Gentlemen,
Atlas used Zamak for material because it is stronger than zinc die cast parts. Zamak is also hard mold capable which creates a finished part in as little as two operations. They are molding and trimming. That was attractive to the manufacturer to reduce overall cost. Unless a restoration is to create a museum piece their is no need to copy exact. For the majority of readers, the goal is to have a functional home shop machine. To make a functional part with minimal effort select a piece of stock longer than the total of the short bits plus the gap. Suitable materials are, Aluminum, Brass and Bronze. These are ductile enough not to damage the surface of the overarm even if over tightened.
Face both ends and drill through for the clamp bolt. Based upon the excellent drawing supplied by Wheels17, the arc center should be 1.25 from the bottom end. Set a fly cutter to a .75 radius. Touch down on the top of the material and zero the depth dial. Proceed to machine the arc to a total depth of .166. Then cut out 0.5 inch through the center of the arc. Deburr, assemble and use.
I have been making parts for various machines since I was 16 years old, and that was almost 50 years ago. In those days I didn't have the money to buy parts after buying the machine. So I learned to make what I need. I acquired the attitude, "Failure is not an acceptable option". Sometimes the first try was not what I wanted. No problem, do it over correctly.
The primary reason I have continued to acquired old machinery (defined as 1870's to 1930's), is they are reparable. If for example you acquire a 1980's CNC and a control board fails, those parts are not available at any price. Then if you have the skill to isolate the defective component on the board, they are long obsolete and not available. Then the only option is to retrofit the entire system with new controls and servos, an extremely expensive option, or scrap the machine. We have home shops to make projects. Therefore, making replacement parts for equipment should be second nature. Enough on the soap box.
A problem that occurred with my Atlas Horizontal, was the table nut wore out. I made a replacement, using Bronze. In a couple of years excess back lash was observed. Upon disassembly, crumbs of bronze were observed in the key way of the table feed screw. Upon close examination, the feed screw had not been properly deburred at the factory back in 1942. I took a wire wheel to the burrs and made an additional nut, all has been functioning well for the last 10 years. The suggestion is to check your feed screw and remove burrs as necessary.
Enjoy your machines and keep the chips flying!
Restorer
