I am looking on having a discussion on joining printed parts.

Basically, I am looking to see if people have suggestions on friction fit
methods for joining parts together (like legos do).  It could be something
you brewed up yourself or something you found elsewhere.  Does anyone have
friction fit joining mechanisms they like?

I am looking for this because if I print a whole model inside the build
volume of a makerbot I'm going to end up with a tiny model that is hard for
me to inspect.

I think I saw a design for prints to interface with LEGOS.

The one time so far that I've done this I used tapered sliding dovetails.
For my design I didn't care if the joint lined up and I figured the taper
would absorb errors in the print.  However, in my print the joint went
together a little too far, whereas some others who printed my design on
different hardware reported having to persuade it together with a hammer.
But I still think the sliding dovetail is a good idea.

We had a recent discussion here about snap hinges.

You don't indicate in your question what the geometry of your connection is,
which might affect the types of joint that make sense.  If you can use glue
you can do a puzzle-cut type approach to divide your model into parts.

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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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