subject: How to create snug fittings for your 3D products [print this page] How to create snug fittings for your 3D products
In Ponoko's making guide they mention 'nodes' as a good idea if you are keen to create more complex 3D designs. But what is a node and how do you create a good one?
A node is often used if your design has multiple interlocking parts that need to join together either by slotting or with a tab and hole joint.
They are little bumps located in the slots or on tabs in your product that help compensate for material thickness variations and the laser kerf. The idea is that they compress when a product is assembled providing friction at specific points rather than along the whole surface of the slot. This means the slot can be s wider at the opening allowing the pieces to be slotted together easily but still create a snug joint.
Getting the right fit between easy to put together but tight when assembled is no mean feat and is probably quite subjective. What you find easy to put together, other people don't. It's best to get a few people to have a go putting your design together if you intend to sell it as a flat pack item.
So what is the key for a successful node?
Symmetry
It's best to have nodes on both sides of a slot mirroring each other. This will minimize any potential twisting that might occur if nodes are offset.
Shape
A gentle curve works well. Something that leads on easily but provides good friction when it's on.
Multiple sets
If the length of the slot allows, you can have two or more sets of nodes. This will minimize any twisting that might want to take place. Put 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 needed to make the pieces easy to slide on and off. In general the recommended minimum length of the node is approximately 0.2in or 5mm.
Width of the node
This will depend on the material you are using. If the material is dense, like MDF, and has little compression then the nodes should be shallow about 0.01in or 0.2mm each. So taking into account of nodes on both sides of the slot, that allows for 0.02in or 0.4mm in variation. If the material is less dense, like Eurolite Poplar, and therefore can compress more then you can use a bigger node, 0.02in or 0.5mm. It might pay to test a few different sizes in some mock ups (like the examples below) before committing to your full design to test exactly what will work with the material you wish to use.
This advice will work best with the plywood and timbers offered on Ponoko. The timbers tend to be a lot more forgiving when creating interlocking designs, while Acrylic can be brittle and a bit harder to work with.
All of this is intended to help you reduce the number of prototypes needed when creating products with Ponoko. It's best 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. Why not be creative with your nodes and let us know any successes or failures? Ponoko is always looking to improve the advice given out to our users.
