Drilling holes in an amp chassis?

SquireJapan

What’s the right (near) way to drill holes in an amp chassis?

i want to put holes in for fx send/return (and maybe a pot for reverb) on the back of my peavey. 

I’d like to do it as neatly as possible as to keep it looking as stock as I can (because I think that’s funny). Do I need to find someone with a stepped drill bit and a pillar drill, or is there another way?

Winny_Pooh

I've done it with a hand drill always as it's awkward having a chassis on a drill press. Your washers will cover any unevenness. Aluminium is a pain though its never as clean a hole, go slow and cool the bit often.

PeteC

To get the cleanest holes with a hand drill I’d suggest starting with a very small bit and working up in 1mm, or better , 0.5mm increments. You can also use a step drill but make sure you have the chassis firmly clamped before you drill it so that the bit doesn’t grab and move the chassis.     

Good luck with it 

PeteC

Ah and clean up with a deburring tool.   Cheap as chips on t’web.  

brucegill

Assuming the chassis is Ally, electric hand drill and these 

Ss shovan 3PCS HSS Step Drill Bits Set High Speed Steel Step Drill Cone Cutter - (4-12mm, 4-20mm and 4-32 mm) Cone Drill Bits Hole Cutter for Wood Stainless Steel Sheet Metal https://www.amazon.co.uk/dp/B077JKSFRJ/ref=cm_sw_r_cp_api_i_e7DNFbKTMG40E

just go slow and don’t apply too much pressure - it shouldn’t grab

SquireJapan

^thanks all above. Slow and steady seems to be the order of the day. 

Much appreciated!

PeteC

One thing that can make a big difference to getting the holes lined up and looking neat is to mark the Centre’s carefully and use a punch or something similar to make sure the drill doesn’t wander.     Good luck and enjoy the effects loop 

ICBM

PeteC said:

One thing that can make a big difference to getting the holes lined up and looking neat is to mark the Centre’s carefully and use a punch or something similar to make sure the drill doesn’t wander. 

Centre punch, pilot hole slightly larger than the centre point of the large drill, drill one size smaller than you need, then open out with the final size. That should give you a properly round hole in the right place.

JohnS37

If you were doing this regularly you could buy chassis hole cutters that had two main parts, with a sharp ring on one and a circular groove in the other.  You drilled a small pilot hole in the chassis, where you wanted the centre of the larger hole to be, then assembled the two cutters on either side of the ally sheet using a but and bolt, then you screwed it all up tight.  This cut a very neat hole, of the right diameter, in the chassis.  Mainly used for valve bases and large capacitors.
You’re welcome.

ICBM

JohnS37 said:

If you were doing this regularly you could buy chassis hole cutters that had two main parts, with a sharp ring on one and a circular groove in the other.  You drilled a small pilot hole in the chassis, where you wanted the centre of the larger hole to be, then assembled the two cutters on either side of the ally sheet using a but and bolt, then you screwed it all up tight.  This cut a very neat hole, of the right diameter, in the chassis.  Mainly used for valve bases and large capacitors.
You’re welcome.

I use those for that sort of hole but I don’t think they’re available as small as a jack hole - the bolt is that sort of diameter anyway.

They’re also very expensive, especially in the larger or specialist non-round sizes (eg IEC socket). 

springhead

Is this an empty chassis or is the amp still in it?  If the latter then use whatever drilling method above but you'll want to avoid spraying aluminium swarf all over the electronics.  Where I've had to do this I've taped something like an old 35mm film canister or similar sealed container to the inside of the back panel where the drill bit will come through, make sure whatever you use is deep enough, especially for stepped bits which have to go in a long way for the larger diameter holes.  Drill with the open side of the chassis facing down and carefully remove the canister full of short-inducing bits of metal.

Danny1969

Centre punch to mark the holes ... then use a small bit like a 3mm to pilot the hole. Then either step cutter or cone cutter. Most metal jack sockets need a 10mm hole, plastic ones a little more. Pots normally need 7 or 8mm holes. 

mooncat

Use a Q max cutter.

They start at 10mm for metric and 3/8" for imperial and start at about £10 a cutter.

SquireJapan

For some context, I’m likely going to be doing this as a one-off (definitely an infrequent task however you cut it (no pun intended ...))

I have an old Peavey practice amp (originally 7W, 8” low spec speaker) which I’ve replaced the speaker for a PA midrange speaker, and will be removing the existing amp and transformer. Currently I’ve got an AMT preamp pedal externally wired to a small class D amp (I think from memory it’s 60W RMS?). 

My plan is to install the innards of the pedal into the amp chassis, trying to keep everything on the outside of the amp as OEM as possible. 

Pedal is an AMT F1, so has channel send/return, as well as FX. 

I might also add internal reverb at a later date, so will likely drill some holes for controls on the back too. 

Hole punch to stop the bit drifting, drill a pilot hole and then use a stepped bit to widen, maybe with a reamer to tidy up seems to be the consensus?

I’ll likely just remove the innards and then put the chassis back in the case, then drill. I don’t have tools to clamp, so it being in a wooden box will make it easier to kneel on I think

Also, I might drill holes for standoffs for the amp board. I’ll likely just use the self adhesive plastic standoffs initially as I’ve no experience tapping things. I’d like to get the final result as professional as possible, so it’s modular, robust and easy to repair. 

normula1

I bought a qmax cutter for my rack switcher as that had a gazillion sockets and it worked very well.

PeteC

Be careful not to have the “hidden” pedal too  near your power supply transformer to minimize any hum issues 

SquireJapan

PeteC said:

Be careful not to have the “hidden” pedal too  near your power supply transformer to minimize any hum issues 

So this actually raises an interesting question. 

PSU is a switched one (it’s an “audio” laptop style one), so basically it’s external. So on one hand it’s great in that it’s well away from the pedal, but the issue might be that it has no earth, so I don’t know what that will mean in terms of interference. 

hywelg

If there's space clamp a piece of wood to the inside of the chassis. 

SquireJapan

Would anybody have any recommendations on 1/4 inch jack sockets? I feel like I should buy some nice ones ...

they all seem much of a muchness. Neutrik seems sensible?

ICBM

For an FX loop I would use Cliff/Re-An type plastic-frame jacks, for preference - they will be isolated from the chassis, so that means you can easily lift the ground on them if it’s necessary to fix a ground loop issue.