Functional Mechanical Parts · Material comparison
Same Bracket, Two Materials: PLA vs PETG
One gusseted L-bracket, printed by FORMYQ twice — white PLA and black PETG — so you can see what changes when only the material does.
Interactive
Slide between the two
Same model, same features, matched framing. Drag across to swap white PLA for black PETG, or pick one to see its specs.
Drag the handle, tap either side, or focus it and use the arrow keys. Same bracket, matched framing. Photos — colour graded.
From CAD to part
Designed on paper first, then printed twice
Before either part was printed, the bracket was modelled in CAD and drawn up as a proper engineering drawing. Here's what each feature is for, the drawing itself, and why it specifies printing on its side.
- 1Two gussets · side view6 mm ribs, flush with the side faces, with 30 × 20 mm legs. They brace the corner so a load on the base can't simply fold the L open.
- 2R2 fillets · side viewRounded inner corner, gusset toe and apex. Sharp inside corners concentrate stress and are where cracks start — especially in PLA.
- 30.5 × 45° edge breaks · side viewExternal edges are chamfered: cleaner to handle and less prone to chipping. Hole edges stay sharp.
- 4M6 clearance holes · front view4× Ø6.6 mm through, 20 mm apart and 10 mm from the side edges — about 6.7 mm of plastic between each hole and the edge.
- 5Short vertical gusset leg · front viewCut down from 30 to 20 mm so an M6 washer and a tool clear the gusset when fastening the back-plate screws.
- 6Base holes at 55 mm · top viewFar enough from the back plate to clear the gussets and leave room for a washer and driver.
Drawing data
FMQ-BRK-001 rev A · Third-angle projection, millimetres · scale 1.5:1
Size
- Overall
- 80 × 60 × 40 mm (base × height × width)
- Plate thickness
- 6 mm
- Gussets
- 2×, 6 mm thick, flush with the side faces; legs 30 × 20 mm
Holes
- Holes
- 4× Ø6.6 mm through — M6 clearance
- Spacing
- 20 mm apart, 10 mm from the side edges
- Base holes H1, H2
- 55 mm from the back face
- Back-plate holes V1, V2
- 35 mm up from the underside
- Countersink
- None — no countersink or counterbore
Edges
- External edges
- Broken 0.5 × 45°; hole edges sharp
- Fillets
- R2 at plate corners, inner corner, gusset toe and apex
- Material
- PLA or PETG, FDM
- Settings
- 0.20 mm layers, 5+ walls, 40% gyroid infill
- Orientation
- On its side (Y=0 face on the bed), no supports
Mass
- CAD volume
- 34,858 mm³
- Estimated mass
- PLA 43 g · PETG 44 g (estimated, not weighed)
Tolerances — proposed, not yet verified by test prints
- Linear
- ±0.3 mm
- Thickness
- ±0.2 mm
- Hole Ø
- +0.2 / −0.1 mm
- Angle
- ±0.5°
- Mounting-face flatness
- 0.3 mm
Estimated from CAD (solid), not weighed. The drawing assumes 1.24 / 1.27 g/cm³; QIDI's datasheets list 1.17 / 1.26 g/cm³, so parts in QIDI filament may weigh slightly less.
Portfolio demonstration part. No certified load rating.
Schematic overlay on the CAD side view. Layer lines are drawn every 2 mm for visibility; real layers are 0.20 mm. Wall on the left, load pressing down on the base.
On its side, as drawn: bending runs within the layers
The L-profile lies flat on the bed, so every 0.20 mm layer is a complete L-and-gusset slice and the layers stack across the 40 mm width. When the base is loaded, the bending stress flows around the corner inside each layer — along the extruded lines, not across them.
- PLA
- Stiffer (4/5 vs PETG's 3/5 in our guide): deflects less under a short-term load. Still brittle when overloaded, and it creeps under a load held for months.
- PETG
- Tougher (impact 4/5 vs PLA's 2/5): bends or yields before it breaks, and creeps less under a sustained load.
Datasheet values compare test bars, not this bracket. Portfolio demonstration part — no certified load rating.
Properties
Where each material wins
Relative ratings from our Filament Guide, then the datasheet numbers behind them.
PLA (white part) PETG (black part)
| PLA | Property | PETG |
|---|---|---|
4 | StiffnessHow little it flexes under load | 3 |
2 | Impact toughnessSurvives knocks and drops | 4 |
4 | Layer adhesionStrength between layers | 4 |
1 | Heat resistanceHolds shape when warm | 2 |
2 | UV / outdoorCopes with sun and weather | 3 |
2 | Chemical resistanceOils, cleaners, mild chemicals | 3 |
3 | Moisture resistanceHigher = absorbs less water | 4 |
5 | Surface detailSharp edges and fine features | 3 |
Relative ratings, 1–5 within FDM filaments, from our Filament Guide. Both are rated lowest-cost ($).
