Only a Machinist Would Notice

For those that have never seen how the plastic bottles are made, you may find this interesting. Typically, the preforms are made at one place, and then made into bottles at the place of bottling.

 
Janderso said:
What are the advantages to multi start threads?
Easier to begin threading?
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Faster action due to fewer rotations from open to close. The classic case that I'm aware of is water-tight bulkhead doors in warships and submarines. Give the handwheel a spin and it's closed very quickly.
 
Twist off caps on beer bottles is probably the most common form of multi start threads.
 
C-Bag said:
And easier for the machine to pick up the threads. Never would have thought of that.
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The 'threads' shown are very shallow so maybe the machine just presses the cap straight on, The threads might only be designed to allow consumers to break the seal with reasonable effort.
 
Haha, the multi start threads was the first thing that caught my eye too. Wow 9, never seen that many before, or should I say never noticed before.

I was curious once about multi start threads & how to cut them. No one could tell me how (before I found/joined this forum) so I went on a mission to figure out how. I ended up using the thread dial & split lines.

I still have the successful test piece. A 20 tpi 4 start thread that is found on Mini Maglites.

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Funny this came up. Just a couple of days ago I was cleaning out my Nalgene bottle that I store cold blue in. Noticed that it had a buttress thread & surprised me. I never did pay much attention to bottle threads before.

20200526_130253.jpg
 
There are about a half a dozen reasons for the thread they used. Buttress threads are used in plastic because of the low strength of the material plus the fact the threads are not very deep. The threads are not very deep because they want a bottle as thin as they can get it. thin bottle = shallow thread and if a single start then you have about 20 revs till the cap is on. This way with 9 starts it only has to rotate 40 degrees till makeup. Plus to find a thread start the cap can be out of sync only 40 degrees so you don't have to spend a lot of synchronization effort to orient the cap.
 
darkzero said:
Haha, the multi start threads was the first thing that caught my eye too. Wow 9, never seen that many before, or should I say never noticed before.

Funny this came up. Just a couple of days ago I was cleaning out my Nalgene bottle that I store cold blue in. Noticed that it had a buttress thread & surprised me. I never did pay much attention to bottle threads before.

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So I'm NOT the only one.
 
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