Do you all have a go-to thing for checking slicer settings for fitting parts? Square/circle/hex peg in a square/circle/hex hole kind of thing is my first thought. There are other types of joints that you want to fit, like press fit connectors and such, but I don’t know if those are sufficiently covered by testing inside/outside dimensions
Most of today’s slicers have no options to compensate for the inherent inaccuracies of FFF 3D printers without influencing some other property of the print as well (which is why the XY scale option in the beta Slic3r builds just makes me cringe edit: see below).
So your best option is to print a part similar in shape and function to your final part and then design the part with those dimensional offsets in mind. I know, that’s not good design practice, but it’s the only way of getting the job done (unless you want to switch back to Skeinforge and tune in the Inset plugin).
I know it’s not open source, and quite expensive, but Simplify3D seems to be getting dimensions correct for me. No tweaking at all. I’ll do a more thorough comparison soon, but @nop_head s cal.stl measures up nicely with calipers and the nuts all fit nicely in their holes.
New slic3r is getting close. They just need to add the ability to alter the percentage flow rate for external perimeters relative to other perimeters and it should be possible to use the formulae from nopheads blog posts to finally get proper dimensions in a modern open source slicer.
@Thomas_Sanladerer care to elaborate on what the inherent inaccuracies are and what in particular you find objectionable about the new XY inset (not scale) option?
Make sure your machine is calibrated. There is a way to do that: http://reprap.org/wiki/Triffid_Hunter’s_Calibration_Guide
You need to double check with every spool as diameter varies. As you get more experienced, you can alter the flow rate by eye and get good results.
It’s also good to make sure the model is designed with tolerances that can handle FFF’s inherent issues.
Some people have thought about a way of having the machine measure the material in real time, but that’s a lot of effort, effort best spent getting better material and getting better experienced.
Triffid Hunter’s guide is awesome and covers all the major bases.
@Len_Trigg it’s a combination of many factors - layers not stacking up properly, imprecise extrusion calculations, positional errors, filament diameter variations, non-rectangular extrusion paths, things contracting/expanding, high print speeds dragging the filament into the wrong places, and so on. All these typically lead to tight fits between parts. If you’re trying to compensate that by scaling parts in X and Y, you’re going to screw up all other dimensions as well. Even if that means ending up with a perfect 10mm calibration cube, but real-world objects will simply no come out right.
Slic3r isn’t clear about whether the “XY size compensation” is actually an Inset feature or simply a scale command. I’ll have to try that out.
@Len_Trigg looks like it’s actually an Inset option, thanks for pointing that out! http://manual.slic3r.org/troubleshooting/dimension-errors