08 November 2001
What the ... ?
I enjoyed Howard Schwerdlin's Motion Fundamentals article on different fastening methods ("Shaft Connections," September 2001). However, when I tried using equation 17 for torque, I found that it didn't make sense—the length Ls is in the denominator, and as the length increases the torque is lowered. My understanding is that as the length of the interference increases, the applied torque increases in a direct ratio.
Am I reading this wrong, or was there a misprint?
Ronald Dufel
Axsys Technologies
Yes, I made a mistake in Equation 10, and this followed through to the rest of the calculations. I should have used dimensional analysis, like I'm teaching my daughter to check her work in junior high.
For the record, these are the corrected equations:
Equation 7: 
Equation 10: 
Equation 13: 
Equation 15: 
Equation 16: 
Equation 17: 
Also, E (modulus of elasticity) is 30 x 106. Sorry about the confusion.
—Howard Schwerdlin
| The modulus of elasticity mistake was ours. We also left out Equation 9 entirely! View or download the complete text. Motion Control regrets the errors. —MC |
Permit me the temerity to comment on Howard Schwerdlin's power transmission Fundamentals. Recognize that as an electrical engineer/systems engineer, some of the basics aren't something I work with every day.
However, in my opinion, every technical article containing equations should include the kinds of units expected. For example, P is pressure, F is force, A is area, etc. Too many of your equations don't include units.
I think if the units and parameters were defined, this would truly be an article to place in my reference book. As it is, it seems useful only to the everyday practitioner who probably doesn't need it.
My intention is to be constructively critical. I hope it's received as such.
Jack McGrath
via the Internet
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