Tightening a Bolt - Without a Torque Wrench

Just tighten it until it stretches 1%.

A grunt and a half should do it .
Del

"to tight a bolt up to 200n/m without a torque wrench", shanemcconn has rightly answered this part.

"to calculate the force per degree", require data like: the material of the bolt, the size and the pitch of the thread.

Effective tightening a bolt starts only after the nut (with washer) firmly contacts the surface. Further tightening should cause the bolt to stretch. This pre-stretch, stores energy and ensures adequate tightness despite possible expansions due pressure (force), temperature etc.

This explains, "tightening a Nylon bolt and a Steel bolt (of the same size and pitch) call for different torque per degree of rotation…

You should be able to determine it from the stretch of the bolt times the tensile strength. You must convert the pitch which is the rise times the number of turns which is the length increase. If you multiply this by the tensile strength, it should be a torque. You can use the flats on the bolthead as reference to mark your start and stop points. I have a rule of thumb that I am trying to remember based on the flats. I am thinking the turns takes care of the bolt diameter.

Thump rules are some time dangerous if not well understood and supported by logics.

Well established data are available from standard design data books and hand books. Torque values required for different sized bolts of different materials with different standard pitches are well indicated, can be used streight...

Yes, I understand that, which why they have to be used in context and with sufficient engineering experience. If I remember, I would add enough caveats to choke a horse or a lawyer. I do see your point.

Slainte!

There is only one thumb rule about this as I remember and that does not belong to this OP .

The thumb rule is about the compression fittings as per the swagelok manual and nowhere else i have seen this.

The way to ensure the torque (and this we do not prefer in critical application) is through wrench.

Else calculate, as mentioned in previous post, number of turn from the bolt pitch to generate the required joint pressure (or the torque if you like, but i don't) from the snug-fit.

But it is very highly error prone, since as you tighten, very often you will observe that the bolt starts biting into the surface of flange/washer etc and that movement will give you a false indication of the tightness. (infact even with torque wrenches due to this, joint friction and several other factors there is false indications by this method). Several papers have indicated this aspec (scatter in the joint pressure on equal torque and believe me it is high)

The end use do not look critical, since you are ready to go by number of turn method. Depending on that you could calculate the turns, but with caution. Most of the bolted joint do not fail due to bolt defect rather due to defective preloading.

And this is from user of bolts (we do not manufacture) in case it is presumed so.

Hi all,

What's the cause of that requirement (200 Nm, not 200n/m).

Tightening a bolt mostly is done to apply a compressional force between the two bolted elements. This compressional force is balanced by the tensile force in the bolt.

The normal way (not the only) to tight a bolt is through wrenches, turning the bolt head by applying some torque. This torque converts in tensile force in the thread. The relationship between torque applied and tensile force in the bolt, which obviously dimensionally is a length, can be calculated by appropriate formulae that can be fin in many manuals and which is a function of thread geometry and coefficient of friction between bolt and nut.

Geometry can be considered for each specific thread as a constant, but COF may vary a lot depending on the sliding surfaces condition, lubrication, etc.

In fact, with COF within "normal" or "expected" values, the same applied torque can result in tensile forces in a ratio of 1:2 (or 2:1)

So, for critical applications is better to rely on bolt strain/stress measurement.

Kind regards

'I want to calculate the force per degree' - Dear DA.ansari, if you want to know how much n\m per degree - this is very difficult task. It may depend on flexability of bolt and joined parts, it may depend on greasing of bolt and nut, it may depend on ambient temperature and speed of tightening. So, if you need to have accurate result how much n\m per rotation, you should have a lot of tests and investigations, and you will need to have at least torque wrench for this scientific job. So, I am sure, that easiest way is to use torque wrench. At least you may try long lever with calibrated spring (or something like handy spring scales).

Why not try the load indicating nuts? or load indicating washers? Do a quick google and you'll find them.

A very good method is the turn-of-the-nut procedure. But you need to know a little about the application.

Check out:

http://www.erl.dot.state.ia.us/Oct_2008/CM/content/Appendix%2011-14.pdf

http://www.erl.dot.state.ia.us/Oct_2008/GS/content/2408.htm

https://www.nucor-fastener.com/Files/PDFs/TechDataSheets/TDS_012_Turn-of-Nut_Installation.pdf

The bolt tension of 200 Nm would be appropriate for 7/8"-1" (22-25 mm) bolts.

If this is a structural or fixed machine, these would be appropriate.

If this is for an anchor bolt, check out:

http://txspace.tamu.edu/bitstream/handle/1969.1/443/etd-tamu-2004A-CVEN-Richards-1.pdf;jsessionid=A9EFAB5F9650CAC312EB66564A50452E?sequence=1

For some science behind this method, see:

http://books.google.com/books?id=Jnhsmzm_EJoC&pg=PA93&lpg=PA93&dq=turn+of+the+nut+procedure&source=web&ots=KGzQQ5uQPX&sig=nFDoZWiSDNlWAhEIntr-gu94aUY&hl=en&ei=48eaSfmyLqKBtwfbiciwCw&sa=X&oi=book_result&resnum=4&ct=result#PPA94,M1

Hope this helps.

Another variable that has only been mentioned in passing is the compressibility of the assembly. A gasketed joint will have a jog in the torque vs clamping force (or bolt stretch) curve, at the point where the gasket is compressing. So, during that compression, perhaps 90 degrees of rotation increases clamping force by 10%, but later, after the gasket is well-compressed, 90 degrees might increase clamping force by 50%.

Of course 99.5 of all bolted joints in the world are tightened by feel alone, and 200n/m is in the range that can be done by feel.

Flog it up until it breaks, then back it off by 1/4 of a turn.