I am working on updating our walking in closet, and have a need for cutting full sheet of plywood into the size of the cabinets. The traditional way to break down plywood is to clamp down a straight guide and cut with circular saw. That will work fine with just one sheet, but my plan is to cut 6 full sheets into 14.5" x 8' strips, it will be a lot of measuring, clamping and mistakes...
So I decided to make a jig for the rip cut.
Step 1: Saw Base Assembly
All material for the jig was from my left over scrap, except the piece of 24” 80/20 Aluminum that I bought on Craigslist for $3.00.
The saw base is a piece of ¾” plywood, 12”x16”. There are two existing holes on the base of my Makita saw, one at the front and one at the back left corner. I was using two ¼ -20 hex bolts to mount the saw onto the plywood base (countersink the bottom side with ½ drill bit). One of the reason is that it provide a mounting surface for the fence assembly, and meanwhile, provide an alternative surface for the Aluminum saw base so that it would not scratch the work piece, also serves as a zero clearance for the blade.
A piece of 1”x1”x11” oak was screwed onto the base (should be square to the left edge of the base) serves as the bracket that will mount 80/20 to the base. I used three carriage bolts to attach the 80/20, because I like to be able to slide 80/20 toward left more if I need and still have at least two bolts to work with. This is additional step because I like to use 80/20 for more adjustment. The front edge of the saw was mounted up against the Aluminum, thus square to the left edge of the plywood base.
I also used a 6 1/2" blade for the initial plunge cut into the base, because the 7 1/4" blade on the saw is protruding out of the saw base even with blade raised all the way up.
Step 2: Fence Assembly
The fence assembly has two parts, the fence is a piece of 1” MDF, the L-shape plywood is a cut off piece of the saw base, which is ¾” offset to the right of the fence as a the spacer to ensure the 80/20 Aluminum bar stays level, and also creates a 90 degree corner on the fence side so that it rides tight against the edge of the plywood when there is a downward and sideway pressure applied.
Two carriage bolts connect fence and 80/20 bar that will provide all the adjustment for ripping capacity over 24”. The fence is 14” long, it provides sideway support after the cut.
Step 3: Rip It!
Measure the distance from the blade to the fence, hook up the shop vac and rip it away. My first 4 sheets of ½” hardwood plywood was ripped into three 14.5” strips plus 4 ¼” left overs are all identical, with no nasty tear out. Vacuum worked great with virtually no dust. I was done within 30 minutes.
If you don't have 80/20 on hand, it also can be done by replacing the 80/20 with a piece of 24"x12" plywood, mount your circular saw at one end, and clamp a fence piece under and parallel to the blade at the other end. It's much more simple jig if you are not ripping multiple pieces with different width, because making adjustment with clamp and ensure it parallel to the blade is difficult task, unless you are able to cut spacers that represent each width as part of the set up.
I started with a complicated idea, but I think the jig worked out good.