My wooden double handle screw clamps would loosen on their own. I would tighten both handles and could immediately watch the handles turn and loosen.
The solution, provided by Jorgenson, use a stiff wire brush to thoroughly clean the threads of the screws. Problem Solved.
Another issue that I learned to remedy by myself was that which affected my Bessy K-body style, Cabinet Master K-body clone, and fresh out of the box Jet K-body clone bar clamps.
The symptom. It seemed that when tightening the clamp handles that there was no lubrication. The motion felt dry and I felt that the screw was providing more resistance than the actual material that I was clamping. I will restate for clarity that all 6 of my Jet clamps felt this way straight out of the box. The Cabinet Masters over several years developed this feel as did the Bessy clamps. Oh, and so did my aluminum bar clamps with the butter fly style screw handles.
For years I cleaned the threads and sprayed a dry lube on the screw with very mixed results with most results being only slightly better.
Jorgensons answer and solution was to send me a free replacement screw head. That worked for a few years but......
Then through divine intervention the fix/answer came to me.
If any of you have witnessed this problem with any of your screw clamps this may be your fix.
I discovered that there is truly friction and resistance in tightening the clamp. As mentioned above it would seem obvious to clean and lubricate the threads of the screw.
I discovered one more spot to lubricate and doing so immediately made all of my brands of clamps operate closer to silky smooth than prior to locating his spot.
Starting to sound like one of those commercials, huh?
On most all of these K-body style clamps and the clones the part you need to apply oil is partially hidden and out of site.
You also need to oil the end of the screw where it is riveted onto the steel washer that delivers all of the clamping force. There is tremendous friction at that connection and a drop or two of oil instantly decreases the effort needed to tighten the clamp.