I was testing my CAD abilities out with a print in place model a few days ago. It was tougher than I expected.
It took me a half dozen prints to get the air gap between moving parts just right. With PLA it works very well, albeit a bit tight to get the moving parts broke loose without breaking it. The "general rule" of double the layer height is a starting point. You definitely gotta tweak it from there to fit the material. For standard PLA, I ended up with just i little more than double the layer height to get it to work.
I made good use of Alibre Design's equation editor with this one, to create parameters than could be changed and re-exported on the fly.
Unfortunately, when I print one in PETG, ABS or silk PLA the air gap dimensions change and it's either locked up solid, or too loose to be useable. It would seem that the air gaps need to be tuned to a specific material. One of these weekends I may print/test and adjust the parameters to get some PETG and ABS versions.
www.printables.com
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The front and rear "extra" parts are snap-off support tabs. They print in place with the model, then are snapped off and thrown in the trash.
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But, we don't buy chip clips anymore :}
On tool storage, I modified my MT3 tailstock rack to create a R8 versions. I have one running in silver silk PLA now. 15 hours to go.
Thingiverse website seems to suck lately. I started uploading my modes to Prusa's version, Printables.
www.printables.com