Which taper for suppressor mount to brake?

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BinaryAndy
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Re: Which taper for suppressor mount to brake?

Post by BinaryAndy » Sun Dec 24, 2017 2:30 am

In the case of a coarse thread and a fine thread, with the same major diameter and length of engagement, the coarse thread will have a higher stripping strength, even though the pitch diameter and minor diameter are smaller. To me, that means the thread itself is stronger.

Of course that only matters when stripping is actually the failure mode, which generally only occurs when engagement lengths are short or the female thread material is significantly weaker than the male thread, like a steel screw in an aluminum or plastic hole. When both parts are similar materials, the male threaded part will usually break first, and the fine threads will be stronger as a system because the screw is stronger.

In silencers, and firearms in general, we're usually dealing with absurdly fine threads compared to the UNC and UNF threads that engineers think about. It's been a while since I've done the math, but I do recall that in the bizarre case of end cap threads, using a finer pitch than necessary results in weaker threads. Going from, for example, a 1"-24 to a 1"-32 has a proportionately small effect on minor diameter and a significant effect on stripping strength. Finer threads also require tighter tolerances to achieve full strength, which becomes complicated when dealing with larger diameters and high temperatures; thermal expansion becomes a factor.
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fishman
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Re: Which taper for suppressor mount to brake?

Post by fishman » Sun Dec 24, 2017 2:04 pm

BinaryAndy wrote:In the case of a coarse thread and a fine thread, with the same major diameter and length of engagement, the coarse thread will have a higher stripping strength, even though the pitch diameter and minor diameter are smaller. To me, that means the thread itself is stronger.
Do you have a source on this? How is a thread with more shear area weaker?
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BinaryAndy
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Re: Which taper for suppressor mount to brake?

Post by BinaryAndy » Mon Dec 25, 2017 12:07 am

https://www.google.com/url?sa=t&source= ... VwpsspbMxH

https://books.google.com/books?id=TAWzn ... ne&f=false

Stripping strength of a thread is a complicated thing to calculate, there are more factors involved than just shear area and engagement length. Coarser threads have greater flank engagement and better load distribution at the same engagement length. They also have greater fatigue resistance, which is perhaps their most important advantage in silencer design.
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gunny50
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Re: Which taper for suppressor mount to brake?

Post by gunny50 » Fri Feb 23, 2018 6:29 pm

mr fixit wrote:I think R8 collets have a 17* angle (8.5 on compound), and 5C have 20* (10 on compound).

I'm thinking 20* would be about right. With that in mind, what thread to mount can to brake and tighten on taper? I've read both fine and course. I've even seen acme threads used. I'm thinking around 20tpi for the taper mount. Suggestions?

I'm using 20* / 10* on compound. With 1mm pitch. But my threads are behind the cone. So larger diameter and also keeping the threads cleaner.

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mr fixit
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Re: Which taper for suppressor mount to brake?

Post by mr fixit » Mon Feb 26, 2018 10:41 pm

gunny50 wrote:
mr fixit wrote:I think R8 collets have a 17* angle (8.5 on compound), and 5C have 20* (10 on compound).

I'm thinking 20* would be about right. With that in mind, what thread to mount can to brake and tighten on taper? I've read both fine and course. I've even seen acme threads used. I'm thinking around 20tpi for the taper mount. Suggestions?

I'm using 20* / 10* on compound. With 1mm pitch. But my threads are behind the cone. So larger diameter and also keeping the threads cleaner.

Gunny
I would enjoy seeing a photo of your mount.

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