3D Printing
Wall thicknesses, tolerances and design moves for FDM parts that print right the first time.
3D Modeling / DFM
16 rules
Slant 3DWall thickness
Start FDM walls at 2–3 extrusion widths — with a 0.4 mm nozzle, that’s about 0.8–1.2 mm — and keep wall thickness a whole multiple of your line width.
Slant 3DTabs & overhangs
Replace a flat overhanging tab with a chamfer that runs from the part body down to the feature, and round every corner so material flows into it.
Slant 3DHoles & bores
Fillet every hole’s edges and oversize it slightly for shrink, then use the fix for its type: teardrop side holes, support or skin holes over air, chamfer blind holes, and use crush ribs or grip fins for press fits.
Slant 3DMicro-feature slots
Cut 0.2 mm slots into the region you want solid; the slicer draws walls along each slot, so that area prints as packed walls instead of infill.
Slant 3DHandles
Pick the handle by what has to pass through it: an indent when fingertips only hook in, a rimmed and angled slot for straps or hands, a solid chamfered bump or ribbed tab for more grip, and a cone-hinged handle if it has to fold.
Slant 3DWalls vs. infill
Add perimeters (walls) before you raise infill; keep infill at 10–25% grid or triangles as the baseline, and if a section truly needs to be strong, model it solid.
Printing & First Layer
3 rules
Slant 3DDesigned rafts
Model a thin raft plate into the part, spaced about one layer height below it, with rounded edges, so adhesion doesn’t depend on slicer settings you can’t control.
Slant 3DRaft tie-down struts
Connect the part’s edges and corners to a modeled raft with small 1 mm struts, so the raft physically holds the part down and the struts break or snip off cleanly after.
Slant 3DStop raft warping
Remove one layer from the middle of the raft’s base so only its outer edge touches the bed, and cut an X through the raft to break up long continuous lines.
Supports & Overhangs
7 rulesSlant 3DHoles over air
Never let a hole start over open air: support large or load-bearing holes from underneath, and use a one-layer sacrificial skin only on small holes that carry no load.
Slant 3DDesigned supports
When reorienting can’t remove an overhang, model the support yourself: either a contoured block with a 0.2–0.3 mm air gap, or a thin fin tied to the part through a 0.4 mm breakaway waist, then slice with slicer supports off.
Slant 3DBuild orientation
Reorient the part so its overhangs self-support before adding any support: a ~45° tilt with the bed edge chamfered often removes support entirely, and no face should hang out at 90°.
Slant 3DSupport thumbtacks
Under a downward-pointing tip, model a thin pin from the tip to a broad, flat head facing down, so support lands on the flat head and the pin holds the tip in place while it grows.
Slant 3DStabilizer fins
Under the heavy side of a tilted or tall, thin part, model a triangular fin spaced off the part and tied in with horizontal prongs about 0.5 mm thick and 0.5–1 mm wide.
Slant 3DBridge support blocks
Bridges up to 1–2 in (25–50 mm) usually print unsupported; past that, drop in a modeled block with 0.2 mm clearance on top and 0.2–0.3 mm below, hollowed or chamfered so it comes out.
Tolerances & Fit
8 rulesSlant 3DBlind holes
Don’t plunge a blind hole straight in: fillet the top edge, add a lead-in chamfer at the mouth, and size the bore for shrink so the part starts easily and tightens as it seats.
Slant 3DPin tolerances
Make the hole about 0.25 mm bigger than the pin, fillet the top of the hole, fillet the pin’s base, round its tip, and make the pin as fat and as short as the job allows.
Slant 3DPrint-in-place clearance
Never model two moving surfaces touching: leave at least one nozzle width (≈0.4 mm) side to side, and at least 0.3 mm under any feature that has to float free above the layer below.
Slant 3DCrush ribs & relief slots
For a one-time press fit, model the bore at the part’s true diameter and add relief slots or crush ribs, so the ribs deform instead of the whole wall stretching or cracking.
Slant 3DCross-section pins
Give a load-bearing pin a cross (+) cross-section instead of a round one, and taper it so the tip is smaller than the hole and the base slightly bigger, so it presses in and wears to fit.
Slant 3DPress-fit lead-ins
Round the vertical edges of both parts, then put a small chamfer or fillet on the insert’s leading edge so it starts loose and wedges tight as it goes in.
Joining & Assembly
4 rulesSlant 3DGrip fins
For a reusable fit, ring the hole with flexible grip fins whose tips sit about 1 mm inside the rod diameter, so they spring against it with the same force every time.
Slant 3DJoining features
Join printed parts with lock-in tabs: two flexing flanges with bumps that click into recesses inside the slot. Chamfer any tongue you do use so it wedges and the layer lines grip.
Slant 3DTongue and slot joints
Chamfer every tongue so it wedges into the slot and the layer lines bind, and use a round eye tongue when the tongue has to print face-down or you want one easy dimension.
Slant 3DSpring T-slots
Curve the T-slot’s two outer flanges so they spring into the slot, chamfer the tongue and flanges, and angle the slot so the first layer is a plain square.
Mechanisms & Hinges
9 rulesSlant 3DFolding handles
Use a print-in-place hinge with nested cone pivots instead of a thin flex strip or a through pin, and print the handle flat so the layer lines run along it.
Slant 3DLiving hinges
Make a printed flex hinge 0.4–0.8 mm thick (at least two layers or two lines), print it with the hinge axis pointing straight up so the bend never pulls layers apart, and use PP, nylon or TPU. PLA lasts a few flexes; anything that cycles daily needs a spread-out flexure or a printed pin hinge.
Slant 3DCircular & zigzag flexure hinges
Swap a thin flap for a circular flexure that shares the bend around a loop, cut grooves into the loop for more travel, and use a zigzag spring hinge where the loop sticks out too far. Print the profile flat so it flexes in the layer plane.
Slant 3DLattice hinges
Print the lattice flat with staggered rows of slots, so the bend becomes small twists in many short links instead of one big bend, and size the pattern to the radius it has to wrap.
Slant 3DPrint-in-place pin hinges
Print the hinge axle flat, so the pin runs along the layers, for strength and for small hinges; stand it upright only when you need smooth, precise rotation, and then make it thick and chamfer every knuckle that sits over another.
Slant 3DCone hinges
On an upright hinge, replace the long pin with short cones about 2 mm deep, point every cone upward so each socket is a self-supporting cone-shaped roof, and print the hinge on its side instead whenever the part allows.