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I was wondering if it'd be a good idea to attach a 10kg load to the end of a movable steel rod by fastening it with just one M5 bolt. Looking at Misumi's datasheet, M5 (Class 10.9) has an allowable load of 111kgf. 111kgf is 10x more than my requirement for static load. However, it's not quite clear if 111kgf is for both axial and radial directions. If the load was de/accelerated in any direction, would an M5 bolt be able to support that? For a 10kg load, does that mean if the de/acceleration of the load stayed below 10*9.8m/s^2 = 98m/s^2 (by F=ma), then a single M5 bolt would still be OK? Perhaps if the load was allowed to swing as well, the centrifugal force wouldn't be too far off?

Any guidance would be greatly appreciated.

EDIT1: Here's a diagram:

enter image description here

EDIT2: Here's a revised version:

enter image description here

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  • $\begingroup$ check the datasheet for axial load or shear. $\endgroup$
    – Solar Mike
    Jun 21, 2020 at 11:38
  • $\begingroup$ Add a diagram showing how you intend to join the parts... $\endgroup$
    – Jonathan R Swift
    Jun 21, 2020 at 11:58
  • $\begingroup$ @JonathanRSwift Sure. I've just added it. $\endgroup$
    – Kar
    Jun 21, 2020 at 12:05
  • $\begingroup$ @SolarMike I'm not sure if I'm reading these tables correctly, but this table seems to suggest that Class 10.9 has a 5.68kN shear resistance. Does that mean if the de/acceleration is kept to < 5*9.8m/s^2=49m/s^2 then it should be fine? That's quite an abrupt de/acceleration though. Is one M5 really that strong? $\endgroup$
    – Kar
    Jun 21, 2020 at 12:12

1 Answer 1

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Simply put this is a textbook example of what not to do.

  • The geometry of the connection, a solid bar to a narrow bolt invites stress concentration at the necking where the bolt enters the rod.

  • The heavy disk will rattle and slowly wear the bolt threads out, allowing play at the connection

  • The play of the disk will cause intense momentum back and forth causing miniature fatigue cracks both on the bolt and on the end of the rod.

  • This mechanism will collect some grind dust lumps inside the sleeve acting like plastic constraints causing pivoting of the bolt around them leading to a sudden complete failure.

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  • $\begingroup$ Will adding a neck to the load mitigate the issues you listed, similar to the revised design in the OP? I suppose the bore and the shaft will need a tight fit to some extent. $\endgroup$
    – Kar
    Jun 22, 2020 at 9:29
  • $\begingroup$ Why wouldn't you use a flange with 3 or 4 bolts and a stem with locking escrow? $\endgroup$
    – kamran
    Jun 22, 2020 at 19:30
  • $\begingroup$ Can I ask what's a stem with locking escrow? $\endgroup$
    – Kar
    Jun 22, 2020 at 20:18
  • $\begingroup$ It is a stem with one or two escrows that lock in to the predrilled holes on the rod. If you Google for the flange of your rod size, you find several types. $\endgroup$
    – kamran
    Jun 22, 2020 at 20:23
  • $\begingroup$ By a locking escrow, do you mean a set screw like this? $\endgroup$
    – Kar
    Jun 23, 2020 at 6:15

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