How to get the bench clamp swivel to hold

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I have a bench vise that can rotate something like 270°. The problem is that the clamp that's supposed to stop it from rotating seems to only work in one direction. I can crank as hard as I can on the handle – really reefing on it. Yet, the vise will still rotate.

Here's a picture of the vise with the handle in question:

Craftsman vise that twists too much

On the bottom there's a square head on the bolt that looks to have an ACME thread. My thought was that I could just grind down a bit off the end of the bolt and that should let me tighten it a lot better against the base of the vise. Does that seem like a bad idea? Are there better ways to keep my vise from rotating?

Edit

Here's the bolt and the underside of my vise:

Bolt before I cleaned off the rust
Underside of vise

Best Answer

Rather than trying to shorten the bolt, what about putting a spacer washer under the clamping nut? You might do this as a diagnostic test to see if the present inability of the clamping bolt to hold the vise is due to the nut "topping out". Of course, if there is not a washer in the original design, there may be a reason, such as, a washer there might jam against the bolt and impede release when the nut is loosened.

I would make measurements of the length of the bolt and of the space inside the nut to see if this could allow the bolt to go farther inside. Maybe the nut is corroded inside and is binding early and so not clamping effectively.

Is it possible to improve the threads of a bolt-nut combination by applying an abrasive paste of suitable grit size to the threads and working the nut back and forth over the bolt?

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