In Part 1 of the CNC Build Series:
- The Mission: Defining what you want to cut (Wood vs. Aluminum).
- The Physics: Why rigidity is the only metric that matters.
- Frame Material: Aluminum Extrusion vs. Steel vs. Wood.
- The Gantry: Fixed Gantry vs. Moving Gantry.
- The Budget: The "Hidden" costs of building your own.
3D Printers add material. CNC Routers subtract it. This fundamental difference means a 3D printer can be made of plastic, but a CNC router must be built like a tank.
Building your own CNC machine is the ultimate maker project. It gives you the power to fabricate parts locally with incredible precision. But if you design it wrong, you will end up with a wobbly machine that breaks bits and ruins material.
Don't Design Alone
Designing a machine requires physics and geometry. Are you looking for a second set of eyes on your CAD drawings? Search for the "Mechanical Engineering" or "Fusion 360" tags on Great Meets to find a mentor who can review your design.
Step 1: Define "The Mission"
There is no "One Machine to Rule Them All." You must decide what you want to cut before you buy a single screw. This dictates every other decision.
The Woodworker
Goal: Cutting Plywood, MDF, and Soft Plastics.
Requirement: Low rigidity is acceptable. You can use belt drives, round linear rods, and NEMA 17 motors. You can even build the frame out of MDF.
The Fabricator
Goal: Cutting Aluminum, Brass, and Carbon Fiber.
Requirement: Extreme rigidity is mandatory. You need Ball Screws, Linear Rails (Hiwin), and NEMA 23 or 34 motors. Any flex in the frame will cause "chatter" and break your cutter.
Step 2: The Structure (The Frame)
Your frame is the skeleton. If the skeleton flexes, the machine is useless. Here are the three most common materials for DIY builds.
1. Aluminum Extrusion (T-Slot / 8020)
The gold standard for DIY. It is like "Industrial LEGOs."
- Pros: Easy to assemble, perfectly straight, easy to mount accessories to.
- Cons: Expensive.
- Tip: For a machine spanning 1000mm, do not use 2020 profile. Use at least 4080 or C-Beam heavy extrusion to prevent sagging.
2. Steel (Welded Tube)
For the serious fabricator.
- Pros: Cheap, incredibly heavy (which absorbs vibration), and rigid.
- Cons: You need a welder and fabrication skills. Steel requires painting to prevent rust.
3. Printed/Wood (MPCNC)
For the budget hobbyist.
- Pros: Extremely cheap. Most parts can be 3D printed or cut on a table saw.
- Cons: Not rigid. Changes in humidity can warp a wood frame. Strictly for light wood carving or drawing.
Need Welding Help?
Want to build a steel frame but don't know how to weld? Search for a "Fabricator" or "Welder" on Great Meets. Many local makers have MIG welders in their garage and are happy to help a neighbor.
Step 3: Gantry Design
The Gantry is the bridge that moves back and forth over your table. There are two main designs:
| Type |
Description |
Best For |
| Moving Gantry |
The table stays still, and the bridge moves over it. Allows for a large cutting area in a small footprint. |
Routers, Plasma Cutters, Lasers. (Most common DIY). |
| Fixed Gantry (Moving Table) |
The bridge is bolted down, and the table slides underneath. Much more rigid, but takes up 2x the floor space. |
High-precision Aluminum Mills. |
Step 4: The Interface Plates
You need plates to connect your motors to your frame and to hold your spindle. This is where the "Chicken and Egg" problem happens: You need a CNC to make the plates to build a CNC.
Options:
- Aluminum Plate (1/4" to 1/2"): The best option. If you can't cut it, buy pre-cut plates or find a local maker.
- 3D Printed (PETG/ASA): Okay for NEMA 17/Wood builds, but plastic will flex under the torque of larger motors.
- Plywood/Phenolic: A good temporary solution to get the machine running, then use the machine to cut its own aluminum upgrades!
Conclusion
Do not underestimate rigidity. A heavy, stiff machine will cut smoothly and quietly. A light, flimsy machine will scream, vibrate, and break tools. Choose your frame material based on your "Mission."
Coming Up in Part 2: We dive into motion. We will fight the battle of Linear Rails vs. Rods and Ball Screws vs. Lead Screws.
Find Parts Locally
Shipping aluminum extrusion is expensive. Great Meets connects you with local builders. Someone nearby might have leftover rails, motors, or extrusion from their last build sitting in their garage. Search for "CNC" and see who is nearby.