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300 times 100 = 50 %. Thus the pulling wire at the root end of the cutting bow should be attached to the 1 metre mark ( 100 %) on the weighted arm , and the tip wire to the 50cm ( 50 %) mark allowing the root to travel at twice the speed of the tip and both ends exiting together . The speed of the cut is controlled by the heat of the wire and the weight of the differential arm , too much weight will cause a backward sag in the wire and too much heat will give a thicker melt and may cause grooves if the wire slows at all . Experimentation is the best way to sort these issues and closing the workshop window saves embarrassing the neighbours when things don ’ t go quite right ! When you don ’ t get it right , a hook-up , or make a miscalculation , you don ’ t get a second chance with that piece of foam . The hot wire will cut other types of foam , blue included , you just need more heat as the density increases .
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Fig 8 . The result , in this case a tapered symmetrical foam core for my FW-190 profile Warbird .
Another neat and handy invention is this hot wire “ scroll ” saw , great for cutting out shapes , designed and built by Mike Anderson from Lake Hawea . Mike is another “ do-it-yourself ” modeller who likes to dabble in things foamy and electronic . The ultimate in foam shaping is of course a CNC cutter which some clever members have acquired or built themselves . I ’ m just waiting for my ten year old Grandson to explain the intricacies of setting up a computer and stepper motors and hot wire controller and programming etc etc , but first he has to show me how to work and program my new smart phone ?
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