Tips and Jigs Part 1: Circular Saw Straight-Cutting jig

Picture of Tips and Jigs Part 1: Circular Saw Straight-Cutting jig
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
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Step 1: Getting Started: Supplies and Information

Picture of 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.

Picture of 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!

Picture of Holes are a good thing!
**Caution: you may want to remove the aluminum base from the saw to make it easier to handle.**

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.
imhusker5 months ago

It appears from some comments that some readers do not realize that the guide shown in step 5 has a groove that captures the upstanding leg of the aluminum angle so that the saw cannot move left or right. The picture is out of focus and it is not obvious. I have made cuts with a straight edge clamped to the wood and pressing the saw base plate against the guide, but on long cuts the saw has wondered away from the guide. This design prevents that and is very simple. Also, an aluminum angle is not necessary, any straight and rigid piece of wood or metal that is available should work. Just make the sure saw guides on the inside and outside edges. Great design!!

jennyross11 months ago

Really comprehensive & useful advice. Specially, thanks for images. Will try to spread the words with our site

joelhunn2 years ago
Wow - what you did isn't very different, fundamentally, from the standard "screw a straight board to a piece of plywood and cut the rest off" kind of guide - but the WAY you did it makes it almost like a track saw. Awesome. The devil is often in the details, and I think you nailed it. Thanks.
fabelizer2 years ago
Is there a reason you do not just use the edge of the saw plate against the guide, thereby not needing to make the plate for the bottom of the saw?
Pkranger88 (author)  fabelizer2 years ago
When you push against the guide, you're putting lateral force on the blade and on longer cuts, tend to twist you're saw. This gives you a stress free cut every time.
gephardt3 years ago
Hmmm. I have always felt safer with a table saw, and mine cost no more than most decent circular saws. Does take up some space, but it suits my needs better.
Pkranger88 (author)  gephardt2 years ago
I also have a table saw and they are very useful, but more expensive. And, in reality, more dangerous.
I have seen the less expensive table saws but you will never get as straight of an edge out of a smaller table saw.
I have a Delta Unisaw, and am retrofitting it with an extension table. But if you're going to be cutting full panels, this is hard to beat.
Wow, this is a lot of work for nothing. Something wrong with just clamping your angle to your piece of wood being cut and running your saw's existing edge against that?
It's not just cutting straight. When working with very high quality plywood, or paneling or any kind of material with a laminated surface e.g. whiteboard, having a zero-clearance shoe will prevent chipping of surface of the workpiece along the line of the cut. Quality of the cut, not speed are the goals here.
Pkranger88 (author)  garethfarfan6 years ago
Saw blade's have a nasty habit of twisting the saw away from the direction of cut. Slight corrections are required that result in a slightly jagged edge. When using a "free" guide, you must create constant pressure on the jig or the saw will drift away. Keeping constant pressure on long cuts is fatiguing and leads to twisting the saw counterclockwise. This jig prevents all this. By creating a "rail" for the guide's groove to follow, there is no correction necessary. You can create higher quality cuts both in accuracy and cleanliness by using jigs like this. This jig is specifically designed to take the frustration out of longer cuts in plywood. Shorter cuts would not necessarily benefit from this jig. The concept is similar to the crosscut jigs used in lumber warehouses to crosscut sheet lumber. A lot of work for nothing? NO. On the contrary, excellent cuts for 2 hours of your time. I just finished building a solid oak framed workbench and all the sheet lumber was cut with this jig. And the cuts were beautiful. No one would have been able to create such square and straight cuts using just a straicht edge. I guarantee it.
yun_cn2 years ago
Great idea to enlarge the base. The motor was the cause not to cut a thick board correctly by using a small circular saw with a blade of 147 mm in diameter. thanks a lot.
evertonp5 years ago

I really enjoied your instructable. Congratulations.

bobtannica5 years ago
Really liked your instructable. I would be very interested in seeing a table saw base as you suggested. Keep up the good work.
This is a great instructable. I thought at first you were going a completely different way with it. Since you have a pretty darn sturdy base on it could you not turn it upside down mount it in a table and put a switch to make a table saw? I have an old wet tile saw that I was thinkin bout turning into a table saw but I have way more old circular saws lying around. Any info would be greatly appreciated.
Pkranger88 (author)  boognishmofo6 years ago
I've thought about making a "tablesaw" base for a circular saw and mounting a switch. I don't see any problems with it other than the difficulty with fine-tuning height and angle adjustments. I may just do one and see how it works out.
jdege6 years ago
What are you doing to ensure that the aluminum angle is straight, when you screw it to the hardboard? The stuff does flex, and any error that's present in it will be replicated in your cuts. Even if it is straight at the time you screw it to the hardboard, screws won't keep it straight. Over time, play will develop in the screw joints, and the angle will move out of true.
Pkranger88 (author)  jdege6 years ago
I clamped a level to the aluminum angle when I mate-drilled the holes to the hardboard. After over 50 cuts, it hasn't bowed yet. Keep in mind that the lateral force it has to maintain is quite small in comparison.
"I clamped a level to the aluminum angle when I mate-drilled the holes to the hardboard." You should add that to the instructions. It's a critical step.
Pkranger88 (author)  jdege6 years ago
Done. Now go build one. I wouldn't say it's a critical step though. Deflection is going to depend on binding the angle when you clamp it. A sharp drill bit and a steady hand will work fine. The first time I made one of these, I clamped and drilled and it was as true as any woodworker could ask for. Thanks for the interest though. I'm working on getting a few more of these up here. Check back often
Pkranger88 (author)  jdege6 years ago
A little glue between the surfaces won't hurt either.