Importance of truing threads?

[STS]

SDS. Good post.

Sleeving bolts would be much less time consuming if we could buy premade split sleeves.

I have my wife make them while I'm away fishing.

 

[shortgrass]

SDS. Good post.

Sleeving bolts would be much less time consuming if we could buy premade split sleeves.

Or a bolt that fits the receiver bore as it should, to begin with!

 

[shortgrass]

On a thru BR rifle this might be of importance. On a hunting rifle or a varmint rifle not so much. I'm not much into using a receiver that's stretched out of shape so much the bolt needs sleeved. Bored to a common size and a bolt of the proper fit installed. There again, boring to size and the cost of a custom bolt? Most will opt for another receiver as low cost as a new 700 (receiver and bolt) is today before spending for sleeving or a custom bolt. I'm not a big BR guy, but I build a lot of varmint rifles and many will opt for a custom action for those. These shooter are real serious about their varmint rifles and equipment. The coyot calling contests in the area pay-off in the thousands of $$$$$$. Don't know what the pay-off is for winning a BR match, but most who are serious will opt for a true BR action designed for that purpose instead of a 'trued' production action produced for a hunting rifle. Thread fit,, not too tight not too loose, let the face of the action, the 'flatness' of the recoil lug if it uses one and the square shoulder on the barrel are what 'counts'.

 

[STS]

Alex that's a great example of the same thing I mentioned earlier. I had a super hot sporter barrel that the threads were REALLY UGLY. Not as bad as those but pretty bad. It truly is amazing that one can get away with that type of shoddy work.

 

[carlsbad]

If I get her the yarn will she knit me one too? (obscure reference to old joke)

http://forum.accurateshooter.com/threads/barrel-tenon.3920701/

I thought of that thread several times during this thread.

 

[eddief]

I feel that consistency of the whole rifle platform in regards to harmonic vibrations plays a role on how forgiving a rifle, load and or load window may be. A lot of world records have been shot with crappy thread fit, but just maybe, a nice proper thread fit helps with the whole platform being just a little more forgiving.

If the customer is paying, he should receive quality work inside and out. Is thread truing needed on a hunting rifle? IMHO, nope. If one wants to eliminate one more possible variable, then it sure won't hurt.

It all boils down to consistency from shot to shot. Weather, rifle, rests, ammo and the shooters bench and or ground manners.

 

[Norton's Bench]

Just some food for thought. I've been a Tool Maker for 30 years and a Tool Designer for the past 15 of those 30 years. I would be laughed out of the shop if I (or anyone else) would use threads for location. If you need location, refer to how a shoulder bolt is used.

 

[Shrek]

So what is the optimum undersize tennon thread in your opinion ? This is to all that have an opinion on this.

 

[carlsbad]

Just some food for thought. I've been a Tool Maker for 30 years and a Tool Designer for the past 15 of those 30 years. I would be laughed out of the shop if I (or anyone else) would use threads for location. If you need location, refer to how a shoulder bolt is used.

Norton,
I understand what you are saying, but in this case, the threads are the only locating feature in the design. Sure it isn't good to .0001". but I'm sure the quality of work you provide, with proper lubricant, will repeat centering to .001" or .002". Which is plenty good for even the most precise action.

--jerry

 

[Norton's Bench]

Are you asking about a shoulder, similar to a shoulder bolt? If so, .0005, if you can go less, better yet. Not intending to open a can of worms, but most home shop type lathes will have a hard time getting there. Not saying it can't be done, but it may be tough.

 

[Norton's Bench]

Jerry,

Repeating .001/.002 is the hard part. If you can disassemble and reassemble and hit that, consider yourself lucky. In a nut shell, threads are for fastening, not locating.

 

[Dusty Stevens]

Just some food for thought. I've been a Tool Maker for 30 years and a Tool Designer for the past 15 of those 30 years. I would be laughed out of the shop if I (or anyone else) would use threads for location. If you need location, refer to how a shoulder bolt is used.

