Designing for 3D Printing

Over the last few weeks, I’ve been designing a complex animal model for a magazine article and thought I’d share some of the things I’ve discovered along the way.

Organic Shapes

I tried to design the main body of my model using my standard approach of sketching and then extruding. I used the spline lines to create smooth curves.

This really didn’t work as the extrude produced straight edges which even with the fillet still produced blocky results.

So I swapped to using the Create Form module which allows you to sculpt a shape by pulling and pushing on the mesh. I found that some of the more extreme shaping produced creases in the model. These can be removed using the smooth option. Another feature I used quite a bit was sub-divide which allows you to add more detail in specific areas. There are quite a few other options available in the form module so I ‘ll need to investigate further.

As my model is a mechanical one, I needed to transition from these organic shapes to the straight lines of my mechanical components. I solved this in a couple of ways. Solid components such as boxes and cylinders were used to slice faces off the organic shapes which gives a flat surface. I also created offset planes and planes at an angle which could then be used to sketch details onto the model.

MeshMixer

When I loaded model in the Automaker software it reported that there were issues with the models that might stop it from printing. After quizzing people on Twitter, I downloaded Meshmixer and used the inspector tool to show where the problems are. It is possible to patch the models here or I might go back to the original and fix it at source.

Mesh Mixer Inspector showing a problem

Robox Automaker new options

Whilst I was looking at the settings in Automaker, I noticed that there was a new option. “Enable offline printer”, this means that you can save your files to a USB stick or memory card and walk them over to a printer using the root or mote remote controls. However, this option is only available in the “Pro” version which would also require a license upgrade.

Another feature in the pro version is to visualise the printing. I can see how this might be useful if you had a complex model that you were trying to optimise.

Design Time vs Print Time

For me, the biggest improvement in time I can do for a print is to minimise the height of the print. So the same model lying on it’s side could print in less time. For this model, I also tried sculpting out the inside so that it would have less volume. However, this approach backfired in that I was using supports and the combination of this and the increased surface area meant that there was more printing despite there being reduced volume.

I also spend 20 minutes redesigning one part and cut 10 minutes off the print time by reducing the volume. If I was printing multiple copies of the part then this would be worthwhile but for a one-off the advantage is marginal. In my case, I was fixing another issue so it was worth it.

Slots and holes for strength

During the week there was a discussion started by @EskiBrew about the use of holes to strengthen 3D prints. This lead to an article and tool by RepRap inventor @adrianbowyer for adding strength by subtracting random cylinders from a body. This causes the slicer to wrap each of those cylinders with some layers of plastic, effectively giving a result like glass fibre. This can be combined with a very low fill factor to give a shape that has strength in multiple directions.

Jumble by Adrian Bower

I used this technique of wrapping a hole to produce a support in the indicator lights on my Upcycling Design challenge. I wanted to use zero fill so that the light would shine through. But I also knew that the screw holes could snap if only supported by the lower surface. So I ensured that the hole went nearly all the way through and added a slot connecting the screw hole to the sides.

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