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Posted by: leighroy01

09/30/2008, 06:50:20

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This must be simple....

I am using a torque wrench to tighten a nut to 100Nm which is fixing .....something to the floor.

There is a washer between the the nut and the something which is....4cm2.

What is the equivalent weight in Kg that is being distributed through that washer

Thanks.








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Posted by: whang

10/01/2008, 14:40:07

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Torque = 0.2 X diameter of the bolt X force

Torque = 100Nm

Diameter of the bolt = ?

force = Torque/.2 X diameter of the bolt

Area of the washer = 4 cm2

the pressure on the washer= force/area

hope the formula will help you








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Posted by: leighroy01

10/06/2008, 00:01:59

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Cheers for that....something nice and simple. Thats all I was looking for







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Posted by: randykimball
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10/01/2008, 17:17:26

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You aren't going to consider the thread pitch of the bolt in the down force?




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Posted by: whang

10/03/2008, 17:56:56

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the thread pitch of the bolt is nothing to do with the down force

it is only easy to move downward with the fine thread then the coarse thread, because the pitch distance is difference.

it can have more clamp force for the fine thread then the coarse thread, because the root diameter is difference








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Posted by: randykimball
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10/04/2008, 03:29:45

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So you guys are telling me that a 1/2-13 torqued to 40 foot pounds will have the same down force as a 1/2-20 torqued at 40 foot pounds of force????/

A thread is an inclined plane wrapped around a diameter. The lower the degree of incline the more can be lifted with push force up the slope. I suggest you apply your theory to a real test and torque both these bolts and see the thruth.

A finer thread pitch is a less slope incline plane. As you said it is "easer to turn"... well ... easer to turn means you apply more down force with the same effort.

The question relates to down force at a given torque.





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Sat, Oct 04, 2008, 03:31:54


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Posted by: whang

10/09/2008, 11:52:58

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Force = Torque/.2 X Diameter of the bolt

1/2-13UNC BOLT 4O FOOT OF TORQUE

Force=40 x 12/.2 x .5 = 4800 in-lb

the 1/2-13UNC & 1/2-20 UNF HAVE THE SAME TORQUE

I am glad if you can proof I am wrong.

If you want to try a real test, Please use the bolt has the same length of shank

the reason to use the fine thread bolt is not gets the parts to losed or for thin plate








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Posted by: randykimball
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10/09/2008, 13:19:11

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I do not see where you added any compensation for the pitch on the calc.

So.... if I had a 1/2" bolt with a pitch of 8 threads per inch, at 40 foot pounds of torque it would still apply same force down to the face.

NO.. it would not.. maybe we are not talking about the same thing.

I'm talking about clamping force force down at the head. If the formula say it will, they need changed to account for thread picth.





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Posted by: whang

10/09/2008, 15:32:03

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For the torque calculate you don't need to consider the pitch of the thread

the pitch of the thread is for use to find the stress area of the bolt

so the fine thread bolt has more stress area then the coarse thread bolt

So fine thread max clamp fore is higher then the coarse thread

1/2 coarse thread grade 5 bolt

the max.clamp force 9075 lb

the max.clamp torque 76 ft-lb


1/2 fine thread grade 5 bolt

the max.clamp force 10200 lb

the max.clamp torque 85 ft-lb

the above information is from the bolt manufacturer

40 ft-lb of torque it is not reach the max.clamp of both bolts

so the clamp force is the same.


It you ask me use 85 ft-lb to clamp the parts and the bolt is 1/2 inch. I don't need to ask you what is the thread

I will tell you it is 10200 lb


If you ask me what is the diameter of the bolt

I will ask you the torque and the clamp force

Diameter = torque/(force x .2) inch

= 85 x 12/(10200 x .2) inch

= .5 inch

Also, 1/2-8 UN it is not exist in the market.

1-8 and up, It is use for high pressure pipe flange and

Cylinder-head studs

Hope this will help you.








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Posted by: randykimball
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10/10/2008, 08:58:44

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...big smile ...
I never said a 1/2-8 was a real bolt size.. I only was expressing the difference. It seems to me, you if you put a 1/2-13 and a 1/2-20 over a load cell and torque both to an equal torque the 1/-20 well exert more down force on the load cell.

