## Introduction: 3D Printed Dowel Connectors

I came up with a set of connectors which can be used with 1/4 inch diameter wood dowels. The idea behind them was to have something I could build with, something I could have a large quantity of and something which could scale. As a longtime fan of K'Nex, I used their connectors as inspiration.

The K'Nex connectors and rods have a nice property which is if you build a right triangle using the smallest rods and a right angle connector, the hypotenuse of this triangle is the second largest rod in the set. Then if you build a right triangle using this hypotenuse as a side, the new hypotenuse is the third largest rod.

Can you see the pattern forming?

In math, this is a form of the Spiral of Pythagoras. Instead of using square roots of sequential whole numbers as the lengths of the hypotenuse, we are using the rods in orders of their length. I kept this idea in mind when designing my connectors. I knew if I kept the angle of the connections the same as the K'Nex connectors, I could create the same types of shapes like the spiral.

The first step was to find a good size for the base triangle. I used the distances from the centers of each of the holes in the connectors as side lengths for the base triangle. In the second photo, you can see my math. Using the Pythagorean Thereom, I worked out the hypotenuse of the base triangle, then created my spiral.

I rounded the actual hypotenuse lengths to the nearest whole number in order to have an easy set of measurements to work with. All measurements are in millimeters so the amount of error is low enough to not be noticeable for the lengths of the rods. I found the longest rod was a bit too short to complete the spiral so I made it slightly longer than what my math worked out to be.

After finding the lengths of the sides of the triangles in my spiral, I adjusted the length of each one to account for the size of the connectors. The connectors have a depth of 1 cm where the rods are inserted so I subtracted 1 cm from each side of the side lengths in order to get my rod lengths.

The third picture shows the rods lengths I came up with as well as a simple shape showing the relationship of the base triangle built using these lengths and connectors.

Note that the 2 cm and 3 cm rod lengths do not fit the pattern for the spiral but these lengths are still useful when building shapes with connectors.

The connectors were then designed in Fusion 360. The hole in each connector is 7mm in diameter. This will allow the connector to rotate around a 1/4 inch rod. The holes in the connectors for the rods are the same. However, I found when printing them, the were slightly less than 7mm.

I printed everything with PLA at 0.3mm layer height and 10% infill. During testing, I printed with supports and a brim. I was able to get away with the supports but kept using a brim as some of the small parts had trouble adhering to my build plate.

The last step was to get a saw to cut the wood dowels. Have a look at the supplies section to find links on where to source everything. The last picture in this step shows the shape we will be building in this Instructable.

## Supplies

I've linked the Amazon searches for everything I used. You can also find everything from other vendors. Home Depot would carry everything except the 3D printer.

Connectors

3d Printer
I used a CR-10S but any one will work. Ender 3 is a nice cheap model.

https://www.amazon.com/s?k=ender+3&ref=nb_sb_noss_...

PLA Filament
Any type should work but PLA is eco-friendly and easier to print with.

https://www.amazon.com/s?k=pla+filament&ref=nb_sb_...

STL Files

EDIT: 5/11/2020

Rods

Wood Dowels
1/4 (6mm) inch diameter wood dowels

https://www.amazon.com/s?k=1%2F4+wood+dowels&ref=n...

Small Saw
I used this one. Make sure to get one with a miter box. It will make cutting the rods very easy.

https://www.amazon.com/gp/product/B000BREQKC/ref=p...

Ruler and Pencil
I hope the pencil is easy to come by. The ruler needs to be in metric since the rod measurements are in centimeters.

https://www.amazon.com/s?k=metric+ruler&ref=nb_sb_...

Hot Glue Gun and Masking Tape
These will help in securing the rods to the connectors. I show some tips at the end of the Instructable.

Once you have your supplies and 3D printer setup, print some connectors. To make the shape in this Instructable, you will need:

1 x 45 Connector

1 x 90 Connector

3 x 135 Connector

1 x 180 Connector

While these are printing, cut your rods. You can get a few lengths out of a single rod as shown in the picture.

To make the shape in this Instructable, you will need:

2 x 5 cm

2 x 8cm

2 x 12 cm

2 x 18 cm

1 x 26.5 cm

## Step 1: Create Base Triangle

You will need:

Connectors

1 x 90 Connector

1 x 135 Connector

1 x 180 Connector

Rods

2 x 5 cm rod

1 x 8 cm rod

Steps

1. Insert the two 5 cm rods into the 90 connector as shown in the first picture.
2. Insert a 8 cm rod into the 180 connector as shown in the second picture
3. Insert the 8 cm rod into the 135 connector and attach the 180 connector onto the 5 cm rod as shown in the third picture

## Step 2: Create Second Triangle

You will need:

Connectors

1 x 135 Connector

Rods

1 x 8 cm rod

1 x 12 cm rod

Steps

1. Insert a 8 cm rod and a 12 cm rod into the 135 connector as shown in the first picture.
2. Insert the 8 cm rod into the 135 connector of the base triangle and the 12 cm rod into the 180 connector of the base triangle as shown in the second picture.

## Step 3: Create the Third and Fourth Triangle

You will need:

Connectors

1 x 45 Connector

1 x 135 Connector

Rods

1 x 12 cm rod

2 x 18 cm rod

1 x 26.5 cm rod

Steps

1. Insert the 12 cm rod and the 18 cm rod into the 135 connector as shown in the first picture.
2. Insert the 12 cm rod into the 135 connector of the second triangle and the 18 cm rod into the 180 connector of the second triangle as shown in the second picture.
3. Insert the 26.5 cm rod into the 180 connector and a 18 cm rod into the 135 connector of the third triangle as shown in the second picture..
4. Attach the 45 connector to the ends of the 26.5 cm rod and the 18 cm rod to complete the 4th triangle as shown in the second picture.

## Step 4: Tips and Tricks

I've added two PDFs you can print and use a reference for building. The PDFs are scaled to be printed on 8.5 by 11 inch copy paper. I would just make sure your print settings use a 1cm or 1/2 inch margin. Adjust accordingly.

The First Shape Printout PDF is the blueprint to create the shape in this Intsructable. All rod lengths are at 1:1 scale but due to the size of the sheet of paper, the final rods and connector are missing from the sheet but I'm confident you can figure out the pattern from the printout.

The Rod Lengths Printout PDF is the blueprint to cut all the rods lengths you may need. All lengths are at 1:1 scale.

You may find the rods fit a bit loose inside the connector. Two ways you can secure them in place is to use either masking tape or hot glue.

For masking tape, add a small piece at the end of the rod. It will act like a shim to add some thickness to the rod. You won't need much. A single layer should do.

For hot glue, add some where the rod and the connector meet. You could also put a bit of glue inside the connector hole then insert the rod. However, adding glue on the outside where the rod and connector meet makes it a bit easier to remove and reuse the connectors and rods.

## Step 5: CREATE!

I was able to build a simple swing set using the rods and connectors. It held up well enough to not need tape or hot glue.

Have a look at the picture and video to see if you can build it!

You can also find new lengths of rods which will work to build triangles and spirals.

How big can you build?