Chronicle 2: Punching the rear panel
I thought since there are some differences in technique required, I'd show how I punched the back panel. In this case, there are two larger holes - one for the impedance switch and a rectangular one for the AC Inlet. To do the impedence switch 1 1/4" round hole, I used a Greenlee hand punch. To do the rectangular hole for the AC Inlet, I cut two 3/4" round holes using my cutting tools and then used a flat file to square off the edges. Not perfect, but good enough for this prototype. My production models will be pre-cut and VERY exact!
So... first I made another template:
In the next two pictures, you can see the template attached. You can see the guides for the two 3/4" holes I cut for the AC Inlet and also the center 3/8" hole I cut for the impedence switch. This 3/8" inch guide hole is used so you can insert the Greenlee punch to cut the larger hole required.
The next three pictures show how I used the Greenlee hand punch to cut the large 1 1/4" hole for the impedenced switch. You simply insert the ball bearing threaded screw (with the die attached) through the 3/8" guide hole you cut, screw on the punch and hand turn the top bolt to punch a very clean hole. It is pretty easy and required little effort (at least with aluminum), but if you had to cut a bunch of chassis by hand, it would get tedious - you'd need the hydraulic punch which would be expensive. As I said, once I have a prototype, I'll contract to have a bunch of chassis professionally cut by machine...
Now I use the file to square off the two 3/4" holes I cut to form a rectangular cutout for the AC Inlet. Although time-consuming, I found it to be pretty accurate. I could not think of another way to do this easier. I tried grinding with my dremel tool, by I just ended up destroying the grinding attachments...
Here is what it looked like when it was done. Although the chassis is a bit scratched up - I'll be able to get it shiny and smooth again with some fine grit sandpaper and then steel wool. It'll look slick, but I'll wait until the top is punched before dealing with making it look nice...
Testing the parts for correct fit - Looks good! (BTW - these pictures show a voltage switch instead of an impedance switch, but it doesn't matter as I have a correctly labeled impedance switch of the exact same size - I was just testing fit and grabbed the wrong one...)
Sitting on my chassis holder waiting for next steps...
Next is punching the top of the chassis (lots of big holes again for caps and tube sockets). I need to wait for a few parts to arrive so I can figure spacing perfectly. I need to add another 6V AC tranny to power the relays and I need to see where/how it will fit before I make any more cuts... I can also have some custom faceplates made now! Then I start soldering! Yeah! Unsoldered everything from my pre-cut chassis and I'm ready to go once the custom one is cut...
Steve
) as it was just more repetition of what I've already showed you. I went without a template this time and just did a bunch of measuring. This was VERY time consuming and tedious and a big pain in the ass in general. You can also see my first relatively decent screwup (of many more to come I'm sure! 
