Vandercook Crescent issue…

Printed tonight on my 219OS, everything (relatively) normal. Start cleaning, put some solvent on the vibrator, let it run for a bit when suddenly it stops spinning. Usually if I use too much solvent it stops because it’s too slippery, but now the vibrator is stuck and won’t move.

I take the top frame out and clean it off and it won’t move. I’ve regularly applied vaseline so i don’t think that’s it. I try unscrewing the crescent and it starts moving fine. I unscrew it too much and it moves quickly but seems to jump a bit at the end.

I hadn’t touched the allen set screw, so I’m assuming for some reason the crescent worked itself tight? Maybe the set screw was always a bit loose and adding solvent when cleaning this time cleaned something out allowing the crescent to screw itself tight?

Searching prior topics I see that I should loosen the set screw, tighten the crescent until the vibrator doesn’t move, then turn it back a quarter of a turn?

When adjusting it tonight, the set screw didn’t seem to lock down. I didn’t tighten it too much because I wasn’t sure what was what until I came home and read the previous threads here describing this. Is it likely that the set screw was just loose and the crescent tightened itself? Could there be damage to the set screw? When loosened, the vibrator spun freely and oscillated as expected.

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I think you’re supposed to pull the crescent holder back 3/4 turn. But on a #4 to keep the vibrator spinning well, I have the crescent holder pulled out about a full turn, then tighten the set screw down so the holder doesn’t move. Use graphite lube on the shank of the crescent and vaseline on the worm. As long as you tighten the set screw and can’t twist the crescent holder, then it’s good.

Also, check to make sure the sharp points of the worm doesn’t have flat spots where you’re having the problem. I had to sharpen one of the points on the worm. Look at the crescent and make sure it has good points as well.

Sometimes the crescent will jam, or repeat in the extreme grooves of the worm, when the points of the worm and/or the crescent are worn or chipped. They would be obvious to a visual inspection.
The set screw keeps the crescent retaining screw (can’t remember the actual name) from moving, but I’d think an outward movement would be more likely than an inward movement. It could happen though, especially if the outer threads of the roller were filled with dried ink. I like to run the crescent retaining screw just below roller surface so there isn’t such a large recess to collect ink. The set screw should only be just tight enough to stop movement, not so tight that it deforms the threads.
If you moved the crescent retaining screw when the lock screw was not loosened, the damage would be to the threads of the retaining screw. That isn’t a major problem, the threads can be repaired with the correct die or thread-chasers or just a fine knife file.
Another point of wear to look for is the post of the crescent, and to the pocket of the retaining screw. They are supposed to be lubricated with graphite grease (just a mix of flake graphite and grease). But when these surfaces wear, the crescent can get wobbly and cause problems. So it has been recommended to replace both rather than just the crescent.

Thanks for both comments.

Back at the studio/shop. I adjust the crescent but when I tighten the set-screw, it doesn’t stop the crescent from turning. Don’t have time to take it part just yet but will soon. The set screw definitely feels tight, like i can’t turn it any more, but when I give a turn of the crescent screw, it moves easily.