paths.
Thus, Arc Welder (plugin or standalone) is needed after slicing to optimize the G-code.
Important Things to Know Before Using Arc Welder
1. Slight Changes in Surface Finish
- Arc Welder approximates arcs based on a specified maximum error (e.g., 0.02 mm).
- Tiny deviations may exist but are almost always visually undetectable.
2. Travel Moves Are Not Arc Optimized
- Arc Welder only optimizes extruding moves (i.e., printing moves), not travel moves.
3. No Infill Optimization
- Arc moves mainly affect outer walls and curves.
- Infill, bridges, and straight segments remain mostly unchanged.
4. Print Time Improvements Are Modest
- Reducing G-code file size and smoothing motion helps, but it won’t cut print times in half.
- Expect slightly faster and smoother prints—not massive speed gains.
5. Firmware Settings Matter
- Check if your firmware limits arc segmentation resolution.
- Marlin, for example, has parameters like
MM_PER_ARC_SEGMENTandN_ARC_CORRECTIONthat affect arc quality.
Arc Welder Settings Explained
| Setting | Description | Recommended Value |
|---|---|---|
| Max Arc Error | Maximum deviation allowed between arc and original curve | 0.02 mm |
| Minimum Segments | Minimum linear segments to form an arc | 10–15 |
| Convert External Perimeters | Whether to optimize visible outer layers | Yes (for better looks) |
| Convert Internal Perimeters | Optional (depends on need) | |
| Convert Top/Bottom Layers | Yes | |
| Optimize Bridging | No (bridges need linear moves) |
When Should You NOT Use Arc Welder?
Arc Welder isn’t always the best option:
- If printing purely mechanical parts where dimension accuracy at microscopic levels is critical.
- If your printer firmware struggles with G2/G3 processing (older 8-bit boards).
- If your G-code is already simple (e.g., blocky low-poly models).
For these cases, linear G-code remains safer.
Real-World Benefits of Arc Welder
Users have reported:
- Up to 70% smaller G-code files.
- Noticeable reduction in print head stuttering on curves.
- Smoother external surfaces, especially on cylindrical or organic models.
- Reduced ringing/ghosting artifacts because of consistent motion paths.
Especially for vase mode prints, round objects, helmets, cosplay props, and artistic models, Arc Welder makes a major visual difference.
Step-by-Step: Quick Start Guide to Using Arc Welder with OctoPrint
- Install Arc Welder Plugin.
- Restart OctoPrint.
- Upload a sliced G-code file (normal Cura/PrusaSlicer output).
- Arc Welder automatically optimizes the file.
- Start printing the optimized G-code.
- Enjoy smoother, cleaner surfaces.
No need to change your slicer profiles or manually modify your G-code files if you use the OctoPrint plugin method.
Conclusion
Arc Welder is a powerful, easy-to-use tool that can help any 3D printing enthusiast or professional produce smoother, faster, cleaner prints by converting dense G-code lines into elegant arc commands.
If your printer firmware supports G2/G3 moves and you’re looking to:
- Improve surface quality
- Reduce ringing and stuttering
- Shrink G-code file sizes
- Smooth out organic shapes
Then enabling Arc Welder is a highly recommended upgrade to your 3D printing workflow.
Set it up once through OctoPrint or the standalone tool, and let it quietly improve your prints with no extra effort.