Small Fasteners, Recommended Torque Values 5

[MrEd]

Can someone direct me to reference table which list the recommended torque values for small, stainless steel installation or mounting hardware when mounting 6061 Aluminum Electronic part(s) into Military Electronic Systems. Application environments can range from Ground Fixed, Ground Mobile, Naval and Airborne, etc.

The size of mounting hardware; we typically use with our products is in the 6-32, 8-32 and 10-32 UNC-2B size range.

Mil-Hdbk-60 dated 12 March 1990 which replaced Appendix A12 of Fed-Std -H28; stipulates torque values from 0.190 upto 1.5 inch diameter fastners or hardware.

However, I'm still in need of some recommended torque values for the smaller hardware fasteners. These range from size(s) of 0-80, 2-56,4-40, 6-32 and 8-32 UNC-2B, and 10-32.

Applications are sometimes into Heli-coil inserts and other time directly into the raw 6061 aluminum tapped holes.

Any Ideas?

Please can anyone help?

Humbly,

Mr. Ed

 

[diamondjim]

The heli-coil manufacturer would list torque
values for the different length helicoils
and grades of aluminum. What grade of bolts
do you use?
Assuming grade 5 bolts lubed. (75% of proof load)
4-40 6 inch-lbs
6-32 12 inch-lbs
8-32 22 inch-lbs
10-32 36 inch-lbs

do not have the smaller values.
Most bolt or screw manufacturers have a slide
chart with the values for grade 8 screws
but you will have to use at least 2 x diameter
deep thread engagement unless you are using
the heli-coil inserts. I am assuming you are
in the 80000 psi tensile range for the aluminum.

 

[MrEd]

To : diamondjim

Thanks for your input, the Tensile strength of 6061-T6 aluminum is ~ 42,000psi and yield is about ~ 37,000 psi.

Yes, we generally do use Grade 5 Stainless Steel fastners which have a proof load(s/tensile stregnth of 750 lbs/1,100 lbs for 6-32 and 1700 lbs/2,400 lbs for 10-32.

We generally do not lubricate our mounting hardware or fastners when installing our solid state transistorized components into the next level assembly.

Does dry installation affect the torque value(s) you were kind enough to calculate for us?

Sincerest and Best Regards,
Satellink, Inc.

Mr. Ed

 

[diamondjim]

Mr. Ed,
Add another 15 percent for dry
conditions or multiply by 1.15 time
the values that I sent. The torque
values that were shown were for 75 percent
of proof load. I still would make a test
block and purposely strip at least 3 of each
size under different conditions to have a
real base. The length of bolt under the head
to the first thread of engagement can make
considerable difference in these little guys.
The values that I listed were from an excell
spread sheet that almost mimics the old sheet
that was put out by Lamson and Sessions back
in the 60s. A good reference to have. It lists
sizes from 4-40 to 1.5-12 bolts. I am sorry
to not know how to attach this or I would.

 

[MrEd]

DiamondJim:

Once again thank you for your excellent and timely response to our request for help!

Sincerest Regards,
Satellink, Inc.

Mr. Ed

 

[Paskenell]

Forgive me for asking a question that may seem stupid but it appears you both are talking about different screws. I am not aware of any stainless steel screw meeting a Grade 5 spec. Neither 18-8 (most commonly made from 302HQ) or 316, which are the most commonly supplied stainless grades in the US, meet a Grade 5 steel spec. Did I misunderstand this conversation, or is one of you talking about stainless and the other steel? The torque values we suggest on stainless fasteners to our customers are lower than given above.

David Long
Marine Fasteners

 

[MrEd]

Dear Mr. Paskenell( Materials)

Thank you for taking the time to review and comment on our prior comments.

You are probably correct about Grade 5 or 5.1!

Mil-Hdbk-60 and most engineering handbooks only give specifics on fastner larger than 1/4-20, etc. and fail to adequately address the smaller sizes of 0-80, 2-56, 4-40, 6-32 and 10-32.

One of Mechanical Engineering Handbooks in our company library had a matrix table showing Grade levels 1 through 8 for various sizes of fastners.

In the table the only grade listed for the smaller sizes mentioned above was 5.0/5.1. I therefore assumed ( i.e., an Industrial No-No ) what we've been purchasing in the way of MS mounting hardware was Grade 5.0/5.1 by default.

