Intro: Three-Legged Knock-Down Sawhorse
The more projects I make, the more I realize that my rickety old sawhorses are inadequate. I think that I am limited by the strength and sturdiness of these sawhorses and I feel like I am always compensating for them. Because these sawhorses are so unstable, I set out to make the most ideal and functional replacements I could.
Ideally, my new sawhorses would be extremely sturdy and collapsible. That way I could take it anywhere and easily put them out of the way in my small workshop. I have a reprint of a woodworking book from the 70's that showed a couple different designs for sawhorses. The one that interested me most was a 3 legged design that touted its sturdiness on uneven ground. My backyard is very uneven and I often have trouble setting up tables or my sawhorses. I reposition them again and again until they stop wobbling.
Unfortunately, the book only had a rough drawing of a 3-legged sawhorse. I looked around the internet but I didn't find any plans for a 3 legged sawhorse, so I had to design my own. I decided I wanted to make my design include knock-down legs, so they could be taken off for storage or transport. I used the following links as guides for the standard parts and adapted a traditional knock-down design to suit my needs.
Knock down Sawhorses
Standard Knock-Down Sawhorse
39 Free Sawhorse Plans
3 Legged Sawbench Design
Step 1: Design
Most sawhorses have the legs set out at 15º for stability. I decided to make the A-Frame legs splayed out 15º, and make that frame and the mono-leg splayed out 15º from each other. The idea was to make this as stable as it could be while still being a 3 legged sawhorse.
To get the length of the legs, you can use these equations or you can just use this calculator. I knew I wanted to make the sawhorse 30" tall, and I knew all 3 angles of the triangles (90º + 15º + 75º = 180º). For the single leg, I ran it through the calculator once and got a leg length of 31.05829"(31 1/16"). For the 2 legged end, I used that result and solved for the hypotenuse again which gave me 32.15391" (32 3/16). This number gives me the length of the compound mitered legs.
For a detailed blueprint, open the attached PDF.
Step 2: Lumber & Tools
One problem I had with my last sawhorses was the wood getting bleached and brittle. When I made them, I didn't expect to use them outdoors as much as I did. This time around I am using pressure treated lumber so they will stand up to the weather if necessary.
The other main problem was the galvanized brackets that I used to put them together. They get bent over time and don't hold the wood tight. By using a knock-down design, I will eliminate these brackets.
I made everything from 2 inch pressure treated stock. Specifically, I used 2 x 6's for the spine, 2 x 4's for the 2 legged side, and 2 x 8's for the single leg side. I had a bunch of 2 x 6 lumber left over from an earlier project, so I only had to buy one 2 x 8. I ripped everything else down from the 2 x 6's. For the last pieces, the leg brackets, I just ripped down all the scrap pieces left over from the other steps to 2" x 2".
When you are measuring and designing something like this, it helps to be familiar with the actual thicknesses and widths of standard lumber sizes. Take a look at this page for more information.
Because of all the angles involved in this design, I absolutely needed my Craftsman compound miter saw. I got this saw as a hand-me-down from my cousin, so I am not sure how old it is, but it still works great. The legs of the A-Frame leg in particular couldn't have been cut without a compound miter saw.
Because I was reusing 2 x 6 lumber and making 2 x 4's out of it, I needed my Craftsman 10 in. table saw. I've ripped down lumber with my circular saw, and it is a big hassle to do any more than 1 or 2 boards. With the table saw, once the fence is set, I can repeat the same cut again and again with minimal effort. This was especially important to make the 2 x 2 leg brackets out of the scrap wood.
My older model compound miter saw doesn't have the slider feature that the newer saws like this one have. This means I can't cut anything wider than about 6" and less if its a miter cut. For these cuts I had to resort to my circular saw.
You will also need a good drill, a sharp set of drill bits and a few medium sized quick release bar clamps. A good hand saw and jigsaw or coping saw will also be handy. To measure, you will probably need a steel framing square, measuring tape and a woodworking protractor.
