Bottle Cap Magnet Insert

This model is intended to hold a magnet centered in a bottle cap, so you can use it as a fridge magnet.

The default STL is sized for the cap from a bottle of Cazadores Reposado tequila and a cheap craft magnet from Walmart, so if you happen to fit that exact scenario, the model I uploaded might work for you. Most of the time, you'll want to change a few of the dimensions. I've provided the model in both Blender and OpenSCAD format so you can modify it as needed, depending on your preferred program. Both files are parametric.

To access the parameters in Blender, once you've opened the file, you can click on the Magnet Insert object, and go down to the Modifiers tab, where the Geometry Nodes modifier will have the list of parameters.

For OpenSCAD, as soon as you open the file, you should be able to edit all parameters from the Customizer panel.

The parameters you can change are as follows:

• Aesthetic
  • Vertices: You can probably leave this alone. This just defines how smooth the circles in the mesh are. 128 should be fine (64 is probably fine, really), but it annoyed me that I could still see the individual faces in the display, so I cranked it up to 512 (although, I probably wouldn't have seen them in the print even at 128). If you want your exported STL to be smaller, or the OpenSCAD render to run faster, you can turn it back down, but the file's already pretty tiny, and the render should only take a few seconds anyway, so that usually won't be much of a concern.
• General
  • Thickness: The total thickness of the insert. If you leave it at 0, it will autosize to the thickness of the magnet you're using plus an extra millimeter to form the backing behind the magnet.
  • Cap radius: The radius of the inside of the back of the cap, where the insert will be inserted. I left a few tenths of a millimeter for margin and glued it in place, but you could try to go more exact and use a friction fit.
• Magnet
  • Magnet radius: The radius of the magnet you're using. Again, you can try to cut it close and do a friction fit, it might work, but I've just been leaving a little space and gluing it in.
  • Magnet thickness: The thickness of the magnet. I've been undersizing this a little to make sure the magnet protrudes by a millimeter or so, because my magnets are pretty weak and I want to make sure they make direct contact with the metal, but sometimes you might want them flush, in which case you would use the true dimensions of the magnet.
• Lip: I originally designed this insert to fit a cap from a liquor bottle, so I removed the cork from the cap and I wanted the insert to go where the cork used to be, but I didn't need it to go all the way back along the cork hollow, so I made it just thick enough to hold the magnet and then added in a little lip that pressed up against the back of the cap to hold it at the top of that hollow. You may want the lip in cases like that, where the back of the cap has a surface and a hollow, but if the back of the cap is entirely hollow (like the cap from a bottle of Coke), you may want to remove the lip and just glue the insert straight to the back of the hollow (in which case you'll want to set Thickness manually to make sure it's thick enough to fill the hollow). Set either parameter to 0 to disable the lip.
  • Lip width: The extra radius beyond the cap radius to extend the lip to.
  • Lip depth: The thickness of the lip. This won't make the insert any thicker overall, the lip will just extend further back down the side as you increase it.

The insert is pretty straightforward to print. If you're not using a lip, just print it the obvious way with the magnet hollow facing upward. If you're printing with a lip, I personally would put the lip side down, and leave supports off, just let the top of the magnet hollow bridge. Depending on your printer's performance that might cause the magnet not to seat quite flat, but probably not, and you can always put in supports if you need them, this is just going in the back of the final craft, so aesthetics aren't really a concern.