Introduction: Wood Arch Blocks in 5 Minutes!

Picture of Wood Arch Blocks in 5 Minutes!

What do Rome, McDonalds, and The Rock's eyebrows all have in common? Arches! Big friendly semi-circles that humans have used for thousands of years in architecture, art, and facial expressions due to their aesthetic and physical properties. Humans and nature have done so much with them from a giant bridge over the Yangtze to nature-made wonder to arch-nemeses. These forms got function!

Now you can build your own in under 5 minutes out of a single board of wood. Lots of them! And they're amazing not only for the pre-school construction worker, but for the advanced physics and math student as well. So arch those eyebrows and get ready for the quickest arch humanity has ever built.

  • What: Wood Arches in 5 Minutes
  • Time: (oh you know)
  • Cost: ~free, just scrap wood used
  • Concepts: physics, architecture, forces, compression, tension, geometry, angles, math
  • Materials:
    • Any piece of wood
    • Sandpaper (optional)
  • Tools:
    • Saw (bandsaws work great)
    • Hot glue gun (optional)

Let's build!

Step 1: Steps Toward Arch-dom!

Picture of Steps Toward Arch-dom!

Building your arch is as simple as 1, 2, 3....well, 4! And mostly just the last three steps repeated.

Here's the system. First, make an angled cut in your wood (see angle chart in next step). You flip the wood over, and measure some distance on the top edge (I chose 1" for my first arch). Then you cut the same angle from that mark, making a wood trapezoid. After that, repeat the marking and cutting, and before you know it, you'll have all the trapezoids you need to build your arch. Huzzah!

You can reference the drawing in this step, and we'll go through step by step below. Let's go!

Step 2: Choose Your Angle and Cut

Picture of Choose Your Angle and Cut

The first thing to choose is what angle you want to cut your wood at. If you want to get mathy here, you can. Neatly, the angle you choose for each cut will determine the total number of pieces you need to make for your arch. I started with 15 degrees (off of 90), set my sled, and cut an angled piece of wood. 15 degrees means I will need six pieces for my first arch. How do I know this? Math!

An easy calculation is that 2*(degree of cut)*(number of pieces)=180 degrees. Then you can solve for the variables from there. Or use my handy-dandy chart!

Step 3: Flip and Cut Again

Picture of Flip and Cut Again

Now flip your piece of wood over and measure along the top edge. I chose to measure 1" for each of these pieces. I then kept my sled at the same angle, and cut again, making a trapezoid.

You'll find that if you want to vary these measurements to make different sized blocks, you can (see Step 6). The important thing is to make sure that you make at least a pair of each measurement, so your arch can be symmetrical on both sides. However, you'll see in Step 6 that you can break that rule, too! :)

Step 4: Repeat for Arch!

Picture of Repeat for Arch!

Once you get going, you simply flip wood, measure, and cut again. You can make an arch in no time!

To speed it up, you can even make a jig so you don't have to measure each time. This cuts your 5 minute arch time down to about 90 seconds. Take that, Ancient Rome!

Step 5: Add Friction to Base

Picture of Add Friction to Base

In arch construction, you'll find a number of solutions for supporting the base (also known as "abutments"). All of the force of the arch acts as a compression force on the two bases, which pushes outward as well as down. Builders have come up with many solutions from buttresses, pinnacles, and more. PBS has actually built a neat physics engine with arches to demonstrate these.

For ours, add a little sandpaper to the bottom of both bases for extra friction. Choose two pieces to be your base, and trace the bottoms on the back of the sandpaper. Cut them out and hot glue them on for some extra friction to keep your arch together. Easy!

Step 6: Build TONS OF ARCHES.

Picture of Build TONS OF ARCHES.

Oh there's just so much you can build! First, try changing the angle you cut, or the distances between each cut. For example, in the first photo, I cut a pair of pieces starting at 3" each, then decreased by 0.5" for each progressive pair of blocks. You'll find that you can even make wonky (but in their own ways purdy) arches by putting them together out of order. You can experiment with forces by applying pressure in different places, and even see the limits of when they fail.

After you've got a bunch of arches, simply keep the blocks in a pile and leave it to your creative builder to make new forms previously unimagined.

If you want to read more about the tension, compression, and physics of arches, here is a great video on the concept.

I'd love to see what you build below! And your comments, questions, and thoughts, too! Have fun, keep exploring, and keep m-arching on. :)


arpruss made it! (author)2016-01-01

Thank you: a great idea!

I made a bunch of these for my kids (3, 10 and 13, and they all like it) for Christmas using a miter saw. Once one sets up the angle and puts in a stop to get consistent length, the cutting is really fast. I fed in some square dowel, some 2x2, and some scrap. I took care not to sand the end-grain too much (just enough to get splinters out), ensuring more friction between blocks.

Some of the pieces I left as is and some I painted with Art craft acrylic paint followed by DecoArt varnish (but I left out the varnish on the end-grain, to preserve friction).

With the rough end-grain, there is no need for sandpaper.

You can also use these to make other interesting structures, like a leaning tower.

I am thinking that a fun toy for a small kid would be some giant pieces of this cut from a 4x4, with Velcro attachments. One could set up a pattern of hooks and loops so that one doesn't need to worry about which side goes with which.

FrankenPaper (author)2015-12-19

Thanks for this clever instructable. FYI: The link at the end about tension and compression does not currently work. Please check the URL.


Kreat0r (author)2015-12-14

good job!

DonBuckPCreacy (author)2015-12-07

This is a good instructable. I've been wanting to make a stone arch for some time... And now I have a shortcut. thank you

Thanks, Don! And I'm mighty happy it's useful to you. :)

DIY Hacks and How Tos (author)2015-12-03

Awesome Instructable. Very well written and I love the GIF illustrations.

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