- Joined
- Jul 8, 2009
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Over the past couple of weeks I've printed a few things that turned out to be mostly just for fun. This is one of them.
![Original.JPG Original.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83023-48f0cad6114caa704bcb4a85147b0f30.jpg)
This sad, and slightly blurry speciman is what's left of what was originally the cap for a salt and pepper shaker set. My wife and I had that set since we got married and that would have been 43 years ago. During the autopsy the cause of death was determined to be tissue rejection. This was a Miller High Life press on cap that was living on a 7 ounce screw top PBR bottle. I guess it was only a matter of time until the cap succumbed.
![Bottle.JPG Bottle.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83024-b3c13743186b7b6d9dbbe0924a7045bc.jpg)
But.... I have a 3D printer. I can rebuild him, better, stronger, faster - well better and stronger at least. A multi-start internal thread in the cap of unknown dimensions... How hard can it be? I can measure the pitch between the threads. I can measure the OD of the bottle above the threads - it's 25.5mm. I know that there's a section at the top of the bottle that's unthreaded. I know how tall I want to make the cap. I know that the threads rise 5mm from start to finish. I know that there are 4 starts to the threads - I counted'em on my fingers to be sure. I know that the major dimension of the threads is 27.5mm. I know that the threads rise 5mm in 90°, 4 starts so it's gotta be 90° right? That means they have to rise 20mm in a full turn, therefore I am making an M27.5x20 four start thread - piece-a-cake. It'll be fine.
This was my first attempt, looks pretty good doesn't it?
![First attempt.JPG First attempt.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83025-f7eac5fdb9d624dece4a50c406809147.jpg)
BUT, it didn't fit. Why not? Well I'm so glad you asked. Somebody, and I'm not going to name any names - but we are VERY closely related, used the minor dimension of the threads as the ID of the cap - then projected the threads inward. Definite whoopsie. Second attempt looked pretty much like the first. Except this time the un-threaded portion of the cap actually fit over the threads like I wanted, but the threads wouldn't screw together.
Wonder why not? The bottles got 4 starts, my cap's got 4 starts. The unthreaded portion of my cap fits over the threads like I wanted it to do. The threads on the bottle only go part of the way around - same as my cap. Ummmm... shouldn't my threads sorta resemble their threads? Aw CRAP! The duration of each thread is 120°, not 90°. Their threads rise 5mm in 120°, while mine rise 5mm in 90°. That means the threads should been M27.5x15, not M27.5x20. (The picture of the threads didn't turn out - SOMEBODY shook more than the camera could compensate for.) Ok, after the third or fouth attempt - who's counting anymore - I had a cap with printed threads that looked like this.
![Threads.JPG Threads.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83027-ce1bd7c46386baca95c9bf38da68afbd.jpg)
To end this long-winded story on a happy note, here's a shot of the PBR bottles proudly wearing their new screw top caps. YUP, one of the labels has a boo-boo - but I haven't been able to find a replacement 7 ounce PBR label of that vintage yet.
![Proud caps.JPG Proud caps.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83026-318020a1cd080527cb34394af3062526.jpg)
Don
![Original.JPG Original.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83023-48f0cad6114caa704bcb4a85147b0f30.jpg)
This sad, and slightly blurry speciman is what's left of what was originally the cap for a salt and pepper shaker set. My wife and I had that set since we got married and that would have been 43 years ago. During the autopsy the cause of death was determined to be tissue rejection. This was a Miller High Life press on cap that was living on a 7 ounce screw top PBR bottle. I guess it was only a matter of time until the cap succumbed.
![Bottle.JPG Bottle.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83024-b3c13743186b7b6d9dbbe0924a7045bc.jpg)
But.... I have a 3D printer. I can rebuild him, better, stronger, faster - well better and stronger at least. A multi-start internal thread in the cap of unknown dimensions... How hard can it be? I can measure the pitch between the threads. I can measure the OD of the bottle above the threads - it's 25.5mm. I know that there's a section at the top of the bottle that's unthreaded. I know how tall I want to make the cap. I know that the threads rise 5mm from start to finish. I know that there are 4 starts to the threads - I counted'em on my fingers to be sure. I know that the major dimension of the threads is 27.5mm. I know that the threads rise 5mm in 90°, 4 starts so it's gotta be 90° right? That means they have to rise 20mm in a full turn, therefore I am making an M27.5x20 four start thread - piece-a-cake. It'll be fine.
This was my first attempt, looks pretty good doesn't it?
![First attempt.JPG First attempt.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83025-f7eac5fdb9d624dece4a50c406809147.jpg)
BUT, it didn't fit. Why not? Well I'm so glad you asked. Somebody, and I'm not going to name any names - but we are VERY closely related, used the minor dimension of the threads as the ID of the cap - then projected the threads inward. Definite whoopsie. Second attempt looked pretty much like the first. Except this time the un-threaded portion of the cap actually fit over the threads like I wanted, but the threads wouldn't screw together.
Wonder why not? The bottles got 4 starts, my cap's got 4 starts. The unthreaded portion of my cap fits over the threads like I wanted it to do. The threads on the bottle only go part of the way around - same as my cap. Ummmm... shouldn't my threads sorta resemble their threads? Aw CRAP! The duration of each thread is 120°, not 90°. Their threads rise 5mm in 120°, while mine rise 5mm in 90°. That means the threads should been M27.5x15, not M27.5x20. (The picture of the threads didn't turn out - SOMEBODY shook more than the camera could compensate for.) Ok, after the third or fouth attempt - who's counting anymore - I had a cap with printed threads that looked like this.
![Threads.JPG Threads.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83027-ce1bd7c46386baca95c9bf38da68afbd.jpg)
To end this long-winded story on a happy note, here's a shot of the PBR bottles proudly wearing their new screw top caps. YUP, one of the labels has a boo-boo - but I haven't been able to find a replacement 7 ounce PBR label of that vintage yet.
![Proud caps.JPG Proud caps.JPG](https://cdn.imagearchive.com/homemodelenginemachinist/data/attachments/83/83026-318020a1cd080527cb34394af3062526.jpg)
Don