Sanding down Chassis (or how to make cool sparks with a rotary power tool)

Believe it or not, I actually got something done that isn't sorting parts into bags and boxes! And it involved playing with a power tool I've never used before! Double win! All whilst under the influence of Lemsip/Beechams/Whatever trying to keep a cold I've picked up at bay. Power tools and muddled mind not always the best combination, but on the other hand you kind of lose sense of levels of what is allegedly safe and definitely experience a dip in caution, so it balances out in the end, with the man flu induced haze and lack of thought balancing nicely against being oblivious...

So, what did I do? I started sanding all the chassis parts that need the paint taking off. Why? Well, so that a lot of things like pots, input jacks and other things that people will be touching or going near will be grounded to the chassis, which will be grounded to the mains. For this I had to remove the paint and get down to bare metal behind the power, standy switches, the input jack, all the front panel EQ and switches and controls as well as the impedancve selector out back and the slave out and level.

However, the bias point, speaker outs and FX loop were not to be done. So basically, i went off and taped up all the holes not to be done, as well as around the holes that were to be done., ending up with the chassis looking like this:

Now, I also have a bit of a test before, making sure jacks fit in jack sockets, and pots fit in the places they were supposed to (just in case the holes were too small) etc. The only thing that didn't fit was the pilot light (all important blinky light) so I marked that as something to do and to widen whilst I was at it.

I also went ahead and marked where i needed to drill holes for the IEC plug earth, the star eart mount and a hole to mount the tag board for the faux centre tap (whuich finally made sense in my head as being like a transformer center tap, no idea why it took so long to register).

i also taped down the cardboard copies of the PCBs I made earlier, and lined them up so that they had enough space after having considered the placement of things like tube sockets, fuse holders, pilot lights, switches etc. The preamp board wasn't a problem really, but the power board is going to be a tight fit next to all the sockets and other big bulky stuff that will be mounted in that area.

This all done, I rigged up the go pro, and started filming, for posterity. It'll probably induce face palm moments and WTF exclamations from people that actually know what they're doing, but as I had no clue which attachments to use, well, I just kind of experimented as I went along.

I picked small sanding attachments to do the inside edges of all the holes, which went well (with the odd cool spark shower which is entertaining, although apparently I am "a foolish human being" for not wearing things called safety goggles, which I don't have either, but hey...). I then moved onto the sanding part, putting the rotary drill through each hole, then attaching a sanding disc, and pulling back through the hole to sand down a circle on the inside of the chassis. First few attempts i didn't quite attach the sanding circles properly, so they ended up flying off a few times, but I got the hang of it after that. It also means I should never ever train anyone on Health and Safety (ie, how not to do anything fun ever again). I lumbered through, and got all the bits done I needed to as a first pass.

The end result? Almost there, whilst it is easy to get rid of the paint inside the holes (the edges), actually getting a nice cleared circle behind each part is trickier, and I'll need to have more of a look at it tomorrow and see if I can have a brainwave of using a different attachment to make it better, but on the whole, it's ok so far:

As you can see needs more of the paint gone, although whilst it might be "ok" I do want to do it properly.

One thing is that it was a pain in the arse to do. I had to put the dremel through each hole, then attach a sanding disc, turn it on, and pull back on it hoping it'd get rid of the paint, not ideal by any means, but no other choice as the rotary tool was too long to fit in the chassis. I'd actually probably end up buying a real dremel if i were to do this again, and get the right angle attachment they make for it. It'd have been faster, a lot safer and I'd have more control over what I was doing as well. But, I'll soldier on with the cheap one I've got (I actually do love this tool, so so so much fun, I must stop myself from thinking of things than need holes made in them, but also means it might be worth getting a proper one of them, but I'll see)

After all the sanding, I attempted to drill the holes for the ground, but kind of discovered that in the battle of drill bit vs steel chassis that the drill bit lost. badly. The first one kind of ended up 1/3rd shorter than when i started, with it barely making a dent in the chassis. The second drill bit seemed to be making headway until it started glowing bright red like the depths of a volcano at which point it seemed prudent to stop. The chassis? No hole, just a slight indentation one side, and a raised point the other. I'm guessing I'll need a proper drill for the holes (which I have, but can't find the chuck to put an appropriate sized drill bit in it) and actual drill bits to go through metal.

So, that'll be the next job, finding a way to drill holes, and probably also countersinking the ones for the PCBs to make it look nicer overall, but first I'll need to find drill bits that don't end up losing against the might of the chassis...

As for the video, I am thinking once I have more footage I'll get all the videos and time lapse them together going from one bit to another to keep it interesting and show the whole amp from start to end.