Parametric cap

Safety notice:

Please note that this is not appropriate for use:

• In households with small children or around pets

• In situations where the printed parts come into contact with food or beverage

• To cap bottles of hazardous items

A fully parametric cap

This model originally came about as a solution to a problem: in our house there is a person with rheumatoid arthritis who occasionally has problems with child-resistant mouthwash caps. I wanted to have an easy-to-use cap that closed the bottle securely but is still easy to open.

The included FreeCAD files were used to generate the two bottle caps and gaskets that are included as 3MF files. You can use them as starting points, should you need to create caps for other bottles.

Creating your own cap

Creating your own cap requires you take a few simple measurements.

1. Open the desired FreeCAD file and double-click on the spreadsheet to open it
   

2. Measure the diameter of the cap with a ruler or calipers. In FreeCAD, enter the diameter (in millimeters) in the row labeled "Neck diameter":
   

3. Measure the distance between threads vertically. You should measure from the peak of one thread to the peak of another. Enter this into row labeled "Thread pitch":
   

4. Measure how deep the threads are on the bottle. In my case, the threads were about 1mm thick. Enter this into the row labeled "Thread thickness":
   

5. The only other measurements you may wish to adjust are "Thread height" and "Cap height", which determine how high to render the threads and cap, respectively.

Once you are satisfied with your measurements, export the cap and gasket to two separate 3MF or STL files.

Printing

Print your cap out of a neutral or non-toxic plastic. The gasket should be printed out of 95A or softer TPU.

Once both pieces are printed, bend the TPU gasket enough to insert it into the cap and work it in to be flush with the base of the cap.

Screw the cap on to the bottle: if necessary, make adjustments to your parameters in the FreeCAD file to get a better fit, and reprint.