Importance of truing threads?

[mram10]

Jerry,
I figure it’s free and makes sense so why not. Thanks

 

[Will Henry]

In some cases it's less about thread mating than reducing the torsional stress on a fastener. In the end, if a fix works, it works. Makes sense that a better contact fit would help. WH

 

[gunsandgunsmithing]

Nothing wrong with a well fitting thread on barrel tenons but, it gains nothing and risks big problems if too tight. On a 1-1/16-18 thread, only about 4-5 threads do all of the load work. If the thread is truly a tight fit when screwed in by hand, when the barrel is torqued, if those first threads begin to yield, all necessary clearance can go away. The result will almost certainly be a mess. Best to err on the side of a tad loose than to try and impress someone by not making one more pass across those threads. Better yet, use wires or a thread mic and thread to a nice class 2A thread. A class 2A is safe in most any properly cut B thread(B is the female).

 

[ridgeway]

Care to elaborate on this?

NO! lol

 

[mram10]

Not understanding how 4-5 threads do all the work. If the receiver and barrel are both a true 16tpi and there is a bit of give to them while torquing, how are they all not touching and being used somehow?

 

[338 Mollett]

Half way in screwing an action on I like about a 1/16 wiggle on the tail end of the action for the final fit.

 

[gunsandgunsmithing]

Not understanding how 4-5 threads do all the work. If the receiver and barrel are both a true 16tpi and there is a bit of give to them while torquing, how are they all not touching and being used somehow?

It's complicated and I can't explain it well myself. I suggest one of the various editions of Machinerys Handbook and searching the term, "thread engagement length"

 

[johnfred1965]

Not understanding how 4-5 threads do all the work. If the receiver and barrel are both a true 16tpi and there is a bit of give to them while torquing, how are they all not touching and being used somehow?

After 40X's question the other day, I mentioned Harold Vaughn's book "Rifle Accuracy Facts" Chapter six deals with the threaded joint between the action and the barrel. If you get a chance to read it, he explains the thread interface and the loads carried by the first few threads. He also includes ways to get a more even distribution of the load to improve accuracy. Sprialock and tapered threads were two solutions.

Another good read is "The Secrets of the Houston Warehouse". That article mentions something elso you pointed out, about threading parts together several times to improve fit. In the article, they actually lapped the threads to get a near perfect fit. A google search will find text for both of these items, as the Vaughn book is rare and prohibitively expensive!

 

[butchlambert]

After 40X's question the other day, I mentioned Harold Vaughn's book "Rifle Accuracy Facts" Chapter six deals with the threaded joint between the action and the barrel. If you get a chance to read it, he explains the thread interface and the loads carried by the first few threads. He also includes ways to get a more even distribution of the load to improve accuracy. Sprialock and tapered threads were two solutions.

Another good read is "The Secrets of the Houston Warehouse". That article mentions something elso you pointed out, about threading parts together several times to improve fit. In the article, they actually lapped the threads to get a near perfect fit. A google search will find text for both of these items, as the Vaughn book is rare and prohibitively expensive!

For a fee my Vaughn autographed book could be bought.

 

[johnfred1965]

For a fee my Vaughn autographed book could be bought.

I'd love to have my own copy, But I don't have the green for an unautographed one!

 

[johnfred1965]

I"d like a copy of Robert McCoy's "Modern External Ballistics" also, but that is another one that costs more than than a new firearm!

 

[Dusty Stevens]

I"d like a copy of Robert McCoy's "Modern External Ballistics" also, but that is another one that costs more than than a new firearm!

Got anything to trade? Most useless book i ever bought and the most expensive for sure!

 

[johnfred1965]

Got anything to trade? Most useless book i ever bought and the most expensive for sure!

Since you speak so highly of it, I could probably sacrifice my 20% off coupon at Harbor Freight, and a coupon for a free tape measure with purchase!

 

[mram10]

Books are great, but it shouldn’t take any more than a simple explanation. Heck, throw some dykem on the threads and see what it shows. After the receiver mates with the shoulder how can it do anything other than add more surface contact? The 4-5 threads doesn’t make any sense if the threads are true

 

[Cloudrepair]

Books are great, but it shouldn’t take any more than a simple explanation. Heck, throw some dykem on the threads and see what it shows. After the receiver mates with the shoulder how can it do anything other than add more surface contact? The 4-5 threads doesn’t make any sense if the threads are true

If you think about the threads are loose enough to screw on by hand then they hit the shoulder you tourqe it down a bit and it makes sense that the first few threads will start loading up more with the more torque used and the trailing threads will releave slitely or the other way around
Maybe taking a sako with a 1.062-1.5mm pitch and a barrel with 1.062-16 inch thread will balance it all out with some anti sieze.

 

[Cloudrepair]

Got anything to trade? Most useless book i ever bought and the most expensive for sure!

Which book are you referring to?

 

[Dusty Stevens]

Which book are you referring to?

Modern external ballistics. Got a copy in my library weighing down a shelf

 

[Cloudrepair]

Modern external ballistics. Got a copy in my library weighing down a shelf

I'm interested and i might even understand it but I may still just be a delusional machinist that thinks he knows a few things.
Then again it may just put me to sleep

 

[Dusty Stevens]

I'm interested and i might even understand it but I may still just be a delusional machinist that thinks he knows a few things.
Then again it may just put me to sleep

Im an engineer and think it sucks

 

[TRA]

If you think about the threads are loose enough to screw on by hand then they hit the shoulder you tourqe it down a bit and it makes sense that the first few threads will start loading up more with the more torque used and the trailing threads will releave slitely or the other way around
Maybe taking a sako with a 1.062-1.5mm pitch and a barrel with 1.062-16 inch thread will balance it all out with some anti sieze.

What would cause the first few threads to tighten any sooner than the trailing few? The only place I have seen this 4-5 thread nonsense is when studs are tightened up against the end of the threads. Studs should be somewhat floating, like the barrel does with a draw tube setup, or a Savage with a nut.