My two cents...
I put a very nice, hard and durable finish on the top plate for my s.e.x. amp, but it was not the kind you can do in a day...
I first cleaned the plate and transformer bell thoroughly and then scuffed them up with some 120 grit sandpaper, and then wiped them down again completely with 100% ethyl alcohol.
I then applied 3 thin coats of SEM self-etching metal primer with about 5 minutes between coats and then let the plate and transformer bell dry for about 2 hours before applying the first coats of finish coat.
For the first round I applied about 6 or 7 coats of Hammerite Rust cap hammered black at 15-20 minute intervals (on a warm, dry day) and then let the plate and transformer bell both "cook" on the radiator in my office for several weeks -- hammerite recommends something like 10 days to 2 weeks between coats if they are allowed to dry more than, I think, 90 minutes.
Then I again cleaned the surfaces with a citrus cleaner followed by 100% ethyl alcohol and applied another 6 or 7 coats to the top plate and another 3 or 4 to the bell, and again let them dry and harden on the radiator.
When all was done the finish was very smooth and even and extremely hard.
Of course the application schedule will vary somewhat according to the manufacturer's recommendations, as well as the final drying time, but typically the longer you can let it sit and harden, the toucher the finish will be.
I will offer that I started just building up the kit on the bare aluminum plate and eventually decided to put the extra effort into putting a nice finish on it, so stripped the whole chassis down to the bare plate and started over. Yes, it was a pain, but worth it, and something that I actually enjoyed doing.
Still not sure what I'm going to do with the Crack as I might decide to eventually build it in another scratch-built chassis as it appears that I may not be able to fit a better tkd volume pot in this one. Then I can also use the stock chassis for experiments with different driver tubes, etc. Worse comes to worse, I can always do what I did with the s.e.x, and strip the whole thing down and finish the top plate and spruce up the base a bit.
HTH,
Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)