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I state that in order to carry out this type of processing, you need to have a good command of the use of a 3D cad, a CAM program and the management of an NC milling machine.

However, nothing is complex, but you need to be patient and understand what you have to do and what you are doing.

The first operation is to establish what size the propeller we want to make should have, in my case I wanted to design a small 7X3 (in inch) propeller, for my small COX motor.
The propeller has a fairly complex shape, and has, in addition to an airfoil, also a variable pitch according to the distance from the hub.
The example described relates to the use of the Rhinoceros CAD program, obviously you will have to find the right sequence of commands with your CAD program, it is still a matter of creating a series of airfoils, positioned at a certain distance from the axis of the helix and with the appropriate angle of incidence, the solid passing through these profiles is then generated.
At the end of the work I got the following three-dimensional model:


In the hub area, the shape is not very nice, but as an example of workmanship it can be fine.
After this solid, I generated a pattern of two more identical helices, which is a total of three helices.
In this way I can make three propellers at the same time in a single process.

Pay attention to the origin of the reference axes of the solid, in my case, I preferred to put the origin of the axes in the hole of the hub of the central helix.
Now that the 3D design of the helices is finished, it is necessary to pass to the CAM program that will generate the tool path inherent to the machining.
I exported this solid in IGES format, but it would also have been possible in STL format, this depends on what your CAM program can import
The CAM program that I used was ArtCam Pro and ArtSurface, they are simple but professional programs, you can still use other CAMs, it depends what you have and which one you are better with.

It will now be necessary to generate two toolpaths concerning the two sides of the helices: above and below.
In order to turn the propellers to perform the two processes and maintain a position reference, I made some 3 mm diameter holes that coincide with the holes in the propeller hubs and other holes for centering.
These centering holes, in addition to drilling through the wooden board from which I make the propellers, also drill the support surface of the board (which is always made of wood), in such a way as to allow the insertion of small centering pins made from a simple 3 mm iron rod.


But let's go in order.
First I took a wooden board about 10 mm thick and fixed it with three screws to the worktop as seen in the photo.
This board must be flattened on both sides and brought to a thickness of 7.5 mm.
To do this I used a two-flute cutter with a diameter of 10 mm performing a simple face milling operation.
Made the first leveling, I measure the thickness of the tablet, the turn, the refix and I execute the second leveling bringing the thickness to 7.5 mm.

In the end I have mine  tablet brought to thickness and with two well parallel surfaces.
Without moving the board now, I now make the various holes for the hubs and for the centering pins.
These holes are obtained from the bad 3D model by means of the CAM and are fundamental for the positioning of the tablet to be positioned and for all its processing.

At this point, I'm going to perform the first machining on this side of the tablet, using the first G-code file relating to the helix machining above.

you can see the holes of the hubs and also other holes of



Now I turn the board and position them thanks to the centering pins to maintain the same position as the zero piece.


Let's face it, such a process is not very simple as you will have understood.
A lot of time is spent in the realization of the three-dimensional model and in the generation of the G-code files with the CAM program.
This is not to say that I am good and that you do not even have to try to do such work, on the contrary, I hope that you are all able to do better than what you see.
You do not have to abandon the company at the first difficulties, I myself made very trivial mistakes during the CAM processing: I managed to combine a right-handed propeller on one side and a left-handed propeller on the other and I only noticed it during the final phase of machining to the cutter.

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