What's the difference between stretching the barrel threads against the recoil lug (against the shoulder at the end of the threaded tenon) without the nut, or stretching the threads with the nut? I don't see any. The threaded shank of the tenon is going to be under tensile force either way - no?
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?To nut or not to nut?
- Thread starter bigngreen
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What's the difference between stretching the barrel threads against the recoil lug (against the shoulder at the end of the threaded tenon) without the nut, or stretching the threads with the nut? I don't see any. The threaded shank of the tenon is going to be under tensile force either way - no?
J E Custom
Well-Known Member
No problem for me to get a better fit than 60%.
If you are referring to nuts and bolts you are pretty close. But we are talking about lathe cut
threads and on firearms that have to deal with tremendous forces and the tenon size has
to be designed to handel this with a 2 to 1 safety factor.
I also made my living dealing with metallurgical connections of all types including bolt strengths
and thread fits and types of threads.
Gun work requires the very best fit possible and if a smith can't do better than 60% then he
is called a plumber (No disrespect to the plumbers but they use taps and dies not a lathe to
cut threads).
If you are happy with 60% thread contact then that is your choice but If I build a firearm it will
have a much better contact area than that or I won't let it out of my shop.
I'm sure there are other smiths on this site that can vouch for 90 to 95% but may not want to
participate in this discussion and some are capable of better threads than that.
The only reason you can't get 100% engagement is that the major and minor diameters
should have a slight radius to prevent galling.
So we are back to the original question To Nut or not to nut. I chose to not use the nut
because it adds one more problem that is not nessary unless you want to switch barrels
often and even Savage will tell you that the barrel nut is for ease of assembly not to switch
barrels.
J E CUSTOM
Trickymissfit
Well-Known Member
mostly shear force. When you seat the barrel via a shoulder against the recoil lug, reciever, etc, you will use the female threads of the reciever as a "jam nut". Odds are very slim that you will ever get the full length of the female thread to ever make complete contact (each single vee form of the thread, and not area contact). Where as the thread screwed into the reciever and then pulled forward two or three thousandths will force the male threadform into the female thread form. When seating on a shoulder you are sorta stuck with the way it comes out (the solid shoulder controlls everything in that setup). Now if you take the Savage barrel or a Remington style barrel and thread it into the reciever, but stopping short a couple turns. Mount a .0005" dial indicator (I prefer an Interapid by the way) ontop the reciever, and somekind of a small smooth block of metal clamped to the barrel. Now try to move the barrel in and out without turning it. You should see a little end play (.001" / .0025") the amount is not super critical as long as it's not excessive. You could make .004" end play work. What you are now seeing is about 50% clearence and 50% lead error in the thread. Lead error will always be in there no matter how the thread is cut (there is another form of error that I will address later). Lead error comes from the device used to cut the threads, but there are some ways to actually fight this. It's mostly caused by wear in the lead screw and half nut (nothing can be made perfect, and the first time you use the half nut you induce wear in it). Now if you thread the barrel up against a once fired case from that chamber (you could also use a go-nogo gauge), and set the indicator back up again. Then tighten the barrel nut. When you seated the barrel against the case shoulders you took out all the endplay in the threads, but now when you tighten the nut you should see the barrel move forward slightly (.0005" to .001"). You've now stretched the thread making it as strait as it can possibly get; plus you have forced the forward face of the thread into the rear face of the female thread for near perfect contact (well maybe 75% at best if the lathe has any wear in the slide or spindle bearings)
Stretching threads is nothing new, but really wasn't thought about much till about forty years ago. Now adays it's a commonly done thing when assembelling machinery that has bearing mounted at both ends of a screw (mostly ball screws).
