joining techniques
- PVA
- Tensol cement
- Liquid Poly Cement
- Contact adhesives
- Epoxy resin
PVA
- join on edge grain
- if properly glued can be as strong as a single piece of wood
- won’t work on end grain
Tensol cement
- joins plastics (eg acrylic) together permanently
- glued surfaces should be clamped together for 24hrs
- gives a permanent joint
- leaves strings, cant clean excess off
Liquid Poly Cement
- plastic weld
- more appropriate for plastic
- works by capillary action
- 2 surfaces together put liquid along the joint
- cleaner and easier to use
Contact adhesive
- to join plastics
- adhesive applied to both surfaces they are pushed together when glue appears to be dry
- used for large surface areas
Epoxy resin
- many adhesives are plastics themselves
- Araldite hardens when a second chemical is added (catalyst)
- can bond most materials
- messy and smelly
- mix two parts for 1 minute
wood joints
can be designed to hold without the use of glue or fasteners
types of wood joints
mitred half lap
mortise and tenon
dove tail
lap joint
bridal joint
rebate
finger joint
dowel joint
compare a dowel joint to a mortise and tenon
compared to a mortise and tenon, a dowel joint is a poor joint. Much of the surface of the dowel joint is end grain, which glue adheres to poorly. In a mortise and tenon joint most of the surface of the joint is longitudinal grain.
mechanical joining
- temporary/ semi permanent
- various mechanical fasteners used, eg nails and screws
- nuts and bolts
- pop rivets
thermal joining
heat is used to cause a joint in a variety of ways: soldering, brazing, welding
soldering
- a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint.
- filler metal has a relatively low melting point.
- heat is applied to the parts being joined, solder melts and is dawn into the joint by capillary action.
- soft soldering (PCB), hard soldering (jewellery), silver soldering (decoration)
brazing
- filler metal/alloy is heated to melting temp
- quick doesn’t need much heat
- widely used in the tool industry to fasten hard metal (carbide, ceramics, cement and similar) tip s to tools such as saw blades.
- can be used for tacking prior to welding
- non ferrous on ferrous
MIG welding
- metal inert gas
- a form of arc welding (electricity)
- used for general welding, mild steel
- as well as welding this can be used for cutting plate metal
TIG welding
- tungsten inert gas
- a form of arc welding
- used for welding specialist materials such as aluminium and stainless steel
- has a filler rod instead of a consumable wire
arc welding safety
specialist PPE must be worn (tinted visor) to prevent arc eye
oxy-acetylene
- combination of two gas tanks oxygen and acetylene
- ‘v’ valley produced through grinding on joining materials
- filler rod used to join similar thickness materials
- mig welding is cleaner and quicker
