3D printing

Get with it!

3D printing is the new in hobby! My son has decided that he would like to try it, and we have together surveyed the available machines, there are quite a few of them. They come in three or four styles.

Machines

The activity called "reprap" (see www.reprap.org), which is short for self replication machines, started at Bath University in UK. Here they have made a number of generations of the machines: they call them Darwin, Huxley and Mendel. Each machine is used to make the parts for the next and so on. There is an off-shoot of the latest called Mendel Prusa and this is the model we have chosen. In the USA there is another style of printers, not intended to be replicating and based not on a sort of wire frame construction, but made in a box-like structure. The biggest maker here is Makerbot.

The Mendel Prusa we have chosen has a trade name of Longboat Prusa and is available from www.thereprapkitstore.co.uk. Here's a picture:

Software CAD

But before going ahead I wanted to investigate what software is used. This is a minefield of very expensive commercial CAD packages, the best being Solidworks, and a few freebies. Among the freebies is a package by Google called Sketchup.

I should mention here that I use a Mac, and quite a few programs are Windows PC only, so take care.

Sketchup supports only its native "SKP" and Collada "DAE" input/output formats. So a couple of plug-ins are needed to support STL, which is used by most of the 3D community (see www.thingyverse.com). The plugins are "jf_stl_importer.rb" (STL import) and "skp_to_dxf.rb" (for STL export).

There is another Sketchup to STL convertor called CADspan, which when installed gives a new menu toolbox in Sketchup which allows you to upload your Sketchup model, process it and download the corresponding STL file from the web. This maybe useful if the export plug-ins have problems handling your model.

One word about STL files. They work with an abstract dimension unit and you have to specify at export and import what is your measurement basis, e.g. 1 unit = 1mm. So take care.

Software slicer

The STL file of your model has to be sliced up for printing, as your printer lays down the model in layers. For this there is a free, but complex program called "Skeinforge". Fortunately there is a derivative of Skeinforge, called ReplicatorG which provides an ugly but functional graphic front end, and has drivers for a number of the 3D printers on the market, manufacturers also provide their own drivers.

ReplicatorG produces an output called "Gcode" which is a CAD/CAM standard. This is in turn sent to your printer over a USB connection to a small on-board computer on the machine and so on to drive series of stepper motors to move the X,Y,Z axes and deliver the liquid plastic through a nozzle to make the print.

The small printer computers, the interface between the USB port and the steppers, and their associated firmwares are made in three main models, Sanginoulu, RAMPS and Gen3,6,7. There is not a lot to chose between them as far as I can see. Anyway you just use the one delivered with your machine. Each uses an Arduino computer board, but with different stepper drivers.

So far

There, that is all I've learnt so far. Now I wait to see if my son buys the machine. Then it will be installed in my study as he has only a small cottage and two kids to fill it up. Then the fun starts as we try to make something, the problem is what...