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3D printing tips · FabraForma

3D printing design tips that save a reprint

Practical design rules from FabraForma, a 3D printing studio in Powai, Mumbai, for parts printed in FDM or SLA resin.

These are the checks we run on customer files every day. Use them before you send a file anywhere. For choosing a process and understanding price, read our buyer's guide.

Geometry

Most failed prints trace back to one of these.

  • Walls: at least 1.2 mm on FDM, 1 mm on SLA.
    Thinner walls print, but they are weak and may not print at all at small sizes. For load-bearing parts, 2 mm or more is a better starting point.
  • Overhangs past about 45° need support.
    Chamfer the underside of a ledge instead of leaving it flat, and the part may print cleanly with no supports at all.
  • Bridges: keep unsupported spans short.
    Short spans print cleanly. Long ones sag. Add a pillar or split the part.
  • Holes print slightly small.
    Undersize holes by design are normal. For a precise fit, model them 0.2 to 0.3 mm larger, or print undersize and drill or ream to size.
  • Vertical holes are rounder than horizontal ones.
    A horizontal hole on FDM prints with a droop at the top. A teardrop shape, or a note to drill, fixes it.
An orange overhang test print on a worn wooden workbench: fins lean out at steeper angles, clean on the left and drooping with rough undersides on the right
Where overhangs start to droopPast about 45 degrees an unsupported overhang sags; a chamfer under a ledge often lets the part print with no supports.

Fits, threads and assemblies

Where two parts meet, clearance decides whether it works.

  • Clearance for sliding fits: 0.2 to 0.4 mm per side on FDM.
    Less for SLA. Print a small test coupon before committing a large part.
  • Threads: print big ones, insert small ones.
    Threads coarser than about M8 print well. For anything smaller, use heat-set brass inserts or captive nuts. They survive repeated assembly far better than printed plastic threads.
  • Snap fits need a flexible material and a gentle lead-in.
    PETG, nylon and TPU flex. PLA and standard resin snap. Make the cantilever longer rather than thinner.
  • Split big parts at a hidden seam.
    Add pins or a tongue-and-groove so the halves register, and put the joint where it won't be seen or loaded.
Upside-down black 3D-printed enclosure lid with brass heat-set inserts in its screw bosses, beside loose inserts, screws and a soldering iron on a bench
Brass inserts for small threadsBelow about M8, brass inserts heat-set into the printed bosses let screws go in and out many times without stripping the plastic.

Strength and orientation

An FDM part is weakest between layers.

  • Orient so the load runs along the layers, not across them.
    A bracket printed on its side can be several times stronger than the same bracket printed upright.
  • More walls beat more infill.
    Strength comes mostly from the outer walls. Raising the wall count usually helps more than raising infill.
  • Pick the material for the environment.
    PLA softens in a hot car. For outdoor or warm use, choose ASA, PETG or a carbon-fibre blend. For flexing parts, choose TPU or nylon.

Details and finish

What makes a print look like a product.

  • Embossed text: at least 0.6 mm tall and 1 mm wide strokes.
    Raised text on a vertical face reads best. Engraved text on the top surface is the easiest to print.
  • Choose SLA for fine detail.
    Miniatures, jewellery masters and small parts with crisp edges belong on resin, not FDM.
  • Tell us which faces show.
    We orient so support marks land on hidden faces, and quote finishing as a named grade: raw, sanded, primed, painted or clear-coated.
  • Send STEP rather than STL where you can.
    STEP stays editable, so we can fix a thin wall or move a hole without rebuilding the part.

Questions buyers ask

Can you check my file before I order?
Yes. Every quote includes a design-for-print review, and we tell you if a wall, hole or overhang is likely to cause trouble.
Which is better for my part, FDM or SLA?
FDM for larger functional parts in engineering plastics. SLA for small, detailed or smooth parts. Our buyer's guide compares them in detail.
What file formats do you accept?
STEP, STL, IGES, OBJ and 3MF. We can also model from a sketch, a dimensioned photo or a sample.

Want a second pair of eyes on your file?

Send it with your quantity and material. We review it and quote within 24 hours.

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