How tight is tight?????
 

Hello to all, today was an interesting day! As I mentioned before, all my time up until now with the barrel project as been threading and chambering... Did good on that so really the worst is over... learned tons of new info. (New to me!) and hopefully will retain enough to sustain me in the next go-around.... Probably next year... Anyway, today was torque, index, and mark at 6 o'clock all the barrels to their respective receiver, or in the case of loose barrels, to a 1920 commercial receiver that seemed to be nominally correct? So, what did I learn today? The first thing I learned, is that the bull barrel clamps up far better that the tapered Luger barrel, but this is to be expected and is no surprise. But, it give one a positive result in repeatability that you normally don't get... As in tight with no possibility of deformity... (I really like that!;) ) So, time to finish torque the barrel to the receiver... 15, 25, 35 pounds, done right? Ahhh, nope! At 35 ft. pounds the torque wrench takes a big skip, and then settles back down to 35? More crush than expected.... Same at 40, same at 45, didn't stop until 50 ft. pounds... and, it was tight, but not overkill... came loose with my receiver wrench just as you would expect? Sooo, it's 50 ft. lbs of torque for me, no matter what the books say? (do they say anything about torque? :) ) Indexing was a simple task of using an "I" letter stamp and also using the existing mark on the receive to time / locate the final position of the barrel / receiver relationship! I'm happy to say, all went well and we are off to the next step! And that means off to Olle, hopefully he will pick up the story on his end of the production, as I find it all interesting and a bit amazing still, that this can be done, and has been done for well over a century now! Best to all, til...lat'r....GT.....:cheers:

BTW, last little bit of info. solid hand tight, and the distance to full 50 lbs of torque tight, was about .080" to .100" of travel to align the index marks... That means, "Real tight, real fast" .... amazing ain't it! ....:cheers:

Good For You!!!

Great info GT.
When my head is clear I'm going to figure out how many degrees of rotation that is.:confused:
Then I can figure how much "crush" there really is!:eek:

Neat stuff!
 

Hi Don, I've wondered about the results of what I just did for years! It seemed that no one had a tried and true barrel torque sequence, that a shade tree machinist like me could understand.... ;)... But, when I hit the 50ft. pounds of torque, the back up and reset to hand tight dimension was the same on every barrel, every time... :).... so, what can one take away from this? If you are installing a luger barrel, and it comes up to anywhere from .125" to .100" left for indexing, you might have to tighten and loosen a few time to get indexed, (or use up the crush?) but it will be between 35 and 50 ft. lbs when you get it lined up! Any more than .125" or really even .100" and you might have to relieve the flange or horse it back and forth a few times to stretch everything in or out... (not recommended!...:eek:) Last little bit of new found wisdom, if, when you bust it back loose... if you hear a metallic squeak! You are on the road for disaster???.... Stop and regroup and collect weapons and ammo... as your going to have a battle on your hands from there on out! ... Best to all, til...lat'r...GT...:cheers:

Thanks GT, more good info.

Depends on the duck! ;)

How do you get your avatar to do that change???

http://www.metacafe.com/watch/449302...ts_why_a_duck/


Avatar's secret: animated .gif!

Great Stuff!!!!!!!~TKS

Microsoft Gif Animator - it's only 1.05MB... :)

from what I've learned.....
 

Hi Rich.... I've not tried to go much tighter then the 50 ft. lbs. as it seems to be plenty... But, on previous efforts, it was hard to gauge as my barrel vice on the taper was inconsistent from job to job.... Was the barrel that tight, or just barrel vice that loose?... Two things made this latest attempt possible, one was the straight, large constant diameter Bull Barrels.. And the other, was a special adaptor socket to fit over the end of the receiver blocks to attach a torque wrench..... I had the set up made about a year or so ago, when I first envisioned making a few barrels... seemed that a little info was lacking in my skill sets so I bought a Snap-on torque wrench, and Walla! We have usable info! ..... :eek:.. Best to all, til....lat'r....GT....:cheers:

Like I have told GT in private conversations, I believe that many are making this more difficult than it really is. I work on Colt revolvers on a regular basis, and I have encountered factory installed barrels that were so loose that it only took a light tug on the wrench to get them off. Still, they had stayed put, despite the repeated beating from .357s and .44s.

When I do revolver barrels, I set them back to index by hand at about 10 o'clock, cut the crush area (about 50% or so) and torque them with a barrel vise and action wrench. They do "float" once they reach a certain torque, but that's the whole purpose of the crush area. They are easy to install and they don't come loose, and I would do a Luger barrel the same way.

Really, it's just a screw and there's nothing magic about it. I believe too much torque is more detrimental than too little.

Ideally, the proper torque should set the barrel threads (any threads) in the elastic limits range of thread material. If the torque is too high the threads could be in the plastic (deformed) region or fail (stripped). Since the barrel has a slightly smaller (male, bolt) thread diameter, the failure would occur on the barrel first.

If the material properties and thread form dimensions are known, calculating of the torque limits is easy.

I have a related question. Is antiseize use advised for those threads?

Absolutely, especially if you're one of the believer in high torque. As the barrel is tightened, the surfaces are pressed against each other harder and harder, and without antiseize they can gall. This is a phenomenon that will make the surfaces stick to each other, and once that happens it won't go any further. You can't finish tightening it, and you'll have a hell of a time trying to unscrew it again. I use copper paste for this, it seems to have the best lubricity of the types I have tried.

Some type of lube is required. You can't get a good torque reading (or 'feel') with dry threads. The friction requires additional pressure to overcome. I've used Nevr-Seize, wheel bearing grease, LSA, and presently am using white lithium based grease.

I stopped using Nevr-Seez (on firearms) because it is too messy. Seems like you can never clean up the excess. :rolleyes:

Galling is much like surface contact welding. If there is a difference in the hardness of the steel screw (barrel) and the steel nut (receiver) galling should not occur. However using a thread lubricant greatly reduces the chance of galling AND improves the torquing efficiency.

I'd say it's very much like contact welding. Also, the increased friction and pressure cause microscopic tears in the surface, which will make them so rough that they don't want to slide anymore. I believe this is what happens in friction welding as well, right before the material starts heating up.

I have had the questionable pleasure of seeing that happen, and I thought I would never get the barrel off again. The shiny contact surfaces on the shoulders were dull and torn, just like if the parts had been welded and then pulled part again.

Using a lubricant or an anti-seize compound reduces the friction. Some threading compounds incorporate graphite and copper to reduce friction. Friction and high contact stress are the enemies of all threaded members. Stainless steels and titanium are awful for galling when attempting to screw those type members together.

Stainless can stick like the dickens, that's why the custom builders always build stainless guns with looses tolerances. If they even use stainless guns, I believe most prefer carbon steel.

I was playing with some of my guns yesterday, and once again I started wondering why Luger barrels "should" be torqued so much. Compare with, for example, an AK-47 where the barrel is pressed into the trunnion, and held in place by friction and a small cross pin. I have never heard about one coming loose. A Luger barrel is threaded so it can't be pulled straight out, so all that's really needed is enough torque to keep it from turning when you shoot. It's not like you're torquing the heads on a Top Fuel dragster, it only needs to be tight enough to stay put and it doesn't take much at all IMO.

I've run a 20 ton hydraulic press almost up to the limit to press the barrel out of the trunnion. And I had to drill the pin out. :(