For advanced prototyping, analysis and direct digital manufacturing (DDM), accuracy assessments must be comprehensive studies based on sound quality control practices. As leader in the 3D printing, Stratasys has paid close attention to accuracy. With production-grade printers like the Fortus 450mc, Stratasys has run studies testing for accuracy and verifies the Documented Achievable Accuracy of the Fortus 450 as:
Achievable Accuracy Parts are produced within an accuracy of ± .127 mm (± .005 in.) or ± .0015 mm/mm (± .0015 in/in), whichever is greater). Note: Accuracy is geometry dependent. Achievable accuracy specification derived from statistical data at 95% dimensional yield.
When CAPINC installs a machine we can do what is called a part based calibration. Every Stratasys 3D printer has one and they vary from machine to machine. This calibration allows us to modify the dimensions in all directions. The tolerance is usually better than what is stated after the calibration. We can also come back and recalibrate the machine if you find the dimensions to be out of specification. After the first year we schedule an annual printer maintenance visit and this calibration can be done at that time, if needed.
Another determining factor of the tolerance is slice/layer height. The slice height is a factor because this determines your toolpath width. The default toolpath width is always twice as wide as the slice height. Some advanced settings allow us to modify them to compensate for varying wall thickness. The machine is accurate at all resolutions, but as you go down in slice height, the toolpath is smaller. Smaller toolpaths allow you to get better detail on the part because the smaller toolpath will fit in smaller detail areas.
Hole tolerances and dimensions will always be better in Z-direction. When you are work with holes in the X- and Y-direction, you have to consider the layer thickness and where the bottom height of the hole is. Smaller holes (.125) printed in the X- and Y-direction can seem oblong because of the layers and where they land compared to the layer height. The smallest hole I have printed is probably a .010 hole in the Z-direction. If a hole dimension needs to be precise, users typically print holes under size and ream them out.