Off w/ the Screw Clamps,, On W/ the Cam Clamps

[Ljohnsaw]

Looking again at yours, when clamped, it appears that you have another ¼ turn of the cam to lock it up. 

On my clamp, I put a long beak on the top.  I do a lot of cedar that has very deep bark with furrows.  I found it necessary to make them like that so I can get a good hold of solid wood.  When my handles are straight up, the clamp can go back the maximum and the beak is still sticking past the vertical post.  That also lets me get over any bumps in the log that would otherwise interfere with clamping.  Just something to consider.