OK…so I’m on wi’ summat

[Cressy Snr]

I need more inputs, as I want to use my Beresford DAC to give hi-fi sound from the TV and AppleTV, via optical, so will be rebuilding the amp into a new chassis over the next few weeks. It's a nice little amp and deserves a bit better than a scratched to fsck bit of bent metal for a case. Obviously I won't be posting all the stuff all over again, just the finished job.

[Cressy Snr]

Right then! Mk2 is stepping tentatively off the drawing board:

IMG_0366.jpeg (96.26 KiB) Viewed 908 times

Holey aluminium has been bent into shape, giving more front to back chassis depth than the mk1, which means…

IMG_0367.jpeg (111.19 KiB) Viewed 908 times

I can bring these three big buggers out of retirement.
It will have a choke-input power supply off a 450V power transformer, giving roughly the same HT as the cap input supply does on the mk1.

In the meantime, the NVA based amp will be brought into service until I get the design rebuilt.

[Paul Barker]

How much is that good looking sheet of aluminium?

I need to start thinking of the JM70 Monoblocks. Probably four boxes two power supplies two signal sections. Only thing missing is a matched choke. If I find some money could buy a matched pair of Hammonds if they do a big choke for choke input.

[Cressy Snr]

It's not cheap, but I think it's worth using.
https://www.wickes.co.uk/Wickes-Metal-P ... m/p/116725

[simon]

I'm no metalbasher Steve, how did you get such a nice corner and straight side at the front?

[Paul Barker]

Thanks Steve.

[Cressy Snr]

I'm no metalbasher Steve, how did you get such a nice corner and straight side at the front?

I use a thick chopping board with a machined straight, flat edge.

Place the metal sheet on the edge of the kitchen worktop, then place the board on top of the metal to be bent and line it all up with the longest part of the metal projecting beyond the worktop edge.

Use a pair of G clamps to clamp the whole sandwich together, then carefully push the metal upwards from below with the thumbs, until the long side projects up at almost right angles to the work surface.

Use a rubber mallet to bash the metal the rest of the way into its final 90 degree angle, staying right on the bend with the mallet, otherwise you just put a bow into the sheet, which looks completely crap.

Loosen the clamps and repeat for the other end so you end up with a U section.

It's takes a lot more time and a lot more work than a folding machine, but for easily bendable aluminium, the clamp, board and brute force method works surprisingly well.

[Mike H]

I like it!

[Ray P]

You could also consider getting chassis panels fabricated by the company I mentioned in the suppliers section, they'll do custom perforation patterns, folding and powder coating and offer steel, stainless steel and aluminium in various thicknesses.

https://www.audio-talk.co.uk/phpBB3/vie ... 91#p209091

[Paul Barker]

I'm no metalbasher Steve, how did you get such a nice corner and straight side at the front?

I use a thick chopping board with a machined straight, flat edge.

Place the metal sheet on the edge of the kitchen worktop, then place the board on top of the metal to be bent and line it all up with the longest part of the metal projecting beyond the worktop edge.

Use a pair of G clamps to clamp the whole sandwich together, then carefully push the metal upwards from below with the thumbs, until the long side projects up at almost right angles to the work surface.

Use a rubber mallet to bash the metal the rest of the way into its final 90 degree angle, staying right on the bend with the mallet, otherwise you just put a bow into the sheet, which looks completely crap.

Loosen the clamps and repeat for the other end so you end up with a U section.

It's takes a lot more time and a lot more work than a folding machine, but for easily bendable aluminium, the clamp, board and brute force method works surprisingly well.

As the method unfolded I knew I couldn’t make it. I’m in the completely crap camp.

[simon]

Nice Steve. Does aluminium work-harden at all or can it be bent "in one"?

[Cressy Snr]

Nice Steve. Does aluminium work-harden at all or can it be bent "in one"?

It does work harden so you probably have only the one chance to get it right. Steel is more forgiving but harder to get moving in the first place. Copper would be a brilliant option for bending.

[Paul Barker]

Mild steel is best for cutting milling punching bending tensile strength weight.

Aluminium tears and sticks

Copper is heavy and costly also hard to machine sticks too but not as bad as aluminium.

I put the 833a amp me and Nick did a joint effort. The copper wasnt worth its added weight.

Some people think a copper chassis would have better faraday and ground plane properties. Just use mild steel and stick thin copper sheet over it as youre magic ground plane if you must have one.

[simon]

Hmmm any ideas how got the ally would need to get to reset it? Might a hot air gun do it?

[pre65]

I'm not a metallurgist, but I can't see that sort of aluminium work hardening in the short term.

Bending as Steve described won't need any heat.