Week 3 – Computer-controlled cutting

Parametric design

Parametric design is a process based on algorithmic thinking that enables the expression of parameters and rules that, together, define, encode and clarify the relationship between design intent and design response.

Parametric design is a paradigm in design where the relationship between elements is used to manipulate and inform the design of complex geometries and structures.

The term parametric originates from mathematics (parametric equation) and refers to the use of certain parameters or variables that can be edited to manipulate or alter the end result of an equation or system. While today the term is used in reference to computational design systems, there are precedents for these modern systems in the works of architects such as Antoni Gaudí, who used analog models to explore design space.

This is a good tutorial for Fusion, about this topic.

The laser cutter

Applications

• Cutting or marking/engraving by varying power

• Raster or vector mode

• Screen printing, by making a halftone (See holes, path)

• Press-fit construction (example: GIK, gik.cad, gik.png)

Joints

Examples

Easy to design <–> Strongest properties

• Slot – simplest, hard to align

• Chamfer – rounded corners help align parts, and can compress materials into slots (eg corrugated cardboard). But still relies on sliding friction

• Bistable (bump and slot), behaves very differetly for different materials

• Flexure – design a bendable part with controllable flex

• Pinned – secure joint with an orthogonal constraint (see also wedged mortise and tenon)

Tolerances

• Slop vs security (range is about 0.1mm)

• Brittle material vs compressible material

• Parametric design is your friend

3D shapes

• Kerfing (incomplete cut)

• Flexures, living hinges (enables twists and bends). See also Inkscape living hinge extension

• Extreme example, a moving platform without moving parts (gears, bearings)

• rotary attachment for the laser cutter

Cutting mechanisms

• burning

• melting

• evaporation

• ablation

The material has to go somewhere, …

Airflow

• Exhaust – draws combustible material out. (Machine: Extractor)

• Assist – injects air at the cutting point. (Machine: Compressor)

If it’s not strong enough, that material stays around – Bad news
You shouldn’t see smoke hanging around in laser cutting chamber
Exhaust fumes are very bad news
Plastic will outgas for a minute after cutting. Leave the lid closed for a minute

Kerf

Some material is removed with the cut.
Some drivers (e.g. mods) allow for this, with offsetting.
Otherwise, you should allow for this in your design (parametrically!)

Safety

All laser cutters want to catch on fire
Card, MDF, plywood and acrylic are all really close to combusting when cutting.
Don’t step away from the machine. Always supervise.
Initial combustion: open the lid. Otherwise, smother or use the fire extinguisher.
Laser optics need to be kept clean, otherwise, heat can build up (so avoid smoke)

WIP: Check safety procedures

Materials

• Cardboard – the good stuff bows, not kinks. Use old boxes. Very forgiving for joints

• Plywood – Real thickness != real thickness – use the callipers.

• PMMA/acrylic/plexiglass/perspex/lucite glue bend

• POM/delrin/acetal – more elastic than acrylic

No-gos

• No PVC – releases chlorine

• Never put a material into the cutter unless you know where it came from – no random plastic.

• Never put anything shiny (e.g. metal) into a CO₂ laser

Preparing artwork (for vector cutting)

• 2D vector file (EPS or DXF)

• Make the format as simple as possible

• All shapes no fill, nd 0.001mm stroke

• Laser origin is top left

How to use the laser cutter in the fablab

See Fab Academy docs here: https://docs.google.com/document/d/1kDd0A60eJdmJgIRt-zmAJwxszw0Gd61VXqHKnizv6hg/edit

Place material

• Consider airflow

• Alignment against the rulers

• Support to distance the material from the bed

• Flat surface – consistent z-height

Set origins and focus

• Use laser pointer

• Set x and y origins

• Use focus tool to set z-origin

Settings for the fablab laser cutter (also instructions above machine)

• Power – too much melts, too little doesn’t cut. Use multiple passes.

• Speed – too slow can cause combustion, too slow doesn’t cut

• Pulse rate/Frequency – too close can melt, too far apart can leave gaps

• Coordinate system, origin is top left

• Vector mode for cutting, raster mode for engraving (but interesting grey areas for experimentation)

Extraction

• Turn on the BOFA extractor (speed approx 330m3h)

• Turn on the air compressor

Whilst it’s cutting

• Always observe the cutting closely

After the cut

• Leave the lid closed with the extractor on for 30 seconds

• If you mess up the bed, clean it up – take it to the sink and carefully clean it without bending the sheet

Vinyl cutter

The vinyl cutter is an extremely quick and versatile tool. It can be used to cut:

• vinyl for stickers ideally use transfer tape

• thermal transfers to iron on to a fabric or surface

• copper traces for flexible or interestingly shaped circuits

here is a guide to use the vinyl cutter in the fablab

All these information are from our study material made by our tutor Derek Covill.

Pen Holder

I used parameters for create a simple pen holder in Fusion. First of all i started to draw the shape of my joint piece.

Then i added my parameters.

These are my 2 joints with parameters.

I needed 8 piece for complete the shape that i wanted.

This is how my Pen Holder look like.

Unfortunately i don’t have the chance to laser cut this project, but i have upload below my DP402 project that was laser cutted.

Another useful tutorial that i used.

DP402 Laser-cut

All my laser cut projects are inside my locker in the university, unfortunately i didn’t take picture to them so i will add the laser cut shelf made by my group mate for DP402 Kyle.

Laser-cut Poseable Person

Here a really interesting project and an example of joints made by Rob Ives.