UNC tapped hole Plate thickness requirement

[Structural noob]

All,

Is there a minimum plate thickness guidance out there for a UNC tapped hole. I have a 5/8-11 UNC tapped hole dia for a 5/8" dia bolt. There are 2 0.5" plates connecting to an HSS member. Is the 1" combined thickness of the 2 plats enough for the UNC tapped hole?

 

[drawoh]

Structural noob,

The Machinery's Handbook, and all sorts of fastener textbooks (Bickford?) show you how to analyze your screw thread in shear. This is your anticipated failure mode.

--
JHG

 

[dauwerda]

What strength is the bolt? What strength is the plate? Does the bolt need to be able to develop it's tensile strength or will it only be loaded in shear?

The Machine Design textbook I have by Robert L. Norton (3rd ed.) has the following statements:
For any UNS/ISO threads a nut length of at least 0.5d will have a strip strength in excess of the bolt's tensile strength (Valid only if nut and bolt are the same material).
It then states:
When a bolt is threaded into a tapped hole rather than a nut, a longer thread engagement is needed. For same-material combinations, a thread-engagement length at least equal to the nominal thread diameter d is recommended.

 

[Structural noob]

Dauwerda,

The Bolt is ASTM A325 (threads included in shear plane). The plate is A992 Gr. 50 Fy = 50 ksi. The bolt needs to be able to develop it's tensile strength, although it is only 1% utilized in tension.

 

[azcats]

Can you tap thru 2 discrete plates? Can they be considered to act as one?

If this is a real, structural application I'd be looking at a blind bolt instead of tapping holes in a plate.

 

[ldeem]

I'd go with a nut if at all possible. The calculation's are probably straight forward but you will have to specify a thread quality. I have found tinkering around that tap's come in a wide range of quality (Project Farm on YouTube has a great video). Specifying a taped hole without making sure the thread quality matches or exceeds the quality assumed in your calculations seems difficult. Especially if the plates are not being made by a a machine shop that is familiar with thread quality.