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  • Dr Izhar Aziz

FDM/FFF Design Table

Feature Recommended value

Wall thickness

0.8mm FDM is able to produce walls down to 0.8mm. as a general design rule of thumb it is good to make wall thickness multiple of the nozzle diameter (if this is known). The most common nozzle diameter is 0.4mm

Overhangs

Over-hanging features less than 45deg relative to the horizontal plane require support material to accurately print

Embossed & Engraved details

All embossed and engraved details produced via FDM should be no smaller than 0.6mm wide and 2.0 high if they are to be readable

Bridges

Unsupported horizontal bridges produced via FDM should have span no greater than 10mm to avoid sagging

Holes

FDM can sometime produce holes that have a slightly undersize diameter. If accurate holes are required drilled adter printing is recommended. Holes smaller than 2mm in diameter should be avoided

FDM will often print vertical axis holes smaller than the intended design diameter. The reason this reduction in diameter occurs is explained below;

a. as the nozzle prints the perimeter of a vertical axis holes, it compresses the newly printed layer down onto the existing build layers to help improve adhesion

b. the compressing force from the nozzle deforms the extruded round layer shape from a cicle into a wider ad flatter shape

c. this increase the area of contact with the previouly printed layer (improving adhesion) but also increase the width of extruded segment

d. the result of this is a decrease in the diameter of the hole that is being printed

for component with multiple holes in different direction, prioritise first blind holes ( because they are the most difficult to post process, then holes with small diameter (less than 3mm) and finally the rest of the holes in order of importance


Design Rules for 3D Printing

Clearance

When clearance is required between parts, a spacing of 0.5mm should be used. This can be varied based upon the type of fit that is required

Feature size

The minimum feature size when printing with FDM is 2mm

Pins

Vertical pins created using FDM should not be smaller than 0.3mm in diameter,If they are functional. Most of the issues relating to min pin size center around cooling, off the shelf pins, inserted into drilled hole are the best solution if functional pins are required in design.

Unsupported edges

Unsupported edges will begin to lose quality and fail to print if they are too long, unsupported edges should be no longer than 3mm


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