Shake proof washer - earth bolt - torque settings? - Page 1
Forum section: electronics / general

author: Mattylad
author_rank: Regular Contributor
timestamp: June 03, 2020, 08:46:44 pm
content: Hi,It's my understanding that for a protective earth/bonding point that uses a bolt, it is best done (as opposed to one with no washers at all or spring washers) using a shakeproof/star washer and that it should be tightened to a specific torque rather than tightened as if your life depended upon it (see what I did there?).Tightening up on a shakeproof washer can flatten it completely (removing the tangs from digging into the metals) or deform the washer.Although I must admit, I have never come across it, can anyone confirm what the torque settings should be for M4,M5,M6, M8 bolts and shakeproof washers?Or have I got the wrong end of the stick?If you have links to technical resources with this info that would be most welcome.Thank you.

author: ogden
author_rank: Super Contributor
timestamp: June 03, 2020, 09:14:34 pm
content: Quote from: Mattylad on June 03, 2020, 08:46:44 pmIt depends. There are washers with datasheets and torque specified, then there are just washers. In case of the latter use torque specs of the screws you use.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: October 03, 2020, 10:37:10 pm
content: " star washers are not being used under any ground connection. It has been proven by GM engineering that with a star washer installed, it will increase the chance for corrosion and prevent the terminal from achieving proper torque"https://archive.is/gtsPx

author: Monkeh
author_rank: Super Contributor
timestamp: October 03, 2020, 10:42:54 pm
content: Quote from: timelessbeing on October 03, 2020, 10:37:10 pmGM are not exactly known for quality anything. Also, that's a specifically adverse environment.One way or another you need to get through paint and oxides.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 03, 2020, 11:36:07 pm
content: Ah, yes, GM. The same group that gave us a torque specification for self-tapping fasteners:“Fully driven and seated but not stripped”.Yep, that’s how I always do it

author: timelessbeing
author_rank: Frequent Contributor
timestamp: October 04, 2020, 03:08:09 am
content: Quote from: Monkeh on October 03, 2020, 10:42:54 pmremove the paint and oxides, and apply anti-corrosive compound.

author: bdunham7
author_rank: Super Contributor
timestamp: October 04, 2020, 03:11:22 am
content: Tighten it until it just snaps off and then back off 1/8 turn.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: October 04, 2020, 03:21:15 am
content: GM aren't the only ones who think so.This is NASA reference publication 1228 (March 1990) Fastener Design Manual

author: timelessbeing
author_rank: Frequent Contributor
timestamp: October 04, 2020, 03:30:16 am
content: A study and paper concluding that "serrated washer shows only marginal improvement of anti-loosening nature"http://www.inacomm2013.ammindia.org/Papers/123-inacomm2013_submission_34.pdf

author: Mattylad
author_rank: Regular Contributor
timestamp: October 05, 2020, 06:08:43 am
content: Marginal improvement over what though?While it may only have a marginal improvement in anti loosening (and an improvement is better than none) surely given that a serrated washer digs into the metal either side, it's an improvement electrically?As for GM's corrosion issues, an electrical control panel etc. does not see the environment that a car does.I cannot remember ever buying an electrical item that has earth fastenings that do not use a serrated washer so there must be something in it?

author: Kjelt
author_rank: Super Contributor
timestamp: October 05, 2020, 06:22:43 am
content: Since the cable lug is usually pure galvanised copper the washer might penetrate through the layer making it a triple metal contact. In humid conditions this could result in electrolytic corrosion depending on the metals.In the Rittal cases I have the earth bond nuts have ribs so kind of a washer integrated.For motion shaking purposes a drop (not too much) of loctite should suffice.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: October 06, 2020, 06:46:15 am
content: Quote from: Mattylad on October 05, 2020, 06:08:43 amFlat washer or no washer.Quote from: Mattylad on October 05, 2020, 06:08:43 amthat depends on production environment, tolerances, specifications, cost, statistical significance etc.Quote from: Mattylad on October 05, 2020, 06:08:43 amI'm sure they know how serrated washers work.Quote from: Mattylad on October 05, 2020, 06:08:43 amConvention isn't proof of efficacy. If it was, nothing would ever change.Quote from: Mattylad on October 05, 2020, 06:08:43 amThey said "star washers are not being used under ANY ground connection." Cars have many interior ground connections in a similar environment to your control panel.Of course there are many variables that affect threaded fasteners. I think the point is that you need to be aware of limitations.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 06, 2020, 07:52:50 am
content: I spent an incredible amount of time over my career determining correct torque settings for fasteners. What I learned is that what appears to be a simple subject has an incredible number of variables and no universal answers.This situation appears to be one of the more complex due to the susceptibility of various materials commonly involved to cold creep, discontinuous load curves and significant property variability over time, supplier and operating environment. Things like solder, gold, pcb materials and layer adhesives.Unless you are willing to commit a lot of time and effort to understanding the details of your application and it's environment, and then another huge batch of effort on process controls ranging from no re-used of hardware, control of details of lubrication, stringent controls on thread forms and surface finish and others you are probably just as well off to use a generic formula and recognize that it won't always work. This is one of the reasons that many applications have many more ground connections than required, hoping they will not all fail. And it isn't a vain hope, several of the failure sources are partially or completely independent.Which approach you take will depend on your reliability requirements, warranty provisions and ability to screen for those loser cases.