I've got that itch again so it's time to get started on another project. This will be my second engine from a casting kit so I wanted something that wouldn't be that hard. I decided on the PM Research 3A.
(Image from the PM models site)
Let's get started. First I leveled base casting in the vise using adjustable parallels. Then I milled the bottom flat.
With the bottom flat I flipped over the base casting and faced the mounting pads. Then I drilled the pads for 4-40 mounting hardware.
Next I squared up a piece of flat plate, transfer drilled and tapped the holes from the base. The casting shifted slightly so one of the holes is off. Three mounting screws is enough for what I need to do.
With the base casting mounted on the tooling plate I marked out the center height of the piston on the bearings and cross head. Then the part was placed in the vise to take advantage of its squareness and rigidity. Then I flattened the face where the cylinder will mate to the base casting.
Next I drilled and reamed the hole in the base that the piston rod passes through.
With the same setup I used the DRO to layout and drill the cylinder mounting holes. This particular operation almost got me. The three holes are no equidistant from each other. Two of the holes are only 90 degrees apart instead of 120 degrees apart. Thankfully I caught it before I drilled the holes.
Then I rotated the part and milled the lower cross head guide to dimension.
Next the part was rotated again and the rest of the cross head taken to dimension and the mounting holes drilled and tapped.
Following that the piece was rotated again and the holes for the crankshaft were drilled and reamed.
Then the tops of he bearing journals were spot faced, drilled and tapped for oil cups.
Here is the finished part with the oil cups installed.
Till next time
Tony
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