A First Functional Project

This project is the last big step of the FDM Beginner Path: a part that has to fit something real and carry a load. It uses only skills from earlier lessons. The example is a wall hook or a small L bracket you design yourself, because both are simple shapes with one obvious way to fail.

1. Write down the job

Before you open any software, answer four questions on paper:

• What does it hold? A set of keys, a cable, a shelf corner. Note which direction the load pulls.
• What does it attach to? Screws, a rail, the edge of a desk. This sets the holes or the clip shape.
• Where will it live? Indoors at room temperature, near a window, in a car. This picks the material.
• What happens if it breaks? If the honest answer is "someone gets hurt or something expensive falls", this is not a first project. Pick something lower-stakes.

2. Measure

Measure what the part meets: screw shank and head diameter, the thickness of the shelf or desk edge, the spacing between holes. Use calipers if you have them, and write every measurement down with its unit. Your part is only as good as these numbers.

3. Design for the printer

Any CAD program works (see CAD, Slicing and the Path to a Print). Keep the shape plain and follow the printer's rules:

• A flat face to sit on the bed. A bracket or hook drawn as an extruded profile has two large flat sides. One of them becomes the bottom.
• Walls in whole perimeters. Prusa notes that a wall thinner than one perimeter cannot be printed, and that one perimeter from a 0.4 mm nozzle is about 0.45 mm, two about 0.9 mm Rule of thumb. Make thin sections a few perimeters thick rather than an awkward in-between value. See Walls and Perimeters.
• Clearance in every hole and slot. Prusa warns that parts drawn with zero tolerance usually will not fit together, and suggests finding values with test prints. Dimensional Accuracy shows how to measure how your printer reproduces holes.
• Chamfers on the bottom edges, not fillets. Prusa points out that a rounded edge on the bed face becomes a steep overhang that prints poorly, while a chamfer prints cleanly.
• Overhangs within reach. Prusa gives 45 to 60 degrees as the range most printers handle without support, depending on nozzle and settings Rule of thumb. A hook drawn flat has no overhangs at all, which is one reason it makes a good first project.

4. Orient for the load

This step is easy to skip, and it decides whether a hook holds. Prusa explains that FDM prints are weaker between layers than along them, so a structural part should be oriented so the load does not pull the layers apart.

Picture a J-shaped hook. Stood upright, every layer is a thin horizontal slice through the curve, and the weight on the hook tries to peel those slices apart right at the bend. Laid flat on its side, each layer contains the whole J outline, so the load runs along continuous lines of plastic. Lay it flat. The same reasoning applies to an L bracket: print it on its side so the corner is drawn in every layer. Print Orientation covers the general case.

5. Pick the material

For an indoor hook at room temperature, PLA is fine. Prusa says PLA softens and deforms above about 60 °C Rule of thumb and is brittle on impact, so it is a poor choice for a car, a sunny window or anything that gets knocked hard. For warmer places or parts that need to flex a little, read PETG; for outdoor sun, read ABS and ASA. Details on PLA are in PLA and PLA Blends.

6. Slice

Follow the same routine as your first print (Prusa's first-print guide walks through it): import, place the flat face on the bed, choose your printer, filament and a standard quality profile, then check supports and infill.

• Perimeters first. Prusa says a model's strength is mostly set by the number of perimeters, not the infill. For a load-bearing hook, add a perimeter or two before you raise infill.
• Infill. Prusa's first-print guide suggests around 15 percent works well generally Starting point. Read Infill Fundamentals before going higher.
• Preview every layer. Scroll through the sliced preview and look for anything printed in mid-air, and check that the thin parts got whole perimeters.

7. Print a test piece of the critical feature

If the part has a screw hole or a clip, cut that section out in the slicer or in CAD and print just that: a small tab with the hole, or a short length of the clip. It takes minutes instead of an hour and tells you whether the screw passes and the head seats. Adjust the hole size in CAD, reprint the test, and only then print the full part.

8. Print, measure, load it

1. Print the full part and let it cool on the bed.
2. Measure the critical dimensions and compare them with your notes.
3. Mount it and load it gradually, a little more than it will carry in use, and watch the bend and the screw holes.
4. If it breaks, look at where. A clean break along a layer line means orientation or layer bonding (Layers Splitting or Cracking Apart). A bend or crack across solid plastic means the section is too thin: thicken it in CAD.

9. Write it down

Save the CAD file, the slicer project and a note with the material, perimeters, infill and the hole clearance that worked. That clearance is the most useful number you will get from this project, because it carries over to your next part on the same printer and material. When you are ready for more, Printing Replacement Parts uses the same steps on a part you cannot redesign freely.