torque wrench

[260Ravage]

Finally, at 62 years of age, I broke down and bought a torque wrench. I am always curious as to how tight my actions screws are. Boy, did I get an education! I came off a farm so nuts and bolts had to be tight.
I had to break the action screws loose with my allen wrench,cuz my 50 inch pound torque wrench would not break them free. Then I re-set them with the wrench dialed at 40 in. pounds. Wow! They almost seem loose. I am guessing I am not the only one that experienced this. Care to comment?
Terry

 

[swt5]

Hi Terry,
I too am a Chronic Over Tightener. Torque wrenches are the only way to go for people like us!

 

[Outrider27]

I'm probably going to open a can of worms here, but with the popularity of using torque wrenches to tighten action screws growing (with good reason, I might add), I'll pass along some food for thought. There have been many tests run over the years (my employer allowed me to fund a small group of them; they aren't cheap) and the end result is that the fastener to fastener preload variation on an adequate sample of fasteners tightened with a torque wrench to the same torque is on the order of 33% on the best day of your life, a situation which our tests verified, though it wasn't our primary goal. On a bad day (inexperienced technician, lack of structured tightening process) that variation can be 100%, that is, the highest preload in the bolt circle will be twice that of the lowest, all with the same applied torque. This is NOT the fault of the torque wrench once the technician learns a structured approach to the tightening process, it is almost totally due to fastener to fastener variations in friction coefficient, the main thrust of our tests. Torque wrenches themselves are in general quite accurate, some of them amazingly so, but the actual end result is thrown into a dither by fastener to fastener friction coefficient variation (and this with all fasteners from the same manufacurers lot ).

So while the use of a torque wrench is an improvement in preload consistency over mechanic's feel (less than you'd think with an experienced technician using the "feel" version of the structured torque wrench process), to improve fastener to fastener preload consistency, we need to eliminate the friction element as much as possible. The torque wrench gives you two important elements - prevention of overtightening, probably the biggest concern with action screws, and a recordable number that you can use for each screw time and again once the optimum number is determined through shooting. The way to eliminate friction if you wish to take preload consistancy to the next level is to use angular turn instead of a specific torque - no involvement of friction coefficient when angular turn is used. The fastener to fastener preload variation with angular is on the order of 15% on an average day.

Torque wrench method:

1.Determine the target torque.

2. Gently snug down fasteners with your weapon of choice to take up slack to initial contact.

3. Tighten the action screws alternately (with only two or three, the pattern isn't complicated, and what order to tighten them in is usually specified in the advice in these forums when it matters) in either three or four equal steps to the final desired value, applying 1/3 (or 1/4, depending on which number of steps you are using) to the first screw, then the second. After a brief pause, go back to #1 and take it to 2/3 of the specified/desired torque, and then do the same to #2, and so on until you reach full target torque. Three steps is good, 4 is better, beyond four doesn't really accomplish much. The brief pauses are to allow for load distribution and some short term preload loss, another contributor to fastener to fastener preload variation. After the final tightening wait at least 2 minutes and do a check pass or two, to finalize preload and check for short term preload loss, another animal that can be bigger than you would think.

To establish angular turn where the angular equivalent for a specific torque isn't available (some computer programs will calculate both)simply tighten a few with a torque wrench, measuring the rotational angle the bolt head is turned to reach final torque and average the results.

Angular turn method:

1. Tighten the fasteners to a repeatable snug - one good working definition of snug is 10% of the final value of the equivalent torque, though with the small size of action screws and the joint designed used, the feel method will work ok in a pinch. Using 10% means your torque wrench is still important.

2. Tighten the fasteners alternately, as in the torque wrench method, using three equal steps of 1/3 of the total angle. Skip the check passes.

For action screws, once you've broken the overtightening habit many of us developed in our younger days, you can skip the whole establishing the angular turn equivalent of a specific torque and just establish snug, apply a known angle, test fire, apply another known angle, and keep on test firing until you find the sweet spot angle just as you do looking for the sweet spot torque.

Again, just some food for thought, but even if you don't want to experiment with angular turn, do get in the habit of using three or four steps and a check pass or two, alternating between each fastener at each step, with your torque wrench. Just that action will help increase precision and eliminate things like prying loads that can mess up the precision what you are trying to accomplish bigtime.

 

[Greg110]

Outrider,

OK, what about using an anti sieze compound? any value please? A possible step to the rear? Just curoius.

Thanks

 

[hotrodlouie]

The manufacture should give there torque for there product and be final,
dry are what type lubrication. All screws sizes even same diameter don't have the
same torque values is based on quality bolt grade rating you need to establish.
Doing my working days we used charts from no lubricant to 6 different lubrication
products had 7 different torque readings for the same bolt size.
Outrider27 is right about human error. torque values are tricky to repeat.
They do have today digital torque wrench readings in the handle are digital.
Also electronic digital adapters 1/4" & 3/8 sq. drive you can use on your wrench.
Brings back some fun times when working we have to torque piston rods to 20,000 ft. lbs.
we send a rookie to the tool room to get a 20,000 ft. lb. torque
wrench the things they come back with, kinda miss the old days.

