Alignment Tip
Tightening Anchor Bolts

Always use a torque wrench when tightening or loosening the hold-down bolts of a machine. Determine the proper torque and abide by it. If space is a problem, you can always use a crowfoot extension adapter on your torque wrench to still get in there. Don't forget to change the setting on your wrench to account for this little extra length! Also, remember to lubricate the threads of your hold-down bolts. White lithium grease or "never-seize"
is good, and don't forget to use the torque values for lubricated threads, as opposed to unlubricated ones.

Tip provided by LUDECA, INC.
Distributor of the smartALIGN laser shaft alignment system
www.ludeca.com
Tel: 305-591-8935

In the Maintenance tips dated 10/14/04, Ludeca suggested adjusting the torque on a torque wrench if a crow's foot is used. Here is a handy formula, you can use to adjust the torque when a crow's foot is used.

X= T(A/A+B). Where X is the adjusted torque reading on the torque wrench, T is the desired torque applied to the fastener, A is the length of the torque wrench from the center of the handle to the center of the torque shaft, and B is the distance between the center of the torque wrench shaft and the center of the crow's foot.

The torque applied at the fastener is greater at the fastener than what is read on the torque wrench when any extension is used.

Thanks again,
Al
Allan R. Litchfield
Dow Chemical Company
Michigan Operations
Maintenance Engineering
1255 Bldg.
989-638-6555

I believe Allan's formula is still inverted! It should be:

X = T((A+B)/A)

Best,
Alan Luedeking

Oct 21, 2004 alignment tip has a wrong formula.
If T=40, A=8 and B=2
if the formula given is used X=80
X=T(A/A+B)
X=40(8/8+2) = 40(1+2) = 120

The correct formula using the same values X=32
X=T(A/(A+B)) will produce the correct answer or
X=(TA)/(A+B)
X = (40*8)/(8+2) = 320/10 = 32
Be careful of precedence when doing math.

Jon McFadden
Vibration Analyst
Kimberly-Clark Corp

Allan, Alan and John,

All right - now I am really confused.

John - Allan and Alan and I had a go around about this formula last week. I appreciate your quick comment as we want to make sure we publish the correct calculation.

Did I input it in the wrong order?

Is there a text we can refer to confirm?

Advice is gladly accepted.

Thank you in advance,
Terrence O'Hanlon, CMRP
Reliabilityweb.com

Dear Terry,

Yes, this is precisely why I had added the extra required parentheses to the formula in my earlier messages, but the formula you published was Allan's unamended original. See my suggested one below (again):

X= T(A/(A+B))

To reiterate, Allan Litchfield's original formula was okay (not inverted) as restated with the new definition for X, etc., but it still lacked those crucial required extra parentheses that you omitted, in order not to suffer from the problems that John correctly refers to. Note that John's first suggested alternative exactly matches the formula I had suggested, as shown above.

Best regards,

Alan Luedeking

Hello Alan,
This is the simplest way to write the formula:
X=TA/(A+B)
This removes all un-necessary parentheses and conforms to suggested math precedence.

Regards,
Jon McFadden

Hi Jon,

I agree completely! Simplicity is bliss.

Alan Luedeking

Hello Alan,
If you will allow me to state one more omission.
You are assuming the crow-foot center is in the same plane as the handle. If an angle is introduced, the amount of torque required will increase. If the crows-foot is at 90° to the handle, no adjustment is needed.
Regards,
Jon McFadden

Jon,

This is true also. However, my original tip only referred to using a torque wrench generically; the crow's foot blurb was intended to calm the fears of those who would worry about the space limitations of getting the torque wrench into these tight spaces. The different varieties of crow's feet was the furthest thing from my mind then. This issue only comes into play now that Allan Litchfield came back with the great idea of the adjusted torque formula. So now this is where YOU come in: make those formulas for the other varieties, and Terry will have to send you a hat too!

As far as omissions or silly mistakes is concerned, the worst was the one another reader caught: that I suggested using the torque wrench to both tighten AND loosen the bolts-- I'm still red-faced over that one!

Alan Luedeking

Hello Alan,
It's a linear solution, so all you have to do is figure the percentage of 90° that the crowsfoot is rotated from the plane of the handle and add that amount to X.

X = Torque reading
T = Desired torque
A = Length of wrench to center of handle B = Center of wrench to center of crowsfoot C = degrees offset (range is 0 to a max of 90° for this formula) D = Amount to add Y = Torque Reading to use

X=TA/(A+B)
D=X+((T-X)*C/90)
Y=X+D

Measuring breakaway torque is a valid use of the torque wrench. The procedure for measuring breakaway torque can be found on page 666 of Audel's Millwright and Mechanics Guide, 5th edition.
Regards,
Jon McFadden

Hello Alan,
Now I made a mistake.
X = Torque reading
T = Desired torque
A = Length of wrench to center of handle B = Center of wrench to center of crowsfoot C = degrees offset (range is 0 to a max of 90° for this formula) D = Amount to add Y = Torque Reading to use

X=TA/(A+B)
D=(T-X)*C/90 (this was the error)
Y=X+D
Regards,
Jon McFadden

If you are looking for a published authority for the formula:
Audel's Millwrights and Mechanics Guide, Fifth Edition, Page 667.
They use the formula:

R=TL/(L+C) or their published version: R=T X L / (L + C)

T=Torque Required
R=reading on scale
L=Wrench Lever Length (center of pivot to end of handle as opposed to middle of handle as was suggested in the tip) C=Extension Length

Alan challenged me to produce a formula to correct for the crowsfoot not being in the same plane as the torque wrench handle. I was unable to produce an authority, but since it is a linear change the following formula will work:

X = (T-R)D/90 (T-R = difference in the torque reading from minimum to maximum)(D/90 = percent of difference) Y = R+X

X = amount of torque to add based on the original formula Y = reading on the torque wrench scale for correct torque

If the angle is 0, that is, in the same plane, no adjustment from R is needed. If the angle is 90, then the adjustment will be entire amount removed or T.

Regards,
Jon McFadden

I wanted to suggest a revision to the formulas presented for the case of the crows foot and wrench not being in the same plane; I propose that the formula:

R = (T * L )/ (L + C * cos (D))

where
R = torque wrench setting
T = desired torque at fastener
L = torque wrench length
C = crows foot length
D = acute angle between wrench and crows foot

I don't believe that the relationship is linear as indicated in the other replies, but trigonometric.

Michael