< Cylinder Head Covers 1 >
The photo shows full size C53 cylinder block. Note the cylinder heads are covered with flanged plates. In case of my C53, its diameter is 73 mm. As typical hammer forming process results bumpy surface, I decided to try 'spinning' process for the covers.
For spinning process, I made a gunmetal roller, 25 mm dia. 6 mm thick. and 8 mm spindle, with 13 mm square bar holder.
The section of the roller must be round for smooth spinning. After cutting calculated 0.4 mm pitch steps, it is grinded with file and emery cloth.
The left one is the spinning die made from steel round bar. Its fillet was cut as well as the above roller, that is cutting small steps and grinding smoothly. The die has a chucking base bolted under itself. The right one is a support disc for spinning process. Note the disc has tapered hole fitting to the lathe tailstock center.
I chose 0.8 mm aluminum sheet as the material. The photos show spinning process. For smooth spinning, grease is applied to the sheet surface. Rotating the spindle and squeezing the sheet surface by the roller from inner to outer. It needs many strokes till the final shape, actually 5 to 6 strokes. You have to change the angle of the roller in each stroke. The toolpost is moved obliquely by x axis and y axis moved together.
I chose the material as follows. First I tried 0.5 mm brass sheet. The outer edge of the sheet is difficult to form. Finally it was broken.
I annealed the sheet 2 times during the spinning process to bright red by hand torch. As a result, the process is much improved but not enough. Incidentally I changed rotation speed from 420 rpm to 210 rpm because the roller spindle was burn out two times!
I annealed the sheet 5 times during the process, then I got final form. After that I tried second batch in the same manner, but failed. The process is so unstable that I gave up using brass sheet.
Next is 0.5 mm aluminum sheet. The bottom end was broken but necessary part is OK. No need of annealing. But its strength is not enough.
Next is 1.0 mm aluminum sheet. I got successful result but it is too hard for the lathe tool post. There is risk of damage.
Next I tried 0.5 mm copper sheet without annealing. It was broken but not so terrible as brass sheet.
I annealed the copper sheet two times. I got the same good result as aluminum. It is useful but bothersome.
I compared hardness of them by grasping them hard and checking deformation. The result is as follows.
0.5 mm aluminum < 0.5 mm copper < 0.5 mm brass < 1.0 mm aluminum
My target of the hardness is 0.5 mm brass sheet's. Therefore I newly chose 0.8 mm aluminum sheet.
After spinning, the bottom excess part of the job is parted off. The photo shows homemade parting tool made from hacksaw blade.
It needs 6 covers for the three cylinders. I prepared 8 covers including spares.