Dynamometric - calibration, compribing.

Hello friends. I want to tell you about a forgotten or unknown tool both by professionals and fans.

Professionals have it forgotten because it is faster to press a nut with a normal key than to look at tables and put measures.

Fans are unaware because the price is exorbitant and believe that it does not compensate to buy it.

But worst of all we do not know because we don't know what measures. Yes, we know that it measures the tightening torque and what is the tightening torque?

I had a dynamometric bought second hand in the drawer for several years because its scale was in Inch Pounds. I did not know what it was and did not find an equivalence table.

The dynamometric units are usually:
Newton Metro (NM), Decnewton Metro (Dan.m or Dn.m), kilogram Metro Force (kg.m), pounds per foot (lb.ft), etc.

And how do we relate the units? Here comes the part of the ignorance we all have from the tool.

We see that the measures have two different units: one of force, that we normally confuse it with unity of weight and another of length.
That is equivalent to:

"Force we do on the screw with a lever of that length."

From this phrase, operation, equivalences and some very simple solutions to check the proper functioning or even calibrate a dynamometric is deduced

that phrase I have not found it anywhere perhaps because with seeing the units we should deduce it, perhaps because in schools they do not know how to explain and we end up being licensed but we have no idea of ​​fundamental knowledge.

If we see the scales of a dynamometric, the Dan.M are almost the same as the kg.m, it is logical because a Dan is 0.981 kp (kilogram or kilogram force)

equivalence more used units:
1pound (pound) = 0.45359 kg
1inch (inch) = 0.0254 m
1FT (foot) = 0.3048 m
1 nw (newton) = 0.1019716 KP
1KP (Kilopondio or kilogram force) = 9,8006652 n

We will convert the unit that caused the dynamometric to have several years in the drawer without using it:
0.45359Kg x 0.0254m
1 Pound 1 inch

1 inch x 1pound = 0.45359Kg x 0.0254m = 0.011521186 Kg.M.
1kg.m = 1/0.011521186 = 86,796619 inch pound or

1 inch pound = 0.011521186 kg.m or 1 kg.m = 86,796619 inch pound.

Be careful when we make the conversions, if the units are small and we use few decimals there will be errors.
In the previous conversion if we only take 3 decimals
1 inch x 1pound = 0.453kg x 0.025m = 0.011kg.m.
1kg.m = 1/0.011325 = 88,300 inch pound

as we see 88.30 is very different from 86.79. In a key that measures only Inch Pound, 700 Inch Pound we can convert them and say that there are 7.92 kg.m (using 3 decimals) or that are 8.06 (using more decimals).

This is very important when trying to calibrate or check the proper functioning of a dynamometric

and now comes the beautiful theme, check or calibrate a dynamometric.
As we said, the dynamometric measures:
"The force we make on the screw with a lever of a certain length."

The simplest method is to wear a bank screw and a dynamometer.
Before there were spring dynamometers, little exact and expensive. But today with the progress of electronics in Chinese stores, we find 40kg dynamometers in units of 20 in 20 gr. They sell mainly to see the weight of fishing catches, suitcases, etc. for about € 8.

Method:
We put the dynamometric on the screw, holding it by the square.
With a piece of rope tied in the dynamometric handle at an exact distance from the square of the square we pull the key with the dynamometer and see what it measures.

For example, we regulate 2kg the dynamometric, we tie it to 33.33 cm we throw from the dynamometer and when we make a force of 6 kg the trustee must jump from the key because by decreasing the distance 1/3 we must exert 3 times more strength.

Precautions / Dangers.
It is a provisional and unstable system, not trying to verify great forces because the key can be escaped and break or give us injuries.

Do not press the screw too much so as not to deform the square of the key and break the retain of the vessels (ball that prevents the glass from falling) especially if it is small, or leave it too loose because it would escape.

Tirming the dynamometer perpendicularly to the key, if we pull obliquely, the decomposition of the pair of forces will make part of the force not used for the turn but to pull the key to the side and can give us 6kg when we are exercising only 5 (it will never give others, always less).

From here, you can prepare levers that turn the key support on a digital kitchen weight, or anything you can think of.
Check the proper functioning of a dynamometric is easy and no laboratory devices are needed for € 3000.
Making a dynamometric with a dynamometer, a key and a lever is not difficult.

But be careful with the strength we are going to do and its possible consequences if the key, the dynamometer, etc. escapes etc. Remember the principle of conservation of energy and laws of action and reaction.

If you think something is wrong and can be corrected or improved for the benefit of all.

Take advantage.

Hello AFTGM, the topic you raise is fine, what I do not agree is in the calibration method with a dynamometro, if there are calibrated benches it is for something (there is a Metrology PDF that talks about this topic).
The unique important thing that is in terms of these keys in their maintenance is to remember not to leave them with tension when they are not used, and not make use of them for another purpose (use it daily as a carraca, or hit with it ..) the calibration usually lasts quite a lot if it takes care of this. After all, it is not such a expensive tool (if you are going to use it ..)
I think the conversion of measures you contribute, since in the manuals, differ from each other in the units (some in Da.nm, others in lbrs ... etc ..) Greetings !!

Hello everyone, AFTGM notable, excellent, very good, also shows that a Hi Tech device is not always needed to verify or calibrate some presentation tool, finally I congratulate you for sharing your thoughts about it, it will be very helpful for many of us. Post like this, bring knowledge to this forum, thank you . Kind regards.

Thanks Ismael. I was indeed forgot to say that you should not leave the keys with tension so as not to harm the dock and that they should not be cleaned with solvents or try to grease them so as not to take away the original lubricant that protects them. With your contribution and those of all those who collaborate we will all learn.

Friend Juan Pablo asked me because the angular tightening is now used and as I didn't know I was looking on the Internet and I found this link (
www.google.es/url?s call "tightening-angle.pdf". They explain that there are differences when passing from one system to another with the measures of the dynamometric, but the most important thing that is deduced is that depending on whether the screw has the more or less polished threads, dirty or greased will offer more or less resistance to being threaded with which some screws are thus more than others to the same torque and that in a joint is not good because it is about compressing it so that it is compressing it. I hope the explanation is convenient for you. It convinced me. Greetings.