For a few weeks I’ve been experimenting with different materials for small gears and in this week’s post I wanted to share with you one of the materials which doesn’t work.

For a while now I’ve been 3D printing replacement gears for a variety of locomotives in Shapeways’ Smooth Fine Detail material (formally known as FUD).  This material has the advantage of being very accurate to the 3D model size; the detail is crisp, which is ideal for small teeth, it’s hard so it wears well, and several gears can be 3D printed in close proximity to each other without actually touching.

The disadvantage of this material is it hardens, which also makes it brittle.  For larger gears this isn’t a problem as the big surface area also adds strength, but with small and tiny gears the teeth tend to break under shock loads such as a locomotive suddenly stopping.  The tiny teeth have no flexibility and crack when overloaded.  The Smooth Fine Detail material is acrylic, or very close to it, and the properties don’t allow for flexibility.

Recently Shapeways’ introduced a new materiel, Multi Jet Fusion Plastic or PA12.  This is a product which comes from Hewlett-Packard and is a nylon plastic.  This sounds ideal for gears as it’s hard, but with a touch of flexibility, meaning the teeth can take a shock impact.  And it comes in dark grey which is nearly black.  Reading the design specifications for this material the level of detail attainable is not as high as the Smooth Fine Detail but I wanted to see how close it was.  So with a set of gears I’ve recently produced for the 009 Society I 3D printed them in both the Smooth Fine Detail and the PA12.

As you can see the PA12 simply doesn’t have the precision of the Smooth Fine Detail. The teeth have rounded as the material has flowed into itself and the gears are all fused to the spindle.  With the Smooth Fine Detail set the teeth are crisp, the same size as the 3D model, and all spin freely on the spindle.  To be fair these gears are particularly small at only 4.3mm in diameter for the larger and 3.4mm for the smaller.  The PA12 may work with some of my larger gears and I’ll give it a go with a later order.

But for now my primary material for gears is still the Smooth Fine Detail.