compareeHub

YOU CAN 3D PRINT A MILLING MACHINE THAT CUTS ALUMINIUM

A milling machine for aluminium whose 3D printed body you fill with concrete, which gives it the weight and stiffness a mill needs.

by Chris Borge

FULL CAD BOM FIRMWARE DOCS

WorkshopOpen-hardware

Built with3D printing

difficulty
●●●●●
time
several weekends
license
CC BY
repo
repo 0 stars

WHAT YOU’LL NEED

Videos
Jump to section

COMPAREE VERDICT

This is an experimental desktop mill, and its designer says so up front: he had never used a mill before he built it. Chris Borge prints a thin plastic shell around a skeleton of steel threaded rod and fills it with concrete, which gives the frame its weight and stiffness. In his video it mills pockets in aluminium plate and cuts out a small aluminium bracket. His cost table puts the whole machine at around 500 Australian dollars, about 300 US dollars, give or take 10 percent; the biggest items are the linear rails and the spindle with its power supply and mount. You print 56 parts on a printer with a bed of at least 220 by 220 mm, and a 36-step written build guide takes you through assembly and the concrete pour. Wiring is not documented yet and the spindle he used overheats, so plan to solve the electronics and the spindle choice yourself.

GOOD TO KNOW

  • —56 STL files on Printables under CC BY, which allows commercial use as long as you credit the creator.
  • —A parts list and a 36-step build guide are linked from Printables as Google Docs.
  • —The creator says the documentation is about 97 percent done; a video on running the wires is still missing.
  • —No firmware or controller configuration is provided; you choose and set up the electronics yourself.
  • —Version 0.9, dated 23 April 2025.
  • —The cost table in the video totals around 500 Australian dollars, about 300 US dollars.

Parts to buy

12 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • M8 threaded rod in several lengthsFind
  • M8 coupling nutsFind
  • Four 10 mm tubes or rods for the counterweight armsFind
  • MGN12 linear railsFind
  • T8 lead screws of 450Find
  • 200 and 150 mm with nutsFind
  • Three NEMA 17 steppers with driversFind
  • SpindleFind
  • 20100 aluminium extrusion for the bedFind
  • Bag of high-strength concreteFind
  • M4 and M8 boltsFind
  • Nuts and heat-set insertsFind

BUILDS OF THE WEEK

Five open-source builds worth your weekend, every week.

Checked like this one: what’s really in the repo, what it costs, how hard it is. One email, unsubscribe anytime.

Can I build this?

Print56 STL files: base, column, covers, axis blocks, motor plates, spindle cover, counterweight arms and small thread-insert pieces. About 2 kg of filament.
BuyM8 threaded rod in several lengths, M8 coupling nuts, a 310 mm length of 40 by 40 mm square steel tube, four 10 mm tubes or rods for the counterweight arms, MGN12 linear rails (two each of 400, 200 and 150 mm, 12 blocks in total), T8 lead screws of 450, 200 and 150 mm with nuts, three NEMA 17 steppers with drivers, a spindle, a 20100 aluminium extrusion for the bed, a bag of high-strength concrete, and M3, M4 and M8 bolts, nuts and heat-set inserts.
Tools3D printer with a bed of at least 220 by 220 mm, spanners and screwdrivers, a soldering iron for heat-set inserts, a bucket to mix the concrete, a palm sander or similar to vibrate it, a drill for the holes in the steel tube, and a square block (he suggests a 1-2-3 block) to square the spindle.
SkillsYou should be comfortable with a long mechanical build and basic electronics. You will align linear rails, set up stepper drivers and a controller without a wiring guide, and learn feeds and speeds for metal. Pouring the concrete is simple but messy.
TimeSeveral weekends: about 2 kg of printing, roughly 640 pieces to assemble by the creator's own count, and a few days for the concrete to set before you continue.
Cost$$ — around 500 Australian dollars, about 300 US dollars, plus or minus 10 percent, from the creator's own cost table. The biggest items are the linear rails (about 140 Australian dollars) and the spindle with power supply and mount (about 140 Australian dollars).
SafetyWear protection around dry concrete powder; the guide says to use PPE around fine powders. When milling, wear eye protection and keep your hands away from the spinning cutter. Keep metal chips away from the electronics: Chris calls running his uncovered temporary electronics near the chips playing with fire.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Build video30:22

'I Printed A Better CNC Mill' by Chris Borge, posted 17 January 2025, about 1.09 million views. The build starts at 1:31, the concrete pour at 6:30, the cutting tests at 13:03 and the cost breakdown at 18:03.

