Beware the Benbo Ballhead

I had a mishap with a Benbo ballhead attached to a Manfrotto monopod. There is no model designation on the Benbo, so I can't be any more specific. The threads in the base of the ballhead stripped out in the "heat of action" and the ballhead separated completely from the monopod. Fortunately I had the camera's strap around my neck so nothing hit the ground, but this could have been a major disaster.

The bolt on the monopod is smaller than the hole in the ballhead, so I had to use an adapter plate that was supplied by Manfrotto. This adapter is quite short, and engaged less than a quarter of the threaded hole in the ball head. I think that this "short engagement" was too little to bear the weight involved and eventually the threads of the ballhead gave up the ghost. I autopsied both the monopod and the ballhead immediately after the failure and the threads in the soft aluminum base were pulled completely off - the bore was quite smooth.

Perhaps I did some things that contributed to the failure of the ballhead. It is possible that I had overtightened the head when I mounted it, but I have no way of knowing. I just tightened it by hand until it was tight enough to stay put. The other thing is that, whenever I mounted a camera on this ballhead/monopod I would lock down the ballhead and mount the camera by turning the whole ballhead & monopod assembly using the comfy foam rubber grip on the monopod. This, I suppose, put some extra strain on the ballhead to monopod connection every time I tightened down a camera.

Whatever the reasons for the failure of my Benbo ballhead, if you have one of these things I advise you strongly to check it now!!!

Unfortunately, threads in aluminum are <em>extremely</em> easy to strip. Even if over-tightening doesn't strip the threads outright, it greatly reduces the strength of the connection. For example, correct torque is critical when rebuilding an aluminum block engine. Correct torques for many bolts are in the 100 inch-pound (8 foot-pound) range.

It's so easy to over-tighten if you're using any sort of wrench that I've seen people strip aluminum threads when they thought they were just snugging things up, in preparation for final tightening.

<p>

Obviously, the problem is much worse if only a few threads are engaging. It might not be a problem in a steel-to-steel connection, but most certainly is with aluminum. If you spun the monopod, the jolt when the bolt tightened could easily apply excessive torques to such a frail connection. Sounds like bad design.

<p>

Any machine shop could easily fix the problem, but don't know how much it would cost. What does your Bembo or Manfrotto dealer have to say?

Just a follow-up on my original post. I went to my photo shop and they suggested that I try a different adapter made by Linhof. This one was at least 4 times as long as the Manfrotto adapter and it easily engaged the remaining threads in the ballhead and could be tightened down firmly despite the missing threads. I remain somewhat paranoid after the mishap, so I applied epoxy glue to the adapter before I installed it into the ball head. After the glue was dry I tested the union between the adapter and the ballhead to 120 inch-pounds with a torque wrench. It held up OK, so for nine bucks Canadian I got the monopod/ballhead combo back in action.