Is there a formula or basic guide line to breaks in each thread on a bottle & cap? (variable helix)

I designed a variable 2.5 rev. helix sweep (extruded on the cap and bottle).
.3 inch pitch on 1st revolution starting from the bottom going up
.09 inch pitch on the remaining rev's.
I used a continuous sweep with no breaks in the threads.
But every bottle & cap I looked at has breaks at certain degrees of each revolution.
Is there a formula or basic guide line to these breaks in each thread?

Answer
 
Comments 0

2 Answers

The breaks in a bottle caps threads are there to allow venting of the bottle as you remove the cap. There should be no set degree of revolution, gap or number required, and will vary by manufacturer.

 
Comments 0

http://www.threadspecs.com/ has a download section where you can get PDF files with details for various thread sizes used on plastic bottles. The site is currently dead, but I was on it last week and it worked well.
I also found this site that has two of the PDF files available: http://imajeenyus.com/mechanical/20120508_bottle_top_threads/index.shtml
The location and duration of the vents you mentioned are detailed.

 
Comments 0