An Easy Design for Print-in-Place Hinges!

Hinged designs that print already-assembled, and which can't just come apart are the best!  I have a few designs that incorporate such a thing, and the approach I take to it these days is really simple!  So, I thought I'd go through it here. 

Where do we start?

Well, first we need to decide what's actually going to be hinged, and to define an axis and a radius for the hinge.  I've used this approach with elements as thin as 3mm, which still strikes me as kind of crazy.  The Chompy Skull has a hinge diameter of more like 10mm, which is obviously going to be fairly strong.

So, let's create a cylinder, and in this case, make it 10mm in diameter:

Divide the hinge into moving sections

A hinge needs to have at least three sections - one in the middle, and two on the outside to hold it in place.  Now, we can have more segments than that (look at the Flat Fold Phone Stand, for example), but we'll just work with three in this example.

Let's divide the cylinder into three parts.  We'll need to use a sensible gap that the printer will be able to handle without fusing the parts together.  I use 0.5mm or 0.7mm.  

No pins!

A regular hinge would generally have a pin running through that, but we don't need to make things so complex.  Instead, just add a cone to one face, and subtract a cone from the adjacent one!  

Note that I've chopped the point off the cone for printability - there's no value in having a potentially-problematic part on the inside of a printed hinge.

That's an exploded view, of course - the pieces should still remain 0.5mm apart horizontally (or 0.7mm if you're trying to roughly keep 5mm distance between the two interior faces, but really, just test how close your printer will let you get, then back off if you want a looser hinge)

Tidying up the faces

So, I'm not all that happy about the edge of the inset cones - it comes to a sharp edge, which isn't ideal for printability.  So, let's just inset the cones a little way from the edge instead.

Actually using this as a hinge!

So, that's looking  pretty neat - let's attach something to it.  For our simple example, we'll just add a slab on each side:

For the sake of clarity, lets move the two sections apart, though obviously that couldn't happen in reality, because our hinge won't come apart :)

Now, there are some obvious problems here. Most significantly, the slabs overlap the hinge parts, so we'll need to trim the slab accordingly.  We'll need to consider tolerance again, here, since we'll have two parts that need to be able to move against each other.  I'll use 5mm as usual.

We're going to trim 0.5mm out from the hinge cylinder, so do this using whatever is appropriate to the CAD package you're using

And then, we trim the slab - not the hinge pieces - at those points where there's no hinge touching:

And we end up with a workable slab-and-hinge assembly!

On the other side, we do the same, but we add another step - we also trim the slab where it runs inside the inset cones, and we trim using the cone diameter itself.  We'll end up something like this:

Note the way that on both sides there's a kind of step that connects the hinge to the slab - that's the key to it working, really.  Without that, nothing would move!

So, put back together we get this:

And we are essentially done!

Making it all more printable

It may be obvious at this point that those curves aren't ideal for printing.  They'll probably be fine, but it would be more robust to draw down that curve more sharply to the bed.  Likewise, the hinge as it currently stands won't bend downwards, because that curve that goes underneath will immediately get jammed up.  It would be trivial to simply trim those bits vertically (or beyond!) to get movement if we wanted it :)

Thanks for reading!

Hopefully this was interesting for someone!  Thanks for reading, and thank you so much as always for being supportive, creative people! :)