Now back to cutting threads one more time. Most of the barrels used here are cut from 400 series stainless steel, but still a few big bore hunting rifles will use C/M steel in various grades (lets hope it's a pretreat form). The Savage uses a 20 pitch thread, while a Remington is an 18 pitch if I remember right. The difference between the two means little here as they are very close to each other in size (it would have been nicer if Remington had used a 1.06-16 thread!). If you take a piece of barrel steel and chuck it up in the lathe to cut a thread, and turn the O.D. to the size needed. Now setup a dial indicator on the O.D. of the piece of steel your threading and the set another up on the slide to see if the slide is doing any shift to the side when it comes under tool pressure. When you make the second pass you may see the idicator jump ever so slightly (lets hope it's less than .0005"). That's known as lag in the spindle bearings, and also is a nature of the beast. The higher the load the more flex. But you actually can releive some of this by using high speed steel to cut the threads (Rex 95, Vasco Supreme, Gorham Cobalt). Still .0003" is about as good as it gets in a lathe, and that figure will double normally. (spindle flex will change the thread form) Now clamp a parrell bar to the slide, and try to pull it sidways in both directions in the area your cutting. That's wear and clearence in the gibs, and will change the thread form 90 degrees to spindle flex. It's also why you cut the threads in a series of passes instead of two passes. Cut a thread about three inches long, and then measure the thread over three wires every half inch. Now do the samething 90 degrees to where you made the last set of measurements. You just saw the lead error in the lathe. If you could examine the thread under a microscope you'd see little bumps and valleys in it as well (there is a way to measure this, but it's not important here). But in the end it just proves that you cannot turn a perfect thread in a hand lathe (even a precision finish lathe)
gary
Trickymissfit
Well-Known Member
actually nuts and bolts are often much looser than 60%. And in most cases the threads are rolled not cut. But if you take an aircraft quality thread (often ground) you'd be lucky to see 65% contact. Take a 1.06-16 male master, and a 1.06-16 female thread master. Screw them together. You'll still see some endplay, and these threads are ground. Guys have been trying to get the movement out of the barrel thread for eons, and there are only two methods that work, and one can be dangerous if done even slightly wrong. (there is a third way that is very tricky todo, and know of nobody that's had the balls to try it yet)
this thread (now there's a pun) has evolved into a good Applied Mechanics (forces and vectors) lesson or Physics 102 question, but better yet how to deal with the beast
gary
specweldtom
Well-Known Member
I just picked up on this thread. It appears to me that Gary and JE may be talking about 2 different interpretations of 100% thread fit. Sounds like Gary is explaining the difficulty of achieving 100% thread engagement on both pitch faces simultaneously. I believe JE is talking about the percentage of engagement on the pitch faces that are under load, (maybe better described as the thrust faces). If this is the case, It's one of those rare instances when I agree with both sides of a discussion. At any rate, a very instructive sidelight to the original question; to nut or not to nut?
My opinion from studying both the Savage and the Remington, is that I very much prefer the Remington makeup. I do like the long Savage tenon, but have no preference between the 16 tpi Remington and the 20 tpi Savage thread. These are just my opinions though, not backed by any science.
Good thread.
Tom
My opinion from studying both the Savage and the Remington, is that I very much prefer the Remington makeup. I do like the long Savage tenon, but have no preference between the 16 tpi Remington and the 20 tpi Savage thread. These are just my opinions though, not backed by any science.
Good thread.
Tom
Trickymissfit
Well-Known Member
in theory a 20 pitch thread will hold it's torque value better than a 16 pitch, but you can't prove it by me! All I'm saying is that a stretched thread is strait and ridgid. The percentage of thread contact becomes a moote point with contact achived via a stretched thread. With a barrel shoulder you put the stress at the shoulder and maybe the closest three to four threads to the shoulder (depending on the lead error stacking up). Then when you have ignition, you have two main vectors of force acting against the bolt and the barrel itself. This is then followed by a like reaction going in the opposite directions. This allows the threaded portion of the barrel to move as pressure builds up. But a barrel in close to full contact will not allow the threaded portion to react nearly as much as the barrel with the floating thread
gary
+1 for Bobby
bigngreen
Well-Known Member
Funny, you should reply Bobby, one of the barrels is a Lawton
it is what got me to thinking because if I trim it down for the nut it will totally screw up a mean looking barrel. Physics aside a guy has to have a lean mean looking rig!! Ya, I know I just dumbed down my own thread. specweldtom
Well-Known Member
Gary, that's a good explanation of what goes on when a cartridge is fired, all the more reason to get the best fit possible on the tenon to barrel thread. Hopefully a good snug thread fit will as you say cut down on any movement of the tenon. An observation that I've made is that a belted cartridge will use up between .001" and .002" of headspace after makeup due to crush and stretch, but a shoulder headspaced cartridge will lose .001" or less (due to crush only). That tells me that the tenon is stretching enough to move the breech back and is not just attributable to shoulder and thread crush. I make up a 1.062" diameter tenon at 75-80 ft/lbs with light oil in the threads. (Absolutely no E/P grease). I believe that this combination of torque and lubrication causes the threads to make up along the whole length of the tenon. Again, no science, just what I reasonably believe is happening.
BignGreen, appearance is important to me. I don't hesitate to use it as a tie-breaker, and frequently make decisions that don't affect integrity or function based on how something looks. The primary reason for me to eliminate the Savage barrel nut is that they are imprecise. A secondary reason is that I also find them to be ugly, even on a factory rifle. They look totally out of place on a fine custom rifle. Again, just my opinion.
Good luck, Tom
BignGreen, appearance is important to me. I don't hesitate to use it as a tie-breaker, and frequently make decisions that don't affect integrity or function based on how something looks. The primary reason for me to eliminate the Savage barrel nut is that they are imprecise. A secondary reason is that I also find them to be ugly, even on a factory rifle. They look totally out of place on a fine custom rifle. Again, just my opinion.
Good luck, Tom
Trickymissfit
Well-Known Member
your post little if any sense. The Remington (and I know that where your going) uses a 1.06-16 thread seating on a shoulder. The shoulder then becomes a fulcrum point to support the barrel itself as well as keeping it strait. But when the shoulder becomes the fulcrum point for support, it also releives the threaded part except for the threads that take up the slack (lead error and actual clearence). So it all depends on the shoulder mass at 90 degrees. Looking at the surface area, you ain't got anything that matters! It would have to be an area at least 3/8th's inch wide all the way around to do that job, but yet leave the threaded portion of the barrel out there doing nothing till ignition. With the nut you put the big end of the barrel in stress, and then making that part far more ridgid. When you stretch the thread into a ridgid contact plus seat the nut on a similar in size shoulder you probably more than double the barrel support at that end.
