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I recently stumbled across this new structural joint in an article on a design blog I follow. It wasn't entirely clear to me how it worked so I decided to try to build it.

It should be noted that the creator Dror Benshetrit retains all legal rights to the idea. The articles say he plans to open source it for use in developing countries, but other commercial uses must be licensed. I reverse engineered a version from frames in the video, although it's close, it's not the proper ratios/dimensions. I did it to get a feel for the concept, and I share it here for the same reason. I don't have a commercial application for it at this time, and if/when I do, I will seek the proper licensing.

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## Step 1: Cut a Strip of Wood

I used 1/4" MDF which seemed proportional to the dimensions I chose of 3" x 2.25".

The first step is to set your saw to a 15 degree tilt. I used a magnetic gauge for this. It's 1 degree off in the photo because the teeth on the blade cause the gauge to sit at a 1 degree angle so I adjusted accordingly.

Next, I set my fence to 3" because I had already cut some off the material so it already had one 15 degree edge on it. If you're starting with a fresh piece, set it to 3.5", cut it, then set it to 3" and cut the other edge.

The goal is to have both sides at the same 15 degree angle as shown in the last photo.

## Step 2: Cross-cut to Size

Next we meed to cross-cut our strips of wood to the proper size.

DANGER: Because the wood is longer than it is wide, it would be dangerous to push it against the fence as we did earlier. The blade would cause the wood to twist and bind against the fence, throwing the wood across the room!

Instead, we will use the cross cut sled that slides in the slot on the saw and allows us to hold the wood at a 90 degree angle to the blade. We will use the fence as a size guide, but it won't be touching the wood when it is cut. We'll get to that in a moment. First, we will cut a small amount off the end so it has the 15 degree angled cut we need.

Notice that our strip of wood is positioned such that the top surface contacts the sled rather the bottom due to the angled cut. If it's not positioned like this when these cuts are made, they won't be in the right direction later.

The fence is in the same position it was for cutting the strips. But now we have added a small piece of 3/4" thick MDF. This will allow us to set the cross-cut length to 2.25" since the fence is set to 3". We position our reference block well before the blade so the wood we're cutting is never in contact with it at the same time it's being cut. It might help to clamp the reference block in place so it doesn't slide forward. Be careful to hold the strip against the sled and not to move it side to side after it passes the guide block, it's easy to do!

Cut a series of these 3" x 2.25" pieces. You will need 4 for each QuaDror module you want to make.

## Step 3: Cut the Narrow Part of the Cut-out

Since my table saw doesn't tilt in both directions, cutting this part would have required feeding the wood backwards which is not feasible or safe. So I had to use my bandsaw for the cut. I set the table to 15 degree tilt and clamped a piece of wood 0.75" from the blade as a fence. Just past the blade, you can see a black mark on the white wood, that is 1.5" from the front of the blade and is the stop point for this cut.

The cuts are made length wise and at a parallel angle to the cuts on either side. In the picture, you can see that the bottom of the piece touches the fence, while the top does not does to the angled cut. That is the same cut that faces the camera in this shot. The top edge is farther from the camera, than the bottom edge (thus the top edge encounters the blade on the lead edge of the piece before the bottom edge.) This positioning is important for later. It's easy to get these angles facing the wrong way, I did it several times!

Once you get to the mark on the fence, back the piece out and move on to the next piece.

## Step 4: Make the Second Cut to Finish the Piece

For this step, we go back to the table saw. We also have to flip the piece over so the side that was up for the bandsaw is now down for the table saw. The table saw is set to 1.5" (plus 1/32" to get a better fit in my experience.)

The first photo shows the orientation of the piece for cutting. Due to the angle, the top surface will contact the fence. The bandsaw cut is closer to us than the blade. We cut one at a time, the stack shows the angles more clearly.

In the same way as the bandsaw, this setup requires cutting part way into the piece and then backing it out. This isn't easy to do safely. I'll leave it to you to figure out the best way to do it on your equipment. I made sure the saw blade was as low as possible to cut cleanly through the material, kept most of my hand on or over the fence and used my thumb and forefinger to move the piece forward and back.

I pushed it forward until the piece became detached, then backed it out, cleared the lose piece with my left hand, and repeated.

## Step 5: Assembly

If all the cuts went correctly. you should be able to position two pieces 180 degrees to one another and have a "V" groove through the middle as shown in the first image. If part is a V and part is not, (as my first ones were,) you got some of the cuts backwards. If none of it is a V as shown in the second photo, then it's just upside down but still correct. If you flip both pieces over, you'll see the V.

You will need 4 pieces to make one module. Two will be V side up, two will be V side down. They should be arranged as shown in the third photo. You will then pick up the bottom-right set and place it on top of the other one. The small "legs" should meet on opposite corners.

Once you have confirmed everything, remove the top layer pieces, keeping their orientation the same. Apply a dot of hot glue where the X marks are, then put the piece shown top-left back into position. I align the edges of the small legs so the surfaces are flush.

Repeat for the other piece using the X marks shown. And you're done!

## Step 6: Stack

As shown in the video, the modules stack easily. However, unlike theirs, mine don't form a solid wall. I don't know whether the angle I'm using isn't right, or if the material thickness isn't right for the ratios I used, or what. But it shows the concept, I didn't have time to refine it further and solve those issues. Maybe someone in the community here can debug it for us.

Also in the video are the open frames, which it appears just have this joint at the ends of the frame sections. The frame itself isn't really a version of this piece as I initially thought.

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## 12 Discussions

this is great. I was wondering if you have the plans for the other piece he has in relation to the quadror. In one the videos off the site he is using 2 pieces to make a table.

You beat me to this! I attempted to make one the other night but realized my geometry was flawed and stopped after cutting only four pieces to go back and review Dror's vids. I think the collapsed shape is a rhombus. You'll never get all the corners to come together w/ 90 degree angles. It's like the tip of a shallow pyramid. I'll try to attach a screencap from the construction vid. The original "frame" of the sketch on http://www.quadror.com/about-quadror/ also displays the shape of the basic piece with an acute angle. At first I thought it was just perspective in the drawing, now I think it's more likely just the shape of the thing.

3 replies

Hmm.. so you're thinking they're not square? I hadn't considered that, but it might make sense. On the quadror.com site, there are videos of actual assembly, but they're pretty small.

My first attempt I had the cuts on the inner cutout backwards so it didn't work. One of the keys is when it's open, it creates a flat surface on the table and mine didn't do that.

My second attempt was right, but I hadn't taken into account the kerf of the blade when I cut the middles out so there was a large space in the middle which didn't give it the support it should have.

I tweaked the sizes slightly in the final batch to get the middle right and the keep the "legs" from sticking out past the edge of the assembled square. I built mine on a 0.75" grid basically. I'm not sure it's the right proportions.

Artifacture: Thanks for posting this. I was trying to make some from the video and couldn't do it until I read your instructions.

The patent application says that the blocks can be square or parallelograms depending on the application. I don't think squareness is the problem here. I'm tinkering with some improvements - namely it says the saw angles can be from 0-15, so maybe 10 or 12 degrees would be a bit more stable. Also, the application claims that the ratios of the side lengths (wrt the shortest) should be 2, 2, 2, 3, 4 exactly, although I think two of those shouldn't effect the stability of the joint (just make the pieces extent past eachother.

The specifics are in the patent for the QuaDror: