This weekend, I experimented with my Flashforge Creator to see if I could produce 3D printed threads. My background research revealed that outside of a couple interesting posts, there wasn’t much information out there on thread-specs that were conducive to 3D printing.
Instead of of opening up my Machinery’s Handbook and jumping straight into trying to make an ISO or Unified Thread Standard (UTS) sample, I decided to start with a familiar thread that would be easy for me to test – a water/pop/soda bottle cap!
As it turns out, the thread specification for bottle caps is maintained by the International Society of Beverage Technologists (ISBT). They’ve been kind enough to publish this standard (for free!). I found a blog post that breaks down the difference between the two predominant standards, but the gist is that PC01881, the newer standard, uses less material than its PCO1810 predecessor. Considering that the Dr. Pepper bottle I was going to be using to test my print was purchased within the last week, it made sense to examine the PCO1881 drawing.
The most interesting thing about this standard is that it only includes the spec for the male threads (the bottle), and doesn’t anywhere mention the cap! Seems strange, but I have to assume caps are proprietary. If has inside info on this, please leave a comment! In any case, before printing a cap of my own design, I wanted to make sure I could replicate PC01881’s male threads. If you’re not familiar with technical drawings, don’t worry. There are only a handful of critical measurements we need to make this print.
Modeling the Male Threads
My first step was to open SolidWorks, then revolve a cross section of the non-threaded portion of the bottle.
Next, I offset a sketch plane 0.115″ from the top lip of the bottle (corresponding to the note that shows this is where the threads start). I then used SolidWorks’ Convert Entities tool to turn the bottle’s outside profile into a 2D circle on the sketch plane.
With this circle established, I created the actual thread’s profile. Two notes on this:
- The 0.032″ height measurement refers to the virtual sharps created after the ends of the thread were rounded. I avoid using this method in a production setting when I need to develop a reproducible drawing, but it’s fine in this context.
- The very bottom point on the thread’s profile is coincident with the circle I previously created.
Next, the Helix/Spiral feature was used to produce the threads. From the drawing, I knew the thread’s pitch was 2.7mm. I also knew the threads continued for 650° (1.8 revolutions) around the bottle. Since I had those two pieces of information, I defined the feature via the “Pitch and Revolution” drop down.
Lastly, I added fillets to the thread’s edges and fired up the printer. An hour later, I had myself a functional “bottle” top made out of ABS! When I say functional, I mean the cap screwed on perfectly. I should have noted the print settings I used, but I’d comment that supports definitely need to be turned off. I’d imagine that cleaning errant support material off of the threads would be next to impossible.
Modeling the Female Threads
Moving on, I next tackled the task of reproducing the cap itself. This was trickier since dimensions for the cap aren’t published anywhere (that I could find). That being said, I knew the pitch diameter would need to be same 2.7mm – that’s how threads work. I also knew the female threads should be undersized compared to the male threads so that the two profiles would mate. Taking the accuracy of my printer into consideration, I settled on a model that I was happy with.
If you’re planning on producing these female 3D printed threads, I’d recommended starting with the geometry shown below. Your mileage may vary based on the accuracy of your printer, or the filament you’re using. Apologies for not taking the time to make this a coherent drawing, but the offset 0.01″ shown is from the profile of the male thread.
The 3D Printed Threads
Below is a video demonstration of the threads mating. If you’re interested in using the final .STL files for these 3D printed threads, check out my Thingiverse!