Bill Stock wrote:
I did a lot of acrylic bending years ago making picture keyframes and
the like. I used a coiled nichrome wire inside a heatproof channel,
lined with asbestos paper (!) connected to full house current.
Thanks Ken. Did you make your own coils of buy then ready made? Do you
remember the gauge/resistance? Did you use an insulator on the coil or let
it hang free in the channel?
How did you construct your channel? I was thinking of MDF base, reflective
aluminum, masonite (channel sides), covered with some heat resistant
material, perhap fiberglass.
It was
about 18" long, and the element, which was about an inch below the
channel's 1/2" opening, glowed a dark red. Turning a piece over once, it
took about 15 seconds to get the acrylic up to bending temp. and it
worked really well.
I would use a coiled element sized to give a much higher temp than 400
degrees at 115v, and with a lamp dimmer (no stepdown transformer). If
your element is only at 400 degrees, you could be waiting forever to
reach bending temp.
Thanks again Ken, useful info.
Bill, the way I made my bender jig I wouldn't recommend doing it the
same way to you, it was pretty cobbled up and not very safe.
I would use a ready-made coiled element or take one out of a milkhouse
heater whose element might be broken, but at least half of it's length
usable. The dimmer will take care of having a shorter length (I
think--see disclaimer below).
Make a U-shape from steel sheet (NOT aluminum) and get some ceramic
insulators from an appliance store to hold the element in the channel. I
think the old Maytag dryers used ceramic thimbles that the element
threaded through, that might be just the thing.
A quartz heater element would be even better, it's self-supporting so
you don't have to worry about shorting a coiled element to the sheet metal.
Won't go too much further into the design, except to recommend that the
channel be a seperate piece from the top surface where you lay the
acrylic--you only want heat to come out of the slot.
I would not use any flamable material, but fabricate the whole thing
from sheet metal probably pop-riveted together, with an enclosed box at
one end to hold the dimmer and protect the connections from fingers (and
vis versa!)
I am NOT an electrical engineer, so I don't wanna tell you how to wire
it and get blamed for your demise--just be safe and find the correct way
to do it! If for some reason the dimmer is not appropriate, you could
use a limiter control from an electric stove, one of the burner controls
which cycles the heater on and off in short periods.
Think I'd better stop here before I *really* get into trouble from those
who ARE electrical engineers!
Ken Grunke
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