Replica back for Wartime Civlian Receiver

[Yorkie]

I have not come across "oil treated hardboard" and didnt know there was two sorts. Can you buy it easily? and is the difference readily apparent?

thanks Gary

Oil tempered hardboard is impregnated with special oil (sometimes just linseed oil) which is polymerised by heat treatment during the manufacturing process. This treatment gives the board increased moisture resistance properties and higher bending strength values. Typical end uses include internal wall or roof linings, signs, fascias and flooring underlay.

It's commonly available - I got mine from B&Q - a sheet 1220 x 600 x 3.2mm will make a jig, and one or two backs depending on the size. It's not expensive even at B&Q prices - under a fiver, but if you have a half decent timber merchant nearby who does retail, you'd probably pay half that price. If you Google 'timber merchants+oil tempered hardboard+location' (your area) and something should pop up!

As to whether you can tell the difference, it isn't so obvious unless you see it side by side with standard hardboard, but once seen, never forgotten. It's slightly darker, and isn't 'fluffy' like standard hardboard, nor is it as flexible. It gives a cleaner finish to holes when drilled or routed, and as Colin has remarked, it tends to blunt tools rather quicker, but then so does MDF.

B&Q's website isn't very helpful, and the B&Q label and barcode just refer to it 'Hardboard' - indeed, B&Q might not even know that it's oil tempered and perhaps just sell whatever comes on stock, but if you look for the manufacturers name and description printed in ink directly on the rear of the hardboard, you need to ensure that it says 'oil tempered'. I've attached a couple of pics of what I bought from B&Q , and though the pic with the maker's printed description is a bit indistinct, if you look at the top right you'll see the words 'oil tempered' after 'Finnish Fibreboard Ltd'.

I'll try to pull all the info together in a coherant fashion Gary, and send it off to Carl Glover for his consideration for the BVWS bulletin. I'm going to try to find time to make a jig for the popular Murphy U198 set - one of my favourites, for which I need a back. The backs are quite thin cardboard and the top right corner to which a heat shield over the dropper is attached, often becomes brittle over time and disintigerates, exposing the dropper, which is a bit dangerous. Although the U198 back is small, it's not a simple oblong, so needs to be cut to shape, but the initial blank must start off as an oblong in a router jig, then cut to shape with a jigsaw of bandsaw afrer the slots have been cut. The slots are the same size and spacing as the two jigs I've already made, and those slots seem to be fairly standard across different makes (DAC90A etc), but they are horizontal rather than vertical. Hence, the blank back panel needs to be stood on its side while the slots are cut.

I made these jigs out of interest and necessity, but there's no way one could do this as a paying proposition, and really, a lot of run of the mill sets wouldn't warrant the effort when a piece of hardboard, MDF or ply with ventilation holes drilled in would suffice. However, for rarer sets where authenticity is desired, in my view, the time taken to make a jig to cut up to perhaps 100 slots will be quciker than trying to do it by any other method and will make a neater job, calling for much less skill than say driling holes and cutting them into slots with a scrollsaw or hand fretsaw, or chisel amd mallet. Or so it seems to me.