Would you care to share the torque values you or our company recommends to its customers?

Sincerely,

Mr. Ed

 

[Paskenell]

Mr Ed

This is a great forum and as he has proven on numerous other forum entries, you have received reliable information on it from "diamondjim". Grade 5 stainless, however, is a term that is used commonly among unscrupulous distributors, and I wanted to make sure you were not another hapless victim.

There are a few sites to find the information you request, but I use

http://www.18-8-stainless.com/stainless-steel-torque.html

Hopefully it will assist you, and thank you for allowing me to stick my nose in without getting teethmarks

 

[MrEd]

Dear Mr. Paskenell:

I'm so old all my teeth have all fell out! There is no need for you to worry about "... getting teethmarks ...."

As far as I'm concerned, you can "... stick your nose in ..." anytime.

The hotlink you provided in your last reply
(i.e.,

http://www.18-8-stainless.com/)

proved to be an extremely valueable place to go.

Once again thanks for your assistance.

Our Best Regards,

Mr. Ed :>)

 

[vonlueke]

Regarding the "18-8 and 316 stainless steel bolts, which are the most commonly supplied stainless grades in USA," mentioned in Paskenell's first post, above, does anyone know which specification (e.g., ASTM, etc.) the strength of the imperial stainless steel bolts discussed herein is specified in? For the metric stainless steel bolts, I know it's in ISO 3506-1. But where is it specified for the imperial size SS bolts? I'm particularly interested in, e.g., the imperial stainless steel bolts commonly available in high-quality, small, USA hardware stores. These bolts are rather expensive and the material appears to be good quality. The hex heads are unmarked, blank, flat, smooth, and undimpled. The smaller SS bolts and screws (in same stores), with other than hex heads, appear to be this same material.

 

[CoryPad]

ASTM International has several specifications for stainless steel fasteners, such as:

ASTM F 593, Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs

which has requirements for seven groups of alloys (including 304 and 316).

 

[MrEd]

We are attempting to get a copy of either of the following two(2)documents or a copy of both.

1st - Mil-I-8846, Rev. D entitled: "Inserts, Screw-Thread, Helical Coil" which was cancelled by the U.S. Government on 30 June 1998. and a copy of

2nd - NASM8846, entitled: "Inserts, Screw-Thread, Helical Coil" which has purportedly replace the Mil-Spec.

Can anyone help us locate a source for these documents or send a free copy via e-mail as an attachment?

Thanks,
Satellink, Inc.

Mr. Ed

 

[Lcubed]

MrEd,
I don't have a copy of either document at hand, but I would get in touch with Heli-Coil or any other insert manufacturer. They should have the documents, and I would expect that they would be happy to send you a copy.

HTH

 

[TVP]

MIL-I-8846 Rev D should be available for free download from the following website:

http://assist2.daps.dla.mil/quicksearch/

However, I just tried to download it, and I experienced an error. You may need to contact the site administrator to fix this problem.

NASM 8846 is the superceding standard, and can be obtained from Global Engineering Documents at

http://global.ihs.com/.

 

[MrEd]

To Both Lcubed and TVP:

Thanks for the leads, I'll check all three(3) sources out!

Greatfully Yours,
Satellink, Inc.

Mr. Ed

 

[Paskenell]

For vonlueke

You ask a very good question about specifications on stainless steel bolts. ASTM F593, as Corypad stated, is a common stainless bolt spec and the one the IFI recognizes. This however would not necessarily apply to the "18-8" stainless bolts you are seeing in the hardware store. I am working on the assumption that they are in fact stainless and not just advertised as such. F593 states bolts must be marked with manufacturers head marking. By manufacturing these bolts without the head marking, the source is advising these bolts can not be certified to this ASTM spec. It gets confusing but I can sell a certifiable F593 marked bolt as 18-8 stainless(which has no certification), but I can not sell you a bolt marked 304 as meeting F593 spec. As to the bolts without "any" headmarking, buyer be wary. If you are working on a home project, these bolts are probably ok. Otherwise, you are better off buying them from a reliable manufacturer or distributor whom should be "less pricey" and more importantly, certifiable to the spec you need.