Under heavier loads, softening starts lower. ASA shown for reference: the usual next step up for heat and sun.
PLA Basic vs PETG Basic, as printed.
The weakest direction of any FDM part.
PLA Basic vs PETG Basic.
As listed by QIDI; other PETG grades are listed higher (PETG-Tough 0.46 %).
Same geometry and settings, so the PETG part is heavier in proportion.
- Ease of printingEdge: PLA
PLA: Prints at lower temperatures with no enclosure; QIDI treats drying as optional.
PETG: Hotter, stickier and prone to stringing; we dry it before every print as standard.
- Surface finishMatter of taste
PLA: Satin to slight gloss, crisp edges; white hides layer lines well.
PETG: More sheen; layer lines softened by the gloss; edges round slightly.
- Dimensional accuracyEdge: PLA
PLA: Very low shrink and warp; small features stay precise.
PETG: Shrinks a little more than PLA, warps very little; small features slightly softer.
Typical values from manufacturer datasheets — not measured on these parts. Numbers: QIDI — Choose the Right Filament: 3D Filaments Guide for QIDI Printers (comparison table, HDT @ 0.45 MPa). Values vary by brand, colour, settings and orientation.
Which would I choose?
Pick by where the part will live
Most of the decision is environment and load, not the spec sheet. And sometimes the right answer is neither.
- PLA
Indoor fixture or display
A shelf bracket in a living room, a desk organiser, a product mock-up. Room temperature, light loads, looks matter.
- PLA
Crisp cosmetic detail
Sharp edges, small text, a part you'll sand, prime or paint. PLA holds detail best and finishes most easily.
- PETG
Takes knocks or flexes
Clips, snap-fits, tool holders and mounts that get bumped. PETG bends before it breaks; PLA tends to crack.
- PETG
Damp, garage or sheltered outdoors
Workshops, bathrooms, gardens under cover. PETG absorbs little water and tolerates warmth and some sun better.
- PETG
Oils, cleaners, mild chemicals
Splash guards, workshop parts, cleaning stations. PETG resists more household chemicals than PLA.
- ASA (PETG only if shaded)
Inside a hot car
PLA is out. PETG is borderline — fine low and shaded, risky on a dash or rear shelf. For anything in the sun, use ASA.
- Neither — ASA
Full sun, all year
Permanent outdoor parts fade, yellow and embrittle in PLA and eventually in PETG. ASA is formulated for UV.
- Neither — PA-CF / PAHT-CF
Stiff, strong and warm
Motor mounts, machine brackets, parts near heat that must not flex. Carbon-fibre nylons are stiffer and far more heat resistant.
Spot the difference
What to look for in the photo
Tap a number. Some differences come from the material; some come from how the part was printed — and appear in both.
Up close
What you'll see when it arrives
PLA: crisp and quiet
- Edges, chamfers and the gusset corners stay sharp — PLA is the best everyday material for detail.
- Layer lines are fine and even, and white hides them well.
- The trade-off is invisible in a photo: PLA is stiff but brittle, and it softens far earlier when warm.
PETG: tougher, a little softer-edged
- Looking into the corner: holes on both legs and the pocket between the gussets.
- PETG usually prints with more sheen than PLA, and edges round very slightly.
- PETG strings when molten. We dry it before printing and tune retraction and travel, then clean any wisps off during finishing.
- Black shows dust and fingerprints far more readily than white — the small light specks here are surface dust.
The build-plate face
- The face that sat on the textured PEI build plate has an even, fine grain instead of layer lines.
- We print PETG on textured plates as standard: it bonds so strongly to smooth plates that it can tear chips out of them.
- If a face must be smooth, tell us — we'll orient the part so that face isn't on the plate.
Engineering notes
Why the same bracket behaves differently
Same geometry, so the differences are the material
Both brackets come from the same model, drawing FMQ-BRK-001 rev A: an 80 × 60 × 40 mm L with 6 mm plates, two 6 mm gussets and four M6 clearance holes. The geometry is identical, so anything that differs between them — how they look, how they'd behave under load, how they'd age — comes from PLA versus PETG, not from the design.
Why the drawing says “print on its side”
The drawing specifies printing the bracket on its side: one side face flat on the bed, so the L-profile and both gussets lie flat and the layers stack up across the 40 mm width. Every 0.20 mm layer is a complete L-shaped slice, gussets included.
That matters because of how a bracket is loaded. Screw the back plate to a wall and push down on the base, and the L bends: the corner wants to open and the back plate bends between its screws and the gussets. Printed on its side, those bending stresses run within each layer — along the extruded lines and around the corner — instead of trying to peel layers apart. The weakest direction of the part, between layers, isn't the direction being loaded.
