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3D Printing 4mm Models on Home
Fused Filament Printers

A look what can and cannot be done

 

The notes and jottings recorded here are the result of my experiments with 3D printing on 'RepRap' type Fused Filament Printers I use as an aid to developing my kits and chassis. They are intended to neither enthuse or dissuade but rather enlighten the reader to the possible application of home 3D printers to our hobby.

Brian Madge 2013

Solution Graphics
Last updated 3 June, 2014
©Brian Madge 2013
Overview
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The term 3D printing broadly describes the creation of objects by additive manufacturing whereby the object is built up from successive layers, these layers can be formed from any fusible or bondable material. High resolution professional 3D printers use lasers or light to cure photopolymer resins layer by layer in a bath or jetted from a nozzle in a similar fashion to an inkjet printer. Not only are these printers too expensive for the home user but also the cost of the photopolymers they use is relatively high. No doubt such machines will eventually become available at an affordable price for the home user. Currently the printer most likely to be adopted by the hobby or home user in terms of both capital and running cost is the fused filament type, it is such a machine that I have used for the following exercise.

Fused Filament printers form the layers by extruding molten thermoplastic material through a nozzle and spreading the plastic onto the previous layer, the height of each layer depends on the height of the nozzle above the preceding layer and the width on the volume of material extruded. At first sight this appears a rather crude method and would be but for the sophisticated digital techniques available to control the flow of material. There are several major issues with 3D printing generally related to available resolution and at least a basic understanding of these is required before we examine how to minimize them in order to achieve an acceptable finish. The higher the resolution of the printer the less pronounced these become but with fused filament printers resolution is limited by the minimum nozzle diameter through which we can reliably extrude the molten plastic.


Fig.1 Stepping on curved surface

Figure 1 illustrates how the printer software attempts to conform to a 6mm radius curved profile while constrained by the extruded filament cross-section from a 0.4mm nozzle and 0.2mm layer height. Layer by layer the printer first prints the perimeter, shown shaded, and then fills in between. Most entry level 'off the shelf' 3d printers run most reliably at 0.2mm layer height but we need a higher resolution for our models. It is interesting to note that many of the samples produced to promote these printers are designed to appeal even at these low resolutions.

The above illustration is for a solid where the extruder always has a previous layer to print on to but what happens when we want to print something hollow? Professional printers have a second extruder that prints a dissolvable support material where required but our fused filament printer will not have that facility. It is possible to have 2 extruders but the support material will either be the same as that used for the main body of the print or a special material requiring additional equipment to remove it from the finished print. Down to about 45 degrees the printer will print overhangs so in the following illustration (fig.2) the first eight layers would not require support but the succeeding layers would. It is possible, and the software will cater for this, to print support structures using the same nozzle and material as depicted in the picture. At larger scales this may be practical but as you can see from the picture is far from ideal in 4mm scale as it is difficult to remove the support structure without damaging thin profiles.


Fig. 2 Unsupported layers in hollow forms.

At this point you may well be writing off 3D printing at home and you would be right if you were hoping to print one-piece body shells but the forgoing was written to demonstrate that was impractical. Now let us take a different perspective and design our model around separate component parts, doing so will allow us to explore designing and orientating each component for best results. Printing the curved solid vertically as in fig.3 for example avoids both the stepping and support issues, we still have the striations but these are a lot more manageable. Note that in the diagrams the layers are accentuated and in reality each layer will be 0.048mm (48 micron).


Fig.3. Selecting orientation for best results.

 

All content ©Brian Madge 2014

Last updated 3 June, 2014