A part that looks right on screen may not print well. Most problems come from the same causes. Here are the most common ones.

1. Designing as if for machining or injection moulding

3D printing allows shapes that cannot be made any other way, but it has its own rules. A part designed for milling can often be printed, but it may not be optimal. The reverse is also true: a shape suited to printing may not be possible to mill. When designing, it helps to know which technology will be used to make the part.

2. Walls that are too thin and details that are too small

Every technology has a smallest detail it can create reliably. Thin walls can warp during printing or be fragile in use. Make sure the walls are thick enough for the load the part will see.

3. Overhangs without thinking about supports

Sections that hang in mid-air need supports. Supports leave marks on the surface and are sometimes hard to remove from internal cavities. You can often avoid them by changing the shape, for example by using a slope instead of a horizontal overhang.

4. Joints without clearance

If two printed parts are meant to fit together, you need to allow for clearance. Printing is never perfectly accurate, and plastics shrink as they are printed. Parts designed to fit “exactly” often cannot be assembled. We set a suitable clearance according to the technology and material, and for functional assemblies it is worth checking it with a test piece.

5. Forgetting orientation and strength

With FDM, the layers are the weakest point. A part loaded in tension across the layers breaks sooner than one loaded along them. When designing, it is therefore important to know how the part will sit during printing and in use.

6. Wrong technology or material

A functional part made of a brittle material, or an outdoor part made of a plastic that cannot withstand UV radiation, will fail quickly. It helps to think through the conditions of use in advance.

How to avoid these mistakes

The best approach is to get advice before the design is finished. We review the model, point out problem areas and suggest changes. For functional parts, we also recommend making a test piece.

Tip: With a new product, plan for several prototype versions. Each one brings new knowledge, and it is cheaper to fix a mistake on a prototype than on a production run.

Related:How to prepare your files →