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SP&S #273
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Machining the Throttle Body
Thursday, August 29, 2002 by John NiemannHere the throttle body is "chucked up" in a vertical turret lathe to cut new seats. This is the position the throttle mounts in the dome and its easy to see how the steam enters both a upper and lower port to the center and exits back and down. We found more severe rust pitting here than on the spool and had to make a cut of .025" to get the seats to clean up. Once again, the same amount off the top seat as the bottom. We built this contraption to mount the body in the lathe and "indicate it in". You can see an indicator riding on the upper seat (top center of photo) and I'm looking up into the body at another riding on the lower seat while the table is turning. The trick is to make both the bottom seat and the top seat run true (to within .002") to the center of the revolving table that it is mounted to. We could move the whole fixture with the 4 opposing jaws of the chuck and we could tilt the body in 4 axis with the 4 jacking screws that we provided around the discharge. These are near the table and are double nutted in the photo. Although it only took about 4 minutes to cut each seat, it took several hours to get both seats dialed in and running true.
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