In this thread, I am appealing to your love of engineering detail, and to your experience with engineering calculation.
I do the following calculations in metric but have also included inch dimensions in square brackets [ 1 mm = 0.03937" is used for converting units ]
I have made an internally threaded tube, two inches long, from a solid metal rod (aluminum or brass) .
The outside is a smooth cylinder with diameter of 11.25 mm [ = 0.443" ]
The starting rod is first drilled axially before tapping. The internal threads are made with a M9 x 0.75 tap (Tapco).
According to usual practice, I chose a drill size for tapping of 9 - 0.75 = 8.25 mm [ = 0.325" ; actually drilled with 0.328" or 21/64" drill ]
Measuring the cylinder ID after threading now gives 8.32 mm [ = 0.328" ]. . The measuring calipers, of course, contact the valleys of the threads.
The OD of the cylindrical tube is the same after threading as before threading, so there has been no stretching of the cylinder OD.
This measured ID seems to be a reasonable result for the internal diameter after the specified threading operation.
The resulting internally threaded tube is weakest where the thread profile comes closest to the external surface of the cylinder.
I now need to calculate the expected minimum material thickness in the wall of the cylinder after threading. . This cannot be measured.
What follows is all pure calculation and is based on the reasonable results described above for the threading operation.
I would expect the threaded wall to have a minimum thickness of ( 11.25 - 9 )/2 = 1.125 mm [ = 0.044" ] .... your opinion is needed on validity of this number.
This "minimum thickness" would occur at every peak of the threading.
Does this calculation/result seem to be reasonable and likely to be correct to a good approximation ? . Thank you for any input you can offer.
Final question ... how much do you think I could reduce the external tube diameter ( current value is 11.25 mm ) and still retain integrity during tapping ?
The material is either aluminum or brass. . Thank you for your input.
I do the following calculations in metric but have also included inch dimensions in square brackets [ 1 mm = 0.03937" is used for converting units ]
I have made an internally threaded tube, two inches long, from a solid metal rod (aluminum or brass) .
The outside is a smooth cylinder with diameter of 11.25 mm [ = 0.443" ]
The starting rod is first drilled axially before tapping. The internal threads are made with a M9 x 0.75 tap (Tapco).
According to usual practice, I chose a drill size for tapping of 9 - 0.75 = 8.25 mm [ = 0.325" ; actually drilled with 0.328" or 21/64" drill ]
Measuring the cylinder ID after threading now gives 8.32 mm [ = 0.328" ]. . The measuring calipers, of course, contact the valleys of the threads.
The OD of the cylindrical tube is the same after threading as before threading, so there has been no stretching of the cylinder OD.
This measured ID seems to be a reasonable result for the internal diameter after the specified threading operation.
The resulting internally threaded tube is weakest where the thread profile comes closest to the external surface of the cylinder.
I now need to calculate the expected minimum material thickness in the wall of the cylinder after threading. . This cannot be measured.
What follows is all pure calculation and is based on the reasonable results described above for the threading operation.
I would expect the threaded wall to have a minimum thickness of ( 11.25 - 9 )/2 = 1.125 mm [ = 0.044" ] .... your opinion is needed on validity of this number.
This "minimum thickness" would occur at every peak of the threading.
Does this calculation/result seem to be reasonable and likely to be correct to a good approximation ? . Thank you for any input you can offer.
Final question ... how much do you think I could reduce the external tube diameter ( current value is 11.25 mm ) and still retain integrity during tapping ?
The material is either aluminum or brass. . Thank you for your input.