Do you think it would be practical to use, like on a rifle action for instance, maybe a shoulder for say .250 then threads for .750? And if you had that setup and was chambering a barrel for it how much clearance would you need on the shoulder dia? Would you need .0005 or would you need like .0015 or .002 to keep the thread grease from hydraulically locking it up? (This is all assuming its even necessary- just for my knowledge. Light bulb lit up above my head)

 

[Norton's Bench]

Do you think it would be practical to use, like on a rifle action for instance, maybe a shoulder for say .250 then threads for .750? And if you had that setup and was chambering a barrel for it how much clearance would you need on the shoulder dia? Would you need .0005 or would you need like .0015 or .002 to keep the thread grease from hydraulically locking it up? (This is all assuming its even necessary- just for my knowledge. Light bulb lit up above my head)

You could probably get by with a shoulder as short as .125. Keep the clearance between the shoulder and the mating part as tight as possible, but not an interference fit. I'd try to keep that at .001 or less. Keep the threads in tolerance. Refer to Machinery's Handbook for this. Do not make the threads tight. Doing so may cause a fight between the threads and the shoulder. You want the shoulder to locate. No grease should be needed. Light coat of oil will work. If you're working with stainless steel use never seize.

 

[gunsandgunsmithing]

Do you think it would be practical to use, like on a rifle action for instance, maybe a shoulder for say .250 then threads for .750? And if you had that setup and was chambering a barrel for it how much clearance would you need on the shoulder dia? Would you need .0005 or would you need like .0015 or .002 to keep the thread grease from hydraulically locking it up? (This is all assuming its even necessary- just for my knowledge. Light bulb lit up above my head)

Another possibility for locating and centering the barrel to the action would be mating tapered shoulders on the barrel and receiver. Although, I don't think it's necessary. There was some discussion of this a few years back on BR Central.

 

[liljoe]

It's been done. The first bunch of BAT DS actions have a bushing in the front to aid in alignment.
Give Dwight a call and ask him about it.
Joe

 

[Dusty Stevens]

It's been done. The first bunch of BAT DS actions have a bushing in the front to aid in alignment.
Give Dwight a call and ask him about it.
Joe

I have one of those that was the reason for asking. Seems like a shoulder and threads would fight against each other a bit

 

[rwk]

Just my opinion JRS, but vee threads and a square shoulder will center it, even if the threads are not tight.

No!

 

[Norton's Bench]

No!

Curious on your reason why this wouldn't work?

 

[eddief]

The only difference in a looser thread is how much clearance there is on the backside of the flank once its torqued. More air or less air gap. To me, zero difference. HOWEVER, I do think there are some very important aspects to thread fit but having the largest pitch diameter possible is not one. The rifle tenon in that thread has logged something like 36 groups which agg out to be mid 3"s at 1k. With the same load. It has to be one of the most forgiving barrels on the planet. Makes you wonder.

Thanks to Machining Fundamentals 101, I am aware of the difference in a looser thread fit vs. tight. I also advocate a little (albeit very little) play in threads so the barrel shoulder and receiver can mate squarely, but from a engineering standpoint vibrations change with thread fit. Heck, vibration plays a part in every aspect of the rifle, and in general, vibration is unwanted wasted energy.

Maybe that barrel would of agg'd out in the mid to high 2"s over time with a better thread fit, my guess is, the shooter had more to do with the 1000yd agg and reading the wind, than the barrel actually had. Hard to tell, but one barrel unfortunately is not enough to make a conclusion.
I have had some good conversations with Greg Tannel and Alan Warner on this, and I enjoy the discussions about any of it, because I believe it all has something to do with the results on paper downrange however small it is.

Does it make me wonder as you stated? You bet it does, I would sleep better if i didn't lay in bed on some nights pondering crazy things

 

[Cloudrepair]

Another possibility for locating and centering the barrel to the action would be mating tapered shoulders on the barrel and receiver. Although, I don't think it's necessary. There was some discussion of this a few years back on BR Central.

When I was turning blanks for core bits we used tapered shoulders and although they may have helped center the joint I was told it was to help lock it together.
They where multiple entry threads for quick attaching and the taper would lock them up so they wouldn't come apart when pulling out of the hole.