Jazz wrote:
wood screws of this size can easily hold 20kg withdrawal force lengthwise each (if penetrated enough in proper wood)
the accordion is not even 10kg total, has at least two anchor points and is not pulling straight out of the wood
(although I agree it would 'feel' more secure to have an expensive accordion fitted with (u-)bolts)
Waldo responded:
If one screw was good enough, then why have 3 holes in the bracket? Another factor; When a load is attached via one point, there is always the potential for a "rocking" motion, in all planes, to loosen the attachment. Two fasteners reduces the "rocking" motion to a single plane. Three fasteners in a triangular pattern removes all the adverse effects of "rocking". Obviously, the designers of the brackets felt 3 screws were necessary.
The bottom anchor point doesn't carry any of the load, only serves to hold the case to the body (I checked this out). The top anchor point was the bracket missing the correct screws (only 1 wood screw). The load is straight out (the least capable holding orientation). Proper design places screw/fastener load (see: F1) in shear (although often impossible).
I my opinion, U-bolts are the proper way to go. As mentioned in a previous post, I suspect they went with the lightest option they had, as the accordion in question was engineered to be as light as possible, considering tone and price.
I wore and played the accordion without failure (although, mostly sitting). Imagine walking down a flight of steps, desending from a stage. Every step would result in several G's being applied to that one screw (that's 20-30kg) as I bounced down the stairs. Luckily, that never happened.
Scuromundo:
Believe it. It happened. I examined the holes from which the machine screws were extracted and there were no "threads" impressed inside the hole walls. They were smooth, as drilled. Could only be that way if the error occurred at the factory.
