Alright folks! It's been a while and I wanted to post a few more pics and put a few manufacturing thoughts out there. I have been revising my engine block model to better match my desired manufacturing process. I am planning to leverage lost PLA investment casting such that I can print a 3D model of these parts and then cast them in aluminum. My goal is to post-process the casting using my manual machines (No CNC access for me).
The biggest feature that I have added is a set of ribs on the deck of the block. These positioning ribs help position the engine block flat when upside down. There may be some marginal benefit for 3D printing. These features will later be removed by machining process, but will provide a strong square base for initial machining operations. These initial operations are quite important as they will ensure that the top, bottom, front, and back are all square and perpendicular to each other. All other machining and drilling operations will depend on the block being square. The block is about 5.650" inches long, so it fits well inside a 6" machinist vice. If I had a 5" vise, I could mill the bottom, front, and back faces in one setup.
I am planning to 3D print setup tooling for machining the block as well. This too may not work the first attempt, but I believe that the surface finish is reasonable and this temporary tooling need not hold any true clamping force. As long as I keep these fixtures as positioning only, and clamp the block cleanly between the jaws, this could save a lot of time machining aluminum setup tools.
I am about to get my feet wet with the investment casting process! Here are some pics of the most recent block model. I first developed the engine block model as a "machined part" so to speak. Once I was happy with the finished product, I added material to generate a "net form" or as-cast model of the block. This included adding material anywhere I wanted to have a machined surface, closing drill holes, and adding enough material to the bottom end of the block to permit drilling and reaming of those features. It is fun to be able to draw and print parts that have undercuts. If the 3D printer can print them (but the part could not come out of a mold) investment casting can cast it. Lastly, I am planning to leverage the mains of the block as the runners from the main sprue when casting the part.
The block that is greenish in color is the latest version of my net form design printed in PLA. This was my first print with PLA and I did have issues with a portion of the model not sticking to the build plate properly. I have increased my model size by 101.8% to account for material shrinkage. It will be interesting to see how the model holds up once I am able to pour the first sample. I may expect some issues as I refine my abilities to cast these parts, but am looking forward to that step.