Step 3: A-Frame Leg
To start the A-Frame leg, I set the blade on my compound miter saw to 15º miter and 15º bevel. I then cut four 32 3/16" lengths of 2 x 4 stock. I made the first cut to establish the angle at one end, then measured the 32 3/16 inches and made the cut with the blade set at the same angle. All 4 legs can be cut with the blade set the same way and the legs can be flipped around to give you the opposite angles.
Next, measure out the plumb cut where the legs meet at the top. Since the legs are on a 15º angle, I wanted to get the most contact between the legs and spine for strength. This required using the triangle calculator again to find the length of the edge that would form the groove for the spine. I made marks at 1 3/32" on the end and 5 7/26" on the side to leave a smooth 5 1/4" surface. For this cut I used my compound miter saw with no angle or bevel.
Next I clamped a scrap of 2 x 6 where the spine would go and attached the 2 cross pieces. The two cross pieces will have 15º angles on each side, slanting in at the top like an isosceles trapezoid. The top cross piece has a 15º bevel on the top edge to accept the spine.
Step 4: Mono Leg
I cut two legs at the same time, one for each horse. I had to use my circular saw because my compound miter saw can't cut boards wider than 6" or so. I set the saw to cut a 15º bevel cut and cut the very end off the board to establish the first angle. I measured out 31 1/16" and made my next cut. I cut the next leg to the same length, making sure that the bevels on the ends were parallel to each other. You are looking for something like a long parallelogram, not a trapezoid.
To cut the notch in the top to fit the spine, I used a coping saw and a woodworking protractor to check the angle I was cutting. You could use a jigsaw, but mine recently broke and I have not replaced it with a better one.
Step 5: Spine
Until this point, I hadn't decided what I was going to do to make the brackets that the legs would slide into. I decided to take all the various scraps of 2" stock that I had and rip them down to 1.5" wide and thick on my table saw. I ended up with a lot of little pieces that were just barely long enough to use.
With these pieces of 2" x 2" (1.5" x 1.5"), I setup a stop block on my compound miter saw and mitered both ends of the blocks to 15º.
I aligned the lower edge of the outer bracket with the edge of the spine. This way the legs will be spread out as wide as possible for maximum stability. I alternated where the screws went on each side, so they wouldn't make contact with each other. Make sure you are attaching them on a 15º angle and that you are leaving 1.5" for the leg to slide into.
Step 6: Finished Product
I really like the way this project turned out. I especially like the way the tops of the leg brackets make a little tabletop that you could rest tools on. If you were only using one sawhorse, you could use the tops of these leg joins to balance boards the long way down the spine.
This was a fun project for me. It was an excuse to get more familiar with features of my tools that I don't use very often and I think the sawhorses will come in very handy around my house.
Step 7: Update: Handle and Clamp Holds
After I used these sawhorses for a few projects, I noticed that there wasn't a good place to grip the mono-leg. To fix this I added a rounded cutout at the same height as the bottom edge of the top cross-piece on the A-frame leg. With this change, the sawhorse is easily movable.
I removed one mono leg and lined it up against the other A-frame. I drew a line marking the underside of the top cross piece. I decided that the best size for this hole was 3 3/8" long and 1 3/4" wide. I drilled 2 holes side by side with a 1 3/4" hole saw and I angled the drill 15° so your hand can get a good grip on it. To connect the 2 holes, I used a jigsaw with the blade set to a 15° angle. I smoothed the hole with a handheld router and a 1/4" roundover bit with a guide bearing. This makes the hole very comfortable to hold.
Because the spine was made of 2 x 6 lumber, most clamps are too small secure anything to the sawhorse. To fix this, I drilled 3 holes in the sides of the spine. This allows me to use average size clamps without any problem. Since the spine is 36" long, I put the first hole in the center, 18" from either side. The other 2 holes I put 10" from the ends to avoid the leg joints.