Why does the wire handling mechanism seem so complicated?

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For EDM wire handling, there are many different wire handling topologies possible. The main thing that the wire handling mechanism needs to do is to tension the wire at the right tension and feed it at the right speed. Unreeling from a new spool at full tension is not preferred, it causes jumps when the wire is spooled off from the center, but unwinds from the side. That actually makes guitar string-like noises. So you need to gently unreel it from the new spool, and tension the wire somewhere else. Tensioning the wire requires that a force is applied to it. For new wire, this needs to be done in such a way that the wire is delicately handled and not damaged, as it is a perfect fit for the wire guide and the slightest deformation will cause it to jam. The preferred way of delicately applying a force is a capstan mechanism, which requires multiple rollers.

In the BaxEDM machine design the new wire spool is on the fixed world and is transported to the C-arc through a Teflon tube. This is conscious design decision. The wire spool is about 12 kg, and having it on the moving world would mean that the center of mass in the machine continuously shifts, which results in distorting forces that degrade accuracy. Industrial EDM machines cope with this by making all the mechanics extremely stiff and bulky. The BaxEDM design is lighter and more cost effective by having the spool on the fixed world. Transporting the wire from the fixed world to the moving world through the Teflon tube must be done at low wire tension to prevent the wire from cutting into the Teflon over time. Therefore, the BaxEDM C-arc has a capstan mechanism to tension the wire locally.

In the BaxEDM MK1 design spent wire is re-spooled onto a spent wire spool. This means that the spent wire spool slightly pulls on the spent wire coming from the C-arc. When the wire breaks, this requires the operator to tie a knot between the re-threaded wire end and the wire end coming from the spent wire spool. Tying a knot every time can become tedious. So instead in the MK2 design, the idea is that the C-arc pushes the wire through the Teflon tube which then ends up in a wire collection bin instead. Industrial machines also do something similar. This should make rethreading much simpler. Note that the design is still a design only, it has not been made and tested yet.