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Printable holes

Posted by Thomee 
Printable holes
September 12, 2007 11:15PM
While working on reproducing some of the Darwin parts in AoI (see main blog post and thread in Mechanical forum for details), it became obvious that creating any of the more complex parts via boolean operations was going to run into a major painful point. Specifically, the teardrop holes that we all know and love are much more of a pain to create than simple round holes. And the hexagonal holes for captive nuts even more so.

So I took a bit of a break from reproducing Darwin parts, and created a script that I think will be very useful for RepRap use in general, for at least as long as we're still using single print head designs. It's called Drill, and creates "drill bit" objects which you can then use with boolean operations to create a hole in an object. They come in three shapes: round, hexagonal with a point down, and hexagonal with a flat down, or, as the script calls them: teardrop, hexdrop(pointy) and hexdrop(flat).

Currently the script makes use of AoI's ability to smooth triangle meshes, which allows for a very smooth teardrop drillbit with relatively few triangles in the mesh. Unfortunately, due to the way AoI does it, the resulting curve sits just a little bit inside the perimeter points on the mesh, so the drill bit is just a hair small. I think it's close enough that it won't be a problem, but I'd appreciate if others could do a bit of testing and give me some feedback. If the amount of error in the current method is an issue, there are two possible approaches to fixing it. The first would be to characterize how much AoI's smoothed surface falls inside the ideal perimeter, and compensate by pushing the actual points out just a hair. I'm not sure how difficult this would be. The other alternative is to simply not rely on AoI's smoothing features, and create a mesh which is a close enough approximation. This is easy to implement, but my concern is how it will impact AoI's performance when doing a lot of boolean operations with these.

And the juicy bit: you can download the current version of my script from [www.nmt.edu]

Re: Printable holes
September 12, 2007 11:18PM
Great stuff! smileys with beer
Re: Printable holes
September 13, 2007 03:32PM
nice! i can see that being very useful. would you like subversion access to put it in a more 'permanent' place.
Re: Printable holes
September 13, 2007 06:08PM
ZachHoeken Wrote:
> nice! i can see that being very useful. would
> you like subversion access to put it in a more
> 'permanent' place.

That would be quite convenient, thanks :-)

Re: Printable holes
September 17, 2007 02:57AM
Ok, there's an updated version of the script up at the original location, as well as in the RepRap subversion repository at [reprap.svn.sourceforge.net]

The original version didn't work in AoI 2.4.1 (I coded it against 2.5), because the functions I was relying in the Extrude Tool on changed between versions. Presumably, this means that's not a tool scripts should be relying on. I learned how to construct my own triangle meshes, and updated the script to remove several external dependancies (for extrusion, closing the ends, and simplifying), which streamlined it a good bit.

I also dealt with the smoothing problem by always turning off smoothing, and calculating the right number of edges on the teardrop to keep the error within a requested tolerance.
Re: Printable holes
September 17, 2007 11:40AM
awesome! i love seeing commits in the repository. it means progress. =)
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