Metals in Props

Advantages:
  * Stronger and smaller per unit size
  * Allows construction of shapes impossible w/ wood
  * Malleable (bendable)

Disadvantages
  * Requires specialized tools, skills
  * More difficult to assemble and disassemble

Aluminum
  * Lighter per unit strength
  * More expensive, but not prohibitive in props size
  * Easier to cut, but difficult to weld
  * Can be cut with metal or wood tools (but ruins the saw)
  * Requires oxygen-free atmosphere to weld
	Only weld with Heliarc or MIG welders
  * Softer than steel, burns at lower temp.
  * Can be buffed to high shine

Metal shapes

Cutting metals; manual
  * Cold chisle and machinist vise
  * Hack saw

Cutting Metals; power
  * Power hack saw
  * Metal-cutting band saw
	Portaband
  * Chop saw
  * Cold saw

Drilling metals
Twist bits
  * Must be high speed steel
  * Must be cut at slower speeds than wood
  * Large holes are drilled with a graduated sequence, from small pilot
	hole to desired size in several steps.
  * Initial pilot hole located with center punch

Drill bits

Drill tip

Welders
  Oxy-acetylene: Oxygen/Acetylene flame
  * Slow but easier to learn
  * Good for thin stock, more controllable
  * Welding tip and Cutting tip
  * Welding tips in various sizes
  * Gas pressures roughly matched

Cutting tip
  * Oxygen about 5 times that of Acetylene
  * Uses much more gas, but can cut very hard or thick stock


Arc Welders
  Stick Welders: AC or DC
  * Good for heavier stock
  Wire Feed Welders
  * Flux core wire
  * MIG Welders
  * Filler metals must match base metal.
  * Must use appropriate eye protection due to UV rays in arc

Soldering and Brazing
  * Joining metals using dissimilar metals. The higher then temperature,
	the stronger the joint.
  * Brazing stronger than solder but weaker than welding
  * Require Flux to keep Oxygen out of joint
  * Acid flux: everything but electrical
  * Rosin flux: for electrical work Solder: originally an alloy of Tin and
	Lead.
	Lead now often replaced with antimony or bismuth
  * Silver solder, uses silver rather than lead; stronger than lead solder.

Brazing: soldering with Bronze; high temp, but less than welding.
  * Uses Borax based flux
  * Works on cast iron
  * Can be used to join different metals

Mechanical Fasteners
  Bolts
  * Available in various grades
  * Grade 1 to Grade 8
  * Sized by number and diameter
  * Threads: NC and NF

  Sheet metal screws
  * Harder than wood screws, sharper points and threads
  * Available in variety of head types and sizes
  * Pan head and flat head most common

  Tek screws
  * Variety of sheet metal screw with attached drill point

  Rivets
  * Rivets: strong and permanent, but difficult to install or remove.
  * Strong as bolts of same diameter.
  * Requires access to both sides of joint

  Blind rivets: (pop rivets) Not so strong, but easy to use
	fastened from one side with setting tool
  * Variety of diameters and lengths

Conduit and tubing
  * Sized by outer diameter, more easily bent than pipe EMT - Electrical
  * Metallic Tubing
	a.k.a. Conduit
  * Thin-wall galvanized steel tubing

  Copper tubing (Rigid and flexible)
  * L and M wall thickness

Pipe and Tubing
  * PIPE: Primary use NOT structural, shape not the most efficient but is
	readily available and can be used with care.

Types:
  * Black iron or Gas pipe
	Cheaper, less slick, rusts
  * Galvanized water pipe
	Same pipe with zinc coating; slicker but won't rust.
  * Uncoated pipe
	Easiest to paint.

Sizing Pipe
  * Available from 1/8" I.D. on up.
	Stage use: usually between 1/2" to 2" typical; 
	Schedule 40 Standard most common.

  * Specified by Inside Diameter (I.D.)

Joining Pipe: Threading
  * Designed to hold gas or fluid, but threading pipe reduces wall
	thickness.
  * Pipe will always be MUCH weaker at joint.
  * Gives easy, trim, neat connection, but prone to break under stress.

Assembling pipe structures
  * Threaded plumbing fittings:
  * Available as straight, T's, L's, etc.

	Neat and trim, BUT threading weakens joints.
	Requires accurate cutting and threading.

Pipe joints are cast iron; inherently weaker and less trustworthy. 
More brittle and less predictable.