Automatic Teardrop Holes

When I design an object, do I need to make the teardrop shape for my holes, or will the RepRap software or skeinforge take care of this for me. I've been playing around in skeinforge and I can't seem to fin a way to do this.

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Build Progress Blog

You'll need to do it yourself, since the teardrop shape isn't needed if the hole's vertical, ie, the necessity for it depends on the orientation of the hole while the part's being built. Orient the object build to minimise overhangs, and the hole might not need the teardrop, or if you've got multiple holes with differing orientation, some will need it but not others.

Right, but wouldn't it be possible to, when it's figuring out it's paths, check if it's past the edge of the layer below by more than half the width of the extrusion and if it is stop it at that distance. Then it wouldn't matter if it a hole at all and you wouldn't nee to worry about designing all your holes funky. You would have to check to make sure it's not going to cut something off completely, but it should work for most small suff like holes,

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Build Progress Blog

That would require the g-code application to also be the design application. If you take the hole in isolation, ie as a hole in a block, orienting it vertically to write the g-code, it's visually recognisable as a hole, swing it through 90 degrees, it's going to have to be a teardrop. That's ok to think about with holes, but how's that application going to reshape a filleted external edge, for example? How's it going to build a sphere? Or a hole passing through a build at 45 degrees (which might be a way of doing it, because x,y ovality might put the z axis tangency within reprap's range)? Support material and ways of handling it are what makes it possible in commercial machines, we don't have automatic methods of handling it. Feature recognition was never a consideration for .stls, one reason why design programs convert to .stl, not producing them natively. A hole in an .stl is just an arrangement of facets.

I don't use the teardrops holes anymore - with a small amount of stretching, even fairly large holes print just fine. Check out the 16 mm diameter horizontal hole on this extruder body:

[www.thingiverse.com]

Prints just fine.

I agree that it wouldn't work for all applications (like a sphere), but for something like a rounded corner of a chamfer greater than 45 degrees from verticle on the bottom edge of an object, it would just end up being a 45 degree chamfer until it meets the edge of the object again. If I'm thinking correctly, I can't find any scenario where this would cause any harm. The only time that this would cause any effect would be where the object isn't physically possible anyway. It might not work on really complex objects, but for simple objects it would make designing parts a lot quicker.

I'm going to have a poke around in the skeinforge code to see if I can't make a tool to do this. My python is a little rusty, so we'll see if anything actually comes of it.

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Build Progress Blog

Actually, that part I posted would not print properly if you chamfered the unsupported lower faces that were greater than 45 deg from vertical. 10 points if you can figure out why not.

Still, it could be a useful addition. I'd have more use for a tool that would convert all the tear drop holes back to round. It's a non-trivial problem, if you don't have access to the design tools that were used to design the originals. The tear drop holes are pretty big stress risers, although I haven't had a part break there yet.

Wade

Consider that each g-code polyline segment would have to be referred back to the facet normal that it's derived from, then the g-code production needs feature recognition from the .stl, which also needs the feature recognition from the originating model to reference holes-at-other-than-z-coaxial-angles, there are two degrees of separation from the design intent.
Non-trivial, yeah.

It can be simpler than that. Take the previous layer's perimeters and offset them by the layer thickness and then take the intersection of that shape with the shape made by the perimeters of the current layer and you get the new perimeters for the current layer that don't violate the 45 degree rule.

The disadvantage, as Wade was alluding to, is that you no longer can span 90 degree overhangs and print something like the whistle. [www.thingiverse.com]

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]