material removal

cutting

cutting

• reduce length of material

• remove section

sawing

• a type of cutting

• each saw tooth cuts a small groove in the material

• teeth angled out from the blade so the cut groove is wider than the blade (so the blade doesn’t get stuck)

• debris is deposited as the saw emerges from the other side

• can only cut as fast as the material is removed, adding extra force won’t make it cut faster

• harder material = smaller saw teeth

different types of saws

• hacksaw - fine teeth for metal/polymers

• junior hacksaws - smaller, for cutting thinner sections of metals/polymers

• mechanical saws - big hacksaws for metal bars/rods

• coping saw - narrow blade for cutting curved shapes in polymers

• tenon/rip/sheet saw - straight cuts for structural timber, with larger teeth than saws used to cut metal

• jigsaw - a motor moves the blade. there’s a wide variety of these

shearing

• a type of cutting

• applying force from opposite sides of a metal sheet

• sheet separates in a line between the two points where the force was applied

• tin snips/shears cut thin sheet

• guillotines cut thick sheet

  • industrial guillotines push a blade made of tool steel

laser cutting

• thin sheets of polymer/metal

• material along cut line is vaporised, and the vapor is sucked from the machine

• controlled by a computer, as it’s unsafe to control by hand

• expensive, but flexible

• accurately makes small quantities of parts

turning

• uses lathe

• parts/features with a round profile

• workpiece held by lathe and rotated

• tool pressed into workpiece to remove material

  • facing off: creates a flat face, at right angles to the axis of rotation

cylindrical/parallel turning on a lathe

• uniform shape, same diameter along the turned length

taper turning on a lathe

• diameter larger at one end and keeps reducing, making a tapered shape

drilling/boring on a lathe

• make holes through round workpieces

• centre drilling: drillbit pushed to the end to make a hole

• boring: produces an internal hole

  • you can adjust internal diameters, produce internal tapers/steps, cut internal threads, etc

• CNC lathes are computer programmed, and fitted with tools so you can do all of the above

milling

• rotating tool removes metal one layer at a time

• can face (make slots/grooves)

• the axis which the milling tool rotates about can be horizontal or vertical

• can make PCBs (can also be made with a computer controlled milling machine)

  • CAD drawing of PCB & a strip of insulating material with a layer of copper

  • tool cuts a groove into copper layer around the outside of the tracks of the PCB design

  • doesn’t use hazardous chemicals (chemical etching)

  • copper tracks are a bit bigger to let the tool access to remove extra copper, so PCB is bigger

Drilling

• makes holes using a rotating tool

  • not centre drilling, which uses a lathe

• hand drill is manual

• portable/battery powered drills use electricity, reducing effort

• pillar drills are used if the part can be moved

  • part held in vice, jig, g-cramp

• different materials, different cutting speeds

chemical etching

• uses chemicals to remove materials

• photo-etching

  • 1. PCB material coated with light-sensitive film over copper

  • 2. transparent material with the PCB design is printed (mask)

  • 3. mask placed over light-sensitive film

  • 4. film exposed to UV. The mask protects the design from light

  • 5. The image of the PCB design appears on the board

  • 6. placed in chemical bath (with ferric chloride), which eats away at areas that were exposed to light, and the copper that is in these areas

  • 7. board rinsed with water, and holes drilled