a luan template is an excellent idea !!
use the "joggle sticks" in conjunction with your plywood template for those pesky complex corners and shapes.
https://www.forum.tinboats.net/viewtopic.php?f=3&t=43390
in my world, I would use a jig saw with a 8-10 TPI wood cutting blade. (TPI = Teeth Per Inch).
the metal cutting blade is very slow going and gets hot too quickly and gums up the teeth.
you will also need at least a 3/8" drill to make pilot holes to start sharp corners.
Note: chips of metal will get under the bed of the jigsaw and scar the metal you are cutting.
if this is an issue, put a couple of layers of cheap masking tape along the cut zones to reduce
the scaring effect. (or turn the metal plate over and cut from the back).
highly recommended to use styrofoam as the support for the plate vs a pallet or wood frame.
since this is apparently your first experience cutting metal, practice on parts of the plate
that will not be used in the floor area to become comfortable and develop your cutting technique
do you have a router or Roto-Zip ???? you can buy some special "downward spiral" bits that
will buzz right through 1/8" aluminum plate.
a hole saw used in the corner of your notch cuts will make very nice looking notches for the ribs.
an assortment of files and rasps will be needed to dress up any sharp edges prior to final assembly.
as far as files and rasps go, my favorite for working with soft metals, wood, fiberglass, Bondo, etc
is the "Vixen" file. it has open moon-shaped teeth that do not clog easily like other files do.
easy to clean with a wire brush - stays sharp forever.
very rarely seen the Big Box Stores. it is a common item in automotive body repair and supply stores.
available on several online stores such as E-Bay, Amazon, AutoBody Supplies, etc.
highly recommended for your tool box. keep oiled and store in the plastic container it comes in.
I have a few that are well over 30-40 years old and still very sharp.
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