An old Premier xylophone in for tuning and repair.
There are two main design issues with this instrument, and a further complication:
The note rails sag in the centre mainly because of the joint, but fundamentally because thin wall tube isn’t strong enough. The simple solution is to weld the joints in place to create a fixed rail.
The second design problem is that the resonators act as a structural component of the frame; this is just silly, doesn’t provide strength and is an example of how instrument manufacturers fail to understand the rigours of life as a xylophone and how they are used.
The complication is the round tube on the lower transoms which hold the castors; again this is just a silly idea which makes caster renewal needlessly difficult.
So this frame wobbles all over the place, and investigations show that whoever repaired it in the past didn’t understand the forces in play.
Newtons Mechanics: p=mv
p is the momentum or force, m is mass, v is velocity. Ignoring units of measurement a 60kg xylophone being wheeled along a corridor at 3mph (slow walking pace) will triple the mass to 180kg.
Put the castor at the bottom of long lever (frame leg), and that 180kg is multiplied again.
Understanding these principles explains why bolts shear, frames break, castors fall apart on commercially produced instruments.
However, understanding the principles also gives the solution for me to make the repairs that will last. I am happy to sacrifice the lifespan of a caster to save a xylophone, that is easy to repair, use stronger casters.
Back to the xylo.
First job is to make new lower transoms that are fit for purpose, and will make the rest of the frame easier to strengthen; solution = square tube