Working with Brown Phenolic Resin Plate

[David Dunlop]

Has anyone had experience working with 1/4-inch thick Brown Phenolic Resin Plate?

Once you have cut, or drilled it, the cut surfaces reveal the inner, much lighter core colour, but when you look at worked examples of this plate in wartime wireless equipment, you see all cut edges have been colour matched to the brown surfaces of the plate.

My first thought was that the resin was simply used to paint these surfaces but that resin is far too thick to easily apply as a light coat of touch up paint. And once prepared, typically cures rather quickly. So I am trying to figure out how to seal these cut edges and bring their colour in line with the surfaces of the plate.

Any experience would be appreciated.


David
VE4DTD

[M0FYA Andy]

Is this a Tufnol or similar material? If so, there are various grades (or Brands as the Tufnol catalogue refers to them as). Not all show a lighter core colour in my experience.
I can imagine in the wartime era a shellac varnish would have been used on the edges.

Andy

[David Dunlop]

Hello Andy.

Rightly enough, there are a number of manufacturers of this product out there and a number of names for it. The one I am working with is referred to as 1/4-inch Brown Phenolic (CE) Resin Sheet. The '(CE)' refers to the fact layers of canvas sheet are embedded in it to strengthen it.

A 9-inch square of this plate was used to mount the Aerial Base C2 for the wartime Wireless Set No. 52 Canadian to one of the steel Aerial Chimneys on the roof of Wireless, or Command Trucks and Lorrys. The Aerial Base C2 That I found for my 52-Set Project was missing this plate and I need to replicate one.

Although my replication will never be exposed to the elements, I want to ensure it is finished and sealed as per the wartime originals once I have finished drilling the required holes in it. The same plate was used for the chassis assembly in the Coils, Aerial Tuning No. 2 A for the 52-Set and I noticed when restoring that item, all the exposed edges had been very neatly sealed with something that was a very good match to the flat, plate surfaces.

Never a dull moment with a project like this it seems.


David
VE4DTD

[Uncle Bulgaria]

I agree with Andy - shellac is a very likely bet. Easy to try, too - just mix up a reasonably heavy cut, or buy some ready-mixed and try the consistency. It's great stuff with many uses.

[Radio Wrangler]

The varnish would also seal up the exposed fibres of the fabric exposed on machined faces, preventing the ingress of moisture, so it may be a lot more functional than just making it look uniform.

David

[kalee20]

I've used 8mm Tufnol carp* brand (phenolic/fine-weave cotton) and found even within a sheet the core can either be pale, or the same dark colour as the surfaces. I don't think it makes the sheet unfit to use, but I agree it would be nice if it was uniform.

* Tufnol did have some interesting names for the various grades (combinations of paper, cotton, asbestos, glass-fibre with phenolic or epoxy resins), such as whale, vole, adder, asp...

[tube-noob]

Shellac would be my goto also.

[Simondm]

In the 1970s I worked briefly in a factory making school science equipment, including a then-diminishing amount of old-style apparatus with brass and mahogany parts.

Plastics (including a small amount of Tufnol) were linished (belt-sanded) with fine grit belts, and then further polished if necessary. it did give a more even colour, although I'd guess the darkening described comes partly from oxidation over the years.

You also see it with Paxolin circuit board: brighter yellow when first cut but darkens after a while.

[David Dunlop]

There is a wood supply shop about 10 minutes from home that my heat and humidity rattled brain just remembered. They are an 'Old School' shop that still sells nails in bulk, or boxed, have a great selection of household lumber they will cut to spec if needed, and also have a good supply of exotic woods for the few furniture and cabinet shops in town still thriving.

I will pop in this weekend with the plate in hand and see what they can come up with for ideas. There are three part-timers on staff who all date back to the pre-urethane era. I can remember my Dad and Grandfather mixing their own shellacs. I think alcohol might have been the thinner, but not the single malt type. They also used to mix their own tints for varnishes. My Grandfather was a Master Stone Mason from Scotland and he had a very keen eye for colours as I recall.


David
VE4DTD

[mark_in_manc]

I am only re-iterating other people's points here - but I turned a missing knob for a 'pull-on, push-off' light switch on a machine tool, out of a big lump of apparently uniform brown Tufnol. It went yellow and streaky-looking during the turning, but as time has gone on (and I have pulled, and pushed, with greasy hands) it is now all back to brown again. Using some kind of varnish, or just oil, would probably speed this process up a lot.

(ETA - if I had an excuse to visit your wood supply shop with an interesting question like you have, I'd definitely find time to go )

[David Simpson]

David, I think what we are talking about here is good old "Paxolin" & it's derivatives. Been in use in the UK, and by the military, for about 100 years. To save one banging-on, just gen up on Google, or use this Forum's "Search" facility.
Can be cut with a fine bladed jigsaw or hacksaw, then the edging finely filed smooth. Further edge smoothness can be obtained using P280 - P600 Emery/Wet & Dry Sandpaper on a "Block". For H & S purposes these days - wear a mask.
NEVER drill straight away with large drill bits for large bolt holes, always drill a wee pilot hole then increase the bit size until the hole size is achieved. Also, never use a coarse C/sink, a fine one is required. This advice also stands for "Ebonite"(seemingly can still be bought from China). Never use an oil based or water based liquid for polishing edges. However, in the RAF we used to use "Hellerene". Cut Paxolin & Ebonite, CTC & Hellerene - - all evocative smells one can never forget !

Regards, David

[Uncle Bulgaria]

On the subject of holes, I've had success with stepped hole-cutter bits. They form a good hole, and a nicely countersunk edge with no further processing required.

[emeritus]

In the 1960's I used to make up my own shellac varnish from shellac flakes bought from the builders' merchant, and methylated spirit. I used to use it for strengthening card that I used for making buildings on my model railway. It was something I had read in a post-war book on modelling, written when materials were still in short supply.