Only a Machinist Would Notice

[MrWhoopee]

On common, everyday items, I see things that only a machinist would notice. A case in point is this milk-jug I use for mixing chainsaw fuel.



That's a 9 lead screw thread! (Yes, I had to count them). That means the cap releases in 40 deg. of rotation. I love my milk, but I've never been in that much of a hurry.

Am I the only one?

 

[C-Bag]

Since I’ve been trying to become a machinist and because of trying to execute designs and do setup I’m much more aware of what it takes to make something. Thread details and just design details in general. wouldn't that 9 lead screw thread be much more expensive to make than a single? BTW I don’t drink milk so have never noticed this on any of our containers.

 

[MrWhoopee]

wouldn't that 9 lead screw thread be much more expensive to make than a single? BTW I don’t drink milk so have never noticed this on any of our containers.

If done manually, definitely. Not so much in a CAD designed, CNC machined mold.
For the most part, the milk jugs I've looked at have single lead threads. This one was different.

 

[silence dogood]

Cameras use multistart threads on the focus and zoom rings. We are also talking about precision machinery especially on the better cameras.

 

[finsruskw]

Most of my containers have pop tops!!

 

[Janderso]

What are the advantages to multi start threads?
Easier to begin threading?

 

[Flyinfool]

That milk thread is not so you can open it faster, it is so the packaging machines can close it faster. This will equate to more bottles per minute.

Yes it costs more to make a thread like that, but it is only made once in the mold, the plastic will mold the same regardless of the thread form.

 

[C-Bag]

And easier for the machine to pick up the threads. Never would have thought of that.

 

[extropic]

Another aspect of "why" may be that the thread will resist a higher pressure in the jug and still be quick to install and remove.
The picture shows the thread is about four pitches high so would resist about the same pressure as 1440° of a single lead thread.

The pressure capacity might be important to you if you've ever dropped a gallon jug of milk and had the cap blow off.

 

[Flyinfool]

Trust me, the multi lead thread will not keep the cap on........