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History of my models for polystyrene cutting

Being able to cut the wings of my models with a numerically controlled machine was an idea that immediately fascinated me.
With the experience of the CNC milling machine, the step was short.
I made several models of this machine, experimenting with different mechanical and electronic solutions, The following is the report of this experience:


This model, unlike the previous one, is lighter and simpler, the movement takes place by means of a toothed belt and the guide system and on particular aluminum profiles with particular skids.
it allows a cut in X of 630 mm and in height of 340 mm, the width about 800-1200. 



Quite large and sturdy model, it allows a cut in X of 1200 mm and in height of 600 mm, the width about 1500-2000.
The guide system is with round bars but also supported by bearings that reduce the bending of the towers, the movement takes place by means of a TPN 12X3 trapezoid bar, the wire can be tensioned either by means of a spring or by a bow, it depends on the tapering of the cut.



This is a fairly complex version that uses  18 mm round bars, displacement by toothed belt and box of  gear reduction on the stepper motor, the whole structure is in  aluminum.
The electronics are for 2.5 Amp / phase single pole motors, suitable for  wire control with GMFC program but can also work with Mach3.
The moving dimension of the axes is about 600 mm for the X axis and 600  for the Y axis, in width it can reach about 1500-2000 mm, it depends  the length of the wire used.



Photo of a  polystyrene cutting machine, "useful" cutting dimensions:
X = 1000 mm Y = 1000 mm



Here is another model of mechanics.
Its construction and rail system mirror those of MillWood2008.
Its entire structure is in aluminum and the various pieces are made on CNC milling machines.
The threaded displacement bars are the classic M6X1, which work on threaded brass bushings, these are easily replaceable in case of wear (very unlikely given the low workload).


These were the very first cuts I made, it's amazing to see how simple it is  structure is able to create such complex shapes as an airfoil.
Making a wing will now get a lot easier, ... too bad I like ribbed wings, so don't expect to see many examples of clipped wings.

As you can see, the wire is not tensioned directly on the structure of the mobile towers, but I use a special bow.
With this solution I avoid flexing the two mobile towers and I can keep the wire tension constant even in the case of very tapered wings.
I usually see that many use to fix the wire directly between the two movable blocks of the Y axes, and insert a tension spring to keep it taut and to compensate for the elongation in the case of non-parallel cuts.
However, with this solution there is the bending of the two towers, which can increase with the cutting of very tapered wings.
Some use a bow whose structure is passed under the entire worktop.
However, this entails having the worktop smaller than the length of the arch, and not having any obstructions under the worktop.
With the solution I have adopted, it allows me not to generate bending at the two towers, to be able to easily put on and remove the bow. to keep the thread tension always constant even in the case of very tapered wings.

The bow is made up of a square aluminum tube at the end I have fixed a sheet of harmonic steel which, thanks to its bending, keeps the wire in tension.
The whole weight of the bow is supported by the two movable blocks of the Y axes, on which a bakelite plate with a small "V" groove holds the wire in place.

What you see on the side is the left tower, the bow is supported only by the wire that runs in the bakelite plate, any variations in length due to tapered cuts involve the movement of the bow from this left side of the machine.


The electronics I use for this cutter is not the classic MM2001, but a particular one again for unipolar motors but with PWM management, i.e. there are not the usual resistances to be calculated according to the type of motors.
You can see the rear mask where there are all the various connectors, this was made on 1 mm aluminum sheet using the MillWood2008, including writings.

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