In response to requests, I will explain how to make louvers in
sheetmetal (for use in hoods or any other body panels).
Tools Required:
a good carpenter's square and a knife or other sharp object for
scoring the paint or metal, to mark the cuts.
a drill with a small (#42 or smaller) drill bit
a die grinder w/ cutoff wheel, hacksaw, or similar tool to cut the
metal
vice-grips with two large plates welded to the jaws, as used for
welding (these are available directly, rather than having to make your own,
as they are commonly used for clamping pieces together when welding)
a body hammer with a square head, or some other square-headed
hammer (doesn't have to be very heavy, typical ball-peen weight is best)
a body dolly (as in most auto-body repair kits), or some heavy but
small object, about 2" in width, .25"-.5" thick (depends on the size of your
louvers), with enough length to get a good handle on. This is used to
straighten the louvers after they are bent into shape.
Basic Shape: (side view)
_____ _____ The pitch angle of the slanted part of the louver
/ / (b) (pardon the poor terminology) (a) is canted at about
/(a) / a 45 degree angle. The size of the various pieces
/ / (flat portion, canted portion) are up to you, but
a good ratio is to have the flat portion (b) about
<-- forward 1/2 as long as (a). Then the spacing between the
louvers is equal to a+b. For example, the stock
hood louvers on the TR7/TR8 have dimensions: a=.5", b=.25", and spacing
=.75"
Instructions:
(1) Scribe your cut lines on the hood. Obviously, you must decide
where to place the things, how big, etc. If you are expanding on existing
louvers, this is all taken care of for you.
For TR7/8's, widening the existing louvers is simply a matter of
scribing lines horizontally as far as you can go. In all cases, the usual
limit (aside from your own good taste) is the braces underneath the hood;
DON'T MESS WITH THESE (unless you know what you're doing). On 7's and 8's,
the distances are about 1" toward the center of the hood and about 2" toward
the side of the car.
Another consideration for placement, if the louvers are going to
be more than purely for show, is to make sure that they are going to be
in an area that will have good airflow *under* the hood. For this reason,
on TR7/8's, it only makes sense to add louvers behind the stock louvers,
because any in front receive no airflow under the hood due to the bulkhead
on the front of the engine compartment (behind the headlights).
Also, before you succumb to the temptation to make your hood look
like a Moggie's, realize that you are cutting the hood, and so it will lose
some of its strength. Therefore, too many and your hood will be like a
thin fiberglass replacement! This is offset, somewhat, by the bending of
the louvers, which stiffens the hood just like corrugated steel is stiff.
However, this is only good if the bending is perpendicular to the direction
of the louvers, and resistance to bending the other way is still lowered.
Design considerations considered, the rest is pretty easy.
Centerpunch and drill at each end of each scribe line. Drilling provides
a nice radius, to keep stress concentrations down and keep the material from
tearing. BTW, it won't hurt to practice this on some scrap beforehand.
Cut along the scribe lines with your die cutter, hacksaw blade, or
whatever, from drill hole to drill hole.
When finished with the cuts, place one of the louvers in the jaws
of the vice grips, and twist down to create the initial bend. Do this at
each end of the louver, at a constant distance from the end of the cut
equal to (a) from the drawing above. This will give you a nice smooth
compound curve for each end of each louver. Let the material do the hard
work of creating the curve, rather than forcing it to your designs.
Reposition the vice-grips with the edge of the plates at a distance
(b) (from the drawing) from the top edge of the louver, even with the top
edge of the louver. Use the hammer to fold down the top edge to be flat with
the surface of the hood, as even as you can get it (this will be improved
upon later). Work your way across the louver using this method. This
shouldn't take very long, at most 1 min for a 6" louver (YMMV, especially
as you gain experience).
Last Step! Take the hammer and dolly (or solid plate) and use them
to get the top surface (b) of the louver even along its length, and even with
the rest of the hood. It helps if the edge of your dolly (the 2"x.25")
is slightly curved. The best way to do this step is to place the dolly
underneath a low spot, and hit the nearby high spot with the hammer (not
squeezing the metal between the hammer and dolly). This will avoid the
problem of cold-working the metal, which will make it brittle and harder
to work. When you have a lot of irregularities in a very small region,
you can use the latter technique to straighten the metal, just keep this
practice to a minimum.
Finally, all that remains is to smooth the metal using body filler
and primer, and paint.
Questions? Reply to scottv@rpi.edu
Vaughan Scott Rensselaer Polytechnic Institute
scottv@rpi.edu Troy, NY
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