In a message dated 98-07-04 17:34:06 EDT, firstname.lastname@example.org writes:
Ok- thermocoal is no magic material. Its called styrofoam here.
Thermocoal is what we call it in the country where I am from.
Here's a brief review of the process of using styrofoam sheets to build
The process is a simple one, but time consuming . All it would neeed
is a slicing software, a overhead projector, slabs of styrofoam & some
patientce. Once the part is sliced, these students used a projector to
each slice on a wall. THey adjusted the distance of the projecttor to the
to scale the slices up to the scale they wanted. Then they placed a slab of
styrofoam on the projection of each slice , outlined the contours with a pen
cut against the outline with a hot knife & then glued the individual slices
together to get the prototype. The thickness of the styrofoam slabs or sheets
determine the layer thickness.
If you use two projectors, one projector displaying the profile of the top of
the layer and the second projector displaying the profile of the bottom of the
layer to be cut, you could superimpose them (in exact registration) on the
material to be cut. If the projectors each displayed a different color of
light, the person making the cut could see the angle of the cut that would be
necessary to eliminate the stair step during the cutting phase of the process
- significantly reducing the time it would take to post finish the piece after
the layers have been bonded together.
Secondary thought . . . If the laser beam, used to polymerize the resin in a
stereolithography machine, was projected from an overhead location that
allowed it to enter the resin at the correct angle it could automatically
eliminate the stair step by projecting its beam through the resin on the
correct angle to weld the outside boundary of each layer to the outside
boundary of the previous layer. This would require that the platform holding
the laser's directional scanning mirrors be NC positionable so that the
combination of the position of the scanning mirrors above the vat and the
angle of reflectance off the scanning mirrors themselves would result in the
correct entry angle of the laser beam through the surface of the resin. By
constantly moving the position of the scanning mirror platform, at a rate
which matches the laser's projection of the beam as it traces the profile of
the layer in the layer that is being drawn, the correct angle of entry could
be achieved to eliminate the stair step between the two layers.
Tertiary thought . . . If a heated nichrome wire were stretched between to two
independently positionable XY(Z?) tables, one mounted above the other, the
wire could be used to automatically cut plastic materials into layers with the
correct slope to connect the top and bottom profiles of each layer to each
other. Significantly reducing the time to make near net shaped layers that
could be bonded to gether to form the final object.
Quaternary thought . . . Could a Wire EDM machine perform the operation
described above while using its normal method of pulling a small brass wire
through the styrofoam? Of course the EDM machine would not need to create an
electrical potential between the wire and the styrofoam. Simple friction of
the moving wire being pulled through the plastic should cut it just as easily
as a wire slices through cheese.
Just some thoughts,
Ken Miller, President
395 S. 1100 W.
Farmington, UT 84025
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