This isn’t much of a crankcase, but that is the best description I can give as it links the cylinder and the main engine frame on my Transitional Engine.
The starting point was a 2.5″ diameter round of mild steel.
The main billet of steel after it had been bored to accept and locate the end of the cylinder.
The basic shape and dimensions of this took some time to work out, as with a lot of my engine designs a lot of it is held in my head. I work by offering parts up, scribbling some dimensions onto scraps of paper and making rough calculations.
The scribed lines show the section of the flange that will eventually bolt to the I-beams on each side of the engine frame.
This billet of steel was bolted through the tapered hole in the rotary table with a large washer and 12mm nut and bolt.
The bulk of the material was then removed using an end mill. You have to take your time here, take small cuts and use a reasonable feed rate and have very clear stop/start angles on the rotary table.
Removing the material from the bottom of the casing using a 12mm slot drill.
The shape of the case is now starting to appear. At this point there was still some material to remove to get down to the upper of the two scribed lines.
The next machining operation was to flycut the arc in the case. An angle plate was bolted to the table using an engineers square to align it. The crankcase was then bolted to the angle plate using the square again to align the flange of the case perpendicular to the table. A single bolt with an oversized washer was again used to fix the crankcase to the angle plate.
Fly-cutting can be rather an aggressive operation and so I ended up adding more support to the crankcase in the form of Stevenson’s (or 123) blocks.
The Stevenson blocks lined up to support the flanges on the crankcase.
The next image shows this setup from another angle and now shows the addition of clamps to hold the Stevenson blocks in place.
This rather Heath Robinson arrangement ended up as a very good system to support the part.
Comparing an original billet of mild steel to the machined part shows just how much material has been removed.
The crankcase offered up to the frame.
The inner faces of the crankcase are machined to meet the ends of the I-beams. I haven’t added any fixings here and just rely on an interference fit.
In the next image you can see that the crankcase is bolted down to the frame using 4 off 3mm caphead bolts.