American Hotwire Machines: Hotwire Tension
To achieve the best cutting results and the highest speeds, hotwire tension is very important. Hotwire temperature, cutting speed and tension are the three most important factors that the operator can control to achieve perfect results. The temperature and the cutting speed of the hotwire are easy to change, but the wire tension is a different story.
Extension springs have been used for a long time to tension hotwires, but they have serious shortcomings. As the hotwire becomes longer in length (up to 1") when it heats up, the extension springs become shorter in length and so lose some of their tension. To achieve the highest cutting speed, the tension on the hotwire should not vary, the wire should be pulled as tightly as possible, without breaking it or making it likely to break when bumped. When you need to do 4-axis cutting, the wire needs to grow in length, and it should be allowed to grow a great deal so as to not limit the shapes that you may be asked to cut.
Extension springs cannot do this very well because they don't maintain uniform tension and they are not suited for long extensions.
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Hotwire machines use very small diameter wires to cut foam, and their low breaking strength can make it difficult for an operator to know if the wire is properly tensioned.
The wrong tension can be the result of the wire being tied to the springs at the wrong length when the hotwire is being made up. Or the wire may be accidentally stretched during installation. It is also common to bump the hotwire when moving a block of foam, or run the cold wire into a stationary block when jogging. Once the wire is stretched, the springs can no longer hold the proper tension on the wire and it should be retied to bring it back to the proper tension, which wastes time and money for the operator.
The operator may not notice when a hotwire is stretched, and begins cutting shapes that are no longer acceptable. He or she will probably waste more time and foam checking the heat and cutting speed of the hotwire before realizing that the real problem is improper wire tension. Because the heat and cutting speed are easily changed, but the wire tension is not, it is very tempting to take the easy way out and just slow down the cutting speed and leave it that way.
Maintaining proper wire tension becomes even more difficult when cutting with more than one hotwire. All the wires should have the same tension. If one becomes stretched, it will have to be retied or the cutting speed will have to be slowed down so that the wire with less tension cuts acceptable shapes.
In order to improve on the performance of extension springs and provide enough extension of the hotwire to allow the machine to cut a wider variety of 4-axis shapes, both models of the SCULPTOR have MAGIC-REELs as standard equipment.
The MAGIC-REEL always maintains the perfect tension on the hotwire, allows faster cutting speeds, expands the possibilities of 4-axis cutting and improves the profitability of any operator by taking care of one of the 3 important variables in achieving perfect cuts.