In article XAn1d.264611$sh.258809@fed1read06,
Daven Thrice wrote:
"jim rozen" wrote in message
...
In article 9Ik1d.263527$sh.202086@fed1read06, Daven Thrice says...
OK, I'm working with 1" extrusions, that are 90 deg. angles. I want to
mark
a hole that is 1/4" in from one edge.
Use a scratch gage. Like I said, employ your dial calipers, or
if you want you can go to the hardware store and purchase a special
built one.
Ohhhh.... I get it. Open the calipers to 1/4", lock them in place, and drag
across the length of the piece. Don't need a straight edge for that. Then,
use the calipers like a compass to mark off one inch increments.
Close -- but if you do this, you will want two calipers. One
with two sharp points, and the other what is called a "hermaphrodite
caliper". That one has one leg bent 90 degrees to point in towards the
area between the two arms, while the other has an adjustable length
scribing arm. You rest the curved leg against the side of the reference
surface, and walk along dragging the point to make the mark. (FWIW, the
legs can be swiveled so the bend leg points out instead, and you can
mark off relative to an inside edge instead of an outside edge (such as
in the inside of your angle aluminum.
You should also consider getting some layout die -- the most
common is made by "Dykem". You have the choice of using blue or red. I
think that red works better with aluminum, but either can be used. This
makes the scribe lines show up clearly. You just brush it on with the
brush in the cap, and then wait a few minutes for it to dry.
An alternative to the hermaphrodite caliper is a standard
combination square -- set the blade to protrude 1/4" from the head, and
slide the head along your reference surface as you hold a sharp scriber
(usually stored in a hole in the head of the combination square) against
the end of the ruler and let its point scribe the workpiece.
Note that when drilling, some grades of aluminum can be rather
gummy, and will drill better if you use kerosene or WD-40 as a drilling
fluid.
Also -- it is easier to start a drill on center (even with a
center punch mark) if you have split point drills. They are far less
prone to "walk" away from where you try to start them. Your 1/4" bit
will otherwise have too large a 'chisel tip" (where the faces of the two
flats on the ends meet) and you will need to drill a pilot hole to match
the length of the chisel tip. (The split points also need less force to
drill cleanly -- not much of a problem with aluminum, but you will
notice it with steel.
I've always built a lot of electronic stuff, but never really made things
out of wood or metal.
Your dimensions sounded *almost* but not quite right for a pair
of relay rack rails and a relay rack panel -- except that the holes are
not all the same spacing. Instead, they alternate -- IIRC, one of one
spacing (between holes) and the next two another spacing, and then it
repeats.
A couple of other things to mention, since you are saying that
you are just getting started into metalworking:
1) Smaller things, and sheet metal must be constrained when
drilling -- the larger the hole, the more important. What
happens is just as the bit is about to break through the tip
grabs the sheet metal, and tries to both lift it from the table
and to spin it. A good drill press vise will help to hold
smaller things in place. For larger ones, make sure that one
end or the other is long enough to rest against the side of the
drill press column, to keep it from swinging around when the
drill bit catches. Failure to do this can result in you getting
some nasty cuts.
2) If your drill press is pristine, you have two choices:
a) Just go ahead and drill a hole somewhere in the table
so you won't feel quite so bad when a drill goes through
the workpiece and into the table.
b) Be careful to center the table so the drill bit will go
into the original hole in the center of the table, or
put some sacrificial material under the workpiece to
accept the tip of the drill as it breaks through. Wood
can work well for this.
For smaller workpieces, you will probably be holding
them in a drill press vise, and you can position it so
the drill bit passes beside the vise, and does not go
deep enough to touch the table. (For drilling the
angle, I would bolt the drill press vise to the drill
press table, and clamp it on the vertical side of the
angle, drill through, loosen the vise, slide the angle
aluminum along, re-clamp and drill the next. (You'll
probably want to reposition the vise for the last few
holes near one end.)
While you're about it -- also get a set of countersinks --
probably the best choice would be the kind which have a cone with a
pilot, and a hole drilled into one face of the cone to form a cutting
edge. This will chatter less than the other styles (which need a bit
more experience to minimize chatter), and use this on *both* sides of
the aluminum angle (and the aluminum panel) to remove the sharp burrs
left by the drilling.
It sounds as though you want to use screws to secure the plate
to the aluminum angle -- and if that is the case, I would suggest that
you drill the angle with a smaller hole -- the right size for a tap
drill for the thread you are using. I guess that you are aiming for
1/4-20, and IIRC, the tap drill for 1/4-20 is a #7 drill bit. Then tap
each hole (get a "gun" tap -- spiral point two flute designed to push
the chips ahead of the tap so you can just run the tap straight through.
You've got few enough holes so you can tap them by hand -- for a lot
more, I would suggest a tapping head (TapMatic is one maker, and the one
which I use.) Having the holes in the angle tapped means that you can
secure the plate to the angle with access to only one side, instead of
having to have the other hand behind the plate to hold a nut in place.
Now, I've got a need to for some sheet metal stuff &
decided to take it on myself. For a little more than what I'd pay, probably,
to have somebody do this stuff for me, I've been able to pick up some tools
and stuff. So there's a bit of a learning curve. I don't know whether this
n.g. regularly gets questions as simple/dumb as mine, but I'm glad I found
this place.
I hope that I haven't overdone it on suggestions -- but one
thing leads to another, and I think of how *I* would do the job (usually
with the tools on hand -- but I've been collecting them for many years. :-)
Good Luck,
DoN.
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