Same problem: If I push two wedges under a weight, one wedge is 10 degrees incline and the other is a larger number of degrees incline. We are taught correctly that the 10 degree incline will provide us with more lifting advantage than the steeper inclined wedge. My friend, a thread is an incline wrapped around a circle. Someone with a load cell needs to take this to the test.

I have been using clamp screws most of my adult life. I came up through the machine shop applying many types of clamps to many different shapes of parts. I (think I) quickly learned I would get more camp effeicncy with fine threaded clamp bolts.

It is my intention here that if our standard charts and formula do not include thread pitch in the calculation of down force.... SOMETHING might be wrong. Now, if someone will proof this on load cells, and the cells registor the same, then I will back off and re-think.

...is that fair?... My challenge is not with you, it is with the system that claims to calculate down force without considering thread pitch (or anti-sieze for that matter), based on the rules of the six simple machines which are all just trade off of force and distance (ie: the incline plane). I was taught in school that a thread is a combination of the lever and the incline plane.

As for using manufacturer's charts... it is clear they all just mostly copy the status-quo.

If a load cell proves the standard formula correct, that is great. BUT.. if we never challange the system when it appears incorrect..... we would be foolish, and the standards would still be what they were 1000 years ago.

So to pick up the challange, this weekend I will construct two equal places in a machined heavy "C" shaped clamp. I will place a strip of aluminum under a 13 and a 20 pitch screw and torque each to several equal torques. I will machine the ends of both bolts to have as close as possible the same sized flat spud to bare down with. The aluminum should displace differently enough to show me if I am incorrect in each instance, being more clear at higher torques. This method allows me to measure the thicknesses after the torque control groups. This method is a non-bias control test. If I am wrong I will proudly admitt that here, for the sake of science. However, if I see a difference, I think we agree, someone needs to take the challange to a heigher level. I will publish my findings here.

It makes no difference to me if I am right or wrong. I just want to proof our standard system for the sake of all.





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Fri, Oct 10, 2008, 09:22:40


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Posted by: whang

10/10/2008, 10:09:51

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Same problem: If I push two wedges under a weight, one wedge is 10 degrees incline and the other is a larger number of degrees incline. We are taught correctly that the 10 degree incline will provide us with more lifting advantage than the steeper inclined wedge. My friend, a thread is an incline wrapped around a circle. Someone with a load cell needs to take this to the test.

My friend,I agree what you said about the wedge. to lift the weight with short distance use less force than the high distance

work = force x distance

I have designed for the hydraulic press and hydraulic cylinder for years, I use this torque formula to get the torque

Look like it is work okay for me.

If you can do experiment to proof the formula work or not

I will be great appreciate.

In my mind the clamp force is base on the stretch of the bolt.

The large of the stretch the higher the clamp force

It is not to do what type of the thread is used.
Please take this in to the consideration.

you are right,who is right or wrong is not a big ideal,it is for the sake of science.

I am very happy you are a open mind person

Good luck for your experiment.









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Posted by: randykimball
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10/11/2008, 13:09:46

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As many of us know, to figure the force provided with a ball screw one figures the pitch (or lead) applied with a given torque. However when we figure the down force at the head of a bolt at a given torque we do not consider the thread pitch of the bolt. This has raised many a bewildered eyebrow. So, the devil's advocate has stepped up to the plate to do a demo and clarify the matter. wink.

While this test was clearly not done in a laboratory environment, efforts were made to assure equal enough conditions were obtained to remove most doubts within realistic limits.

