Tolerant Press Fitting Circles

thingiverse

Building stuff to assemble and manufacture? You're likely to want to make bits that fit together perfectly and aren't crooked, so you need to know how your printer performs compared to what you're designing - then you can figure out a fix elsewhere. #### What's in the box? Three parts consisting of a set of discs related by simple multiples: - A: 12mm thick, outside diameter (OD) of 36, inside diameter (ID) of 24 and 6 - B: 6mm thick, OD of 48, ID of 24 - C: 12mm thick, OD of 24 In a perfect world, these would fit together flawlessly. Reality has tolerances and manufacturing issues - that's half the fun! #### What goes where? - C fits into B - A fits into B - C fits into A, both ways You can get two 12mm layers (theoretically); or a 6/12/6 stack; or a 12/6/12 stack. #### Things to consider: 1. There should be no orientation requirement - if you have round circles. If not, different rotational orientations are crucial. This affects your relative X/Y precision. 2. The tighter they fit, the more your filament/infill/temp/etc settings match your mathematically precise model. - Shrink pulls material towards itself, so in B, the hole gets larger and the OD smaller. A print at 20% fill is likely to be tighter than the same print at 100%. - However, a print at 100% has no dimensional give, so if it doesn't fit at 100%, you'll need to drill out the hole. If you're less than 100%, there might be some flexibility which will get you where you need to go. - Your tolerance relative to your nozzle width is a constant factor, while shrink relative to material is roughly proportional. 3. The degree to which things loosen up after fitting/removing several times reflects your material wear rate. 4. As cylinders, they should be completely immune to layer height settings, but because that changes the amount of material extruded and also the droop on each layer, you'll be able to quantify how much that affects your tolerance calculations. 5. You might find that all your parts have a bit of the "elephant's foot" (and same for the top as well), which affects pressfitting. 6. The tiny 6mm stick is likely to take less than your minimum layer time to print. It's almost certainly going to be the one that's out of whack the most if anything (retraction, most sensitive to absolute errors relating to nozzle size and your gross printhead positioning).