M3-CRETE Frame Assembly
These development notes describe the reference frame sequence in plain language for qualified technical teams. They do not establish structural adequacy, load capacity, accuracy, or assembly safety and do not replace engineering review, measured inspection, guarding, or an approved work plan.
The aluminum beams are long and heavy, and cut ends can be sharp. Wear eye protection, work with a helper for the big pieces, and watch your fingers at every joint (pinch points). Use adhesive in a ventilated space.
What you need
Tools:
- A set of hex (Allen) keys.
- A tape measure and a big square (framing or machinist square).
- A spirit level.
- A rubber mallet (to seat parts without marring them).
- Structural adhesive (for the X-beam splice) and blue threadlocker (for motor screws).
Parts (all from the M3-CRETE Bill of Materials — export the list and check off each item first):
- 4080 C-beam aluminum lengths (the thick main beams), all cut to the same length.
- 2040 V-slot lengths for cross-bracing.
- Corner plates (5-screw T-plates or L-plates), T-nuts, and M5 screws.
- The X-beam splice kit (an internal slot-link connector) plus three short V-slot bars.
- Polycarbonate V-wheels, eccentric spacers, and gantry plates.
- GT2 belts (a wider one for Y, a narrower one for X), idlers, and the Z hub disks.
- The seven motion NEMA23 motors and the 3D-printed brackets / motor mounts.
Words to know
- Extrusion
- An aluminum beam with slots along its sides. "4080" and "2040" are sizes.
- C-beam
- An extrusion shaped like the letter C. The open channel hides and protects the belt.
- T-nut
- A small nut that slides into the beam's slot so you can bolt things on anywhere.
- V-wheel
- A wheel with a V-shaped groove that rolls along the V-edge of a beam.
- Eccentric spacer
- A spacer with an off-center hole. Turning it pushes a wheel tighter or looser against the beam.
- Gantry
- The bridge that carries the print head and slides along the rails.
- Z-post
- An upright beam. The gantry moves up and down these.
- Plumb / square / tram
- Plumb = perfectly upright. Square = corners are true 90°. Tram = everything lined up flat and even.
- GT2 belt
- A toothed rubber belt that the motors pull to move the axes.
- Hub disk / idler
- Pulleys the belt wraps around to change direction (used on the Z-axis).
How the frame is designed (read this first)
A few design choices make M3-CRETE easier to build. Knowing them up front prevents mistakes:
- One length of beam. Every main beam is cut to the same canonical length — no custom cuts. Check the BOM for the exact number.
- Open channels face inward. The C-beams point their open side toward the center of the printer, so the belts run inside, away from concrete spray.
- The long X-beam is two beams spliced in the middle. The join uses an internal connector that sits below the wheel path, plus bonded V-slot bars inside the channel. Nothing sticks out to block the wheels.
- Four Z motors, no lead screws. Each corner has its own belt-driven Z motor, so the gantry can level itself in software later.
- No leveling feet. Leveling is done by measurement at the print surface, not by adjustable feet.
Build it
Lay out and check every part
Open the BOM and lay the parts out by type. Confirm every 4080 C-beam is the same length and the count matches. Finding a wrong or missing part now is much easier than after assembly.
Build the base rectangle
Join the bottom beams into a rectangle using the 5-screw corner plates and T-nuts. Keep the C-channel openings facing inward. Tighten the screws only snug for now — we square it before final tightening.
Square the base
Measure the two diagonals of the rectangle (corner to opposite corner). Gently tap with the mallet until both diagonals are equal — that means the corners are true 90°. Now tighten all corner screws firmly.
If the base is not square, every layer the printer makes will be skewed. Five extra minutes here saves hours later.
Stand the Z-posts
Bolt an upright Z-post at each corner of the base using corner plates. Use the level to make each post plumb (perfectly upright) in both directions before tightening.
Add the top brace
Connect the tops of the posts with the top cross-brace. This locks the posts square and also holds the Z motors later. Re-check that the posts are still plumb after tightening.
Make the X-beam (the splice)
Join the two X-beam segments end to end with the internal slot-link connector. Then slide the three short V-slot bars inside the C-channel, staggered across the join, and bond them with structural adhesive — the middle bar should sit equally over the join. Keep everything straight, let the adhesive fully cure, then run your finger across the join: it should feel smooth, with no step the wheels would bump over.
Fit the V-wheels to the gantry plates
Attach the V-wheels to the gantry plates, using the eccentric spacers on one row. Set the wheels so they sit firmly in the beam's V-edge — snug enough that there is no wobble, loose enough that the wheel still spins freely. You adjust this by turning the eccentric spacers.
Nothing should stick out past the gantry faces — all bracing is inside the channel. An outside bracket would block the wheels.
Mount the gantry and check the roll
Place the gantry onto its rails. Roll it from one end to the other by hand. It should glide smoothly with no rocking and no tight spots. Fine-tune the eccentric spacers until the motion is even along the whole length.
Mount the motors
Attach the seven NEMA23 motors with the 3D-printed mounts. The mounting holes are pass-through, so use M5 screws with M5 nuts and a drop of blue threadlocker. The four Z motors sit on the top brace (body up, shaft pointing down) with a hub disk underneath to guide the belt.
Route and lightly tension the belts
Run the GT2 belts inside the C-channels — the wider belt on Y, the narrower one on X. For each Z-axis, the belt goes from the hub disk, over the brace, down the post, around an idler at the bottom, and back up to the carriage. Anchor the belt ends and take up the slack using the motor-mount slots. Leave final tensioning for the validation step; for now, just remove the slack.
Final check
Re-measure the base diagonals (still equal?), confirm the posts are still plumb, and roll the gantry through its full travel once more. The frame should feel solid with no twist. You are done.
Quick checklist
Print this page and tick the boxes as you go.
- All parts laid out and matched to the BOM.
- Base rectangle built, C-channels facing inward.
- Base squared — both diagonals equal — and tightened.
- Four Z-posts plumb and bolted.
- Top brace fitted; posts still plumb.
- X-beam spliced, bonded, cured, and smooth across the join.
- V-wheels fitted; gantry rolls smoothly with no wobble.
- Seven motors mounted (M5 + nut + threadlocker); Z hub disks in place.
- Belts routed inside the channels and slack removed.
- Final square + plumb + full-travel roll re-checked.
If you get stuck
- Check the part against the interactive BOM and the CAD on GitHub.
- Ask on the M3-CRETE Discussions page — build photos help a lot.
Part 2 — Wiring. Mount the power supply and control board and connect the motors. (Coming soon.) After that comes Part 3 — Software.
M3-CRETE is an experimental open-hardware reference, not a finished certified appliance or construction machine. It is intended for qualified technical users, R&D labs, supervised institutional programs, and experienced builders. Hardware is published under CERN-OHL-W-2.0; this guide is CC BY 4.0.