London Power 3 channels amplifier project

[Vostre Roy]

Hi Vostre
There is no need for the tubes to go through the chassis unless you put the parts on the same side of the board as the sockets.The usual mounting has the components and tubes on opposite sides, allowing just the tube socket to protrude slightly or be flush with the chassis outside surface. The other issue could be of using stand-offs that are unnecessarily long.
For the 9-pin tubes, it is about 0.75" if you are really precise, but 1" if you need some slack - this is also good clearance for the tube itself. The stand-off might be 1/4" here.
For the octals, 1-1/8 to 1-1/4" hole depending which part of the socket you have to clear. The stand-offs would be 1/4" to 3/8".
Step bits work well in thicker material than Hammond's chassis. The steel is actually not that thick but if you are used to aluminium then it will seem pretty tough - stainless could seem impossible! With most consumer-grade drill bits and cutters, the number of flutes and hence the number of cutting edges is usually minimal. For example, counter-sinking bits are most often three-flutes and sometimes only two for the smaller sizes. Good counter-sinks are five-flute. I had to order them from China recently because no one had them locally.
With the low-flute-count drill bits and a slightly wobbly drill chuck, it is difficult to get a smooth cut unless the drill speed is a bit higher. That can lead to an out-of-control situation pretty quickly, though, but one defence against it is to loosen the belt in the drill press. This will keep the bit from grabbing the piece out of your hand, or out of any jig or holder.
Another way to fix the holes is to use a nibbler. This is a single-tooth cutter that you use to nibble away material - great for making the IEC mins plug hole.

Greetings Kevin,

Regarding the tubes, I probably misinterpreted the mounting diagrams that were included in the kit, really thought that the tubes had to have their base through the chassis, which required the largest size of the only step bit I own ahah. And yeah, that step bit only has two straight flutes (I guess the "flutes" are the vertical grooves) so an upgrade wouldn't be too extravagant I guess. Need to get myself a steel nibbler too so I'll get an Amazon order ready for my next time off.

Oh and yeah, I experienced the out-of-control situation pretty quickly, pretty sure that this chassis is screwed now. Won't cry over it, I'll use it to do some more test and get a better hand before doing the next chassis try.

I would encourage you to persist with the  Hammond steel chassis or get a non-hammond Aluminium chassis.  I've found the Hammond Aluminum chassis to be rather flimsy at only .04" thick.  With your drill press you may need to change the speed, use a newer step bit, and use metal cutting oil to ease getting through the larger holes.  I've used many Hammond Steel chassis and generally with a good bit and the proper speed you'll get though it just fine.  To clean up the burs I'll use a grinding stone on a hand drill for large holes and countersink bit on smaller holes. For the hard to reach spots on the panels I use a drill bit holding extension arm (what are they really called?) with the grinding stone.  You'll clean em' right up!
If you prefer to go Aluminium I'd suggest that the chassis be .07" to .09" thick.  There's seller on Reverb that can make them custom sizes and make bottom plates if you need one.

I hope that helps!

Greetings!

Well I totally understand what you mean, reason why I wanted to try the steel chassis this time is because I've used Hammond's Aluminium in my previous build and I can feel the transformer "bounce" a bit when I carry the amplifier around. I'm sure that the amp will be fine in the long term but I really wanted something sturdy for this project. Guess I'll bit the bullet and as I said a little earlier, I'll use this chassis to perform some test (since I screwed up quite bad) and I'll get a new one of the actual project.

And yeah, some cutting oil is a good idea too, tried to work without it as my "workshop" is actually my adjacent garage with my summer car parked in it (which takes most of the space). Even though I'm putting a cover over it, I don't want oil going all around the place ahah

Cheers and thanks for your inputs guys! Sorry for the late reply!

EDIT: Oh and quick question, anyone tried a metal hole saw for those kind of jobs? Just curious as multiple flutes step bit seems to be quite rare as Kevin mentionned