Thanks for answering that one
Another one regarding the upper assembly, is it angle iron or anodised aluminium ?
One final question
, not specifically to this design but others I've seen - where the secondary is held in place by a 'wire' based spider, how is it arranged so that the secondary holder-assembly doesn't "bounce around", if you get my drift....there must be quite a bit of tension in the wires to stop that from happening which in turn would mean the secondary frame has to be pretty sturdy to stop it from warping...