creating a bolt torque calculator

[eng1234]

Have any of you taken the time to create a recommended bolt torque calculator? I'm in planning stages of this project and looking for tips on how to create the data? I have found some good ones on line, but we would like to have our own in house.

 

[pmover]

eng1234,

1) no, i have not. there are some online. is there a problem with those?

2) create data? do you mean output (results) or input data (data used for determining bolt torque)?

if developing a workbook for in-house use, recommend obtaining input data necessary to create the workbook. traditionally, i have the input data on a dedicated worksheet, calcs on another worksheet, and input/ results on another worksheet.


hope this helps!
good luck!
-pmover

 

[electricpete]

I have a spreadsheet I created for this. If the columns line up it should be self-explanatory (maybe?)

Quantity Units Symbol Value Formula (if applicable)
INPUT Nut factor None K 0.20 Note 1
INPUT Diameter inches inches D 0.75
INPUT fractionM of yield None M 0.50
INPUT Stress - Yield psi psi Sy 95,000
INPUT Threads per inch TPI TPI 11
CALC Thread tensile area inch^2 As 0.34 =0.7854*(D-0.9743/TPI)^2
CALC Target stress psi Starget 47,500 =+Sy*M
CALC Fpreload lbf Fpreload 16,321 =+Starget*As
CALC T (inch-lbf) inch-lbf Tinchlbf 2448 =+K*D*Fpreload
CALC T (ft-lbf) ft-lbf Tftlbf 204.01 =+Tinchlbf/12
Note 1 - Nut factor K is empirically determined value of T/(D*Fpreload) with units (inch*lbf) / (inch*lbf)
Nut factor is assumed 0.2 for normal thread lubrication
Note 2 - Thread Tensile area formula from EPRI Good Bolting Practices, Volume 2


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[electricpete]

This might be easier to look at. Same data as above, but I took the heading and put it in capital letters with colon ) to the left of each entry. The seaparated the rows with carriage returns. Sorry to make somethign so simple be so complex.

INPUT DESCRIPTION: Nut factor UNITS: None SYMBOL: K EXAMPLE VALUE: 0.20 FORMULA: INPUT (Note 1)

INPUT DESCRIPTION: Diameter inches UNITS: inches SYMBOL: D EXAMPLE VALUE: 0.75 FORMULA: INPUT

INPUT DESCRIPTION: fractionM of yield UNITS: None SYMBOL: M EXAMPLE VALUE: 0.50 FORMULA: INPUT

INPUT DESCRIPTION: Stress - Yield psi UNITS: psi SYMBOL: Sy EXAMPLE VALUE: 95000.00 FORMULA: INPUT

INPUT DESCRIPTION: Threads per inch UNITS: TPI SYMBOL: TPI EXAMPLE VALUE: 11.00 FORMULA: INPUT

CALC DESCRIPTION: Thread tensile area UNITS: inch^2 SYMBOL: As EXAMPLE VALUE: 0.34 FORMULA: =0.7854*(D-0.9743/TPI)^2

CALC DESCRIPTION: Target stress UNITS: psi SYMBOL: Starget EXAMPLE VALUE: 47500.00 FORMULA: =+Sy*M

CALC DESCRIPTION: Fpreload UNITS: lbf SYMBOL: Fpreload EXAMPLE VALUE: 16321.07 FORMULA: =+Starget*As

CALC DESCRIPTION: T (inch-lbf) UNITS: inch-lbf SYMBOL: Tinchlbf EXAMPLE VALUE: 2448.16 FORMULA: =+K*D*Fpreload

CALC DESCRIPTION: T (ft-lbf) UNITS: ft-lbf SYMBOL: Tftlbf EXAMPLE VALUE: 204.01 FORMULA: =+Tinchlbf/12


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[eng1234]

Thanks Electricpete,

for your suggestions. I have basic formula's written out and need to put them into Excel or something. I was thinking a pull down menu listing all bolt sizes, K factors, etc., but that seems like a lot of typing.

 

[electricpete]

The spreadsheet does what I need it do do, although I have to admit I’m not an expert in mechanical stuff like bolting. Now I am wondering what kinds of improvements could be made... would like to understand your comments.

I always use nut-factor or K-factor of 0.2 corresponding to good lubrication conditions. Are there circumstances during machine assembly/reassembly when different K is appropriate?

M fraction % of yield is somewhat subjective...user preference 50% to 75% I’d say. I don’t think table lookup adds anything.

There can be a few different TPI for each bolt diameter so from my perspective, the user has to know and enter the bolt diameter and tpi... I'm not sure what table lookup would add.

The only enhancement I can see would be regarding yield strength Sy. It would be nice to have a pulldown list of typical bolt materials and have yield strength determined from table lookup. Is there anything else you think needs to be addeed?

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[electricpete]

There is a forum on somethign like "fastener engineering". That would be a good place to ask if you don't get any other response here.

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[eng1234]

Electricpete,

I can see only adding a few more details, like one time assembly or re-tightening considerations. Also what type of material the fastener will be used for instance steel or zinc. ALso additional materials like stainless steel, etc.

Did you create your calculator in an Excel format?

 

[electricpete]

Yes, I created mine in excel using the formula's above.

5 input varaibles. 5 more intermediate/output variables. One equation per output variable as listed. Pretty simple.

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[electricpete]

I think if you sat down and tried to derive it yourself, you could derive the whole thing by starting with the defintion of K...[Nut factor K is empirically determined value of T/(D*Fpreload) with units (inch*lbf) / (inch*lbf)]

EXCEPT for thread tensile area. That part can't be derived. I got the formula out of an EPRI handbook. As = 0.7854*(D-0.9743/TPI)^2 (units as listed above). I don't know how they came up with that, but I verified that the results using this formula agree with other bolt torque calculators.

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[desertfox]

Hi eng1234, electricpete

Have a look at this internet site you may find it useful

http://www.boltscience.com/pages/info.htm?

regards desertfox