bore diameter in a 1/4-36 UNS-2A thread

[jjbiot]

I need to bore a hole in a male 1/4-36 threaded feature. The thread is about 0.6 inches long. The minor diameter on a 1/4-36 thread is about 0.212 inches. I need the largest possible bore. The material is 6061-T6.

Question: what is the largest bore I can get away with given the 212 mil minor diameter and without compromising the structural integrity of the thread?

Any help is always appreciated.

 

[pmarc]

Keep in mind that it is not only the size of bore that is important. Bore-to-thread coaxiality error will also be a contributor.

 

[jjbiot]

Assuming a concentricity tolerance of 0.001 inches is applied to the axis of the feature, or assuming a runout and/or position tolerance is applied to achieve the same, i.e.: all median points shall fall within a 0.001 cylindrical zone around the datum axis - how large a bore diameter do you think I can get away with given the material and given a minor thread diameter of 0.212 inches?

 

[dgallup]

Without knowing the loading of this part it is impossible to give a recommendation.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[drawoh]

jjbiot,

This is not a dimensioning and tolerancing question.

Try forum725 or forum404.

--
JHG

 

[MintJulep]

The largest hole that you can bore without compromising the structural integrity of the bolt is zero.

The largest hole that could be bored while keeping the stress levels acceptable for your application is unknown as you have not provided any information that would allow anyone to even make a guess.

 

[jjbiot]

I was seeing this as implicitly a tolerancing question because - knowing the bore size as a function of material limits - allows me to tolerance the bore as a function of machine limits. I have never been able to separate these two (but that's just me). This is a hole in a bolt problem and the loading is light. The bolt gets torqued to 8 in-lbs, max. Assuming concentricity as defined in the earlier post, and assuming torque as stated, I'm not clear how close the bore can get to the minor thread diameter. If this were a bore in a 0.25 pin I know that 0.05 is the least I can get away with between OD and ID; but a bore in a 1/4-36 bolt is confusing since the threading adds another structural element. So the rule for a bore in a threaded feature may be different from the rule for a hole in a pin due to the addition of threads. I guess I'm just wondering if the minor diameter forces a condition where the ID muat be less that it would otherwise be if the pin were a bolt of the same outer diameter.

I will try 725 or 404.

Thanks for the time.

 

[drawoh]

jjbiot,

My very quick and dirty estimate is that a 1/4-32UN thread out of aluminium 6061-T6 can take around 60lb.in of torque. This is affected drastically by friction, a problem with aluminium, and by the safety factor you must use on this relatively brittle material.

If your torque is 8lb.in, you can reduce the strength of your screw by quite a lot. Still, this is a structural calculation. On this forum, you ask us how to specify the location of the drilled hole.

Are you screwing this into another aluminium piece? Aluminium galls, especially if it is not anodized.

--
JHG

 

[nobog]

Never seen a 1/4-36 - but maybe that's just me.

 

[KENAT]

Hence "UNS" nobog.

Posting guidelines faq731-376

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

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

 

[CorBlimeyLimey]

nobog,
Take a look at

http://www.efunda.com/designstandards/screws/unified.cfm

for many other thread pitches.

 

[jjbiot]

nobog,

In the world of microwave connectors, 1/4-36 is one of the more common threads shared by 3.5mm, 2.92mm and SMA connectors. The latter may be the most ubiquitous microwave connector in the world. They are staples in the cell, web and radar infrastructure, and in virtually all forms of modern communication.

 

[nobog]

CorBlimeyLimey: thank you, that link was helpful. The medical industry pretty much stops at 1/4-32, thus my ignorance.

Jim