The following experiment was carried out:
A 1 inch thick piece of stress proof was machined with two thru slots at inch wall thickness from one edge of the 3 inch width. Both slots were machined within reasonable same/same dimensions. From the edge one slot received a -13 threaded hole and the other a -20 threaded hole such as to provide two clamping chambers. Two similar bolts were selected, one a -13 and the other a -20. Both bolts were centered in the lathe and received the drill point from a .375 diameter drill at the threaded ends. A .432 inch diameter hardened steel ball was selected and ground on one side to have a .330 diameter flat as to form a stylus with a flat larger than a standard micrometer thimble. A .625 wide strip of 2024 T3 of .051 inch thickness was selected from the junk pile and received a series of inked circles equal enough distance apart (aprox 1 inch). During the procedure the ball was placed under each bolt with the flat side towards the test coupon (2024 strip) and inserted into the bolt's drill point "receiver" to assure that both thread pitch tests used the exact same sized stylus. Both bolts were seated by placing a piece of tool steel in the test chambers and applying a torque of 80 foot pounds for 1 minute to the ball and tool steel. Finally the test strip was placed into each test chamber and torque was applied at each of the inked circles for that thread pitch at progressive prescribed torque setting. Only one torque setting and torque stage was applied to each circle. The duration at each prescribed torque was held for 1 minute before being removed. The torque wrench used was a deflection beam style so the torque process could be observed to assure fairness in torque application. A standard one inch Starrett micrometer was used to obtain the measurements. Both bolts were similarly lightly oiled, and all threads appeared to be in similar condition. The test was carried out two consecutive independent times without clear measurable differences.

Results:
at 40 foot pounds of torque both tests obtained a new thickness of .0495 inches in their depression;

at 60 foot pounds of torque both tests obtained a new thickness of .0410 inches in their depression;

at 80 foot pounds torque both test were inconclusive because of what appeared to be extremely similar coupon fracture failure around the depression before the specified torque could be obtained. Although it was difficult to pin-point, this failure appeared at a similar torque of aprox 72 foot pounds in each case.





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Mon, Oct 13, 2008, 13:36:02


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Posted by: whang

10/13/2008, 10:17:30

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My friend you did a great job. Thanks







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Posted by: Kelly Bramble

10/01/2008, 21:43:53

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Also, see the following Pre-Load Calculator www.engineersedge.com/calculators/machine-design/bolt-preload/bolt-preload-calculation.htm






Modified by Kelly Bramble at Wed, Oct 01, 2008, 21:45:18


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Posted by: john2003

10/24/2008, 02:48:15

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At this link http://euler9.tripod.com/fasteners/preload.html thread pitch is taken into account in the "K" factor for the formula to calculate bolt preload / axial load based on a given nut torque.

It makes sense that the thread pitch would effect clamping force.

How about this, take two long hex head bolts, same diameters and grade, (say 1/2" or 5/8" OD) one with fine pitch threads & one with course threads. Install a washer over the fine pitch thread bolt, run the bolt through a very stiff die or compression spring, install another washer so the spring is sandwiched between the washers, then install a nut on the bolt. Tighten the nut down good so the spring compresses by a fair amount.

Then, measure the torque on the nut at that point with a torque wrench, then give it a little more torque and record for reference. Then measure the distance between the two washers.

Do the same exact thing with the course pitch thread bolt, using the same washers, compression spring, torque wrench, & the recorded torque value for the fine pitch bolt.

It seems to me the fine pitch nut / bolt combination should compress the spring further than the course pitch nut / bolt, with the same torque applied to both nut /bolt combinations. Provided each bolt has the same diameter, a more gradual thread incline should equal a greater mechanical advantage and more axial clamping force for a given amount of torque on the nut.

A thread is basically an inclined plane wrapped around a cylinder. It's very similar to a disk cam, which is like an inclined plane wrapped around a circle. However, with a thread and nut, the nut is basically acting as both the cam and the follower at the same time, it's like an inverse cam, but still seems to be the same principle as far as forces and mechanical advantages are concerned.

The important thing to remember is that you can't just always say that a more gradual incline equals a greater mechanical advantage, if your comparing bolts they have to have the same diameter, if your comparing cams, they have to have the same radii at the follower contact point.

A small cam (with small radius at cam curve and follower interface)having a steep cam curve incline, can have the exact same mechanical advantage as a larger cam (with a larger radius at the cam curve follower interface)and a more gradual, less steep curve.

What really determines the mechanical advantage is the velocity ratio between the input member (cam) and the output member (follower) at any given point of the cam curve and follower interface. The velocity ratio between the input (driving) and output (driven) member should govern mechanical advantage in any mechanism.

