Nice one Kevin

I wonder if the 'rods' will pull out, so you could adjust internally ?
Yes, Hi Jon, the rods pull out and are about 12cm long on each side. The inside tube (created by bending the sheet round is so crude that it barely represents a circle. When I pulled one of the bars out it had a small sliver of wood jammed in there to create some extra friction. It is a disappointing bit of engineering, sourced by the dealer and so may not be an MMC part. I'm tempted to make up a set of my own from tinted perspex, using the same mountings and having a thumbscrew through the clamp to apply some pressure.