1 DESIGN GUIDELINES for FDM (Fused Deposition

DESIGN GUIDELINES for FDM (Fused Deposition Modeling) components.
ABS (Acrylonitrile Butadiene Styrene) is an industrial plastic, widely used in thousands of applications.
ABS+ thermoplastic used in our 3D printer is tough enough for prototyping, functional testing or
producing manufacturing tools and end-use parts. ABS thermoplastics are stable and have no
appreciable warpage, shrinkage, or moisture absorption. Parts produced are accurate and durable.
FDM begins with a software process, which processes an STL file (Stereo Lithography File format)
mathematically slicing and orienting the model for the build process. The machine dispenses two
materials – one for the model and one for a disposable support structure. Support structures are
automatically generated.
FDM is accomplished by extruding thin layers of molten thermoplastic layer by layer until a part is
produced. Two LAYER THICKNESSES can be used to choose whether to print 30% faster at resolution
.330 mm (.013”) or at a finer resolution .254 mm (.010”).
MAXIMUM PART SIZE X (width) × Y (length) × Z (height) is: 203×203×152 mm (8×8×6”). In
orientation should be noted that extruded plastic has its strongest strength in the tensile mode along
the X-Y plane. The lowest strength is in the Z-direction for both tensile and shear modes.
Recommended minimum WALL THICKNESS (to eliminate brittleness) varies depending upon the slice
thickness that will be used to build the part, being about 1 mm (.040”) with higher resolution and
about 1.30 mm (.050”) with lower resolution.
Minimum SIZE OF FEATURE is a function of part orientation and selected resolution. Usually smallest
size can be figured out roughly: X-Y (width-length) 4× resolution, and Z (height) 2× resolution.
WARP is not a common problem. However, to avoid potential warping (deformation of vertical walls)
when building thin-walled sections of a model, usually ribs are added.
When designing built-in THREADS, avoid sharp edges and include a radius on the root. Also, use a
“dog point” head of at least 0.8 mm, this makes starting the thread much easier. Small threads,
smaller than 8…10 mm, are not recommended and hand-tapping probably required to smooth
threads and correct clearances. Easy alternative is to make holes smaller than required for the thread,
and drill and tap thread, or use self-tapping threaded inserts. Lock nuts, embedded nuts, or metal
inserts are stronger fastening options than adding threads to the FDM plastic.
UNDERCUTS for design features such as O-ring grooves are easily handled without causing
manufacturing issues.
FILLETS are not necessary, but they can be used to increase the overall strength of the part. Design
fillets with an outer radius equal to the inner radius plus the wall thickness to maintain consistent
thickness.
Exterior dimension SHRINKAGE is usually to about 99.7% of their modelled size. Interior dimensions,
such as holes, shrink to about 98.5% of their modelled size. Thereby, a pin printed the exact same size
as a hole will not fit in the hole once it’s printed. When tight tolerances are required, holes will be
drilled or reamed to ensure accurate diameter.
OVERHANGING NON-SUPPORTED FEATURES require a foundation of support material to be built,
which increases build time and material usage. For example, half of a box-shaped casing will be
usually built with the main exterior facing down, so that no internal support is needed.
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In ASSEMBLIES proper clearance should be given between mating assembly parts to prevent them
from fusing together. The standard guideline for creating clearances on assemblies being produced
fully assembled is a minimum Z clearance of the slice thickness. The X-Y clearance is at least the
default extrusion width based on a suggested minimum wall thickness. The minimum clearance
needed for mating parts, when not producing the components fully assembled, is .13 mm (.005”) in
static assemblies.
Parts may be SECTIONED in CAD. Sectioning is usually used:
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When build parts are too big for the build chamber.
To eliminate excessive amounts of support structure.
To cut and build separately overhanging features from the top of the part.
To preserve fragile features that may be damaged in post processing.
To section fragile features from the part and build them separately, in an orientation that
produces a stronger part.
There are a number of bonding methods to reattach features and join sectioned parts. Typically
sections are "fused" or "welded" by melting them chemically together with a solvent. The common
solvent for this purpose is a mixture of Methyl Ethyl Ketone (MEK) and Acetone, or Acetone alone.
LIVING HINGES can be used for a small number of cycles, if additional cycles are required consider
using a different hinge design.
DIFFERENT TYPES OF FILL can be used for solid areas of model interior, to reduce build time and use
less build and support material. There is three options to choose from:
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Solid - used when a stronger, more durable part is desirable. Build times will be longer and
more material will be used.
Sparse - high density - the default model interior style and it is highly recommended. Build
times will be shorter, less material will be used, and the possibility of part curl for geometries
with large mass will be greatly reduced.
Sparse - low density - the interior will be "honeycombed/hatched". This style allows for the
shortest build times and lowest material use.
Minimum suggested TEXT size on the top or bottom build plane is 16 point boldface, and on vertical
walls 10 point bold.
The parts produced are capable of many of POST-MANUFACTURING and FINISHING PROCESSES,
including drilling, tapping and sawing, or sanding, polishing, painting and plating.
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