Garage on Backend Engineering Strategy Tools

Optics — Can We Print a Lens?

Wed, 03 Jun 2026 00:00:00 +0000

The question: can a 3D printed part function as a lens? Not a perfect optical instrument — but something that focuses or diffuses light usefully.

A Fresnel lens is the natural starting point. Instead of a thick curved lens, a Fresnel collapses the profile into a flat plate with concentric stepped rings — each ring approximating the angle of the equivalent curved surface. Much thinner, printable in flat layers.

Step 1 — Print and test

Two approaches to try:

FDM — clear PLA Printed on the Kobra X. Surface finish from FDM is rough at the layer scale — likely too much scatter for a clean focus, but worth seeing what you actually get.

Resin — clear resins Better surface resolution and the material can be optically transparent after curing and polishing. More promising. Several clear resins ordered for this:

ABS-Like 2.0 Clear — structural, less brittle
Standard Clear — higher detail
High Clear / Transparent resin

See 3D Printing for the full resin inventory.

Not started. Print attempts and results to follow.

Building the Foundry

Tue, 02 Jun 2026 00:00:00 +0000

Started with tin — a small camping burner and a steel ladle was enough. Then the obvious question came up: could we melt the aluminium cans now?

Aluminium needs higher temperatures than tin, and the gap matters:

Metal	Melting point
Tin	232°C
Zinc	420°C
Aluminium	660°C
Brass	~900°C
Copper	1085°C
Cast iron	~1200°C
Steel	~1370°C

We looked at buying a small foundry online, decided it would be more fun to build one. My son and I built it.

The Build

Sand and gypsum cast inside a metal rubbish bin, steel mesh for reinforcement. Used an old fire extinguisher as the form for the central cavity. Added a pipe for the air inlet and a hair dryer to force air through — charcoal from the grill as fuel.

The foundry.

The hair dryer died on the first serious session. First upgrade: a proper fan from Biltema.

What We’ve Melted

Once the foundry was running we tried everything we could get hold of. Also picked up some wax for eventual lost-wax casting experiments.

Material	Source
Tin	Second-hand shop finds
Aluminium	Cans + scrap
Brass	Scrap
Copper	Scrap
Wax	Candles

Photos to follow.

We bought some tooling online — tongs, crucible, mould for casting bars.

Tongs, crucible, and bar moulds.

And ofc safety kit on every session: heat-resistant gloves, safety glasses, face mask (steam explosions from moisture in moulds are real), fire extinguisher within reach, and distance from anything hot.

Stock — Bars Cast

Melted-down material poured into bar moulds for later use.

Material	Stock
Tin	1047g
Aluminium	1398g
Brass	200g
Copper	2310g
Wax	1730g

Cast bars ready for future use.

Moulding Methods

Different methods suit different metals, temperatures, and detail levels.

Silicon mould — works well for tin and other low-temperature metals. Quick to demould, picks up good detail. Proven success with the scout badges. Not suitable for aluminium temperatures.

Gypsum mould — tried with tin, not great. Must be completely bone-dry before the pour or moisture turns to steam instantly.

Green sand — mixture of sand and a binder that holds a mould impression. Tried making it from cat litter as the binder. Goes into a flask — we made one from wood. More experiments needed.

Red sand / oil sand — similar principle to green sand but oil-bound. Don’t have any yet.

Lost-wax casting — make a wax model, invest it in plaster, burn out the wax, pour metal into the void. Haven’t tried it yet. I have melted some candle stumps for the wax stock, will try and go from there.

Next: Casting Part 1 — Scout Badges

Casting Part 1 — Scout Badges

Tue, 02 Jun 2026 00:00:00 +0000

When I was a kid and scout we cast the scout emblem in tin — naturally we had to do this again with my own troop.

I’m lucky to have a fellow scout leader who does casting professionally. I modelled the master in resin and he made the silicon moulds from it.

For the tin, I went to second-hand shops and gathered everything tin I could find to melt down. Ordered crucibles and pliers online. We melted the tin by putting the crucible in the fire, then the kids could do the pour into the mould, demould, and finish.

