A finished 3d print of the Mk V(B) helmet.

 

3d printing is a type of CNC process in which a 3d model is broken into layers. There are many types of printers, but the two most common and commercially available methods are Fused Deposition Modeling (FDM) and Photopolymerization. The machines are more affordable than most CNC machines, and can cheaply produce decent products. However, the strength of the printed parts tends to be weak, build times are prohibitively long, and it is difficult to clean up the "stacked lines" look the layer process creates. While it is excellent for prototyping, and with extensive use of time and skill could be used for master mold making, it is not efficient as a means to produce quality armor on its own.




Process[edit | edit source]

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The Mk V(B) helmet mid print.



Major Concepts[edit | edit source]

The Mk V(B) finished, support material and raft still attached.

Support Material[edit | edit source]

Support material is extra plastic that is built underneath overhanging sections of the model in order to keep it from sagging during printing. Some software will design this automatically when turned on, but it is possible to design support in the 3d model itself. Modern compilers like Makerware will use the very minimum amount of support, mostly only to support overhangs that are perpendicular to the build plate, as curves and steep slopes are usually supported by previous layers of plastic.

Raft[edit | edit source]

The raft is 1-3 layers of thinly spread plastic upon which the object is built. The original purpose of the raft is to help "anchor" the object to the build plate, as the flattened nature of the raft provides better adhesion to the build plate compared to some models with very few points of contact with the plate, such as a sphere. This anchor is important especially when printing in ABS which has a tendency to curl up and disengage from the build plate, both of which are problems the raft addresses. The raft also serves extra purposes in that it can "eat" imperfections in the build plate, as bubbles or tears in the tape can create indents in a printed object, those indents occur in the raft instead.

Temperatures[edit | edit source]

A photo of a cold print resulting in layer separation.

Different plastics have different temperature ranges in which they operate optimally. PLA is notable in that it has a very wide range of temperatures it can print in, depending on the printer it can extrude at relatively cold temperatures. ABS on the other hand has a very narrow margin of error for temperature, and if it gets outside this margin it will curl, melt, or suffer from severe layer separation.

Both infill and shells are used to calculate the strength and density of a "solid" object. That is to say, a solid cube would have infill and shells in its entire center, while a hollow box will have infill and shells between the inner and outer walls of the box.

Infill[edit | edit source]

A photo demonstrating infill and shells.

The infill of an object is the density of it. This is usually accomplished by printing a mesh or web of plastic inside the object, and how tightly woven the mesh is determines the density. While it may seem important to print objects at 100% infill, this is actually detrimental to the print reliability. Because of the Square-Cube law, the volume of an object increases much more than its surface area, and so the time it takes to print the outer walls is substatnially less than the time to print the infill. During the infill printing time, the outside of the model will cool and cause difficulties having layers adhere to each other. A general rule of thumb that works well on Makerbots is to print at less than 50% infill for small parts, less than 10% for large parts, and 100% ONLY for thin walls as the slicer struggles to do infill less than 100% when the inner and outer shells of an object are close together.

Shells[edit | edit source]

The shells of an object define how dense the walls of a solid object are. Major slicers and compilers will build inwards to create the shells, and the thickness of the object will override shells, meaning if the compiler is set to build 10 shells but the object is only 7 shells thick, it will print 7 shells. Shells give substantially more strength than infill, and will also print in much less time, so if extra strength is desired (for instance printing a pistol grip), then giving it more shells and less infill will ensure a good layer adhesion and high strength.

Plastics[edit | edit source]

Fused Deposition Modeling[edit | edit source]

  • ABS
    • Pros: Strong, flexible
    • Cons: Expands as it prints, toxic to consume, reliability directly related to temperature
  • PLA
    • Pros: Reliable prints, can be food safe, maintains dimensions
    • Cons: Physically weak, brittle, susceptible to high temperatures
  • Nylon

Photopolymerization[edit | edit source]

  • Resin
    • Pros: Strong, highly accurate to model's dimensions, higher resolutions possible
    • Cons: Slow, expensive, toxic to consume.

Tips[edit | edit source]

  • If the object is disengaging from the build plate or curling inwards, use a raft.
  • If the object's layers are not adhering (It starts to "slinky") then reduce infill or adjust temperatures.
  • When printing hollow objects (tubes, boxes) and the printer is not printing infill, set the compiler to 1 shell and 100% infill.
  • If the object's top collapses, the object needs more infill.
  • Most of the build time comes from layer height (resolution) and infill (density), adjust these for better times.
  • Temperature and Extruder Speed are closely related and when one is adjusted, the other may need to be as well.
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