[drxlcarfreak]

A 2x4 just got in between my carriage and bumper stop on my new Nema 34 R&P and snapped.the pivot bolt before I was able to react and hit the E-stop button. I am trying to find a replacement to get me back up and running as quickly as possible. Does anyone know the specs of the pivot bolt? From CNCRP's site, I see that it is a 3/8-16 thread, and measuring the shoulder it appears to be 1/2" dia and 2" long. Is that correct?

[Jim Dawson]

''3/8-16 thread, and measuring the shoulder it appears to be 1/2" dia and 2" long. Is that correct?''

That is a standard shoulder screw size. I would check at your local Ace Hardware in the morning. My local Ace has them.

Worst case McMaster-Carr https://www.mcmaster.com/91259a720

[wmgeorge]

You have to wonder, snapping a 3/8 diameter bolt takes a Lot of pressure. A lot more I would think than a NEMA 34 stepper motor could generate. Is it a "special" soft or shear bolt?

Spec for that bolt if standard shoulder bolt > Minimum Shear Strength 84,000 psi

[drxlcarfreak]

I'll check Ace out today. Thanks for the suggestion!

That's a true thought. I myself have broken many a bolt when tightening them. It could have been the shock of hitting the 2x4 at speed made an instantaneous spike in force. It did break right at the machining line where the threading starts. Maybe because it was a hard line instead of filleted, that was a weak point and had lower shear strength? With the torque multiplication of the belts at that speed, I know these servos can put out much, much more ft-lbs than I can with a ratchet. Thinking about the softer aluminum and bearings around it, I'm now hoping nothing else broke.

[ger21]

With the torque multiplication of the belts at that speed, I know these servos can put out much, much more ft-lbs than I can with a ratchet.

If you did the math, you'd likely find that they are not nearly as strong as you are.

It could have been the shock of hitting the 2x4 at speed

Yes, it's the inertia that provided the power.

Never seen a shoulder bolt at my ACE. I'd get it ordered from McMaster Carr. They're very quick.

[wmgeorge]

Or more than likely a Chinese made shoulder bolt.

US sourced bolts spec'd here > https://www.mcmaster.com/91259a720

[Jim Dawson]

...

Never seen a shoulder bolt at my ACE. ...

Gerry you're just shopping at the wrong Ace

[ger21]

When you have 5 Home Depots and 3 Lowes within a 10-15 minute radius, you wouldn't think that there's be too many Ace's. But I think there are 3 within 3-4 miles of me. I'll need to check next time I stop in.

[drxlcarfreak]

My Ace did not have shoulder bolts, and actually didn't know what they are.

I just ordered a replacement from McMaster. Thanks guys!

[drxlcarfreak]

So I received the bolt yesterday. Fast shipping, though shipping did cost 3 times the cost of the bolt! The machine is back up and running. I will say that the bolt I broke must have had a slightly thicker shoulder as it took some effort to push it into the pinion drive. The replacement I got slipped right in and had a tiny bit of play. That slop did go away when I tightened down the eccentric collar and the spring loaded bolt. It could just be within the tolerance of the bolts, but if this happens to someone else, I think I would recommend getting the bolt directly from CNCRP and not be in such a hurry.