First real casting project — a success.

Master

Modeled in Blender, printed in resin as the master for the silicon mould.

↓scout_emblem.blend ↓scout_emblem.stl

Moulds

Silicon moulds made by my fellow scout leader from the resin master.

Silicon moulds made from the resin master.

The Pour

We set up a practice station first — gloves, face masks, and pouring water into a PET bottle before anyone touched real tin. Once they had the motion down, they moved to the actual pour.

Done in small groups: two leaders, two kids at a time. Went smoothly.

Result

Finished tin scout badges.

Casting Part 2 — Belt Buckle

Tue, 02 Jun 2026 00:00:00 +0000

Aluminium casting of a scout belt buckle. The buckle geometry was reverse-engineered and built parametrically in Blender Python — see Scout Buckle — Parametric Design for that side of the project. This page covers the casting execution.

From Model to Mould

Notes to follow — taking the parametric model into a casting-ready form. Draft angles, wall thickness, sprue placement.

The Pour

Notes to follow — aluminium, setup, result.

Status

Work in progress.

The original — a scout belt buckle picked up at a visit to the Scout Museum in Gothenburg, the model we are reproducing.

Original scout belt buckle from the museum visit.

A fellow scout leader kindly donated a few used fire extinguishers — more than enough aluminium for this project once melted down.

Resin Badges — Packat & Klart

Tue, 02 Jun 2026 00:00:00 +0000

Resin-printed ‘packat & klart’ badges for the scouts heading out on their first overnight trip, i.e. ‘Hajk’.

We had a meeting where we went through what one should bring, then ran a competition where the kids got points for guessing what was in the pack I brought along. They got a badge if they did well — they all passed. Success.

First attempt at producing physical scout items rather than sourcing them.

The Badge

Modeled in Blender, exported to STL, printed in resin.

↓packat_klart.blend ↓packat_och_klart.stl

Print

Printed on the Anycubic Photon Mono 2 in Craftsman resin for the extra detail. In hindsight standard resin would have been fine at this size.

Scout Buckle Clone — Parametric for Casting

Tue, 02 Jun 2026 00:00:00 +0000

Clone of a Scout buckle — built in Blender Python for casting rather than FDM printing. The goal is a dimensionally accurate reproduction suitable for resin or lost-wax casting.

What makes this different from the rack brace: the buckle geometry is not a simple boolean grid. It has compound curves, a tongue mechanism, and tolerances that matter for function. One-shotting it in Python is harder — the script has gone through multiple partial rebuilds rather than a single config-block iteration.

Scripts

↓buckle_v1.py ↓buckle_part1.py ↓buckle_part2_v1.py ↓buckle_part2_v2.py

The split into part1 / part2 reflects the geometry breakdown — building the frame and the tongue separately before joining, which turned out to be easier to iterate on than a single monolithic script.

What the iteration looks like

Notes to follow. The short version: parametric geometry that has functional constraints (a tongue that must seat and release under load) fights back more than decorative geometry. Changing one dimension propagates into several others in ways that aren’t obvious from a config block alone.

Casting considerations

Notes to follow. Draft angles, wall thickness minimums, and sprue placement are constraints that don’t exist in FDM — the script needs to know about them.

Status

Work in progress. Geometry is close; casting prep not started.

See also: Rack Support Brace — simpler parametric baseline using the same approach.

3D Printing

Sun, 12 Apr 2026 00:00:00 +0000

Two printers: an FDM machine for structural and functional parts, a resin printer for detail work. Different tools for different jobs — the resin produces sharper geometry at the cost of more process overhead.

FDM — Anycubic Kobra X

Current machine. Workhorse for rack accessories, enclosures, and anything that needs to be durable and dimensionally accurate. Printing in PLA for most jobs.

Replaced an older Prusa i3 MK0 that still works but is no longer the daily driver. Shelved for now. CNC conversion or rebuild is somewhere on the list, parts donor if it comes to that first.


