The con rod shafts have a taper of approx 1.5 degrees. I turned the shafts between centres, using a tangential tool.(a Diamond tool holder from Eccentric Engineering). The HSS cutter has a round cross section which gives a good finish, and automatically fillets the joins.
Of course left and right hand tools are required to do the whole taper.
The con rod casting is difficult to hold accurately for milling, so I made a jig to assist.
10mm aluminium plate, with a cut out section to accept the con rod casting.
The jig had to be made as accurately as possible. So it was milled square and parallel, then centre pins were installed to hold the casting by the previously drilled centres. A further pin with a sharp point was installed to stop the casting from rotating during the drilling and reaming for the gudgeon pin. That gudgeon pin hole was continued through the jig, so a large pin could be inserted to really hold the casting securely. It also allowed an accurate 180 degree rotation of the casting.
A bit clearer with the swarf swept away!
You can see the gudgeon pin in place, while further surfaces are milled.
Close up of the jig and my metal workers’ dirty hand. Just as well there is no more gynaecology.
Not a clear shot, but here I am using the flutes of a milling bit to smooth the flat section under the gudgeon pin. Not ideal but it worked OK. Tomorrow I plan to round off the external surfaces and mill the slot for the cross head. Not much to show for a full day in the workshop, but it was fun…