More builds like this

All projects
You can build a soldering station that runs off a USB-C laptop chargerWorkshopYou can build a printer that makes pottery from raw clayWorkshopTurn a laser cutter into a printer that builds from powderWorkshop

Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Download the 56 STL files from Printables (CC BY licence. The page also links the parts list, the build guide and a short build-notes document.)
  2. 2.Read the parts list and the build guide end to end before buying anything (The guide has 36 steps and is written to be used alongside the build section of the video.)
  3. 3.Check your printer and tools (You need a bed of at least 220 by 220 mm, about 2 kg of filament, spanners and screwdrivers, a soldering iron for heat-set inserts, a bucket for the concrete and something to vibrate it, such as a palm sander.)
  4. 4.Plan the electronics and the spindle yourself(There is no wiring guide yet. You need three NEMA 17 steppers with drivers, limit switches and an emergency stop, and the spindle he used overheats, so look at alternatives first.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • This is version 0.9 of an experimental design. Chris writes that it was designed by someone who had never used a mill and that things could go wrong or not work.
  • Wiring is not covered. The build guide ends by saying wiring still needs to be done, and the missing part of the documentation is a video on running the wires.
  • The spindle in the parts list vibrated and overheated in his tests. He calls the printed spindle plate the single most problematic part of the design and plans to mill an aluminium replacement on the machine itself.
  • Getting the linear rails to run smoothly is trial and error. The guide admits his method was to try random adjustments until something worked.
  • Concrete curing warped his parts slightly: the guide adds 1 mm spacers on the Y axis for that reason, and says the X axis cover bowed in his build unless it is glued or bolted in the middle.
  • M8 coupling nuts hold much of the design together, and he notes they are easy to find in Australian hardware stores but not everywhere.

Has it actually cut metal?

Yes. In the video it mills test pockets in an aluminium plate, then drills two 1.6 mm holes for an M2 tap and cuts out a small limit-switch bracket with a 3.175 mm end mill. Chris says these were his first real cuts in metal ever, so he kept the settings conservative.

Why concrete, and not epoxy granite or lead shot?

The build guide answers this directly. Epoxy granite would be better but is expensive, does not flow like concrete, and sets so hot that it would likely warp the printed forms. Lead shot only adds weight, while the concrete is also the structure of the machine, poured into printed walls about 1.5 mm thick.

What spindle should I buy?

The parts list links the spindle Chris used, but he writes that he is not in love with it: in his tests it vibrated and overheated, even when it was not mounted on the machine. He mentions DIY brushless spindles as an option he is considering. This is the part worth researching most before you buy.

How much filament will this take?

About 2 kg, according to the parts list. He printed in cheap PLA and says PETG or another engineering filament would not hurt. The spindle plate is the one part he says should ideally be printed in a more heat-resistant material.

What electronics does it need?

Three NEMA 17 stepper motors with drivers, limit switches and an emergency stop. The parts list suggests an old Ender 3 could provide most of the electronics; his own steppers came from an old 3018 CNC. There is no wiring guide yet.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion

No comments yet — ask the first question.

Chris Borge

Chris Borge is a 3D printing hobbyist from Australia who designs printed machine tools. Before this mill he built a 3D printed lathe filled with concrete, and the concrete method here comes from that project. He first posted the Rock Solid Milling Machine on Printables in March 2025; the current version 0.9 is dated 23 April 2025, and he says the documentation is about 97 percent done, with a video on running the wires still to come.

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
GitHub repo