Monday, October 31, 2016

Hollow Bolt Torque Specification

While I've come up with a variety of sources for torque tables for both English and Metric bolts, I've run into a problem with finding a good torque setting for my uninsulated binding post for grounding. It's this one, which is made of nickel coated brass and is hollow to accept a banana jack:

https://cinchconnectivity.com/OA_HTML/ibeCCtpItmDspRte.jsp?sitex=10020:22372:US&item=4252201
https://octopart.com/111-2223-001-emerson+network+power+-+johnson-29988

Its "datasheet" is sparse and blithely omits maximum torque for the nut. As it turns out, torquing it to 77 inch-lbs as you would for a brass 1/4-32 bolt simply pulls this thing apart!

http://www.engineersedge.com/torque_table_sae.htm

There are a variety of similar uninsulated banana jacks or binding posts which also don't have mounting torque specified.

http://www.grayhill.com/assets/1/7/pushpoststerm.pdf
http://keyelco.com/userAssets/file/M65p111.pdfhttps://cinchconnectivity.com/OA_MEDIA/specs/pi-108-0740-001.pdf
http://www.pomonaelectronics.com/pdf/d3267_1_01.pdf
http://www.caltestelectronics.com/images/attachments/CT2220_drawing.pdf
http://www.caltestelectronics.com/images/attachments/CT2232_drawing.pdf

Torque is specified for all kinds of plastic-bodied banana jacks, but those values are going to be lower than what I'd want to use because I want this thing to be given the best possible connection to the front panel to ensure good grounding.

This catalog contains one tightening torque for a panel mount banana jack. Its 120 N*cm which translates to about 10 inch-lbs, which is interesting because this is for a plastic mounting body. https://www.radiall.com/media/wysiwyg/BananaPlugs_catalog_D7M00CE_1_ed_2011_.pdf
This datasheet seems to be useless, it specified a torque but it seems to be for the little terminal screw on the back rather than the body. It's also a shockingly low torque spec. http://www.pomonaelectronics.com/pdf/d72930_002.pdf
There is one torque spec in this PDF of three different parts' datasheets. It's 6 inch-lbs, but it's clearly for a plastic-bodied part.
https://www.egr.msu.edu/eceshop/Parts_Inventory/datasheets/insulated%20binding%20post.pdf

I looked around again for online torque calculators, but was unable to find one that produced results for anything but standard bolts.

This seems to be a pretty nice torque calculator, and it even had a "hollow screw" option but for some reason that option didn't work, the tool simply resets. http://www.online-iso-calculator.com/online-bolt-torque-calculator-metric-vdi-2330/us/index.php
Here is another nice torque calculator, but it didn't seem to have a "hollow screw" option. It does allow you to put in your own tensile strength, and I played around with putting tensile strength for brass into this one but still got ridiculously high torque specs: http://www.futek.com/boltcalc.aspx
Here is a cute online calculator for converting between Nm and inch-lbs: http://www.numberfactory.com/nf_torque.html
I found several references to a "NASA Fastener Design Manual" NASA-RP-1228. However even NASA sites like this one had dead links to it: http://www.grc.nasa.gov/WWW/StructuresMaterials/TribMech/publications.html
I did eventually find a copy of NASA-RP-1228 and it's very nice but largely filled with theory with nothing I can just directly reference for this problem

I finally had an idea that a similar product that would be more likely to have a torque spec would be panel mount BNC connectors. It was still hard to find something, and the information that I found had to be derated because BNC connectors are usually steel rather than brass and a wider diameter.

Here is a page all about BNC connectors with unsourced recommendations for jam nut torques (below the section for interconnect torques, which are a much bigger deal for BNC and other RF connectors). For 1/4-inch it has an implausibly low 3-5 inch lbs recommended. https://www.microwaves101.com/encyclopedias/connector-torque

This datasheet had an extremely high 25 inch-lbs listed for jam nut maximum mounting torque. Presumably I could apply some derating to that: http://www1.futureelectronics.com/doc/TYCO%20ELECTRONICS/5227169-8.pdf



I eventually also had the brainstorm that toggle switches are also panel mount, hollow with jam nuts, and about the size of my insulating binding post. Amazingly, it was still difficult to find a switch datasheet that had a spec for a mounting nut torque.

The best source that I found for switches was the NKK datasheet for their M series (minature) toggle switches. Its spec is still a bit murky however, it lists an incredible 26 inch-lbs for "large bushing" switches, and two specs, 13 and 6 inch-lbs for double nut vs single nut (not completely sure what that even means but I think it's whether there is a nut on the shaft in the back or if only a front nut is used). http://2t70un3m1d9z1kztamkdrd38.wpengine.netdna-cdn.com/wp-content/uploads/2016/02/MtogglesBushing.pdf

NKK's extremely well organized site with other links is here: http://www.nkkswitches.com/products/toggle/#jump-post-103