Fixing the Broken Axe

I received the new couplings today for the HB2 from PDJ, Inc.. The new one is the bright and shiny one in the picture. The black one is the original style that has been giving me problems with breakage. (6208K6 @ McMaster-Carr)

The new one is rated for 495.6 oz-in. The old one is rated for 42 in-pounds (peak). That is 672 oz-in! So the old one should be the strongest, right? The new one LOOKS stronger and is a different style. They are both considered Helical Beam Couplings. If you want to see what a broken one looks like check HERE.

So what gives? Well, the old couplings certainly do. Maybe the key word is the “peak” rating rather than a continuous rating. I can’t tell. The Mark One eyeball says the new one is stronger. That’s old Navy jargon for eyeball engineering.

I think I will soften the acceleration on the steppers a bit more to lessen the start stop shock loads.PDJ has been using these shiny couplings without failure so I hope my problems are over, at least with the couplings.