Partially Threaded Bolt

[ForrestLowell]

How do I find the strength of my bolt if it is only partially threaded?

There is the general rule that a half inch bolt needs an half inch of thread to fully develop. I can't get a half inch, so what do I do?

 

[BAretired]

Get a longer bolt.

BA

 

[slickdeals]

I believe the code requires that the bolt need not extend beyond the nut, but it cannot certainly be partially threaded.

 

[jberg]

From the RCSC Specification (available at

http://boltcouncil.org/files/2004RCSCSpecification.pdf)

Sufficient Thread Engagement: "Having the end of the bolt extending beyond or at least flush with the outer face of the nut; a condition that develops the strength of the bolt."

JWB

 

[msucog]

i believe it may be allowed to puddle weld inside the nut if the bolt doesn't extend past (i am not a fan of this). there is a blurb included somewhere in aws or rcsc if memory serves me correctly. however, i dont think it's intended for all the bolts to have this condition. in general, jberg is correct that the bolt should extend at least past the nut. i am not aware of a specific distance past the nut that is required (unless the designer specifies otherwise).

 

[dik]

It's possible to calculate the bolt capacity based on limited thread engagement. I'll see if I can dig up a *.pdf file on it. In general, it's not really a good thing to do, but if you can get sufficient engagement, a capacity based on the internal and external thread engagement can be calculated.

Dik

 

[dik]

Do a search for "The Engineer's Edge", I seem to recall that there are formulae on the site.

 

[kelowna]

Are we sure ForrestLowell is talking about nuts? The way he posted the question I thought he was talking about a bolt on a threaded hole in a steel plate.

In that context I have heard about the 1 diameter depth on the plate to develop the bolt capacity.

No sense to speculate unless he clarifies

 

[dik]

The same calculations are involved...

Dik

 

[ForrestLowell]

I am talking about drilling and taping a plate. So no nut is possible.

 

[BAretired]

In that case, use a reduced strength of bolt = (t/0.5)*Fb where t is the plate thickness and Fb is the strength of the bolt. The plate will need to be checked to ensure it has the capacity to resist a point load.

BA

 

[desertfox]

Hi ForrestLowell

Have a look at this site:-

http://www.engineersedge.com/thread_strength/thread_minimum_length_engagement_fed-std-h28.htm

Your thread engagement could be very important, you need to look at the strength of the plate your tapping in comparison with the bolt grade you are using.

desertfox

 

[agostage]

I've used the formulas for stress areas and lengths of engagement of screw threads in the Machinery's Handbook

 

[racookpe1978]

If (literally!) you're in that much trouble that you have to START by only partially-treading the engagament of the bolt)(in a new design ??) than you MUST understand that the first 5/8 of the firstthread in the tip of the bolt is NOT a strength fitting.

The first thread of the bolt is only half-size (half-cut) its first 180 degrees, and the next 90-some-odd degrees may appear to be full-sized, but that part of the thread is is not fully supported by metal between the thread's upper face and the "tip" of the nut.

Result? Much less strength in that first "thread" than in the 2nd, 3rd, 4th, ... ) 32 threads (or whatever your TPI number is). And it is the rest of those that is the reason for the bolt's (nut's) AVERAGE published values.

 

[apsix]

Do some real life testing, that will settle it.

 

[NS4U]

Pretty much what this PDF says is that if you have 0.8xD engaged you will fully develop your connected piece