Paul
Halfords do a rattle can of Matt lacqer for £8. I’ve not used it but I would have thought it a better bet for larger areas.
I like the dexion speedframe idea. Any noticeable sag on the cantilevered arm? I’m starting to think about the lighting rig for Cheddar.
The led supports are 50 x 25 x 3mm alloy in 3 runs of 2.75M. This gauge chosen to give the required beam stiffnes so that the distributed load and the four gallows supports cause a maximum deflection of so few mm that the eye doesn't notice it at all. The spans between the supporting gallows vary but the longest is 2.7M and the beam calculations allow for that. The 4 gallows locations coincideT with 4 of the 6 steel trestles that carry the layout. Again beam calculations told me that the spans between trestles won't allow the baseboards to sag.
The load included on the overhead alloy beams is a PVC 40 x 40 x 2 inner angle cunningly arranged to pivot and carry the leds. Thus the 50mm alloy face is vertical but the inner PVC carrying the leds can be tweaked to give best angle for illumination.
I use 3 led strips per section to give the CRI and colour temperature required. The led strips I used are rated at 72 Watts/M and each 2.75m run of 3 strips deliver 3000 Lumen/M. They are 650mm above baseboards which are 1300mm above the floor.
These heights ensure that smaller viewers need hop-up stools and don't rush about, tall viewers are less likely to bonk the overheadf rig, and I get baseboards at a good level for operating as well as construction. The sight lines to the backscene are to my liking also.
The temperature rise of the leds is 18degC after 30 mins so will be fine all day. Note that users of the latest higher power LED strips need to mount them directly to the alloy support to provide heat sinking as they consume nearly double the Watts/M producing most of that as heat.
NB I used these on Highbridge's new rig where the alloy beams are 50 x 50 x 3mm and hung so the angle edge is on top so both faces are 45 deg off vertical. Lenghts are 3 and 4M. This being a permanent rig, no nice vertical face is required for labels etc.
Now to Andrews question.
The gallows and their load have been erected for over a year and I just put my set square to the rear top right angle joints.
3 are pretty much still square, bear in mind that my horizontals are only 640mm. Wider baseboards would require more length here.
The worst sags by less than 18mm. It looks as if I haven't quite driven the joint home so that may improve after a visit from the mallet. Obviously safety consideration at a show requires certainty and one can easily add triangle plates to reinforce those joints.
Speedframe joints come in 2 flavours, permanent and dismantleable. I used the former as the gallows are small enough to travel as rigged.
I suspect that sag at those joints would increase with wear of the latter type.