I think the same thing applies to a nut and bolt except the nut is acting as both the driving and driven member at the same time. I suppose you could try to convert rotational degrees to distance and then calculate the velocity ratio between the input motion (rotation of nut) and output motion (axial translation of nut).

All things being equal, thread pitch must effect axial force, but perhaps you could still have a formula to calculate axial force that does not *directly* take into account thread steepness.

John







Modified by john2003 at Fri, Oct 24, 2008, 13:20:15


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Posted by: john2003

10/26/2008, 15:26:51

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Hi everyone,

Randy, the way I interpreted your tests, it appeared that both the fine and course pitch threads produced the same axial load, even though torqued to the same values, is this the case ?

I researched this a little further and found the following...

I have read that even identical bolts, when tightened to identical torque values, can vary in their actual tensions from +/- 25% to +/- 50%, because 85% of the torque is consumed by friction. This friction varies on each bolt, & can even vary on the same bolt at different times. I can't post the link to the source of the information because it's a commercial site, but could send the link via direct email if you wish. They claim NASA uses their products.

They claim that "There are approximately 75 factors which affect the tension in a bolt when torque is applied. Here is a partial list of those factors: hardness of all parts, surface finishes, material type, plating, lubricants, tightening speed, thread fit, and surface pressures. Some of these variables can be identified, but seldom can they be characterized for a production lot. The only way to determine the "ideal" torque for any application is through testing."

If the information given above is reliable, then it seems almost impossible to do a real world test to accurately measure differences in axial loads of fine and course pitch bolts torqued to the same values. A variation of plus / minus 25% to plus / minus 50% on identical bolts seems huge.

From what I have found in other engineering forums and searching around online, it is indeed generally assumed that a fine pitch thread will exert a greater axial force than a coarse pitch thread of the same diameter torqued to equal values.

Purely from a theoretical standpoint, (and everything else being equal) the fine pitch thread will apply more axial force than the course pitch thread torqued to equal values, but the difference is small.

Here's the thing, the mechanical advantage difference between a fine pitch and course pitch thread is fairly small, and this is overwhelmed by the system friction. With mechanical advantage difference being slight, and negated by friction, it seems you could torque a fine pitch and course pitch bolt of the same OD, and either bolt could produce the higher or lower axial force of the two.

What puzzles me, is that will all the variations and variables even in identical bolts, how did you get the exact same results for two different bolts having different thread pitches ?

So many things are specified with a torque rating, torque an engine head bolt down too much or in the wrong sequence, and you can get distorted cylinders and/or heads. About every nut and bolt on a vehicle has a torque specification. Not to mention all the industrial machinery and tools that have torque specifications.

My point being that the +/- 25% to 50% variation in axial load mentioned above (if reliable) would seem to have a significant impact on the use of a precision torque wrench. You take the time to keep your top of the line torque wrench calibrated, but then identical bolt's vary enough so that you can get a +/- 50% variation in axial load even with a perfect torque wrench.

Even if the point of torquing is more to generate friction than axial load, axial load could effect many applications, i.e., engine cylinder head bolts, too much axial tension there would seem to distort cylinders or heads.

I did not know there was that much variation in identical bolts, +/- 25% to 50% seems like quite a bit to me.

This seems like a case where practical application counters theory and common sense reasoning, mainly due to friction.

Any further feedback would be appreciated.

Thanks
John







Modified by john2003 at Sun, Oct 26, 2008, 15:32:10


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Posted by: randykimball
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10/27/2008, 13:47:38

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I think you are right, friction being the devil in most of the variation cases you are speaking of. Threads vary from bolt to bolt and hole to hole in surface texture and angular contact. I have no doubt that these factors effected my test. I too, find it extreeeeemely odd that I got equal results as accurately as I could mike out with a good quality tenths reading thimble micrometer, but the results were the results. I take from this testing and reading around that results do vary, but the difference from the 13 pitch and the 20 pitch (and the variations factor) aren't enough to fret over "as long as" we assume low end clamping numbers for safety.




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