"Jim Lesurf" wrote in message
...

However as Iain has pointed out, note that the anodising produces an
*insulating* layer on the surface. So mask off any areas which you need to
ensure remain conducting for ground contacts, etc - or be prepared to
abrade them clean of anodising afterwards.



Jim. This point was brought home to me when looking at the construction
of a pre-production audio workstation, just recently.

The chassis (four of them) were of slab construction,
6mm anodised aluminium. In the lower right hand corner of
each plate was a tapped 4mm hole, with a bright steel machine screw
a tag, with serrated washer, and a ground wire going direct to
the chassis star ground.

Iain.

I'm not going to tap the holes, because I screw through into a threaded
strip under the top plates, usual 2.5mm holes since it's 19" subrack
stuff.
I like the idea of an earth point underneath, though I don't see why
the anodised surface should suffer from drilling 3mm holes in a drill
press - surely this is pretty low risk? .

Andy Evans wrote:
I'm not going to tap the holes, because I screw through into a
threaded strip under the top plates, usual 2.5mm holes since it's 19"
subrack stuff.
I like the idea of an earth point underneath, though I don't see why
the anodised surface should suffer from drilling 3mm holes in a drill
press - surely this is pretty low risk? .

The risk is a function of your equipment and skill. :-)

I believe anodizing makes a thin layer of the surface harder than the body
of the metal, and maybe more slippery as well - there's always the chance
that the drill could slp before it bites.


--
Wally
www.wally.myby.co.uk
http://iott.melodolic.com

"Wally" wrote in message
...
Andy Evans wrote:
I'm not going to tap the holes, because I screw through into a
threaded strip under the top plates, usual 2.5mm holes since it's 19"
subrack stuff.
I like the idea of an earth point underneath, though I don't see why
the anodised surface should suffer from drilling 3mm holes in a drill
press - surely this is pretty low risk? .

The risk is a function of your equipment and skill. :-)

I believe anodizing makes a thin layer of the surface harder than the body
of the metal, and maybe more slippery as well - there's always the chance
that the drill could slp before it bites.



You should never attempt to drill metal without first using a punch to make
a little dint for the drill - I use a masonry nail which allows pinpoint
accuracy and then I make a pilot hole with a tiny drill for starters, even
when using the drill press...

On Wed, 22 Feb 2006 23:13:08 GMT, "Wally" wrote:

Andy Evans wrote:
I'm not going to tap the holes, because I screw through into a
threaded strip under the top plates, usual 2.5mm holes since it's 19"
subrack stuff.
I like the idea of an earth point underneath, though I don't see why
the anodised surface should suffer from drilling 3mm holes in a drill
press - surely this is pretty low risk? .

The risk is a function of your equipment and skill. :-)

I believe anodizing makes a thin layer of the surface harder than the body
of the metal, and maybe more slippery as well - there's always the chance
that the drill could slp before it bites.

Yes, that's absolutely true. Those modern metal speaker cones which
you see advertised as 'ceramic/aluminium sandwiches' are actually just
deep-anodised aluminium, as anodising *is* a type of ceramic, hence
very hard and slippery. Best to pilot drill all holes *before*
anodising, then drill out to the required size and use self-cutting
screws to ensure good contact. NB - getting a good electrical contact
to an ally chassis is always a tricky business.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Wally" wrote in message
...
Andy Evans wrote:
I'm not going to tap the holes, because I screw through into a
threaded strip under the top plates, usual 2.5mm holes since it's 19"
subrack stuff.
I like the idea of an earth point underneath, though I don't see why
the anodised surface should suffer from drilling 3mm holes in a drill
press - surely this is pretty low risk? .

The risk is a function of your equipment and skill. :-)

I believe anodizing makes a thin layer of the surface harder than the body
of the metal, and maybe more slippery as well - there's always the chance
that the drill could slp before it bites.

Agreed. I have, to my regret, scratched a few panels. That's why I think
that anodising should be the last step before assembly.

Iain

In article , Iain Churches
wrote:

"Jim Lesurf" wrote in message
...

However as Iain has pointed out, note that the anodising produces an
*insulating* layer on the surface.

Jim. This point was brought home to me when looking at the construction
of a pre-production audio workstation, just recently.

The chassis (four of them) were of slab construction, 6mm anodised
aluminium. In the lower right hand corner of each plate was a tapped
4mm hole, with a bright steel machine screw a tag, with serrated washer,
and a ground wire going direct to the chassis star ground.

My awarness of this is a result of deliberately using anodising to ensure
that some close-fitting parts in microwave oscillator were insulated from
one another whilst being able to slide. :-)

Provided the surfaces are clean and have no burrs or sharpnesses, the
result is remarkably durable as a very thin insulating layer.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html