Holiday special post!
After spending quite a while thinking about how and whether to re-engineer the piston I finally decided to duplicate an older Aurora assembly shown to me by Dr. Pootoogoo, famed baristorian. This design allows the piston head to "float" and self-align to the cylinder bore and compensating for any machining error (the so-called axial alignment problem that I identified with the first prototype of the group body casting a number of months ago). Although it obviously slightly more complicated than a fixed piston (extra parts and assembly) it will resolve any alignment errors that may be present in the first run of production castings. Additionally, swapping to the fixed piston design will be easy as the piston head itself will be machined from the same rough casting or stock.
Starting from a piece of 2" C360 brass:
Then I add a couple of angled cuts to the tip to approximate a radius - this is quicker to setup than cutting an actual arc and makes no difference to functionality.
Then, using a cut-off/grooving tool I add an undercut below what will be the flange.
Another groove is cut above the flange to create the boss that will align the spring.
Then the part is cut-off from the stock...
... and flipped around to be drilled...
... and tapped with an M10 thread.
After that I move the part to the mill and centre it with a probe.
Three clearing holes are drilled in the flange and boss.
To be continued!
After spending quite a while thinking about how and whether to re-engineer the piston I finally decided to duplicate an older Aurora assembly shown to me by Dr. Pootoogoo, famed baristorian. This design allows the piston head to "float" and self-align to the cylinder bore and compensating for any machining error (the so-called axial alignment problem that I identified with the first prototype of the group body casting a number of months ago). Although it obviously slightly more complicated than a fixed piston (extra parts and assembly) it will resolve any alignment errors that may be present in the first run of production castings. Additionally, swapping to the fixed piston design will be easy as the piston head itself will be machined from the same rough casting or stock.
Starting from a piece of 2" C360 brass:
Then I add a couple of angled cuts to the tip to approximate a radius - this is quicker to setup than cutting an actual arc and makes no difference to functionality.
Then, using a cut-off/grooving tool I add an undercut below what will be the flange.
Then the part is cut-off from the stock...
... and flipped around to be drilled...
... and tapped with an M10 thread.
After that I move the part to the mill and centre it with a probe.
Three clearing holes are drilled in the flange and boss.
To be continued!
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