ETA 15D MK 3 AND ELITE - 5cc ENGINE BUILDS
Part ten - by Ramon Wilson
Part four - by Ramon Wilson

The conrods were made from a tough aluminium called Alumec 89.  It machines beautifully with an almost chromium like sheen and while it's easy enough to bandsaw it it's a real devil to hacksaw as it soon work hardens to that process. First off was to cut a slice of a small block then cut that into strips about 50mm long. These were quickly milled to square section .5mm over finished size then held in the SC4jaw turned to 11.1 diameter for about 30mm then reversed in a collet to give five round blanks.

These blanks were then drilled and reamed on the mill, stops being set to maintain consistency.
Held in a 7/16" collet the first (bottom) end was formed using the original tooling made from a small piece of GFS.
Then it was extended out of the collet to turn the shank, supporting it with the brass bush which has a 30 degree taper for the centre to impinge upon and a 45degree taper to support the rod. The shank is turned parallel to it's major diameter first, then taper turned using the top slide to flair into the big end. The excessive overhang of the tool is to allow clearance of the top slide against the tailstock.
First stage looked like this along with the split bush turned at the same setting as the rods. The small end diameter is worked out according to the length of the bush, drilled through at that size, then carefully bored until the taper cut finishes as it breaks the small end.
Holding this in a collet provides more than adequate gripping power to form the second ball end. Incidentally, the tool is set symmetrical about the hole by eye, inking up and moving the top slide until both sides of the hole appear even.
The finished little end....
... and the finished rods

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See part one here  part two  part three  part four  part five  part six  part seven  part eight 

part nine  part 10  part 11