Mating Threads

[rctong]

When designing threaded parts that mate together, (for example a threaded bottle neck and a cap), are there generally gaps or spacing anywhere designed in to for tolerances? Or are the mating threads line to line? It seems like there should be some sort of gap but im not sure.

Thanks!

 

[MikeHalloran]

For, e.g., a bottlecap, you can get a line to line fit on the thrust faces of the thread (the 'normal' face of a buttress thread), and the neck/cap/seal faces, but you must have clearances everywhere else.



Mike Halloran
Pembroke Pines, FL, USA

 

[dhengr]

Be careful with mating threads. They are really very prolific, and you’ll have the darn things all over the place in no time.

 

[rctong]

How much gap is typical for plastic designs (caps) versus metal designs (nuts & bolts)?

Can you recommend any websites or literature showing mating thread profiles?

Thanks
Ryan

 

[MikeHalloran]

Gap is typically twice whatever tolerance you can hold on your part.
I.e., .010" or so.

There are 'standards', but I've had better luck just detailing a part to mate with whatever part I could buy.



Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

A (commercial products) typical plastic cap-and-thread shouldn't really be "designed" but rather specified so it can be executed hundreds of thousands of times a day by the bottling machine - and seal adequately for the product.

So, rather than talk to a mech engineer about threads - as if this was a conventional thread problem, I'd recommend talking in depth to the design/fabricator company of the bottling machine that you will use.

 

[MikeHalloran]

If you're buying a bottling line, then caps and bottles are produced on-site, and the detail design of the fit is indeed someone else's problem.

If you are designing a custom cap to fit a commercial bottle, or conversely, I stand by my advice. It's worth at least what you paid for it.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Google still works:

http://www.plasticbottle.com/techinfo/spi.html

Ted

 

[juergenwt]

rctong- For threads being used on plastic bottles I would stick with a standard. Look up DIN 6063 T1 and T2. All dim's are there. You have a choice between "Buttress or Trapezoidal" threads.

 

[KENAT]

There are Industry/National/International standards for all kinds of threads, including 'bottle threads' and the like.

If at all possible start with one of these.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​