chharding / lattice

Lattice - make lattice dogbones

• Lattice is made from crossing "strands" (symmetrical)
• Lattice is defined by a radius, a number of horizontal steps h (must be ints) and a number of vertical steps v
• h and v values will be relief stamped into teh STL files, along with the angle (aXXXXX), which is useful for setting up tracks parallel to the strand orientation in 3D printing.
• Lattice will clipped and be placed at the center of a D363 Type 1 dogbone
• The central part is 13 mm in x, 3.2 mm in y and 57 mm in z
• The radius of the cylinders is always 1.6 mm to match the thickness of the dogbone
• Cylinder is approximated with 8 sides

This shows the pre-clip lattice:

• before clipping 2 cylinders are posted left and right (will be clipped in half) to provide a frame. 2 cylinder with 1.6 mm radius will be added on top and bottom to connect to the non-central D363 parts

• This shows the clipped lattice:

• Realistically, h values makes only sense from 1 up to and including 4. Good v values vary depending on h. Heres h=4 for v from 24 to 60:

File format conversions

• Initial model is created programatically in SCAD (but using https://github.com/SolidCode/SolidPython) and saved in a scad file (which is not pushed to github as it's just an intermediate format)
• I create a "no-stamp" version first (w/o the parameters relief-printed) and save this as *_ns.scad, then add the reliefs and save this as *.scad
• The no-stamp model file is then loaded/imported into FreeCAD (using its Python package/binding), rendered (which takes a long time!) and then exported into a STEP file (step folder)
• The with-stamp model file is given to the CLI version of Open SCAD, rendered and exported as STL (stl folder)

Preview and Downloading

• STL files can be previewed on github
• stl/combos contains some collections of models I made so that their parameter changes can more easily be compared.
• STEP files cannot be previewed (well, they show up as text files ...)
• To download a STEP file, right-click on its name/link on the left column) and save it manually with something like Save link As..

Tensile strength test of 3D printed dogbones - links (ongoing)

1. https://youtu.be/LTmuwfyYUJQ?t=252 Testing Carbon fiber infused Co-polyester (expensive, needs high-temp 3D printing 250 C).More info: https://www.patreon.com/posts/filament-test-16238656
2. https://youtu.be/uAoZCpXoPWo?t=344 Compares Tensile strength of normal PLA (here called Polylite) with a PLA "PLus" material (which has some additives ...) PLA PLus is weaker but has a ductile phase that normal PLA doesn't, it just ends in brittle failure.
3. https://youtu.be/ycGDR752fT0?t=492 Tensile stength test (and other tests) on common materials, uses a hook test (not a dogbone). blog here with more details: https://www.cnckitchen.com/blog/comparing-pla-petg-amp-asa-feat-prusament
4. Comparisons (incl. ABS/carbon composite) https://toner-plastics.com/tesile-testing-results-of-toner-plastics-3d-filament/
5. https://www.protolabs.com/resources/blog/tensile-testing-for-3d-printing-materials/
6. https://onlinelibrary.wiley.com/doi/10.1002/pc.26187 (includes wetness, which is bad!)
7. https://www.researchgate.net/publication/308709141_Materials_Testing_of_3D_Printed_ABS_and_PLA_Samples_to_Guide_Mechanical_Design (includes FEM analysis)
8. https://www.mdpi.com/1996-1944/13/2/352/htm (Talks about temperature anealing of ABS)
9. https://www.uni-miskolc.hu/~microcad/publikaciok/2018/b/B_Halapi_David.pdf (good overview and categorization of all materials)
10. https://mendelnet.cz/pdfs/mnt/2018/01/90.pdf
11. https://nvlpubs.nist.gov/nistpubs/ir/2015/NIST.IR.8059.pdf NIST additive manufacturing testing standards (more than tensile strength)

3D printing (Cura profile, future topic)

• To increase tensile strength, I think it makes sense to set up a Cura profile with:
  • no part cooling(!)
  • only 1 wall
  • only top/bottom layers (i.e. no infill layers) with no skin
  • pattern as lines
  • directions along the strand orientation, flipping each layer (this is why the angle needs to be recorded!)

• open topics:
  • layer height?
  • material? (good candidates are PLA, possibly annealed and PC (tricky to print, needs 250/260 C)
  • how to force the fill to go more regularly from one side to the other? (rather than jumping around):