Comment on thread404-143701

[nukti]

thread404-143701

Although the thread has been closed, I just saw it today. A comment from rb1957 (Aerospace) says:

rb1957 (Aerospace)
4 Jan 06 15:13
a word of caution about diamondjim's table.

preload can vary by a third when using torque control ...
ie on a 1.5" bolt (his last line) a torque of 142,200 ft.lbs. is expected to produce a preload between 2400 to 4800 lbs (on dry threads, round numbers)

In diamondjim's table, the last line is:

142200 3560 2660 1-1/2 12

In this, 142,200 is preload in lbs and 3560 lb-ft is the required torque to produce this preload in dry bolt and 2660 lb-ft is the required torque to produce this preload in lubricated bolt. These are correct numbers for nut factor K of 0.2.

I can't make sense of rb1957's wording. He seems to have it backwards.

 

[rmw]

I concur that he/she got some things turned around. The spreadsheet speaks for itself.

rmw

 

[drawoh]

nukti,

Diamondjim's table shows the torque values for threads dry and lubricated. I am guessing this is based on the standard torque equation of T=CDF, where C is the torque factor, .20 for lubricated joints, and .15 for dry joints. D is the thread diameter, and F is the tensile force.

3560/.20*.15=2670

There is a slight rounding error due to me not working from diamondjim's original numbers. This shows the importance of having the spreadsheet and not just the numbers.

Rb1957 is not showing dry versus lubricated. He is showing what it looks like when torque varies by a third. The torque factor C, above, is very crude.

3600 * 2/3 = 2400.

3600 * 4/3 = 4800.

JHG

 

[rb1957]

exactly

 

[nukti]

I'm sorry, I don't understand this. 4/3 is twice as much as 2/3 and not varied by a third.

All I was trying to say was that 142200 is the tensile force in lbs and not torque in ft-lbs as suggested by rb1957.

So, 3560 ft-lb torque applied on a 1.5" bolt will produce a tensile force of 142200 lbs for C factor of o.2 and not the other way round.

Thanks.