Prints not fitting together

I have a perfectly callibrated (x, y and z axis and extruder) prusa i3 variant and all of my prints come out great, however If I print out something that is supposed to join together with something else, they dont fit together, the parts wont go. This guitar and sword for example:
[www.myminifactory.com]

[www.myminifactory.com]

it happens with everything, even if I printed a modular tool holder set or a bottle and cap. the parts wouldn't fit together.

Any ideas why?

Have you checked that your prints are calibrated? You need to print a small 20mm cube [www.thingiverse.com] and see if it actually measures 20mm. Some stuff you download may require you re-size it a bit based on what filament your using or how your printer prints.

i've done that calibration many many times. its definatly 20x20

Lets assume that your printer is properly calibrated in all axis. If you try to make a 1" peg fit into a 1" hole, it will work in CAD but not in reality. In reality you need an allowance, an allowance is the amount of "wiggle room" a part has when it is fitting into a hole. so a 0.9" peg in a 1" hole will have a 0.1" allowance. whenever anything is made, it also has a tolerance. A tolerance is basically the range of sizes that a part is most likely to be. So if you machine is trying to make the same 1" part 6 times, you might get sizes 1.01, 1.00, 0.99 1.00, 1.01, 1.00 which you could express as 1.00" +- .01".

When your machine has tighter tolerances you can have lower allowances. If your machine has looser tolerances, then you need to make bigger allowances. It is very possible that the people who designed the thing you are trying to make either 1) made a file that won't fit as designed, or 2) will only fit on a higher performance printer.

so here are a couple things you can do, 1) fix the printed parts, if its too tight of a fit, then drill the hole out bigger, or take a file to it and make it smaller. 2) if you have access to the files, then change the allowances to work with your printer. 3) do anything you can to help the tolerances on your printer, make sure everything is tight, use finer layer resolution and print slowly.

Even if your 20 mm cube is perfect, I discovered thanks to the guys here, that there's one MORE step after that. Go on Thingiverse and find a single thickness test piece and slice it. Look at the GCode (select verbose if using Slic3r) and see that the wall should be 0.48 mm. Now run the part and carefully measure the top row or two, no more. It's probably well over 0.48 mm. In the extrusion multiplier, enter 0.9 and run it again. Measure and keep lowering the multiplier until it IS 0.48 mm. Then your parts will have a much better chance of fitting.

This solved the problem for me!

[www.thingiverse.com]

Edited 1 time(s). Last edit at 03/30/2016 02:27PM by tjnamtiw.

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Folger Tech 2020 i3 and FT-5 as well as modified JGAurora A5 with direct drive E3D/Titan. All running the BLTOUCH.
Great kits. Having fun and running the heck out of them.
Running Marlin 1.1.0 RC8 on the i3 and FT5. Custom firmware on A5.
Folger Tech Wiki board >[folgertech.wikia.com]

Outside dimension is a function of the XYZ movement plus the extrusion width, inside dimension, minus. So you have to account for this for parts that have to fit together. It is why there is correction multiplier.
Of course, you have to provide proper clearance first when designing the parts taking into account it is plastic !