3d Printed Screw Switch

Aquaman33 · Postby **Aquaman33** » Wed May 15, 2019 11:17 pm

I am continuing my 3d printing adventures with screw switches.

I have a couple of these on their way to me:

But I started thinking maybe I could come up with a more elegant solution.

So I spent a little time in SketchUp and came up with this:

And when printed it looks like this:

The switch is just a Jaycar Micro Switch with the lever trimmed.

The upright design means it doesn't take up too much space on my ebay and the screw will be just a few mm inside the body tube for easy access. This one is designed for a 4 inch tube.

I printed them on their backs, to avoid the whole thing snapping off under pressure due to z-axis weakness.

I could of printed a thread for the screw or tapped one, but I decided to just use these M3 inserts instead.

They seem to work well.

The screw head screws down hard against the plastic in the "On" position. So I don't think they will come loose, but I might be wrong.

I am keen to get people's thoughts on this design or suggestions for improvements.

Also if you have seen better solutions please share.

Thanks

Derek

OverTheTop · Postby **OverTheTop** » Thu May 16, 2019 7:22 am

Hey Derek,
Nice design. Looks like it does what you want it to and you have thought about failure modes. Don't forget about z-axis weakness too. The way the switch is, even if it snaps at the base (highest bending moment is there) it will still keep functioning. Nice design.

I would suggest rounding the inside corners with fillets to reduce the stress raisers. Only a small radius is needed.
https://en.wikipedia.org/wiki/Stress_concentration
Look at the picture of the bricks in the above article to illustrate how a stress raiser increases stress. The stress is inversely proportional to the radius.

Oldboy · Postby **Oldboy** » Thu May 16, 2019 10:09 pm

Cool design.
Can the design be orientated to the horizontal plane?

air.command · Postby **air.command** » Fri May 17, 2019 2:41 pm

Nice work Derek, those look great. I agree it would be good to be able to mount them at 90 degrees, so that you could easily access them from the outside. Perhaps just moving the mounting tabs to be in line with the top.

Aquaman33 · Postby **Aquaman33** » Fri May 17, 2019 4:42 pm

Thanks all for your comments.

I have some learning to do with regard to stress forces and also refining SketchUp diagrams!

Yes, a horizontal version could easily me be made with some small changes to the design.

It terms of accessing the screw: This vertical version was designed to be mounted in this orientation so that it can be accessed through a hole in the tube. Only difference being that it will stand vertically on the ebay unlike traditional screw switches. So the access hole is at 90 degrees to the edge of the ebay rather than close to the ebay edge.

I am not explaining myself very well, so here is a bad (not to scale) drawing:

The advantage of this design is marginally smaller footprint on the ebay. The disadvantage is greater stress on the base.

But having said all that I am having second thoughts about the micro switch (as a point of failure). So I am working on another version that is a bit smaller and doesn't require a micro switch.

I'll post more details soon, but it will be more like this:

I am pleased that it accidentally came out looking like a droid from Star Wars.

Aquaman33 · Postby **Aquaman33** » Fri May 17, 2019 7:17 pm

Prototypes of the simple screw switch (without the micro switch).

This blue version failed to print properly but the "accidental window" shows the metalwork inside.

Basically just 2 threaded inserts that are inserted through eye crimp connectors. When the screw is tightened it connects the 2 inserts together and completes the circuit.

The gap is a lot bigger than it needs to be so I'll compress it a little.

This design (with the metal core) is really solid. Even if all the plastic disintegrated you would still have a good connection once that screw is tight.

I tried to snap the legs on the blue version with my hands and I couldn't break it. Not a very scientific test, but I think its strong enough.

This design without the micro switch will take up less room so I will probably make a horizontal version.

Watch this space.

Oldboy · Postby **Oldboy** » Sat May 18, 2019 10:28 am

Thanks for the reply.
If north is the top of your picture then mounting it horizontally could it not be accessed on an east west orientation.
This would give you a more solid block.
Still a cool design

Aquaman33 · Postby **Aquaman33** » Sat May 18, 2019 12:28 pm

Oldboy wrote:Thanks for the reply.
If north is the top of your picture then mounting it horizontally could it not be accessed on an east west orientation.
This would give you a more solid block.
Still a cool design

Yes, makes sense.

More solid east/west version coming shortly.

Aquaman33 · Postby **Aquaman33** » Sat May 18, 2019 12:39 pm

The latest version will mount flat on the ebay board.

Much stronger than the previous versions.

I left an open "window" in the middle. Its handy to be able to see the screw position when working with it on the bench.

Apologies for the terrible photos, but hopefully you get the idea.

First prototype:

Components ready for assembly:

Closed position ON.

Open position OFF.

18mm motor for scale.

Its 28mm wide, 16mm deep and 10mm high.

With M3 bolts inserted ready for mounting.

air.command · Postby **air.command** » Sat May 18, 2019 6:22 pm

I like it. An elegant and compact solution.

How well do the inserts hold in the plastic? I'm just thinking what happens say during transportation, is there a chance that vibration could make those come out? Landing impact shouldn't be an issue since the bolt is holding them together. I guess they could be glued in if needed. I'm trying to think of a way you could do it with just regular nuts that could just be inserted into the plastic.

Aquaman33 · Postby **Aquaman33** » Sun May 19, 2019 8:01 am

air.command wrote:I like it. An elegant and compact solution. How well do the inserts hold in the plastic? I'm just thinking what happens say during transportation, is there a chance that vibration could make those come out? Landing impact shouldn't be an issue since the bolt is holding them together. I guess they could be glued in if needed. I'm trying to think of a way you could do it with just regular nuts that could just be inserted into the plastic.

The insert fit is very snug. I had to tighten the bolt to draw them into the holes as I couldn't push them in by hand, and they are hard to remove once they are in there. But I will use a little glue as insurance. The inserts are slightly tapered with fluted ridges, which also helps keep them in place.

I had considered making these switches in 2 parts and the second part would trap the inserts, but I don't think that will be necessary.

The other idea was to have the inserts snap into the plastic from above and then have a lip that stops them sliding out the sides, but this would be a weaker switch.