Design Tip: Incomplete Polygons!
Incomplete polygons
3D printers can have a difficult time printing small holes. This is never a catastrophic problem and really only requires a little bit of time reaming the hole out with a drill bit, bolt, etc. One potential problem with printing small holes is that the print head could move across the hole causing a string to inadvertently be deposited. One way to compensate for this is to make sure those holes are less complex – opting for a hexagonal or octagonal hole instead of a circle. With a circle the ‘bot has to make a large number of calculations relating to the various points along the edge of that circle. One other issue is that even when the hole is a low-count polygon (such as the aforementioned hexagon or octagon) the extruder can leave extra plastic in and around that hole as it travels to and from the various points around the hole.
Zach thought up a new way to compensate for this issue. In the above picture he’s printed a motor bracket where the holes at the base of the thing aren’t actually holes. They are holes where there is a 0.1mm slice out of the edge. The two ends of the “hole” are not touching, which causes Skeinforge to draw the two sides of the hole independently. However, they are close enough together that the thickness of the molten plastic laid down at that layer touches – and they fuse together.
The result is that you end up with not-holes that really are holes – without the problems of filled in holes and the not-holes are just as strong as if they were designed as holes in the first place!
| Tagged with | design tips, hoeken, small holes, zach, zach hoeken smith | 12 comments |
12 Comments so far
Marty
Nice hack! It took me a minute of visualizing to figure out what you meant – the missing 0.1mm “slices” go from the edge of the hole to the edge of the model, right?
Carmiac
That is a great idea!
And on that note, I think it is time for there to be some work done on a “best practices for printable objects” document, preferably as a wiki. I could see it being hosted by Thingiverse or 3dprinterforums.org. Would Makerbot industries be interested in setting that up, since you already have the hosting?
MakerBlock
@Carmiac: I think that’s a great idea! The MakerBot wiki is wide open – if you started a page, we could all start dropping little design tips into it.
Dave Durant
The Comb module in skeinforge is, IMO, one of those must-enable-this things and it works really well.
Older versions of skeinforge sometimes had unhandled exceptions when Comb was enabled. And there were some parameters you had to get right.
With the newer versions, there aren’t even any parameters in there to mess with – you just enable it and it will avoid any travel (travel = non-printing movement) across things like bolt holes. No more threads to clean up, ever, unless your Thing has non-contiguous bits.
MakerBot Industries
[...] One commenter posted that it took him a little while to really get the “incomplete polygonR…1 thought up by Zach to avoid oozing and threads around interior holes in objects. Above you can see my dramatization of how this works. 2 With a normal closed polygon hole, Skeinforge lays down a regular path all around the edge of the interior hole. However, the plastic extrusion is much thicker than the ideal mathematical path plotted out by Skeinforge. As a result, it can cause little blobbies to appear inside the hole. [...]
Carmiac
@MakerBlock I didn’t realize the MB wiki was open. Cool!
MakerBlock
@Carmiac: Dude, at MakerBot we don’t just believe in open source, we LIVE it!
Carmiac
And… it’s done!
MakerBlock
@Carmiac: You’re the best! I’ve been tagging these kinds of little tips with “design tips” and have similar tips in my personal blog under the category “design tips”
josh
Oh so what it is is if I made a polygon in heeks cad lets say 32 sides for large 8 or 16 for small holes then cut a notch from the end for exapansion or contraction by heat changes and flex my holes and mounts will be better.
They mention this in heeks cad tutorials I beeleve but it is good to have this design tip.
I will use that in heeks cad I am waiting for the first wave of thingomatics to get assembled and a fue positive posts about them to know everything went with the kit and no problems then I will order mine.
How important is a napkin sketch? - MakerBot Industries
[...] napkin sketch above was drawn over dinner some 11 hours after the physical object it describes popped into existence. by MakerBlock | Categories: Thingiverse | Tagged: ideas, [...]
Matt LaBerge
Dude, my mind has been blown!