First Steps On the New Engine

The first steps have all been done with CAD. 

The design for the Webster internal combustion engine was released to the public domain by designer Joe Webster in 2004 with 2D drawings of the parts as .DXF format files.  My CAD program, Rhino3D ver 5, imports DXF format files but they're still 2D shapes; from there, I have to convert it to 3D if I want a 3D drawing.  If I'm going to cut it out with CNC, this is the first step.  Let me show an example.

The first part is the base, a roughly 8x5" plate of 3/8" thick aluminum with a handful of holes drilled in it.  For something this simple, I'll just drill all the holes using the mill as a precision drill press and then cut out the plate's outline with an end mill in the CNC mill.  Most of the holes have far side features (countersinks) and I'll do those after the plate is cut out.  The DXF looks like this:

I turn this drawing into a 3D solid object with some Rhino operations.  I highlight all the curves that make up the outline of the part and combine them into one curve.  Next, I Extrude the Curve to the 3/8" thickness, and then cap the top and bottom to make it into a solid.  The part looks like this as a 3D solid:

I save this solid model in the .STL (stereolithography) format the CAM program can use, import that file into my CAM program and generate tool paths for cutting the outline.  This is a screen capture of the part with the tool paths shown (horizontal red lines).

The part is ready to be fabricated at this point. 

The second part I've made a model of is a bit more intricate and will require more operations.  Making a model like this starts out as taking the outline, extruding it to the right thickness, capping it and then creating all the holes.  Each hole has to be created by the tedious process of creating a cylinder to the dimensions of the hole, putting it where it belongs in the part, and then doing a Boolean operation to subtract the cylinder from the hole.  In the end, it looks like this:

You can see that it has holes along the two sides that can be seen.  The vertical face on the bottom right in this view is the bottom of the part; it's overall size is 2.750 in the long direction; the width is 1.500, that notch on the left is 5/16 wide by 1.25 tall.  The part is 3/4" thick.  The large hole in the top section is for the spark plug on the engine, so its exact dimensions depend on which plug I can get.  The far side of that hole, though, has bore that's 1.000" diameter and 0.500" deep. 

This one has a simple shape, the challenge is the holes on the different surfaces, top, bottom and left side.  I think it's enough like other parts I've made that I know how to get there, and won't do CAM tool paths for this one. 

This is a few afternoons worth of work before I can cut metal.