Introduction: Tips and Jigs Part 1: Circular Saw Straight-Cutting Jig

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About: I am a Product Development Engineer for an OEM of Food Production Equipment in Riverside, MO. I have previously ran the 3D Prototyping Laboratory for the National Institute for Aviation Research and still do…

For many of us, the cost of a table saw is too much just to be able to make long straight cuts in sheet lumber. If you buy a smaller table saw, you are actually creating a very dangerous situation as these are not meant to cut large pieces of lumber. What about space. A table saw is a space hog, especially when not in use.

SOLUTION? BUILD A JIG! A circular saw is a very common tool for home owners. You can buy battery powered versions that come in kits or go for a nice corded one. This should take you about an hour if you have all the supplies.

This instructable is a follow-on to a concept presented by https://www.instructables.com/id/Cutting-plywood-the-easy-way/

Step 1: Getting Started: Supplies and Information

Items you need:
Circular saw (1)
Hand Drill (1)
Countersink (1)
#10 Drill Bit (1)
Countersunk 10-24 sheet metal screws (15)
10-24 nuts (15)
lockwashers (15)
Sheetrock screws
4x8 1/4" Hardboard
1"x1"x1/8" Aluminum Angle (Length as desired)

Step 2: Get Out the Saw! Cut the New Base.

I used a scrap piece of 1/4" hardboard, but if you don't have any, use your circular saw to cut a square a few inches longer than the aluminum base of your saw and a few inches wider than your saw's overall width.

Step 3: Holes Are a Good Thing!

**Caution: you may want to remove the aluminum base from the saw to make it easier to handle.**

OPTION 1:
Drill holes in the aluminum base of your saw.
I drilled 4 holes, 1 in each corner of the base.
Lay your aluminum base and mark the holes on your cut piece of hardboard. Make sure the smooth side of the hardboard is facing down.
Drill your holes to match.

OPTION 2: (Preferred)
Clamp your hardboard to your aluminum base and mate-drill the parts together. Make sure the smooth side of the hardboard is facing down.

Again, I drilled 4 holes, 1 in each corner.

Using your countersink bit, countersink each of the holes such that the 10-24 screws will set flush in the holes. You need to countersink the underside of the panel.

Step 4: Mounting the Saw for the Cut

Mount your circular saw to the hardboard panel. You'll notice that you need to release the height mechanism and set the depth for "0."

Clamp the assembly to a structure such as a workbench so that there is nothing beneath the saw blade.

Once you have the assembly clamped in position and verified that you have clearance beneath your saw, turn on your saw and cut through your hardboard until your saw reaches it's maximum depth. This creates a slot for you blade to pass through.
I would recommend using the widest kerf blade you own to make the cut and removing some extra material around the blade with a chisel or a rasp to create a clearance. You do not want to have your blade rubbing against the hardboard when you are making your long cuts.

Step 5: Make the Guide for the Saw

I took 2 pieces of scrap poplar and cut them to the length of my already cut panel. I used my router to trim away some material for the guide, but you can also just use a shim to create the offset. I opted for the router because it was set up and I thought would give me better result.
I used some other scrap to get my fence gauged right. I make the cut such that I created a shelf in the wood that was as deep as the thickness of my aluminum angle.

Step 6: Mount the Guide

The key to this step is being "square." Ultimately what is important in this step is to ensure that the guide and the saw blade are as close to being parallel as possible. I mounted my saw on the panel and then proceeded to take measurements.

Lower your blade through the precut slot as far as it will allow.

Use a scale to create marks as equal distances from the blade at the front and at the rear. Mark a line between the marks to act as an alignment for the guide.

When you are ready, apply glue to the bottom of the guide and to the top of the panel and clamp in place.

Step 7: Mount the Aluminum Angle on Hardboard

If you are making 4 foot long guide, cut your aluminum angle to 4 feet.

Take one end of your sheet of 1/4" hardboad and clamp the aluminum angle so that your panel with guide is fully resting on the large panel. To help ensure straightness of the angle while you mate-drill the angle to the panel, clamp a level or another straight, long piece of material to the side of the angle. This will aid in keeping it straight.

With the aluminum in place, drill holes evenly spaced along the length of the aluminum angle at approximately every 6 inches. This frequency will prevent your aluminum from flexing during use.

Step 8: Set Up for the First Cut

Place your circular saw with the sled attached on the newly mounted aluminum angle.

Lower the saw until the blade is at the correct depth.

Start the saw and make the cut along the hardboard.
This cut represents the inside cut edge of the jig, thus, anytime you make a cut using the jig, line the edge of your jig up with the lines marked on your sheets.

Now you can run the saw, still attached to the sled on the opposite side to cut the jig away from the rest of the hardboard.

Step 9: Cut AWAY!!! Tips and Lessons

Now, you can use the jig to cut large sheets of lumber without the pain of "trying" to maintain a straight cut.

I use 1.5" c-clamps to hold my jig to the lumber. It's very quick. Sometimes, if those clamps are being used, I can get away with spring clamps.

I drilled a hole in both pieces of the jig so I could hang them on the wall.

If you want a longer jig, use a longer piece of angle and mount it lengthwise on the hardboard. Then you will have a sled for both. I have a 2 ft, 4 ft and 8 ft jig.

SAFETY!!! This sled was built in a manner that disables the built-in guard. I recommend cutting a notch in the back of the sled around the blade so that the guard will still work.