Like many makers, I have a lot of stuff and space is at a premium. As a result, I try to make things dual purpose when possible. Have a look at my fantastic sewing machine for example. When you stow it away, it makes a nice drawing surface.
I recently developed a need for a drafting table and having a parallel straightedge is very handy. Here I'll show you how to make a parallel straightedge that you can add to any tabletop for under $30.
Step 1: Tools & Materials
- Tape measure
- Drill & bits
- Tap & Die set (optional)
- 1/16" wire rope (cable) Thinner if you can find it.
- Suitable straightedge surface (I'm using an aluminum yardstick)
- Suitable gripping handle (I'm using ¼" x 1¼" aluminum bar)
- Screen door rollers (4-8 ea. depending on where you have to route the cable)
- Suitable screws or bolts.
Step 2: Theory of Operation
The way this works is easy enough to understand, but routing the cables to make it happen can be tricky.
We'll begin by assuming the most basic configuration. That is, straightedge protruding over the sides of the table with four rollers under the table.
- The cable attaches to the left side of the straightedge and passes through the top left roller.
- Next it passes through the bottom right roller and attaches to the right side of the straightedge.
- From there it passes through the top right roller and goes to the bottom left roller.
- Finally it reattaches to the left side of the straightedge.
When you push up on the straightedge, the cable is fed from the bottom, and because of the routing it is also taken in at the top. It's pretty clever and once you align it square, it will remain square.
Step 3: Make the Straightedge
You can use any hard material for the straightedge. I like the look and feel of aluminum, plus I'm going to use this to cut pieces for models so I want something my blade won't gouge. Wood or plastic would work too if you're just drawing on it.
I found a nice wide yardstick to use as a straightedge and cut it to protrude over the sides of the table top, but I wanted a handle on it. A thick piece of rectangular aluminum bar would do nicely. Rounding the edges would make for a nice gripping surface. Did you know that a router with a carbide tipped blade will work just fine on aluminum? Well it will! I cut it to length and rounded over the edges on my router table. A little bit of sanding and it was ready to attach to the yardstick.
Drill two holes in each end and tap them if you're able. Screws and nuts work well too if you don't have a tap & die set. Also cut two small pieces of aluminum to clamp onto the cable. Drill matching holes in the clamp pieces and run the screws through.
Set this aside for now.
Step 4: Establish Your Cable Routing
For this application, it wasn't practical to route the cable under the table, so I routed it on the sides and around the back. It took a couple extra pulleys, but it turned out nice. I recommend using pulleys with bearings in them if you can afford it. I didn't, so eventually, these will wear out and need to be replaced.
The main thing here is that the cable routing be exactly the same length on both sides and that the tops of each side be routed to the bottoms of the opposite sides.
Step 5: Thread the Cable
Using a cable clamp, make a small loop in one end of the cable. This application needs a little bit of flex, so I added a spring to the end of the cable. In most cases you can live without it. Route the cable through your pulleys and attach the other end to the loop. You can use a small turnbuckle, a screw and nut with washers, or just another loop and clamp.
Step 6: Attach and Square the Straightedge
Loosely run the cable through the clamps on both sides of the straightedge. Measure from the bottom of the table to the straightedge. When you're confident that it's square, tighten the clamps.
Try it out! It should slide smoothly across the table and remain square. Mine had a little binding that I was able to fix by sanding the clamps. The sharp edges were digging in to the wood of the table.
The biggest issue most people encounter with these is cable tension. If your cable is loose, it won't stay square. If it's too tight it will bind. You can see in this case, because I added the spring, I'm able to stretch the cable and get the straightedge up onto the top shelf of the table to access the sewing machine.