Design Revision Notes

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Design Revision Notes

High Chairs

An infants chair with long legs and a tray, for use at meals.

This piece of equipment must bear three years of tough daily use, so it's worth some careful thought before you buy. Fortunately there is a safety standard for high chairs. In order to be certified to meet the ASTM/JPMA voluntary safety standard, a high chair must:

  • Meet general requirements (such as not containing any hazardous edges).
  • Pass several tests, including drop tests of the tray, and load and stability tests of the chair.
  • Meet requirements that dangerous coil springs be inaccessible and offer protection from pinching and scissoring.
  • Have a restraint system and complete label and instructions.

Swivel Chairs

Safety guidelines for office chairs include the following:

  • Do not lean back in office chairs, particularly swivel chairs with rollers.
  • Do not climb on any office chair. To reach high-placed objects use an approved ladder.
  • Office desk chairs should have adjustable back supports and seat height. Make sure that your chair's back support position and seat height are comfortable.
  • Take care when sitting in a chair with rollers. Make sure it does not roll out from under you when you sit down.
  • Repair or report any chair damage that could be hazardous.
  • Do not roll chairs over electrical cords.

Joining Wood

Much furniture is based on wooden frames.

Butt joint - The simplest frame joint is a butt joint. It is easy to make, but weak. You can strengthen a butt joint by fixing a reinforcing plate over the joint.

Dowelled joint - A butt joint can be strengthened by gluing dowel into both parts. This is called a dowelled joint.

Halving joints are stronger as there is more contact for gluing. Also the shoulder gives extra mechanical strength.

Mortise and tenon joints are stronger still, because of the shoulders. If you are joining near to the end of a piece of wood, use a haunched mortise and tenon joint.

Box joints are used for anything that has a box-like form - drawers, cabinets, jewellery boxes.

Butt joint - The simplest box joint is again the butt joint. This can be strengthened with blocks, screws or dovetail nailing.

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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 ...

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