by TomMcNally » Tue May 24, 2011 8:51 pm
I don't use a drill press, although I have one.
Tools needed ---
Silver or Black Sharpie depending on your chassis
China Marker - white or black
General Tools Automatic Center Punch
Battery or Electric Drill
decent ruler
cheap slide caliper
drill gauge - plate with lots of holes
cheap slide "square" - simple L shape with movable end
drill bits: (don't buy cheapies)
1/16 for pilot holes (have spares in case you break 'em)
7/64 for # 4 hardware for mounting tube sockets, IEC jacks
9/64 for # 6 hardware (not used too much)
11/64 for # 8 hardware - leaves a little wiggle room
1/4" for starter holes for UniBit
genuine UniBit stepped drill 1/8" to 7/8" is good
common hole sizes are 3/8" for for insulated RCA jacks,
1/2" for insulated binding posts (use the drill index)
Greenlee chassis punch ... 1 1/16" is about all I use for tube sockets
appropriate socket wrench for Greenlee punch
a Dremel tool and Gyros brand Fiber Disk cutting wheels for IEC jacks
Here's my method ...
Lay the chassis on a piece of cardboard to avoid scratches
(forget taping it all up - not necessary)
If you're using a circuit board, like a get*set*go or ST-35,
lay it on the chassis, tube socket side up, make sure it's
centered side to side, and set back about 1/4" from the front.
Hold it down firmly and make a dot in each mounting hole, and
the tube socket center holes with a silver Sharpie.
Align and center up the transformers and make a dot at each
mounting hole and between the holes for a grommet or snap in.
Be sure to thing about orientation between the power transformer
and outputs, and thing about overhang at the chassis edges.
If you have chokes, same thing.
Make some centered/measured dots on the front and back for
speaker terminals, RCA jacks, pots, fuse holder, switch, etc.
Remember that standard banana jack spacing is 3/4" ...
Mark any tube socket spots, just the center for now, and
be very sure the tubes aren't too close to each other or
to the transformers.
Now ... we're ready to get started ...
Use the Automatic Center Punch, to "ding" the exact center
of all of your marked spots.
drill 1/16" holes all of the "dings"
** clean the shavings from the holes off after each
set of holes is drilled, and clean your cardboard
by tapping it over a trash can
Now enlarge the transformer mounting holes for # 8-32 hardware
with an 11/64" bit
Drill the circuit board mounting holes for # 4 or # 6 hardware,
whatever your spacers are
Drill out the tube sockets centers in a couple of steps up to
1/4", then to 3/8" with the UniBit
Use the Greenlee to punch out the tube socket holes, get
some cutting oil and put it on the punch now and then,
a little goes a long way
Drill your RCA jack holes, speaker terminals, etc on the back panel
Lay your tube sockets upside down on the top of the chassis,
and carefully center the mounting holes and make sure they
are square, then mark them all, drill them to 1/16" and then
to 7/64" for # 4 hardware
If you're using an IEC power jack, use the slide caliper or
ruler and square to make an outline on the chassis.
With some practice, you can cut a hole with the Dremel tool
that doesn't even need to be filed. Don't worry about all of
the sparks that fly with a steel chassis, they won't burn you.
Once the hole is ready, put the jack in the hole and use it
as a template and mark and ding and drill the holes for
# 4 hardware to mount it.
Flip the chassis upside down and clean up the burrs on the
holes by either using a bigger bit and gently touching
them, or by grinding them smooth with the edge of the
cutting wheel on the Dremel
When you're sure you drilled all of the holes, and de-burred them,
clean the chassis with soap and water. If it's pre-painted like
my favorite Black Hammonds, don't use paper towels on them,
it gets into the paint, use an old towel or t-shirt, etc.
Goo-Gone is good for getting rid of marks from the Sharpie
or China Marker too.
Your chassis should be ready for mounting parts when it's dry.
It usually takes me an hour or two to do the chassis, it depends
on how much thought has to go into it. On a new design, I can
stare at it for hours before drilling.
I like to do the chassis 100%, mount the parts, put some tubes
in the sockets, admire your work and start wiring another day.
Common pitfalls ...
putting the speaker jacks holes on the front because
you got disoriented when you flipped the chassis over
putting things too close to the edge making it hard to put the
mounting hardware in
forgetting something and having to drill after components are
mounted, risking scratches
going to far with the UniBit and winding up with too big
a hole ... be careful !
scratching the paint ... grrrr
putting the tubes too close to the edge, so ST (Coke bottle)
shaped tubes hang over, or worse, touch the transformers
putting something like a pot or a switch too close so when
a circuit board is mounted, it's in the way .... ugh
