Testing done with Black Inland PLA sliced with S3D I almost always use 0.4mm nozzles, once in a while i will go with something larger. I am about to embark and a multiple roll of filament printing spree with well over 100 bolt holes. To prepare I printed off a couple test blocks testing m4 and m3 hardware clearances vertically and horizontally first with an 0.4mm nozzle at 0.3 layer height. I had to give a little extra clearance and reprint and got a passable result didn't think much of it. Here is where its a little odd. I decided that I should probably up the nozzle size as these prints are going to take a long time so I went up to a 0.6mm nozzle at 0.3 layers and reprinted the test blocks and now my holes are way to tight I would have to drill every hole out which I definitely don't want to do. I adjusted the model tolerances again and reprinted, the horizontal holes are fine but the vertical holes are still too tight especially for the m3 and while the horizontal holes are almost too loose for the m3. I created a new test print 20x20x10 cube with a 10mm diameter hole in the middle with fillets to round the edges. I get almost perfect measurements on the outer dimensions but the hole I measure is about 9.4-9.6mm in diameter (I was even slightly under extruding during this test to rule out over extrusion) Just to rule out esteps as the issue, I printed a 140x140 cube and measured with my calipers and the esteps seem spot on. I am thinking about trying a different slicer tonight to see if I can get a different result. Does anyone have any thoughts or suggestions?
I think that's likely to be a feature of the overall process. From my reading and my own (very unscientific) observations, I think that in general the wider the nozzle, the more likely you are to get a more undersized hole. Likewise for increasing the layer height. This is (I think) mainly due to how the slicer handles the direction changes as it goes from polygon to polygon (all stls are polygons, with no actual true circles) but I can't claim to have spent much time testing and measuring. My approach is more of a 'try it and find some sizes that work', which suits what I do well enough. I suppose I should try a more scientific approach You may be able to improve accuracy a bit by manually setting the extrusion width and printing outer perimeter first, but you'll still need to figure out the right clearance to use. These might help (or not). http://hydraraptor.blogspot.com/2011/02/polyholes.html http://hydraraptor.blogspot.com/2014/06/why-slicers-get-dimensions-wrong.html https://forum.simplify3d.com/viewtopic.php?t=9580 https://reprap.org/wiki/ArcCompensation I'm not really sure what the best solution is. I believe that the required clearance will differ for each combination of nozzle diameter, hole diameter, material and layer height. The formula in the last page linked to might help as a starting point. Will also probably vary at least a little from slicer to slicer.
If the holes are accessible, and to save wasting time and filament whilst you find the final solution but you could try the correct size drill bit but turn it........... anti-clockwise! This sounds nuts and I didn't believe it when told, but it works. It is not likely to work if the hole is too much under-size but there again you could start with a slightly smaller bit size.
I have done a lot of reading and tests. From my observations the holes are off a similar amount regardless of radius of the hole and nozzle size does effect the accuracy but not as dramatically as one might think.. That said I have I wouldn't say my test have been exhaustive by any means but, 0.4mm nozzles are a bit better but across a range of holes between 3 and 6 mm I get around around 0.4ish reduction in radius on each hole, with a 0.6mm nozzle I get about 0.5mm reduction. I don't have the time or inclination at the moment to test other nozzle sizes or hole sizes not sure how the trend would fair if the holes were very large or the nozzles were but I have a suspicion it would. I did find an issue with my slicing profile, not sure how it may have effected the holes for sure, but when my printer started printing again after a reaction, it would lay down a little extra plastic, I ended up with about a -0.2mm restart after a retraction. I figured this out after the 0.6mm hole test and before the 0.4mm test, meaning I am not sure if it effected the holes measurements in anyway or not. The post about arc compensation I have read a few times, I am tempted to pull that super old slicing software and play with it but again I am limited on time. I think this is something that in not accounted for in modern slicers. For now the moral of the story is, add 0.5mm to the radius of any 3d printed holes + the tolerance and try a test print, should get pretty close to the desired end result. I just hate adjusting the model for the slicing software, I hope someday we move away from STL's
Out of interest then what fits into the holes if they are no accessible and similarly how are you measuring them?
A bolt is much easier to get into a hole then an entire drill, the geometry of the part is such that a short bolt and Allen wrench to tighten it will fit not much else. I am not measuring those holes, I created a test block with m3 and m4 hardware holes for the bolts and nuts so I can test fit the hardware before I waste a huge amount of time printing the large pieces. If your asking with what am I doing the measuring that would be a pair of calipers, I have 2 pair and they both agree.
I have found some interesting reading about file types for 3d printing. https://all3dp.com/3d-printing-file-formats/ So one of the big limitations to accurate parts is the file type most commonly used STL, So I started reading and discovered that S3D supports two other files times OBJ and 3MF. More detail can be found in the link but the summery is OBJ and 3MF should provide more accurate geometry, so when I get home I will create a new test block and export in each files type and print each one and see if there are any differences in the end result.
hmm seems I am just spinning my wheels with the file format thing... Fusion360 doesnt seem to directly support the two formats. You have to use the website to export the OBJ and a plug in for the 3MF, it appears to do this is turns it into a standard mesh using the exact same settings as the low poly option for STL and then proceeds to turn that mesh into an OBJ or 3MF which completly voids the entire point of trying to export either of those file types. You are not getting any new information your just converting the STL into the other files types so you get the same result in the slicing software Maybe some future update will being a truer account for the files types in Fusion.
