Bolt & Cap Nut lock themselves together - need to modify design
Bolt & Cap Nut lock themselves together - need to modify design
(OP)
I've taken over a project where basically two parts are mated using a 1 5/8 - 5 1/2 thread. One is essentially a bolt, the other essentially a cap nut. When the parts are screwed together, the nut bottoms out on the bolt head.
When it bottoms out, the two parts actually lock together (unintentionally). I have to tap the nut with a hammer while turning it to get them apart.
Any ideas as to why it locks together, and how the design can be changed to avoid this?
When it bottoms out, the two parts actually lock together (unintentionally). I have to tap the nut with a hammer while turning it to get them apart.
Any ideas as to why it locks together, and how the design can be changed to avoid this?





RE: Bolt & Cap Nut lock themselves together - need to modify design
it sounds like you need to add a washer (so that the bolt head doesn't bind up against the nut body).
RE: Bolt & Cap Nut lock themselves together - need to modify design
Perhaps the thread is bottoming out first and locking the parts together. Add an unthreaded portion to the end of the bolt like a dog point that will bottom out inside the end of the nut before it runs out of thread.
Timelord
RE: Bolt & Cap Nut lock themselves together - need to modify design
but the OP also refers to "the nut bottoms out on the bolt head" which sounded to me like the bolt head is contacting the "nut" body (which i why i thought he needed a washer under the bolt head)
RE: Bolt & Cap Nut lock themselves together - need to modify design
The shaft is undercut on the bolt between the threads & head, so the nut is only contacting thread-to-thread until the nut body touches the bolt head.
I would guess I washer would work, but for this application, that wouldn't work so great. I do think it is acting like a double nut.
And I could make it truly bottom out, where the end of the bolt contacts the cap part of the nut before the bolt head and nut body contact, but that's not ideal either.
One thing I noticed with 2 different sets (from different manufacturers) is that the one has some play in it as you're threading them together and that one doesn't lock. The one that locks (on all parts from this manufacturer) has a nice, tight-but-smooth fit for the threads. Does this play a role in it? It's my best guess so far, but I thought maybe there was some principle behind this.
RE: Bolt & Cap Nut lock themselves together - need to modify design
RE: Bolt & Cap Nut lock themselves together - need to modify design
RE: Bolt & Cap Nut lock themselves together - need to modify design
Thus lube and/or reduce the speed and driving torque of assembling
RE: Bolt & Cap Nut lock themselves together - need to modify design