3D printing drawing: 5 simple solutions

Stringing appears as hair-thin plastic strands bridging two separate islands of the same part. The cause is simple: molten polymer keeps flowing out of the nozzle during a travel move, then freezes in mid-air. Printers with a Bowden extruder show it more than direct-drive machines because the pressure in the hot end takes longer to release.

Start with retraction distance. On a direct-drive toolhead, 0.8–1.2 mm is usually enough. Bowden setups often need 4–6 mm. Retraction speed matters too; 25–40 mm/s works for most filaments. If strands persist, drop nozzle temperature by 5 °C at a time until the surface starts to look dull, then step back 5 °C.

Two slicer options help more than people expect. Enable coasting so the extruder stops slightly before the end of a perimeter, and set a minimum travel threshold of 3 mm so short hops skip retraction entirely. Dry filament also matters. PETG that has absorbed moisture strings badly no matter what settings you use.

Not every string is a defect. If the strand sits inside the part and never touches a mating surface, it is cosmetic. Clean it with a heat gun or a deburring knife and move on.

A wall that looks solid on the screen can print as two loose lines with a gap between them. This happens when the extrusion width does not divide evenly into the model wall thickness. A 0.4 mm nozzle laying 0.42 mm lines cannot fill a 1.0 mm wall cleanly; you get one line plus a sliver.

Design walls as a multiple of your extrusion width. For a 0.4 mm nozzle that means 0.8 mm, 1.2 mm, 1.6 mm or 2.0 mm. Many functional brackets are drawn at 1.5 mm because it looks tidy in CAD, then fail at the layer bond. Change the model, not the slicer, when the wall carries load.

Set perimeters to at least three for anything structural. Two perimeters on a 1.2 mm wall gives a hollow core that splits under a screw. Three perimeters plus 25–35% infill handles most brackets and enclosures we see.

If the wall cannot be thickened because of fit, rotate the part 90° in the slicer so the thin wall runs vertically. Vertical walls print as continuous extrusion; horizontal thin walls are cantilevered and droop.

Warping starts at the corners of the first layer and pulls the part off the bed as it cools. The material shrinks as it solidifies, and each new layer pulls on the one below. Long, flat parts with sharp corners are the worst case for this reason.

An enclosure is the single best fix. Keeping the air around the part at 40–50 °C slows cooling and reduces the shrink gradient. ABS and ASA almost always need one; PLA usually does not. A cardboard box over the printer is ugly but works for one-off parts.

Bed temperature and first-layer squish come next. Run the bed at the top of the material range, and set the first layer to 0.25–0.3 mm with a slightly wider extrusion. A brim of 8–10 mm lines adds grip without the cleanup work of a raft.

Round the corners in CAD. A 3 mm corner radius spreads the stress that would otherwise concentrate at a 90° point. If the part is longer than 150 mm in ABS, split it or plan for a post-print straightening step.

Printed holes are always smaller than the model. The nozzle squishes the perimeter outward, and the slicer's arc compensation only partly corrects it. A nominal Ø5 mm hole commonly prints at 4.7–4.85 mm on a well-tuned machine.

For clearance holes, add 0.2–0.3 mm to the diameter in CAD. For a press fit, print a test coupon first; the right offset depends on your printer and material. Do not chase the number in the slicer alone.

Vertical holes print rounder than horizontal ones. If the hole is a bearing seat or a dowel location, orient the part so the hole axis is vertical. Horizontal holes sag on the top of the bore and need support or a teardrop profile.

When the hole tolerance matters, print undersize and ream or drill to final size. A printed part with a drilled Ø6 H7 bore is a normal production approach for jigs and fixtures. The plastic cuts easily and the hole comes out round.

Some parts should never be printed, no matter how good the settings are. If the drawing calls for a tolerance tighter than ±0.1 mm, a thread that takes load, or a surface below Ra 3.2 μm, FDM will not hold it. Move the part to CNC.

The same applies to thin features under 0.8 mm, deep small holes, and any part that sees continuous stress across layer lines. Layer adhesion is the weak axis of every FDM part, and no slicer setting removes it.

We run both processes, so the choice is not a sales pitch. Printed prototypes are useful for form and fit checks in days. When the design freezes, we machine the same geometry from aluminium or stainless on 3-, 4- or 5-axis centers. Tolerances hold at ±0.005 mm, and the surface comes off the machine at Ra 0.8–1.6 μm.

A hybrid path works well for many projects. Print the housing to check cable routing and mounting, then machine the load-bearing insert or the mating plate. You get fast feedback and a functional part without redrawing anything.