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Buncha
24th Mar 2009, 08:55 PM
Hello Hercus users,

After replacing my broken backgear with one purchased on Ebay, and brazing up a new tooth on the spindle gear I have my ancient 75 year old Hercus going again. The first job was for work. I work for a company that manufactures injection moulded parts to the local car manufacturers, and we had to perform a low temperature impact test with a 500 gm steel ball dropped 500 mm. As we could not find the one we used to have, and the submission was urgent, I made one on the Hercus.

I didn't have the time or know-how to make a proper ball turning fixture, so I did the following;

I calculated that the ball should be slightly under 50 mm diameter, so I bought a car tow ball from Repco. I mounted the threaded section in the chuck and drilled and tapped an M6 hole in the other end (top).

I then fitted the live centre to the tailstock and removed material from the shank, leaving a 6mm shank and enough to create to remainder of the sphere.

An old credit card was scribed and cut to create an R25 template. A cutting tool was blued and marked using the template and then then ground on the wheel. This tool was then used in small increments to extend the existing spherical surface to the shank.

The piece was then removed and the threaded section removed and an M6 stud fitted into the other end. This was then mounted in the chuck and the turned surface was polished with oiled emery cloth.

Finally, the stud was removed and an eyebolt fitted.

As an untrained artisan I was quite pleased with the result.

Buncha