There are numerous items that can be used for a rip guide that I
have used over the years. A piece of 1/2" plywood about 12"
wide will not flex very much and makes a good straight guide. A
better item is a piece of aluminum plate 8' long and about 6"
wide and works real well. I have a piece that is 1/4" that I use
all the time.
I have a few pieces of RACO top track that are aluminum and
absolutely stay straight. They come in 10' lengths and make
great saw guides. Another item that I have used is a piece of
angle iron 2" x 4" x 1/4", but it is very heavy.
My first thought would be an 8' length of 1 x 12 mdf shelving.
Other shelving material may be as good.
The factory edge on 4 x 8 plywood is often very straight, dunno
if it will be as straight you want.
The home centers sell straightedges that come as two 4' sections
and a spline that joins them to an 8' length. You can use one of
those to rip a straight edge onto whatever you want to use for
a fancy guide, though they are sold for use as a simple guide
themselves, for less than $20.
I use a piece of aluminum U that came from Lowe's. It is bolted to an
8 inch wide piece of 3/16 plywood. The saw slides on the plywood with
the left edge guided by the aluminum U. The first cut cut the plywood
to size so this edge is what is clamped on the marks. The clamps set
on the left of the aluminum guide.
I've prepped a plywood plank by ripping it carefully on a table saw,
and re-ripping until it really WAS straight, then carefully
pegged a dismountable joint so two sections (about 6' and 3')
can be joined to overreach an 8' plywood sheet, or
I can use the 6' section for a 4' crosscut.
Then I made a sled for the circular saw, that engages a rib
glued to the plank. It does make a clean straight cut, because the
sled keeps the saw base from rocking if it's not flat, and
the rib engaged over a long length (remember the overhang of
the guide, it's LONGER than the 8' work) keeps the motion
Simply holding the saw base against a straight edge is not
nearly as good.
"If" you can find a dealer that carries 1/4" melamine, that
makes a wonderful straight edge.
The other choices are 1/2" MDF, which is VERY straight.
I would use 1/2" plywood as my base and one of the above
for the fence.
I own a 96",50" and a 24" saw guide.
You will need a 50" to cut the sheet goods down to size.
The 24" is just damn handy.
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