Sizing parts to fit and printer precision
I've done a number of tests along the way to make my printed parts fit together, and to make sure my parts fit around things like aluminum rods or tubes. I haven't found much variation between filament types when doing this sizing. But it has let to me printing out different fitting tests, maybe like this:
(That's not the best example of a sizing test, but you get the idea.)
Also, when looking over numbers, on a stock MKS3+ (or 3.5, if upgraded), the print head is a .45mm diameter, but I've read that the XY positioning resolution is about .3mm for the head. So when I design a piece for slicing and printing, I figure if I have to make a hole to fit something through, I can work with about a .3mm resolution. But I've found that if I use 1/4mm measurements in my designs, that has always worked out for me.
I've found if I'm making larger threaded parts (like more than about 10mm in diameter for the bolt), that for making the threads fit properly, resizing the female thread to a scale of 1.01 on XY, but not on Z, makes it fit fine. (I've had very few exceptions to this.)
Often, when I'm printing rectilinear parts and want one to fit in the other, creating a gap of .25mm on each side seems to make them fit with some friction. (For instance, if I have a square printed cylinder that's 10mm on each side, making the hole it goes into 10.5mm often makes it fit and often with friction, so it won't just fall out.)
Of course, ultimately, when sizing parts, I find I have to do test prints of the joints to make them fit. (I'll generally cut out just the joints and test their fit before printing the entire piece.) And I think most of us like to start with a fair idea of what's going to work to reduce the amount of test printing needed.
I'm wondering what other people do to size their parts for a good, tight, fit between printed pieces. Do you find fits change between filament types? Do you have a table of sizes and clearances to use when designing interlocking or fitting parts? What about special tricks or procedures you might use to make things fit?
This is one topic that I would think a lot of people have different ways to handle this situation.
RE: Sizing parts to fit and printer precision
This depends entirely on the type of plastic you use, the type of nozzle and the temperature you print it at. All plastics (used in 3D printing) shrink when they cool, some more than others. Example ASA has shrinkage of ~0.50%, Polycarbonate ~0.75% and an extreme example POM at ~3.5%. Accounting for shrinkage is important when sizing parts, especially long parts. As for accuracy for small things like threads, that is more controlled by the extrusion which is set in PrusaSlicer by appropriately changing the extrusion multiplier. Shrinkage is an intrinsic property of the plastics and is a "set once and forget". The extrusion multiplier is a bit trickier because it depends on what you are printing.
RE: Sizing parts to fit and printer precision
This depends entirely on the type of plastic you use, the type of nozzle and the temperature you print it at. All plastics (used in 3D printing) shrink when they cool, some more than others. Example ASA has shrinkage of ~0.50%, Polycarbonate ~0.75% and an extreme example POM at ~3.5%. Accounting for shrinkage is important when sizing parts, especially long parts.
Good that you included this. I guess I've been lucky with my fitting things together so far!
As for accuracy for small things like threads, that is more controlled by the extrusion which is set in PrusaSlicer by appropriately changing the extrusion multiplier. Shrinkage is an intrinsic property of the plastics and is a "set once and forget". The extrusion multiplier is a bit trickier because it depends on what you are printing.
I do as much as I can in the design so I don't have to remember things like resizing or similar changes in the slicer. I have notes in my design files to keep track of issues with printing or sizing. Within my files, I may have multiple versions of an item that are different sizes or may have other variations depending on intended use, or other factors. There are a lot of cool and useful tools and features in PrusaSlicer, but I do what I can before slicing, since I know how I think and where I'll remember to make changes and adaptions.
RE:
I would never set dimensions in my CAD design for the type of material I plan to use, I let the slicer manage that. If you need an 10mm hole for example then you should size it in CAD for 10mm. In PrusaSlicer you then calibrate your plastics for shrinkage and extrusion. That will compensate for any errors in dimensional accuracy.
RE: Sizing parts to fit and printer precision
I will add that the same approach applies across different colors, as long as the filament is well-calibrated (in the slicer). That said, different pigments can slightly change melt behavior and shrinkage, so flow or temperature may need minor tweaks as well by color. I still wouldn’t bake filament specific offsets into CAD; it’s better to adjust filament settings (or accept a small tolerance band) than redesign parts in the CAD tool.