< Driving Wheel Assembly 4 >
The first and third crankpins have coaxial
double screws of right and left handed threads,
so as to prevent the slack. I employed fine
8 mm thread and L.H. 4 mm thread for them.
Both screws have slits for screwdriver. The outer slit is cut by 1 mm end mill.
One of the second crankpins should be eccentric. First, rod side of the crankpin is turned in the lathe, then the job is reversed and chucked in a desired eccentricity - 0.24 mm, and wheel side of the crankpin is turned. Note the swing of DTI should be twice as the eccentricity. Before release, the eccentric direction has to be marked out.
'Return crank' will be onto the second crankpin. It will be tightened with a cross screw. The photo shows cutting a recess for the cross screw. After that, the crank pin is glued into the driving wheel in desired angle.
Only the second crankpin will receive rotation force by the return crank, so it should be fixed firmly. I employ 3 mm spring pin. 45 degrees inclined hole is opened across the crankpin and the wheel. First I cut a starting hole with 3 mm end mill, and then drilled the hole through.
The spring pin is hammered into the hole. After assembly, the hole and the pin will be hidden with 'side rod '.
Second driving wheel assembly was completed. It is correct this time for sure!
All of wheels were fit on the main frame. At length, it appears like a locomotive!
I tested the chassis on 7.5 meter radius track. It did not derail but made rattling noise in somewhere.
I found the second wheel was touching the brake hanger casting. There is little clearance even in full size design. Moreover the model's wheel has axial play. So the wheel could not clear the casting with the original design.
I milled down the thickness of the casting from 5 mm to 4.5 mm. The photo shows the castings before and after milling. Finally the chassis cleared 7.5 meter radius track without interference. But I cannot be relieved because there will be many difficulties as side rods, brake shoes and piston rod covers.