Preferred way to design and print a part with embedded nut

[graymon 0]

I was hoping someone could help me out.  What is the preferred way to print out something with a metal nut embedded in it.  I have two models - one of the part with the space for the nut removed, and the nut itself.  I can get the printer to pause at the correct place, and if I use just the part (not the nut), and only add supports to the buildplate, it seem to work okay.  But if I would like supports everywhere - of course is fills in the space for the nut with supports.

 

I've tried bringing in the nut into the project, positioning it where it goes, but then is prints the nut too, and just fills the whole thing in.

 

What's the right way to do this.  Thanks all.

[GregValiant 1,342]

You could put a support blocker in the hole.  They can be moved and scaled like any model/mesh.  That would allow you to have supports everywhere except in the hole.

[eldrick 65]

https://www.mcmaster.com/threaded-inserts/

 

[Mari 37]

... I did print with "support everywhere" by accident... luckily I have a set of tools that makes removal of support in small places possible (was printing OpenRC F1, there are also slots/holes for nuts)...

 

But I like @GregValiant idea of using a support blocker 😉

 

[GregValiant 1,342]

So many people believe that the printers should deliver a part that needs absolutely nothing for it to be perfect.  We just don't live in that world.

A micro-tool set, a micro-file set, an exacto knife set, and a selection of different grits of sandpaper are what makes for near perfect parts.  It's called "Bench Work" and it has never gone out of fashion, nor has it become fun.

 

The threaded inserts have their uses.  Sometimes you need to have a pocket and drop a nut into it.  It is pretty much design specific.  These plastics move under pressure so the pocket way isn't the best as the plastic between the nut and the screw head is going to cold-flow away from the pressure.  This causes a condition known as "loose nuts".  Very serious.

[Mari 37]

You can make near perfect designs, but sometimes you need to redesign to make it more perfect... I like "Bench Work" and I think is fun to do 🛠️

[GregValiant 1,342]

OK.  I guess it's fun when it's your own stuff.  I like power buffing my own motorcycle parts even though it's a dirty filthy job.

I had to polish an injection mold for a car dashboard once when I was a kid.  It took a couple of weeks of knuckle busting labor.  Not a lot of fun there.  It was that job that convinced me I'd rather be a designer with a pencil in my hand (we were still using PencilCad then) than with a whetstone in each hand.

[graymon 0]

Thanks all for the help.  Either using a model or the cube as a support block and the pause at height seem to do the trick.  Thanks for the help.  If you dump a model of a nut into the project - one with clearance designed in - you get supports around the edges - which was a mistake.  You can scale up the model of the nut of cube blocker a little past the clearance, and then it works well.

 

Unrelated note, my extruder heater just died - no longer heats.  I gotta replace that before I can start testing this again.

 

But thanks everyone.

[geert_2 558]

What you could also do, is make a hex cage with a protruding ridge at the bottom, for retention. And then using brute force, push the nut through the opening past the ridge. Then it can't fall out. It will take a bit of trial and error to get your tolerances right, but then it should work fine.

 

If you use a conic top surface of the cage, you need no supports. Also use a conic chamfer at the bottom, to make sliding the nut in easier, and to remove elephant feet due to printing.

 

I find it easiest to design the nut separately, then move a copy into the model and subtract it. This is way easier than designing the cage directly in the model, and easier to make multiple holes: you only need to make one nut, and then you can copy and subtract it as many times as required.

 

Obviously, do this on small test pieces first, using the same printing parameters (speed, temp, flow, layer-height,...) as you would in the real print, until you get your dimensions and tolerances right.

 

See the designs below. Left is the base model with a hole where an M4 screw has to go through. Center is the nut with all features described. And right is the nut subtracted from the base-model, leaving the cage.

 

Using a metrinch-style nut makes printing easier: it gives less problems with rounded corners due to the print-head slowing down and lines getting thicker, and due to the filament being pulled inwards. So it allows for tighter tolerances, and less risk of the nut rotating in the cage. I designed the metrinch-aspect just visually: I started with an hex-shape for an M4, and then added both rounds on the flats and corners by guestimating. But it works. If you keep this special nut as a separate file, you can re-use it later in other desings.

 

Edit: for clarity: in this way you can use cheap standard metal or nylon nuts, no special inserts or other things required. To make inserting the nut easier, you can temporarily mount it on a screw: that gives a better grip.

 

 

 

 

 

Edited September 8, 2020 by geert_2

[geert_2 558]

Forgot to say in the above post: that method is only good if the load is directed inwards, obviously. I used it to clamp two mould-halves together.

 

For a load in both directions, or outwards, I use side-openings for inserting the nut afterwards. Sort of slots where the nut slides-in. This too can be with or without retention ridges, to prevent the nut from falling-out if the screw is removed. It is not suitable for every model and every print-orientation, but if it is, it works very well. Here too, I can use cheap standard nuts.

 

See these real models:

 

 

 

 

[graymon 0]

Sorry for the delay is posting back - I got it working.

 

Use a second model (the nut) defined as "Don't support overlaps".  I didn't use the block.  I paused the machine on the layer before the overlap with the "Pause at height" post processing plug in, stuck the nut it, and then printed over it. 

 

Thanks for you help all.  I hope this helps someone else in the future.

[GregValiant 1,342]

Here's it's mate.  Two pieces with the hex in the collar part.  I just threaded the horseshoe so no nut there.

 

Edited September 15, 2020 by GregValiant