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

In article , Iain Churches
wrote:


It is much better practice to drill and tap before anodising, and then
fit plastic machine screws into these threads, to keep tjem clean.

Again, I'll support what Iain says here. The standard approach in my old
lab was to use plastic screws to 'mask' the region around holes if we
wanted those locations as electrical connections after anodising. This is
in addition to using a 'scrape' washer when the final connection is made
after anodising.

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

Iain Churches wrote:

Like little grub screws? Fine if you have them handy, I suppose...

The anodising shop which I use have boxes and boxes of
white plastic screws, cheese head in all metric sizes.
They fit these to threaded holes, before anodising. The
screw head also covers the area needed by a serrated
washer. I am sure this is common in the UK also.

I've had very little to do with anodising, so it would seem like a good idea
for the anodiser to have the inserts. :-)


Do you tap threads by hand? :-))

Yes, but I use my mill or my lathe to hold them. ;-)

I power off the machine and rotate the chuck by hand. If it's a deep thread,
I'll release the tap and use a handle on the rest.


I think a panel which comes from an anodising shop should be a
finished panel, not requiring any further work except assembly.

If they can take care of the above-mentioned bare bits for connections and
the like, then I'm tempted to agree.


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

"Andre Jute" wrote


For my protos I use standard Hammond 17x10in ali bottom covers, bolted
to a 19mm sheet of ply for stiffness. The ali is only 1.2mm and drills
like soap with titanium drills, stepped drills, coned drills, and
finishes off burrfree with the application of various stones which I
also use for enlarging holes. I buy these cover plates by the dozen.
The Hammond boxes themselves I leave undrilled except on the blind edge
through which I put studs to fix the stiffened bottom plate; the boxes
themselves are therefore just covers, not carriers. The bottom plates
have four holes punched which is useful for marking out.



Interesting. Which side do you have facing front - the concave or the
convex....???

Check the bottom edges in this pic:

http://www.apah69.dsl.pipex.com/pass...witchbox11.JPG

....I have one each way here.....

Keith G wrote:

"Andre Jute" wrote


For my protos I use standard Hammond 17x10in ali bottom covers, bolted
to a 19mm sheet of ply for stiffness. The ali is only 1.2mm and drills
like soap with titanium drills, stepped drills, coned drills, and
finishes off burrfree with the application of various stones which I
also use for enlarging holes. I buy these cover plates by the dozen.
The Hammond boxes themselves I leave undrilled except on the blind edge
through which I put studs to fix the stiffened bottom plate; the boxes
themselves are therefore just covers, not carriers. The bottom plates
have four holes punched which is useful for marking out.



Interesting. Which side do you have facing front - the concave or the
convex....???

Check the bottom edges in this pic:

http://www.apah69.dsl.pipex.com/pass...witchbox11.JPG

...I have one each way here.....

Right. I can see where you went wrong. In addition to the four holes
already in the bottom panel, you should drill a further two, one in the
middle of each long side.

Perhaps my description of using the Hammond bottom panel to mount
equipment was not complete. Take the bottom panel, lay it on the box
which will be nothing more than a cover. Mark out and drill one hole
through the return or lip of the case/cover. Bolt. Drill another
another hole diagonally across. Bolt. Drill remaining two holes. Mark
middle of long side holes. Drill though bottom plate and case/cover
both.

The bolting proceeds as follows. Put a bolt through from inside the
case. Put a nut on the bolt and tighten. If you need air circulation,
instead of a nut use hex standoff of the right length. Put the cover on
top of that and use another nut to hold it. Use washers as appropriate.

To use the bottom cover as a construction base, with the actual case
merely as a cover:

Proceed as above. Remove bottom plate, mark out, drill, punch, cut etc,
using the pre-sized stiffening board bolted to the cover plate as
backing. Debur and otherwise finish/paint bottom plate. Enlarge holes
in stiffening board to take and hide boltheads. Finish/paint/varnish
stiffening board (which will be the visible face on the outside of the
finished assembly. Carefully bolt components to ali cover plate. Attach
cover plate to stiffening board (if separately fixed together) or fit
carefully over studs sticking out of case/cover. Voila, you have an
assembly.

The assemblies in the photos at
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
http://members.lycos.co.uk/fiultra/t39kiss001.jpg
have seen years of development handling as they are used for successive
versions or entirely different amps. I expect your work, for an amp you
intend to keep, will be neater. (OTOH, your primered examples imply
that you care more about the sound than the appearance, as I do, so
perhaps not...)

The key thing here is the ease of drilling and cutting holes in the
thin plate while you experiment. You can buy thicker plate (including
pre-anodized -- look in the rackmount boxes section) out of the RS
catalogue or get it cut locally but it is time-consuming to work and
metalwork is the part of DIY hi-fi I like least. Notice on one of the
illustrations offered the reduced, very detailed printed layout which I
stickytape onto the plate in lieu of hard metal markout (1). When I
want the final thicker plate made professionally in thick ali or
preferably stainless steel or copper, I just print off another copy.
The guys at the local metal shops love me because I am so organized. A
few weeks ago I walked in, picked a piece of offcut out of the rack,
taped a plan to it, leaned it at the end of the queue in another rack
and asked if they could work it for me before the end of the week;
instead the guy looked at his watch, told me it would cost me a
sandwich and a beer, and cut and drilled and folded it right there and
then before we went off to the pub. Ten minutes of work, fifteen bucks
for our sammies and beer (wouldn't cover cover the cost of the material
if bought separately); it's the sort of thing that if they have to do
the markup, the price is suddenly a hundred euro.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

(1) Since you built your own speakers, you will already have discovered
that measuring three times and cutting and glueing once means that the
greater part of the time is devoted to markout. I got my last set of
horn plans silkscreened onto the wood and built the pair in a single
day instead of a week...Like most things in the life of an efficient
person, craftwork happens mostly in your head before you ever pick up a
tool.