Originally Posted by
Don Clement
My experience with tens of thousands of form tapped 4-40 holes in 6061-T6 is excellent.
Don
Like you I've had great success with roll taps on the hundreds of thousands of 4-40 holes that I've tapped over my career .
my point was that roll form threads in 6061 is not stronger than cut threads .
I needed to test to see which thread was stronger , I currently work with medical products and we cannot afford for threads to fail . We can't have customers over tighten the equipment , strip the threads then blame us for faulty products , we need bolts to snap before our parts fail (which would be to an extreme) .
When I requested to introduce form taps to the machining process I was told to test the thread strengths between roll and cut taps , the point was to strip threads and to snap high grade bolts and to document the results .
The documentation consisted of how much torque was required to strip each of the threads which had an equal thread percentage at each given depth .
I tried threads at a variety of thread percentages and each at different depths . The results for both forms of tapping required nearly exactly the same amount of torque to strip the threads out , and both were equally the same when it came to the point of busting the heads off of the cap screws .
these tests were done numerous times and the averages were documented . This proved that roll taps would be sufficient for the products we manufacture but it has also proven to me that in the aluminum both threads are equal in strength .
Other materials may and probably will differ but that's not my concern at this point of time
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A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........