If you're working to create complex 3D designs, 'nodes' are recommended for ensuring strong joining of parts. But what is a node and how do you create a good one?

Generally, a node is used if your design has multiple parts that need to be joined together either by slotting or with a tab and hole joint.

Nodes are little bumps located in the slots or on tabs in your product that are there to help compensate for material thickness variations and the laser kerf. They compress when a product is assembled providing friction at points rather than along the whole surface of the slot, reducing stress points. This means the slot can be fractionally wider at the opening allowing the pieces to be slotted together easily but still create a snug joint.

Ensuring you have a good balance between simple to put together but sturdy when assembled is no mean feat and is also quite subjective. What you find easy to put together, other people don't. If you intend to sell your item as a flat pack item, try having a few different people put it together so you can get a good idea of how your product works.

So what is the key for a successful node?

Symmetry

Nodes work best when they're on both sides of a slot mirroring each other. This helps minimize any potential twisting that might occur if nodes are offset.

Shape

A gentle curve works well – allows the piece to be put together easily but provides good friction when it's on.

Multiple sets

If you have the space for it, you can have two or more sets of nodes. This, like symmetry, will minimize any twisting that could happen. Try having one pair near the start of the slot and another about halfway between the middle and the end of the slot.

Length of the node

The longer the node the gentler the curve required to make the pieces easier to slide on and off. A good minimum length of a node is approximately 0.2in or 5mm.

Width of the node

This depends on the material you are using. If using a dense material, like MDF, that has little compression, then the nodes should be shallow - about 0.01in or 0.2mm each. Taking into account of nodes on both sides of the slot, that size allows for 0.02in or 0.4mm in variation. If the material is less dense, like Eurolite Poplar, and therefore compresses more, then you can use a bigger node, 0.02in or 0.5mm. Try to test a few different sizes in some mock ups before committing to your full design so you know exactly what will work with the material you wish to use.

This approach will work best with the plywood and timbers offered on Ponoko. The timbers tend to be a lot more forgiving when creating interlocking designs whereas Acrylic can be brittle and a bit trickier to work with.

Now this information is to be used as a guide to help you reduce the number of prototypes needed when creating products with Ponoko. It should be used in conjunction with the information on the laser kerf in a previous article to help make a best guess at how to design your joints. Feel free to be creative with nodes and let Ponoko know any successes or failures so they can update their guides and let others learn from them.

Vist Design your own for more free advice and information.