Con rod machining

The con rod has been machined!! it looks quite good, prior polishing and final work on the bearings. On the sequence below you can see the different machining stages.

The material used on the con rod is 7075 T-6. The bearings are LM-7 Zn bronze, with the top one pressed in and the main one being split. Bolts are M2.

At 14000 RPM the con rod sees a maximum compression load of 820 N and a maximum tension load of 391N. Coefficient of safety is n = 4,4 static and n = 1,1 fatigue (infinite life). I expect fatigue wise it will be safe as 14000 RPM seems quite optimistic for the first test engine for both speed and life time.

After polishing the part will look even better. I will polish it to remove all the tiny notches and sharp edges which will make it look better and improve fatigue resistance.

I will make the split bearings with a tang on each one, and a dowel pin for the real engine. This will improve fitting quality and repeatability of the tolerances.

Next part is the piston, which is one of the most exciting parts of the project.