As for will the guy be happier going with a shoulder verses keeping the barrel; that's his call. But his local gunsmith will love him for it (yet he won't even buy him a Big Mac). I know more than one guy shooting a Savage that went with te shoulder, and of those folks I can think of one guy that kept it. But on the otherhand I also know of at least a half dozen Remington guys (and one Winchester fellow) that use a barrel nut. Some have been using them for 15 years, so you'd think they'd be sick of the nut by now. Wouldn't you? Myself I use both setups, but all my Savages kept the nut for a reason. My one lone surviving Remington will get a barrel nut when I finally get rid of the tomato stake Remington put on it.
gary
Trickymissfit
Well-Known Member
try this (note: it can be slightly messy at first). Coat the threads with a very light application of Neverseize (DO NOT use Loctite Antiseize!!). You can actually get a better torque rating at 50ft.lb. than using oiled threads at 80 ft.lb. A pint can of the stuff will last you two lifetimes, and when you go to pull the barrel you will be pleased with the results. Also the stuff withstands heat extremely well.
I don't understand where you'r comming from when you speak of imprecise. Both styles deal with a chamber and a certain headspace (these are not variables). One method head spaces off the shoulder and the other does as well, but I do see a glimmer of light in your thoughts! That is the nut taking up slack in the threads and also the crush involved. But here's where we differ; When you screw the barrel into a gauge or whatever you want to use you automaticly take up all the slack machined into the threads. But then the nut will stretch the thread about .0005" to .0015". (you probably don't crush in male to female thread much more than .0005") But the actual movement measured is on the backside of the nut. But please allow me to take this in another totally different area to make it easier to visualize. Everybody here knows what a connection rod looks like in a race car or even your John Deer tractor or a Indy car. We all probably know they use a bolt and nut to hold them together. And when we rebuild them we most often tighten the nut with a torque wrench. But in very precision apps they don't do that! They tighten the bolts till they reach a certain thread stretch. This is also done in critical die and mold work as well. Why? It's a well known fact that the parts last longer, and it takes the error out of the threads.
As for looks, that's in the eye of the beholder! I have a couple Weatherbys that make the Remingtons seem ugly! Yet it means little to me. I think a Hi-Wall is the class of the field when we are talking looks! My favorite field gun is a Remington chambered in .223. This rifle is beyond ugly! I wouldn't call it a tack driver, but it will shoot all day long in the low fives and high fours. But for what I put it together for it's near perfect (coyotes under 250 yards). Still at longer ranges it just can't run with the big dogs, and I know this upfront. I have a Savage chambered in 6mm/250AI with a 1:8 twist barrel. It will shoot as far as I care to, and probably well past that mark. The barrel is a virtual tuning fork, but yet shoots .25" groups at 100 yards. I hate the 1:8 twist, but it also will shoot 107 grain bullets very nicely. No doubt in my mind that the harmonics alone would be far worse without the nut. It gets a new barrel this winter that will be 24" (3" shorter), and a strait 1" tube (also a major chamber revision). The nut will be twice as long with the longer threads of course. Right now I can't make up my mind on the twist rate as I'm looking for 185,000rpm on the bullet at impact (going back to Berger 88's). Looks mean little to me when I'm laying in the snow
gary
Sense is a key word in this. Your going on about stuff that may of may not make a difference here. By everything you have posted on this subject im leaning on the side of not making a difference. What i want to really know is why you have been so involved in this subject because it seems to me there is a underlining reason. You have brought up some interesting ideas but nothing you have said has made me think that staying with the nut in his case is gonna help anything but a little piece of mind at best and thats marginal... at best. If you want to put a smaller barrel on a larger caliber and go out and hammer on it thats your choice. But for safety reason i always recommend stay with the larger breach and having the extra metal there to keep chamber strech down to a minimum. Maybe some day when i have a lot of time soon i will go back through all these long posts of yours and explain what my take is on it and why. Until then.....
bobby
Trickymissfit
Well-Known Member
my post was simply from an engineering standpoint; as well as taking into the physics and aplied mechanical parts happening during the chain of events called ignition. I might just add here that I've ran these exact sceneros thru a couple mechanical programs that take off where CAD ends. The programs confirms everything I've written, and takes it into several other levels. Remington uses a 1.06-16 threaded barrel as standard equipment, and Savage uses a 1.05-20 pitch thread. Now that's a whole .010", or .005" a side. But you will also find that Savage bases their actual pitch diameter off a 1.60 major diameter. Being as the Savage and the Remington have close to the same O.D. on the reciever, and there's very little difference in the pitch diamter of the threads I just don't see where your comming from. Savage (I would also assume Remington does as well) also uses a larger diameter thread in some of their calibers
gary