Build volume	260 × 260 × 260 mm
Bed	PEI spring steel, max 100°C
Nozzle (stock)	0.4 mm hardened steel, max 300°C
Speed	300 mm/s recommended, 600 mm/s max
Extrusion	Direct drive
Leveling	LeviQ3.0 auto-leveling
Multicolor	4-colour native (ACE 2 Pro), expandable to 19
Extras	AI spaghetti detection, HD camera, filament runout

Nozzles on hand: 0.4 mm (stock), 0.25 mm (not tried yet). Expandable to 0.6 / 0.8 mm.

Filament on hand

Brand	Material	Colour	Qty	Notes
Verbatim	PLA	Black	1 kg	Original stock
Bambu Lab	PLA Basic	Orange	1 kg
Bambu Lab	PLA Basic	Green	1 kg
Bambu Lab	PLA Basic	Magenta	1 kg
Bambu Lab	PLA Basic	Clear	1 kg
Bambu Lab	PLA Basic	Red	1 kg
Bambu Lab	PETG	Red	1 kg	Refill spool
Bambu Lab	PETG	Blue	1 kg	Refill spool
Bambu Lab	PETG	Black	1 kg	Refill spool
SUNLU	PLA	Black	0.25 kg	Sampler pack
SUNLU	PLA	White	0.25 kg	Sampler pack
SUNLU	PLA	Grey	0.25 kg	Sampler pack
SUNLU	PLA	Red	0.25 kg	Sampler pack
SUNLU	PLA	Light Blue	0.25 kg	Sampler pack
SUNLU	PLA	Light Yellow	0.25 kg	Sampler pack
SUNLU	PLA	Green	0.25 kg	Sampler pack
SUNLU	PLA	Orange	0.25 kg	Sampler pack
SUNLU	PLA	Pink	0.25 kg	Sampler pack
SUNLU	PLA	Lavender Purple	0.25 kg	Sampler pack
SUNLU	PLA	Brown	0.25 kg	Sampler pack
SUNLU	PLA	Olive Green	0.25 kg	Sampler pack
SUNLU	PLA	Oak	0.25 kg	Sampler pack
SUNLU	PLA	Skin	0.25 kg	Sampler pack
SUNLU	PLA	Transparent	0.25 kg	Sampler pack
TECBEARS	PLA Matte	Black	10 kg	High-speed rated (600 mm/s), bulk stock

Resin — Anycubic Photon Mono 2

Mono LCD resin printer. Used for detail parts — scout badges, finer geometry — where FDM resolution isn’t enough. Paired with an Anycubic Wash & Cure 3 for post-processing.


Build volume	143 × 89 × 165 mm
Screen	6.6" Mono LCD, 4096 × 2560, ~2000 hrs
XY resolution	34 μm
Z accuracy	10 μm (single linear rail)
Print speed	≤ 50 mm/hr
Leveling	4-point manual
Light source	Parallel matrix
Build platform	Laser-engraved aluminium alloy
Data input	USB Type-A 2.0

Wash & Cure 3


Wash capacity	Fits Mono 2 build plate
UV wavelength	405 nm
Cure time	~2–3 min

Resin on hand

Resin	Type	Colour	Qty	Notes
ABS-Like V2	ABS-Like	Black	~3 kg	Structural / strength
ABS-Like 2.0	ABS-Like	Beige	8 kg
ABS-Like 2.0	ABS-Like	Translucent Green	1 kg
ABS-Like 2.0	ABS-Like	Clear	1 kg	For lens work eventually
Standard V2	Standard	Black	~0.5 kg	Display / detail
Standard	Standard	Light Beige	8 kg
Standard	Standard	Translucent Green	1 kg
Standard	Standard	Clear	1 kg	For lens work eventually
Craftsman	Detail	Grey	~1 kg	Sharp detail, brittle

Detailed resin mixing notes and maintenance log kept separately.

Slicer / Workflow

Notes to follow — slicer setup, print profiles, export workflow.

Rack and homelab prints: 3D Printed Rack Parts