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| p.1 #8 · Switching between a ballhead and gimbal head. |
You are very right Patrick that a big lens like a 600mm over the shoulder can develop a lot of torque, and far more than anything I would create with the gear I use. In thinking about the situation of the round dovetail plate on the ball head base, the place where the actual slipping starts is between the plate and the ball head, and once it happens in the correct direction, the screw may still come loose even with Locktite. The extra tight screw clamping of the plate at the center does not necessarily provide enough clamping at the rim of the round dovetail surface. I suggest you consider finding some very thin double stick adhesive tape, and carefully place shaped pieces around the rim of the plate that averages about a half inch wide, to match the outer area of the base of the BH-55 that is not slightly recessed. That will provide a lot of adhesion out near the outer diameter of the plate when the surfaces are clamped together, and should prevent any break away of the plate when in torque.
The only possible negative I can see is that the tape will be a non metal item that will make the whole assembly slightly less rigid. That is why it is important that the selected tape be very thin. I have seen such tape available from industrial suppliers that has very high adhesion, but am not sure about what is available in the general retail market. You could even try the double stick version of ordinary "Scotch Tape", which has less adhesion than a high performance tape, but is quite thin.
Another option is to increase the friction between the metal surfaces. My BH-55 seems to have a matte type finish on the bottom that should help with friction, but the TH-DVTL dovetail plate has a much smoother glossy finish that seems like it would slip fairly easily. If you have a similar situation, you could consider doing some careful sanding on the dovetail plate on its mating surface around the rim to increase friction. I would suggest you make the strokes in the radial direction and try only a minimum amount of sanding. Obviously it will ruin the finish on the plate, but that area is of course completely hidden when the plate is installed.
And I would think that Really Right Stuff should consider a design change that provides a slight recess in the center part of the dovetail plate, and make the finish on top more of a sandblast matte to increase the clamped friction. The BH-55 all ready has a slight recess in the middle, but people use the dovetail on other items also, so adding a slight recess would help for those.