My next area of focus is the front of the cylinder block, but I want to machine the front of the oil pan at the same time to get a nice blend between them.
So, to the oil pan. First the inside. I square up a block of aluminum to the total outside dimensions on the mill, load it into the CNC router vise and let-r rip. I run three programs, one to rough out most of the aluminum, one to finish the flat bottom surfaces, and one to finish the curved surfaces that ride against the main bearing caps. Finally I use a 1/16″ end mill to drill the .070″ clearance holes for the 0-80 hardware to secure the oil pan to the cylinder block. There is a 5 degree draft on the sides of the oil pan, but I did not run a finishing pass on these as they will be inside and not seen. You can see the roughing steps in the long inside wall of the oil pan.
I need access to the complete outside during the machining operations for the bottom and sides, so traditional clamping does not lend itself well. Instead I clamp an old 2X4 into the vise and using a wood router bit, flatten the top and cut a small ledge near one edge (see red arrow below). By pushing the oil pan down flat against the smooth routed surface and up against the little ledge, I have squared the part with the X, Y and Z axis of the CNC router. I use 5 minute epoxy to secure the work piece to the block and wait an hour before machining. I run three programs, a roughing pass to remove most of the material, a horizontal pass to give me a nice finish on the top and the flats where the screws mount. Finally I use a ball end mill on the rounded corners and the sides, which have the 5 degree draft. I use a .004″ step-over on the sides, but 5 degrees is really too steep to get a nice finish on my machine. It might have been better if I had finished the two sides separately from the bottom, but it would have meant two more set ups and the alignment of the side to the bottom is problematic. This way I have nice corners, but the sides will require more finishing work by hand.
For machining the front of the engine, I need to secure the oil pan to the cylinder block, so I start by tapping the 0-80 screw holes in the cylinder block.
In my quest to find small hardware I tried some screws I had in a glasses repair kit, but the threads were wrong. I lucked out and my hardware store stocks #0, #1, #2, #3, #4 and #5 hardware. But just like Henry Ford’s Model T, they come in any color you want, as long as its black. Fine for now.
In the photo below I have highlighted a few features on the front of the engine that need special attention, particularly the fillets, or absence of them. Where the timing gear case rises from the front of the engine, there is a 1/16″ radius fillet all the around, except where the water pump mounts. Also, inside the timing gear case there are no fillets to clear the gears.
Below are a couple of examples of models to get the CAM program to give me the tool paths that I want. For example, the top photo cuts the clearance for the water pump.
Above is a photo on the machine as the final finishing passes are run with the 1/8″ ball end mill.
The photos below are right off the machine.
I will machine the back of the cylinder block and oil pan in the same manner. It is starting to look like an engine.