Turning Archive 2007

Subject:
PM3520 Rocking Headstock - Update *PIC*

Jerry Hall
>A while back I asked for help on a 1/64th or so, fore and aft rocking of my headstock. It was particularly noticeable with large wet blanks. I got a lot of good ideas, and some confirmation that a few others had had a similar problem. I cleaned under my ways, and put a longer handle on the cam lever and thought I had solved my problem for a while. Not. It was better, but my feeler gauge at .005 moved easily under the drive end, even when well locked down. So today I bit the bullet and removed the headstock. There were shiny spots under the camshaft, and my straight edge clearly indicated a a high point on each side, and also around the set screw. I covered the center of the base around the camshaft with a black sharpy, made a lapping block of mdf and 220 grit PSA paper and lapped away, being careful not to touch the fore and aft surfaces. Washed off the sandpaper regularly. My straight edge showed I was making progress, but slowly. So on one side I used a very fine mill file, carefully, checking often and finished up with my 22O. Reinstalled the headstock and turned a fairly heavy round with no problems.

But I still have a concern. How did it get that way? I note there is less than 1/4" of iron casting under the bored out eccentric shaft at the thin point. Could my heavy blanks be distorting the casting? I hate to think the Mustard Monster can't handle repeated heavy blanks. For now I am assuming the machining of the holes caused "green" iron casting to create the high spots and that it was not milled flat afterward.

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