7
8
9
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.
7
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?
8
9