Hi Folks,
I have an interesting problem to solve, and I am not sure how to do it. I am building a large Foam Hotwire, ~7' X and 4.5' Y travel with about 6' wide wire length when both wire trucks are at the same XY location. What I am trying to cut with this 4-axis cutter are wing cores and molds. The wings could be highly swept or have a strong taper. I believe this drives me to needing a fairly variable wire length. In an extreme case, I could see where having 1 truck all the way to the left and top, and one all the way to the right and bottom of their travels, making the long diagonal of the cube.
I intend on making a pulley that will hold the extra wire along with a constant force spring (Like a tape measure) to keep wire tension. I will use a tensioner system to keep the wire in contact with the electrical leads to keep the part of the wire in the cutting zone live, while the pulley will be electrically dead.
What I am worried about is, if the wire can grow to almost twice its length over the course of travel, the wire resistance will increase, and consequently, the heat generated in the wire will be changing. I believe this will cause un-even cutting sizes as the temperature changes.
Does anyone have a simple solution to this problem? I am thinking some sort of resistance measuring and voltage system that will regulate the power to keep constant temperature.
Am I just way off base and making this too complicated? Has anyone ever desired to have the ability to stretch the wire along the diagonal like that, or is that found to not be important?
Thank you for your advice and input?
-Chris