Saturday, January 26, 2013

Fencing From Just €0.15 A Metre!

As I mentioned in a previous post, when I place an order with Shapeways for 3D printed items, the order usually contains a number of items. The last order, as well as containing the test print of the 7 plank wagon, contained a new item to add to the range available through Penistone Railway Works: concrete fence posts.

So far the items I've designed for Penistone Railway Works have all been based off photos or measurements made by other people. Whilst this makes life easy, I decided that I wanted to try modelling something from scratch. When I walk to the train station one thing I pass a lot of are concrete fence posts. There are actually quite a few different designs that vary in height and shape. I might, in the future, model some of the other forms, but for now I'm focusing on the 5 foot tall posts. I chose these for two reasons; firstly they aren't just square posts, and secondly they contain a braced variant giving me something extra to model.

So on a cold day at the end of November last year (when on the way to the shops to buy lunch) I took a tape measure, a camera, a notepad, and a pencil and set out to take detailed measurements of the two fence posts. Whilst I did get a few funny looks from people walking past, I came home with copious drawings (not very good ones) and lots of helpful measurements.

After refreshing my memory of trigonometry I proceeded to turn the measurements into a 3D model. Fortunately for a shape as relatively simple as a fence post this isn't actually very difficult. The most difficult decisions relate to balancing a desire to produce an accurate model with producing a model that can be both printed and is useful. Hopefully I've managed to achieve that balance with this model.

Because printing a single fence post seems rather daft, I've actually strung 21 normal fence posts together on a simple sprue. The sprue isn't, however, simply waste plastic as I've added holes to it that act as a guide for drilling 1mm holes for the fence posts at the suggested distance apart (5cm on the model which matches the average real life spacing between posts). Given the recommended distance between posts, this means a single sprue will allow you to build a fence a metre long on your model; which at a scale of 1/76 results in being able to model 76 metres of fence. At the current price for printing this equates to approximately €0.15 to model a metre of real fencing.

The second sprue contains four of the braced posts, and again contains guide holes, this time for drilling the extra hole needed for the braced leg. These posts are needed where a fence ends or where it turns a sharp corner; a sharp corner usually consists of two fences ending at the some place.

Having now handled the test print, and checked that I can actually thread wire (I'm recommending 0.125mm enammeld copper wire from Maplin) through the holes, I'm really happy with how they've turned out. At some point I'll actually fit them to a test track so I can take a photo of them "in use". Given that I'm happy with how they've turned out they are now available from Penistone Railway Works, so if you should be in need of 4mm to the foot scale concrete fence posts you know where to go!

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