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creating a bolt torque calculator

creating a bolt torque calculator

creating a bolt torque calculator

(OP)
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.

RE: creating a bolt torque calculator

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

RE: creating a bolt torque calculator

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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RE: creating a bolt torque calculator

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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RE: creating a bolt torque calculator

(OP)
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.

RE: creating a bolt torque calculator

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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RE: creating a bolt torque calculator

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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Eng-tips forums: The best place on the web for engineering discussions.

RE: creating a bolt torque calculator

(OP)
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?

RE: creating a bolt torque calculator

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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RE: creating a bolt torque calculator

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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