Formula : Threaded Holes on both the plates

[Madhu454]

Hi,
Appendix B of 2009 std explains the formula for Fixed and Floating fasteners.
For some reason if I want tapped holes on both the plates. How to calculate the positional tolerance for such cases?
Can anyone help please me on this.

 

[KENAT]

Madhu - that is a fixed fixed situation for which there isn't really a solution because threaded fasteners tend to center on their pitch diameter so there is no real allowance for misalignment other than parts distorting. Additionally, usually there would be an issue getting the threads in the 2 parts to be aligned to create a single long 'nut'.

Please explain the situation in more detail in case I'm misunderstanding you.

http://www.eng-tips.com/viewthread.cfm?qid=255441

may be vaguely relevant. What my lengthy 29 Sep 09 10:41 post overlooks is the effect of the angle tolerance on countersink head an hole - my proposed counter sink dia may still not always work.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

Madhu454,

How do you fix something with two tapped holes? You need the threads of both pieces located accurately to a common helix. The only easy way to do this is to assemble and then tap.

--
JHG

 

[JNieman]

I had the same curiosity as drawoh & KENAT regarding two in-line tapped holes. It's not even ideal for two plates to be tapped together if they are loose, as you'll never get the proper torque on a screw in some situations, without separating or galling threads - at least that's how it'd go in my mind... I can't say I've ever done it with plates meant to be fastened.

The only situation I could think of it if the threaded shaft going between them is not meant to fasten, but there are very few situations I can think of where that would exist. Even where it exists, it seems like the plates would have to be able to move/flex away/toward each other to suit the thread helix, which would be strange to allow.

A very unusual requirement, I'd say... one worth avoiding at all costs as far as I can imagine.

@Madhu54, maybe you could sate my curiosity as to why you're looking into this, since I'm not the only one left wondering.

 

[MikeHalloran]

I have done it, but not with interchangeable parts.

I joined two aluminum sheet parts by clamping, match-drilling, match-tapping, and then screwing in an aluminum Pem-stud and trimming it on both sides. ... then peening the trimmed ends of the pem-stud into the small countersinks I had left on the drilled holes. When complete, it was ~flush on both faces, and looked a bit like a spot weld.

Too labor intensive for production, of course.


Mike Halloran
Pembroke Pines, FL, USA