 

[Outrider27]

Hotrodlouie, you brought back lots of memories, lol.

Greg110, antisieze compounds have great value. We'll try to keep from writing a book here; it's a subject that can get huge. One of the main goals in tightening groups of 2 or more fasteners is to reduce fastener to fastener preload variation as much as possible when the same torque is applied to each. The key to this is reducing the range of friction coefficients any given material combination will yield (how much the extremes vary from the mean friction coefficient), the extremes yielded when a combination such as a steel bolt and steel nut (or steel capscrew and tapped hole) are tested. The worst case is unlubricated, which has the widest variation of friction coefficient from fastener to fastener, followed by lubricating with oils (gun, tool or motor oils), which do not reduce the friction coefficient significantly in fastener applications, nor do they significantly change the extremes of the range from unlubricated. Next is greases like axle grease; with their pressure additives, we would expect an improvement. It doesn't happen - for fastener use, both the actual friction coefficient and the extremes of it's range don't change significantly among unlubed, lubed with oil and lubed with grease, including greases with teflon additives. The reason for this is that when you approach the target preload when tightening the fasteners, the PSI loads are terrific, both for thread flank engagement and between the fastener head (or nut bearing face) and the clamped material, and these types of lubes, while they make things very smooth during initial takeup, don't do much of anything at the extremely high local psi loads in the final stages of torquing the fasteners - you are essentially metal to metal, just as with unlubed.

What is needed, in addition to to the oil or grease carrier, is what we might as well call micro ball bearings, additives capable of carrying very high loads while the mating surfaces rub against each other under high stress. This is where antisieze compounds shine. The microfine ground up materials that they contain in colloidal suspension in their carriers apply that needed effect. The two most common additives are microfine graphite or microfine molybdenum disulfide, usually in combination with some microfine ground up metallic material - copper, zink and aluminum are among the most common. Antisieze compounds both reduce the mean friction coefficient and reduce the range between the high and low extremes.

If you have a torque value that is based on dry threads (or oiled threads) for action screws, it needs to be reduced when an antisieze compound is applied (antisieze needs to be applied to both the threads and the underside (bearing surface) of the fastener, or to the area it bears against on the clamped material. The reduction to achieve the same preload for MoS2 based antisieze compounds is on the order of 40% - 45% of the dry or oil lubed torque, around 30% - 35% for graphite based antisieze compounds. Since we're going to vary the applied preload in looking for the sweet spot when tightening action screws, all that is really necessary is to remember that if you are given a dry torque and wish to further reduce fastener to fastener preload variation by using an antisieze compound, you need to to start your search with a significantly lower initial torque.

When using angular turn, friction isn't an issue and no adjustment to the angle is needed when using a previously developed angle.

When you are screwing a stainless steel fastener into a hole tapped in stainless steel, use of an antisieze compound is highly recommended as stainless on stainless is highly prone to galling. For titanium fasteners into holes tapped into titanium, use of an antisieze is mandatory - that's the most galling prone combination we have ever seen. From a galling standpoint alloy steel on alloy steel is about the least galling prone, but still benefits just as much as the others when it comes to using antisieze to reduce fastener to fastener preload variation.

Just to give an idea of why friction coefficient is so important, consider this: when you are tightening a fastener you are applying energy to the joint system. In round figures, about 50% of that energy goes to overcome friction between the bearing surface of the nut or tap bolt (as in our action screw joint), about 40% goes to overcome friction in the thread flank engagement, and 10% goes to trying to stretch the fastener, which is what generates the actual preload. Not a pretty picture as far as friction is concerned.

 

[DennisH]

Torque wrench method:

1.Determine the target torque.

2. Gently snug down fasteners with your weapon of choice to take up slack to initial contact.

3. Tighten the action screws alternately (with only two or three, the pattern isn't complicated, and what order to tighten them in is usually specified in the advice in these forums when it matters) in either three or four equal steps to the final desired value, applying 1/3 (or 1/4, depending on which number of steps you are using) to the first screw, then the second. After a brief pause, go back to #1 and take it to 2/3 of the specified/desired torque, and then do the same to #2, and so on until you reach full target torque. Three steps is good, 4 is better, beyond four doesn't really accomplish much. The brief pauses are to allow for load distribution and some short term preload loss, another contributor to fastener to fastener preload variation. After the final tightening wait at least 2 minutes and do a check pass or two, to finalize preload and check for short term preload loss, another animal that can be bigger than you would think.

The above sounds about the best/easiest way to torque bolts! I usually put a dab of oil on the bolt to releave friction issues!

Kinda interesting to torque a stock to an action!