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Tapped Holes

Tapped Holes

Tapped Holes

I have a question I am searching an answer for. We make large weldments and are constantly tapping holes for bolts. We calculate the max torque value based on the plate because that is normally the weak link. For lack of better information we use 80% of yield strength for proof stress of the plate. Are there better numbers to use?

RE: Tapped Holes


There is a publication that answers your question. The book is "Introduction to the Design and Behavior of Bolted Joints" by Bickford. It is published by Dekker. You can also find it through ASME. They use Bickford's book in their Bolted Joint training coures. I do not know why he called it an introduction, it is a really good book.

Typically, plate materials (carbon steels) have a lower yield than most bolt materials you would use. Bolts are similar to springs in that the stress in a drawn up bolt will not increase until the joint parts. Bickford does an excellent job of explaining this.

Bickford has equations for calculating the depth of tapped holes for an equal strength between the bolt and the tapped hole. Three relations are offered. One for when the hole material has a higher yield or ultimate strenght than the bolt material, one for the opposite circumstance, and one for when they are equal.

If you can not get the book quickly enough for your needs, email me at pworthi@astro.as.utexas.edu,and I will email you the equations. Let me know if you can handle MathCAD 2000 format. If not, I will just put it in the body of the reply. I am at the house and do not have the book with me.



Tom Worthington

RE: Tapped Holes

I have checked a couple of places for the book but can't seem to be able to get it. If you have any info that you could offer please let me know.

Troy Allee

RE: Tapped Holes

Have you tried Barnes and Noble online. Most engineering books I look for I find through them. You may also find it through the ASME book club. You can always contact Dekker, the publisher.

I will search the Barnes and Noble site tonight.

Tom Worthington

RE: Tapped Holes


You can find the book at Barnes and Noble. The book can be shipped within 24 hours. It cost nearly $200.00. I know it is worth it. It is a large book and a very good treatment of bolted joints. I have pasted the book listing below. Look at www.barnesandnoble.com. Search under "Bickford". It should be the third listing.

Good luck,


3. Handbook of Bolts and Bolted Joints
In-Stock: Ships within 24 hours.
John H. Bickford (Editor),Sayed Nassar (Editor) / Hardcover / Marcel Dekker / July 1999
Our Price: $195.00

Tom Worthington

RE: Tapped Holes

Amazon.com has "An Introduction to the Design and Behavoir of Bolted Joints" for $135.

Check it out.


RE: Tapped Holes

The mode of failure for the tapped hole most likely would be a shear failure across the threads in the plate. You can calculate this stress by using the equation:
Now, compare this value to the shear yield of the plate material. Typically, you should have about 1.5 diameters of thread engagement to keep this stress low.

The tapped hole should also not be too close to the edge of the plate. A good rule of thumb is to keep the centerline atleast one diameter from the edge of the plate.

RE: Tapped Holes

If you're a practical guy and you want less academic answers, here's my side of the story. You can try looking up for the torque values (in manufacturers' catalogs) of the standard nut corresponding to the thread of the bolt you use. Of course you should find the value for the nut with the same material as your plate. Since your plate would not always be the same thickness as your standard nut, you may need a little linear interpolation or extrapolation if necessary.

Hope I've been some help.

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