MYP Design 3D Printing Notes

Printing Builds Up, Machining Cuts Away

1. A 3D printer makes a part by adding thin layers of material one on top of the next until the shape is finished.
2. That is additive manufacturing, and it is the opposite of drilling, milling or laser cutting, which all remove material from something bigger.
3. Because material only goes where it is needed, a printer can make hollow shapes and internal channels that no drill could reach.
4. Your CAD model reaches the printer through a slicer such as Cura, PrusaSlicer or Bambu Studio, which chops it into layers and writes the machine instructions.
5. The slicer is where almost every decision about strength, time and surface finish is actually made.

FDM Is A Hot Glue Gun On Rails

1. FDM stands for fused deposition modelling, and it is what nearly every school printer does.
2. A motor feeds plastic filament, usually 1.75 mm across, into a nozzle heated to around 200 degrees Celsius.
3. The nozzle draws the outline of the layer, fills it in, then the bed drops or the head rises by one layer height and it starts again.
4. Each new layer welds onto the one below while it is still hot, which is why a printed part is always weakest along the layer lines.
5. Print orientation therefore changes strength, so a hook printed flat on the bed holds far more than the same hook printed standing up.
6. The first layer decides the whole print, so a bed that is not level gives a part that lifts off halfway through.

Resin Trades Speed And Safety For Detail

1. A resin printer cures liquid photopolymer with ultraviolet light, hardening a whole layer at once against a clear screen.
2. Layers can be 0.025 mm thick, so you get crisp text, jewellery detail and smooth curves that FDM cannot match.
3. Finished resin parts come out wet and have to be washed in alcohol and cured under UV before they are safe to handle properly.
4. Uncured resin irritates skin and eyes, so gloves, goggles and ventilation are not optional.
5. Resin parts are usually more brittle than PLA, which makes them good for looks and bad for anything that gets dropped.

Filament Choice Changes What The Part Can Survive

1. PLA is made from plant starch, prints easily at about 200 degrees, barely warps and is the right default for models and casings.
2. PLA goes soft around 60 degrees, so a PLA phone holder left on a car dashboard in summer will sag.
3. PETG prints around 240 degrees, bends before it snaps and copes with heat and water, which suits brackets, clips and anything outdoors.
4. ABS is tough and heat resistant, the plastic used in Lego bricks, but it shrinks as it cools and needs an enclosed printer.
5. ABS also gives off an unpleasant smell while printing, which is why most schools stick to PLA and PETG.

Layer Height And Infill Are The Two Dials That Matter

1. Layer height is the thickness of each slice, typically 0.1 mm for detail, 0.2 mm as standard and 0.3 mm for speed.
2. Halving the layer height doubles the number of layers and roughly doubles the print time.
3. Infill is the pattern inside the part, given as a percentage, and 15% to 20% is plenty for most school work.
4. Going from 20% to 100% infill can triple the print time and the plastic used while adding much less than triple the strength.
5. Adding perimeters, the solid walls around the outside, strengthens a part far more efficiently than raising infill.
6. A 60 mm cube at 0.2 mm and 15% infill takes roughly three hours, so plan your week around the printer queue rather than the lesson.

Overhangs, Supports And Why Parts Lift Off The Bed

1. Plastic cannot be printed into thin air, so every layer needs something underneath holding it up.
2. Up to about 45 degrees from vertical each layer still overlaps the one below enough to hold, which is the usual overhang rule.
3. Steeper than that and the slicer adds supports, scaffolding printed underneath and snapped off afterwards.
4. Supports waste plastic, add time and leave scars, so redesigning a feature to print at 45 degrees is usually better than supporting it.
5. Warping happens when the plastic shrinks as it cools and drags the corners up off the bed, which ruins ABS prints most often.
6. A heated bed, a clean surface and a brim of extra outline around the first layer all help the part stay stuck down.
   1. Rounding sharp bottom corners with a small fillet also cuts warping, because there is less concentrated pull at each corner.

What A School Printer Is Genuinely Good At

1. 3D printing is excellent for one off shapes, complicated curved forms, hollow bodies and parts you want to test then change tomorrow.
2. It is good for checking whether a shape fits a hand, because holding a printed handle tells you things no render can.
3. It is poor for flat panels, which a laser cutter makes in seconds from 3 mm plywood while a printer takes hours.
4. It is poor for quantity, since printing thirty of anything means thirty print times, not a faster run.
5. It is poor for tight tolerances, so a hole modelled at 6 mm often prints at 5.7 mm and needs opening with a drill.
6. Design in 0.2 mm to 0.4 mm of clearance where two printed parts have to slide or snap together.

Finishing A Print Without Wrecking It

1. Snap supports off with side cutters rather than pulling, which tears the surface underneath.
2. Wet sanding from 240 grit up to 600 grit hides layer lines on PLA before painting.
3. A coat of filler primer fills the remaining ridges and gives paint something even to sit on.
4. Leftover PLA and failed prints should go in the recycling bin your school keeps for them, not the general waste.