Dovetail joints are very strong and look good.
Comb joints are easier to make (especially by machine) and offer good contact for gluing.
Dowelled joints are good for joining man-made boards (modified timbers) which might split easily if screwed or nailed.
Housing joints are used for shelves.
Joining Metal
Use soft soldering for a permanent joint for copper, brass, tinplate or light steelwork. Soft solder melts at about 200°C. The solder flows into the heated metal along the joint, and grips the two pieces together when it all cools.
Use hard soldering for stronger joints. Hard solder melts at 625ºC.
Brazing is used for very strong joints. Brazing rod melts at 875ºC.
Welding
Welding is different from soldering in that the two pieces of metal are melted along the joints, and actually fuse together when they cool. In oxy-acetylene welding a very hot flame is used. In electric arc welding a spark is used to heat the metal. In both processes a filler rod of the same metals to be joined is used to get a really strong joint.
Knock-Down Fittings
Finishing
Plastics Most plastics do not need an extra finish - they come out of the mould already finished. Sometimes, however, you need to finish the edge of plastic, for example where you have cut it. Stages of finishing plastics:
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File it carefully.
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Use wet and dry paper in stages, starting with the coarser grain and moving to the finest grain.
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Machine buff it using a polishing mop and polishing compound.
Wood
The best way to get wood smooth is to plane it. This keeps the grain clear and beautiful to look at.
If it is to be painted (or if you cannot use a plane) sand it down with abrasive paper. To get an even finish, wrap the abrasive paper around a sanding block (usually made from cork).
The end grain of wood is hard to plane - use a disk-sander or band-facer, or do it by hand. Don't forget sand down the insides of things you are making before you glue them up. The inside is hard to reach later!
An electric orbital sander saves a lot of time and energy.
To make wood proof against water and stains, you might wish to apply a polyurethane varnish.
- Sand it down all over to remove any marks.
- Remove the arris (the sharp edges) with abrasive paper or a plane.
- Paint the varnish on thinly, sanding down lightly between coats.Usually three coats brings up the natural pattern in the wood.
If you are going to paint wood, you need to:
- Sand down and remove the arris.
- Seal the knots with knotting.
- Roughen the surface with coarse glass paper so that the paint can grip the wood.
- Apply a primer.
- Apply an undercoat.
- Apply two coats of gloss paint.
For outdoor furniture, use an oil (such as teak oil) to protect the wood from water etc.
Metal
How to make it smooth
- Smooth the metal with cross filing.
- Remove any remaining bumps with draw filing.
- Use wet and dry emery cloths (starting with a coarse one, finishing with the finest).
- Use a drop of oil with the finest - this gives a smoother finish and prevents rusting.
- Use a buffing machine with metal polish.
How to prevent rusting
Oil blacking involves heating the work and dipping it into oil.
Painting - usually a primer is needed first. But some paints (e.g. Hammerite) can be applied directly. The surface must be clean from grease (use paraffin followed by washing with hot water and detergent).
Lacquering copper and brass prevents oxidisation.
Dip coating - heat up the metal to about 180°C. Dip it into fluidised plastic powder. Reheat in an oven, and the plastic fuses into an even finish.
Man-Made Boards
Modified timber products are made in factories, using natural wood and adhesives. Usually the wood is the waste from saw mills, such as sawdust or small branches which cannot be converted into planks. They are produced in large boards such as:
- chipboard
- blockboard
- plywood
- MDF (medium density fibreboard)
Vacuum Forming
The Process
Clamping
The clamp frame ensures the plastic sheet is held firmly in place during the forming process.
Heating
Radiant heaters are normally used to heat the sheet which has been positioned over the aperture of the vacuum forming machine. For thicker sheet both surfaces may need to be heated and more sophisticated machines allow this. Heaters move into position both above and below the sheet.
Pre-stretch
Is used to achieve "even" wall thickness. Air is introduced to blow a small "bubble" and the mould is then raised into the pre-stretched sheet.
Vacuum
A vacuum is applied, the sheet is drawn into intimate contact with the mould and the mould detail is picked up.
Plug Assist
Where a deep draw is required a top "plug" may be used to push material into the mould during the forming process.
Cooling and Release
The material is allowed to cool. The cooling process may be shortened with blown air or even a fine water spray. The moulding may then be released from the mould by introducing a small air pressure.
Finishing
After moulding, any mould finishing may be performed, trimming, cutting, drilling, polishing, decorating etc.
Ergonomics & Anthropometrics
Erg is a rarely used measurement of work done. There used to be a common unit of force -the 'dyne' before the fuller acceptance of the more usual SI units of 'Newton, metres, etc.. - the 'erg' was the work done by one 'dyne'… more detail isn't necessary here but the syllable erg is clearly associated with work being done effectively - in our case it relates
to efficiency of the design. Onomics is: Economics ends in the same way as our word…and a little thought might suggest it is related to the effective application of something. In this case the effective managing of the economy but our word 'erg' ...onomics - it is also about effective management' - but the management and minimising the work done.
Anthropos is a Greek word meaning 'man' and since the English language is filled with words that have Greek, Latin, French, German, Norse and other origins - it's not really surprising to find a common example. Metrics is anything that looks as though it associated with a very familiar word 'metric' should certainly be associated with measurements.
So what have we finished up with ?
Overall we have the study of people and their sizes - size of hands, size of legs, length of lower leg, size of head, etc etc.
This information can be discovered by checking out a sample of people - the larger the better - then - how we apply it is up to our ability as designers..
Our design has to show consideration of the people we are designing for - We will then have a product that fits properly and ultimately might sell more because it is comfortable to use and effective in its actions. Much of the information that has allowed an effective design to be created has been found out from our study of anthropometrics.
Our design has used this information well - we have made the chair comfortable by applying knowledge. We have made it an efficient ergonomic design. We may have included speakers in the seat around the head area to allow effective radio communication in a jet aircraft - or easy listening on the flight to a holiday destination - or perhaps just made it fit the 4 year old children at the nursery….