Version 2: Utilizing captured nuts and printed threads

With this remix we removed the need for the heat-set threaded inserts to attach the cover and GoPro mount to the base.  These components are expensive and take special equipment to insert them in to the base and activation surfaces.  We also replaced the 1/4 inch bolt with a printed post and a screw-in collar (with its own Teflon tube lining) to make the connection between the activation surface and the internal spring more stable and the action smoother.

As a result of assembling my Prusa i3 MK3 printer I learned an interesting way to join printed parts with a nut and bolt.  The trick is to build a trap for the nut into one of the parts.  The nut is “squeezed” into the trap (so it doesn’t easily fall out) and then the bolt is inserted through the other part and screwed into the nut.  This method works quite well to hold the parts together and supports easy disassembly and reassembly.

I also had a brainstorm regarding how to make the action of the center post even smoother.  It occurred to me that I could place one Teflon tube inside another and each tube would be fixed to the collar or the post so the only sliding surfaces would be the two Teflon tubes sliding against each other.

Finally, I learned how to create threads in Fusion 360 which were very reliable and realized that I could create my own post with its own characteristics that would facilitate mounting and removing activation surfaces and I could create a more robust connection between the collar and the cover – it’s necessary to create them as separate parts in the first place in order to allow the cover to be 3D printed without supports.

First Things:

Obtain the updated STL and Fusion 360 files at Thingiverse at this URL: https://www.thingiverse.com/thing:2870415

You’ll also need to purchase the following components:

You’ll then need to print each of the STL files from Thingiverse.  I recommend printing all parts with 2 perimeters/shells, 3 top and bottom layers, and 20% infill.  The one exception is the post.  I recommend printing that with 100% infill and at least 3 perimeters/shells for as much strength as possible against shearing forces.  No supports are needed for any of the parts.

I include two versions of the collar.  It’s really hard to predict how 3D printers will print parts with fine tolerances.  First print the standard collar and it you simply can’t insert the wider PTFE tube into it then print the second collar – it has a slightly larger hole.  It’s important that the tube fit snugly in the collar.  That’s less critical for the PTFE tube that fits over the post but a snug fit will lead to a more stable activation surface.

Assembly Process:

Step 1: Insert 2, M3 hex nuts into the slots in the bottom of the switch base.

If you initially have trouble pushing the nuts into the slots you can insert a screw from the other side and use the screw to pull the nut down into the slot.

Step 2: Insert two M3 hex nuts into the two cages on the bottom of the switch cover.

The nuts should fit snugly but don’t force them into the cages – the cages will break and you’ll need to print another cover.  If necessary use a small file to slowly open up the slot in the cage until you can insert the nut without overly forcing it in.  Note that the nuts should be inserted with a flat side on top and on the bottom:

Use a narrow tool to align the holes in the cage with the hole through the nut.

Step 3: Assemble the electronics just like the original proof of concept and insert them and a spring into the base.

Step 4: Insert a 1/2 inch piece of the wider PTFE tubing into the collar from the non-threaded side.  Again, if the tubing just won’t go in, print a new collar using the design with the larger hole.  If you’re careful, you can insert the full length tube and then carefully trim the tube to the face of the collar:

Step 5: Create a PTFE sleeve for the post using the thinner PTFE tubing.  Trim the tubing right below the threading on the post:

Step 6: Screw collar onto the cover and insert post through hole in the collar from below:

A closer view shows the two PTFE surfaces that will slide against each other when the post is depressed by the activation surface:

Step 7: Attach the activation surface. Press up with your finger on the bottom of the post.  It will slide in between the two bumps on the bottom of the cover:

Now screw the activation surface onto the threaded end of the post.  The bumps on the underside of the cover will hold the post in place and keep it from rotating.  Don’t over tighten the activation surface.  Though the post has been printed for maximum strength, 3D printed parts are only so strong.  Note that you can remove the activation surface later without taking the cover off by pulling up on the post and rotating it slightly until it slides between the bumps.  You will be able to unscrew the activation surface without the post rotating.

You may find that the user wants to apply lots of force to the edge of the activation surface which will put a large amount of shearing force on the post.  If the post does break, it will likely do so at the bottom of the threaded portion.  In that case, replace the printed post with a stainless steel hex-head bolt that is 1/4 inch in diameter and 1-1/4 inch long (you will still want to sheath it in the PTFE tube:

Unfortunately, the diameter of the bolt head is too small to engage the bumps on the underside of the cover so you may need to remove the cover in order to mount and unmount activation surfaces.

Step 8: Bolt the cover onto the base.  Don’t over-tighten the bolts – you could cause the nut to rotate in the cage – and it’s just not necessary.

Step 9: Optionally, you can attach the GoPro mount component to the base.  There are 4 holes in the mount and only 2 will be used.  Providing 4 holes allows you to attach the mount with a different orientation with respect to where the cord will leave the switch.