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I've always thought they were to tighten the ways to keep the tables from creeping up or down.
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Wild Turkey
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(joined 10/1999)
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Location: Mobile, Alabama
gamma,
I have been to the Vintage Machinery site numerous times and have downloaded and printed the manual for my specific machine. Unfortunately, it says nothing about the use of the wingnuts/knobs on the back of the machine. However, I note that the manual you posted, while not exactly the same, states that the infeed table is adjusted up and down by first loosening the "hand knob" on the right side before turning the adjusting crank. I can only guess that the same features on my jointer are siezed up and ineffective for locking down the adjustment. I'll try some WD40 and gentle persuasion on it. Otherwise, everything works as it should.
Thanks