Designing for 3D printing: the general rules

This page is general knowledge about printing on a filament printer (FDM), the kind most makers own. It is not specific to ShapeDis, and the right numbers vary with your printer, material and settings. Where ShapeDis checks one of these rules, the text says so. Where it does not, it says that too.

Orientation decides most things

A printed part is built in layers, so it is strongest along the layers and weakest between them. Print a bracket so the force pulls along the layers, not across them. Orientation also decides which faces are rough from supports and which sit smooth on the bed. ShapeDis measures overhangs in the orientation the design chose to print in, so when you ask for a part to be turned, the check updates. See what the checks look at.

Overhangs and bridges

Steep undersides sag. A common rule of thumb is that a face leaning less than about 45 degrees from vertical prints cleanly, and a face leaning further needs support. ShapeDis draws its overhang line at 45 degrees. A short flat span between two walls (a bridge) can print without support, but the longer it is, the more it sags. ShapeDis does not check bridges separately: a flat underside counts as an overhang.

Wall thickness

The printer lays plastic in lines as wide as its nozzle, 0.4 mm on many machines. A wall is best made a whole number of lines wide, and a wall thinner than one line does not print at all, while a wall of a single line is fragile. Thin walls are the most common reason a good-looking design fails, and ShapeDis does not check wall thickness yet, so read the sizes in the view or section the part and ask for the thickness you want.

Holes, slots and fits

Holes tend to come out a little smaller than modelled, and the first layers tend to spread a little at the bed. For a screw or a pin that must fit, many makers print a small test piece, measure it, and set the gap in the design from the result. The slide-in test finds collisions in the model, and the test print tells you how much room your printer needs.

Corners and edges

Sharp inside corners concentrate stress, and a part that is going to be loaded often cracks there first. Rounding the corner (a fillet) spreads the load. A small chamfer on the bottom edge also stops the first layer from squashing outwards. You can ask the AI for either, after pointing at the part you mean.

Contact with the bed

A part needs enough flat area on the bed to stay put. If it is tall and thin, a brim, which is a thin flat skirt printed around the first layer, helps it hold. Brim and supports are slicer settings; ShapeDis can recommend them, and you apply them. See print settings.

When a part is too big

Split it. Cut along a flat face, give each piece a flat side to print on, and add pegs and sockets or a lap joint so the pieces line up when glued. The Print tab tells you which parts are larger than your bed. See printer bed sizes.

What ShapeDis checks from this list