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Minimum Gap Distance

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Hi everyone,


I'm running nylon for the first time and the default settings are working pretty good. Not sure if that plays into my question but, what is the minimum gap between parts or walls before they fuse together? Does this have anything to do with tip size as well?


I have a ring type form that is not completely joined, which is part of the design. You're supposed to be able to pull it apart The gap right now is .006 in which is roughly .15 mm, I figured it would fuse. Anyone have a recommendation on this gap distance?


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It varies too much.  If I raise the temperature by 10C it can seal up a 0.1mm gap that was there before.  There are test prints on thingiverse that are helpful.  Really you just have to experiment.  Also when I am near the end of a spool of filament I get more underextrusion which is only obvious on gaps like this which grow a bit.


Also the bottom layer has special requirements.  You want to overextrude the bottom layer and by default it does.  This makes the parts stick much better to the print bed.  But it also can fill small gaps like this.  So you might want to set "initial layer horizontal expansion" to a negative value.  But if you set it to an overly large negative value and you have thin walls then the walls won't print at all on the bottom layer.  So you might have to increase the gap size in cad for the bottom layer.  Or just cut the bottom layer with a knife after the print is complete.


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Thanks. I hate having to pull this many levers in CURA and chase my tail while the customer waits. It's nice to have that sort of flexibility to do those things but I'd rather change the CAD and see. Any sort of ballpark dimension on what you think a gap should be? My instinct tells me maybe as a rule of thumb that twice the width of the tip you're using may be a place to start. We'll see if anyone else chimes in on this.

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For this sort of things in PLA and PET (I haven't used nylon yet), I usually take 0.3 to 0.5mm gaps. As gr5 says above the bottom layer sometimes does fuse a little bit, due to that layer being squeezed well into the glass and spreading out. But it is easy to cut. Further there are occasional strings, also easy to break.


I would suggest you design a couple of small test models with variations in gaps, and print them at different speeds and temps in the range you usually use.


The gap in the keyring here is 0.5mm. For size-estimations: the ribs on the pink support block are 0.5mm wide, with 1mm gaps. The pink block itself is 5mm wide. Vertical gaps between the pink support block and the overhanging yellow part are 0.3mm: they fuse slightly, but can be wiggled out. The cyan part is ca. 50mm long and 25mm wide. Gives you an idea.




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