A letterbox which avoids the majority of the foregoing objections consists of two major components - a base and a cover. Each component takes the form of a rectangular sheet with two opposite sides bent at right angles as shown, Figure A.
The base has four pre-drilled holes to accomodate the owner's mounting screws. Two holes are drilled in the sides of the cover to accept a pivot or hinge attached to the base.
When the cover is mounted onto the base-fixed pivots, the assembly forms a closed box with an opening for mail insertion, Figure B.
The overhanging cover at the front of the box not only helps prevent rain ingress but also assists the insertion of floppy mail which is slid up the front of the box until its top edge automatically enters the slot.
Mail is easily removed from the box by lifting the rear of the cover, which then tilts about the pivot at the front, Figure C. Not shown are a couple of holes through which a padlock may be threaded to lock the box if desired.
Further advantages of this design include -
cutting of component shapes could hardly be simpler; there are no costly tolerances required for satisfactory operation
right-angled corners are rounded easily on a belt sander for safety, as indicated more clearly on the manufacturing assembly drawing -
bending is straightforward (with the correct height of sides easily assured by stops on the bender)
there are no expensive and corrosion attracting joints, so coated sheet would be used to obviate painting
transport is facilitated by the rectangular shape though it is anticipated that slight springing will enable compact storage of covers and bases separately, with shop assembly to purchaser's colourscheme
access by postman is easy and he can lift the cover to add mail if the slot is jammed with junk
access by the owner for mail removal and cleaning, is easy (eg. owner doesn't have to bend down and peer into the box from the rear).
The box is not without its disadvantages, however -
The horizontal flat unstiffened surfaces would be relatively flimsy unless the box is constructed throughout from relatively thick 16 gauge sheet (1.5 mm) - this is still thin enough to be handled by the manufacturer's guillotine and bender. The thicker sheet is less prone to gash and will promote an impression of a well-built product (the cost of the extra material is negligible).
As usual, a new solution to a problem begets secondary problems - the least tractable in this case being the hinges. Further practicalisation is necessary, with some candidates shown below :
consists of short lengths of rod welded or stuck to the cover and free to rotate in brackets screwed to the base
rod(s) attached to the base protrude through the pivot holes in the sides which are sprung during assembly
a bifurcated rivet is poked through the hole in each cover side and Araldited to the base
a tab on each side of the base is bent up, and the pivot takes the form of a metal tapping screw through the cover side hole and into the tab
a plastic button is equipped with internal teeth which are forced over the base when the button is pushed through the cover side hole; when the button is fully inserted the teeth spring into a hole drilled in the base thus retaining the button in position.
This last candidate is favoured as the necessary large hole in the cover side will reduce wear; the buttons can be assembled in the retail outlet and held as a separate stock item in the event of excessive wear.
Other problems arise (of course!)- how to make the large holes in the cover sides, is the complex shape of the button feasible, is a die necessary for plastic injection too expensive, etc? Answers to these questions must await experimentation. But this practicalisation provides confidence that secondary problems can be licked.
"The simpler the artefact, the more difficult it is to effect improvements"is a truism. That's why there aren't many new designs for scissors, clothes pegs and mousetraps.
When faced with the problem of a new letterbox, students often dream up a shape which is unconventional, however the above design arose from ideating on how to retain mail - and Nature provided the example of a pair of cupped hands.
Boxes to this improved design have been in successful operation for many years.
Copyright 1999-2005 Douglas Wright,
doug@mech.uwa.edu.au