[OpenSCAD] Joining parts

macdarren macdarren at mac.com
Thu Jul 18 17:00:36 EDT 2019


Finally something I can contribute too...maybe....

I print mostly on a Resin Printer...so not much for layer lines....I have
found (and you will have to conduct some tests on your equipment) that a
friction fit can be achieved with anything less than about .2 mm clearance. 
What I did was create a ring with a fixed size inner bore....I think I used
10mm...be sure the ring is thick walled so there is no flex and normal
shrinkage happens....then I created a series of small inserts, basically
cylinders with a little allen key hole in the middle...each cylinder was one
(pixel, spot size whatever the minimum resolution your printer uses) bigger
than the next..I started two sizes smaller than the ring inner diameter and
several larger in one step increments.  While the smaller ones should not
ever fit you never know.  Once things are clean and cool I inserted the
cylinders into the ring...I used the allen key just to rotate to judge
binding...you will need something to poke out the tight ones.  Also I
suggest printing some sort of indicator on the cylinder top that tells what
size it is so you don't get them mixed up while testing....I just used bumps
to indicate the step sizes.

I have printed several items using friction fits similar to lego and also
some sliding guides that must slide but not be sloppy and even a few round
bearing type parts.  So far what I learned on my ring and insert test served
well...the only issue is some care in orientation is warranted as not all
orientations result in identical prints...but just print a ring set that
matches how you need to print the final parts....Also on a Resin machine the
resin type / brand matters when you want those really perfect fits you have
to test.

With FDM printers overhangs tend to close up spacing and for me at least
inner diameter holes tend to run small while outer are mostly right on.  I
often have to make a few runs to get the friction I want...but lego printing
works pretty well once you dial it in...even print speed can affect the
final product.



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