< Crossheads >
The crosshead has complicated shape. Moreover it needs much tolerance and strength. There are various method to make crossheads. I chose BMS one-piece crossheads for my William.
Boring cavity for the small end. Bottom of the cavity should be flat and has a hole holding the gudgeon pin.
Cutting out the shape roughly with drills, fretsaw and files.
Dividing from center and boring a passage for the small end by drill and endmill.
Milling the curved surface on the rotary table.
Milling the bush roughly on the rotary table. I can't use lathe here because any tool would crash the crosshead shoulder.
I prepare a handmade tool to finish the bush. Note the hooked shape of the tool which clear the flange of the bush. After that a center hole for the piston rod is drilled and threaded.
Upper and lower grooves for the slide bar are milled symmetrically as follows.
1) Screw a piston rod into the crosshead and fix it with a locknut.
2) Put a true flat bar in the vise and put the piston rod onto the bar.
3) Close and tighten the vise jaws and mill the upper groove.
4) Reverse the job on the bar and mill the lower groove to the same depth.
Finished crosshead body.
The drop link is normally bent from a thin plate. It sounds terrible for me so I made the drop link from a thick bar. I prepared 2 in 1 at start.
To form the steps, the bar is cut from center ,reversed and cut from OD. Note the bar is fixed by two screws from backside of the faceplate.
Milling the outer shape.
Dividing from center and milling the round top.
The drop link is gathered with a thin washer by the gudgeon pin and nut. The washer is close fit to the cavity of the crosshead and will hold the gudgeon pin in correct center.
BMS crosshead against BMS slide bar will have irregular wear in use. Case hardening is typical answer of the problem. I case-hardened the crosshead grooves as follows.
1) Heat the crosshead to bright red with a blowtorch.
2) Throw the job onto the case hardening compound and coat it (see picture).
3) Re-heat the job for few minutes and quench into cold water.
In the same manner I case-hardened the lower hole in the drop link which against a pin for anchor link. The gudgeon pins were made of high-carbon steel, so I hardened and tempered them.