< 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.
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