In any case, any attempt to be precise will be of little help to viewers as there
are likely to be many variables. The maker will have to experiment with the materials
and power source he or she chooses to use but fortunately the requirements are not
Sk. 1 and Photograph 1 show the unit I made that will bend up to 500mm long but no
dimensions are given regarding length as this can be varied to suit the users requirements.
It consists of two lengths of white melamine faced board, 150mm wide, and coupled
together using a length of softwood screwed to the rear of each but leaving a gap
between the two of 15mm.
An M4 csk screw is threaded into the softwood at each end, just using a tapping size
drill and forcing the screw in. This makes the screw tight and can be used to adjust
the height of the heater in the channel formed by the two boards. The gap between
the heater and the plastic sheet placed on top is in the region of 1mm. Use of a
countersunk screw ensures the head of the screw is below the top face of the bender,
permitting sheets larger than the bender's width to be bent if localised bending
only is required. The arrangement is seen in SK. 2 and
With the plastic sheet laying on top of the bender with the bend line coinciding
with the heater, the current is switched on. Depending on the heat developed by the
heater will be the time taken for the sheet to become hot enough to bend easily.
Preferably, if large, one edge of the sheet should be clamped in position with two
small clamps to avoid the sheet moving when being tested. When the outer face becomes
too hot to touch, attempt to lift the unclamped edge. Continue doing this until it
is found that a bend can easily be formed by lifting the edge up to and past the
90 degree position, assuming a right angle bend is required, switch of the power
to the heater.
It will be found that the sheet will attempt to spring back quite a way, but as it
cools the bend will become more ridged until the spring back will almost have gone.
During this final stage the angle can be finally set. As the sheet cools rapidly
after removing from the heat the process of finalising the bend takes only a few