Print the same bracket standing upright (base on the bed) and the layers are horizontal. Now the back plate's bending stress runs vertically, straight across the layer lines just above the gussets. That's exactly where an upright-printed bracket tends to split along a layer. Upright printing gives tidier holes and faces, so it's tempting for looks — but for a part that carries load, on its side is the better choice.
How PLA and PETG change that picture
- Printed on its side, the in-layer properties dominate. PLA is stiffer (rated 4/5 for stiffness in our guide, PETG 3/5), so under a short-term load a PLA bracket deflects less. PETG is tougher (impact 4/5 against PLA's 2/5): overload it and it bends or yields before it breaks.
- If a customer insists on another orientation, layer adhesion becomes the weak link and PETG's advantage grows. QIDI lists PETG Basic at 37.52 MPa between layers against 32.46 MPa for PLA Basic.
- Under a load held for months, PLA creeps more than PETG and creeps faster when warm, so a PLA bracket holding a heavy shelf can slowly droop. For sustained loads we lean towards PETG.
- When it fails, PLA snaps with little warning; PETG usually bends visibly first. For a bracket, seeing it bend is the safer way to fail.
Datasheet figures are measured on test bars, not brackets. They tell you how the materials rank, not what this bracket will hold. In the drawing's own words: “Portfolio demonstration part. No certified load rating.”
What the gussets and fillets do
Without gussets, an L-bracket is two plates joined at a corner, and all the bending concentrates at that inside corner. The two 6 mm ribs brace the corner, stiffen both plates and spread stress over a larger area. The drawing adds R2 fillets at the inner corner, the gusset toe and the gusset apex — the three places where a sharp corner would concentrate stress. That matters more in PLA, which is notch-sensitive and cracks from stress concentrations.
The vertical gusset leg is deliberately shorter than the horizontal one (20 mm, cut from 30) so an M6 washer and a tool clear the gusset when you fasten the back-plate screws.
Temperature
QIDI lists heat deflection temperatures (at a light 0.45 MPa load, as printed) of 55.3 °C for PLA Basic and 72.9 °C for PETG Basic. A closed car in summer can exceed both, and under heavier loads softening starts lower. So:
- PLA: indoor, room temperature, away from heaters, lamps and windows in direct sun.
- PETG: warm rooms, workshops, sheltered outdoor spots — not dashboards or anything that runs hot.
- Hotter than that: ASA (93.0 °C HDT in the same QIDI table), PC or the carbon-fibre nylons.
Holes, bolts and inserts
The four Ø6.6 mm holes are M6 clearance holes, 10 mm from the side edges, with no countersink or counterbore — a bolt and washer clamp each plate. For a joint that will be assembled repeatedly, or bolted to a part that needs a thread, we'd use heat-set inserts:
- PETG takes inserts and self-tapping screws well; it's less likely to split.
- PLA works with inserts too, installed with a lower iron temperature, and it's more likely to crack if a bolt is over-tightened.
The drawing calls for 5+ walls: more perimeters around a hole add more strength than extra infill does.
Shrink, tolerances and fit
PLA shrinks and warps very little, so it holds dimensions and sharp features best. PETG shrinks a little more but still warps very little. In both, small holes tend to print slightly undersized, which is why the drawing's proposed hole tolerance is +0.2 / −0.1 mm. Those tolerances are marked “proposed, not yet verified by test prints” — we'll publish measured values once the parts have been checked. More in our guide to tolerances for FDM parts.
The short version
- Choose PLA for indoor parts where looks, crisp detail and stiffness matter and nothing gets hot.
- Choose PETG for functional parts that get knocked, flexed, warm or damp, or that hold a load for a long time.
- Print load-bearing brackets on their side, so bending runs within the layers.
- Choose neither for full sun or real heat (ASA), or for stiff, hot, heavily loaded parts (carbon-fibre nylon).
Full details, with sources, are in the PLA and PETG pages of our Filament Guide.
Problem
“Should I print this in PLA or PETG?” is the question we're asked most. Spec sheets compare test bars, not parts, so we printed one everyday part — a gusseted L-bracket — in both materials and put them side by side.
Requirements
Identical geometry in both materials, from drawing FMQ-BRK-001 rev A: an 80 × 60 × 40 mm L with 6 mm plates, two 6 mm gussets, four Ø6.6 mm M6 clearance holes, 0.5 × 45° edge breaks and R2 fillets. Any difference you see comes from the material, not the design.
Manufacturing notes
Both parts were printed by FORMYQ on FDM printers and are shown as printed — the layer lines and the textured build-plate face are real. The photos were colour graded for presentation; their captions say so. Design data comes from drawing FMQ-BRK-001 rev A: the drawing's mass is an estimate from CAD (not weighed) and its tolerances are proposed, not yet verified by test prints. Material comparisons on this page are manufacturer datasheet values, labelled as such. Portfolio demonstration part — no certified load rating.