Michael, The joints on a Caterpillar are simple steel to steel using a steel bolt and a steel nut with, perhaps, a steel washer or two. Make it stout and crank it tight. Simple.
Battery connections, in comparison, are quite complex with their use of multiple soft metals and ridiculously low torques. Please also notice that the purpose of the joint is entirely different, with conductance instead of mechanical adherence being the key goal. Nordlocks DO work. Given their great expense, nobody would use them if they didn't. Lock washers they are not. Somebody posted a picture of a typical early OEM pack where they did almost everything wrong. They dug through the bolt bin and came up with a zinc plated body bolt. Joined dissimilar metals without a protective paste (NOT Vaseline it's flammable!!). Used leaky cells with crap chemistry (IMHO). And sometimes fail to even tighten them correctly. Other OEM packs might be perfectly engineered. Please research the use of dielectric grease to protect electrical connections in Industrial, marine, military, aerospace, automotive, and household applications. It greatly reduces corrosion that WILL happen. OEM battery pack is perfect example. If those had a light coat of dielectric grease they would look perfectly brand new when it was wiped off. Do some research and let me know if you find a single instance of it causing a problem vs. the array of problems that can arise when electrical grease is not used. It is cheap insurance. Best regards, Marcus On Fri, Jan 10, 2014 at 10:58 AM, Michael Ross <michael.e.r...@gmail.com>wrote: > Yes Evan, you have it exactly right. The popularity of lock washers is > without merit. I will give you a caveat though, I am talking about joints > where there is all metal in the sandwich. More detail below on > non-metallic stuff. > > I believe you are wrong about the Toyotas at leas with all metal joints. > Tie rod ends are not castellated on my car, they are big and torqued hard > with a tapered fit that really does the work. There is no thread locker > that I have seen, and no nylocks. If you show me I will believe, but I do > my own wrenching and have not seen any. I have seen some deformed nuts > where they whack the end of the nut into an ellipse for use on exhaust > stuff that has extreme thermal cycling). There are things like battery > hold downs - not an all metal joint, but I am pretty sure even these are > not nylock or deformed. > > You are right to press me on this - Why on earth are there all these lock > washers used? Why do so many people think they are useful? Heck, Nordlock > may be quite sincere in thinking their fancy washers do something. Part of > this is tradition that is self sustaining - they are everywhere so the must > be good, right? Also, lock washers do get applied places where, > unfortunately they help, because of design flaws (usually material > selection). In every case they are a bandaid for a joint that could have > been better, but maybe cost too much better, or there wasn't time to do > better, and besides, everyone uses them, right? > > That does not change the fact that a split lock washer, or a Nordlock is a > waste of money in a joint that is tight enough not to come loose. And you > can design or modify joints so they don't come loose. > > Here is why I think I know what I am talking about: > I worked as a mechanical engineer for Caterpillar. You will not find them > on a Caterpillar track type tractor, front end loader, or backhoe loader > (these three products I have done design work on). I have a copy of the > bolted joint analysis and design specs for Caterpillar in the 1990's - no > lock washers are to be used - ever - for metallic joints. This spec is the > bible for getting bolted joints to survive in the absolute worst > conditions. I doubt if Cat has a part number for a split lock washer, > though you never know what a green engineer might do. I have done > mechanical work primarily on Toyotas in modern time (VW, Audi, Porche, > Subaru, & Honda in the 1980's) and there are no lock washers used on them. > > Part of what confounds common understanding about lock washers is that they > will paper over joints coming loose that are prone to become loose: > There are joints where, due to unfortunate design, materials that creep are > necessary, or in other words they compress with time and thermal cycling > (plastics and other composites). In these cases you really should use very > light clamping forces, align the parts with pins and other features, and do > not apply the assembly in the presence of any thermal cycling or vibration > of any kind. Think electronic components for use indoors only. > > There are a variety of washers for special purposes where clamping force in > not a primary concern. Star washers for instance can pierce oxides and > plating to improve low voltage, low current connections. Metallic inserts > are used in plastic part design to remove a threaded interface in plastic - > because plastic will deform with constant force and thermal cycling. If > you can make very deep thread engagement with plastic it can work with > special threads (think thin sharp threads like a drywall screw). All sorts > of weird stuff is needed when the joint has materials that are plastic in > behavior, not stable and elastic as are metal joints. Look in a Richco > catalog for all manner of plastic fasteners. Penn Engineering for metal > inserts. > > Bottom line you will see lock washers in use, but they may not do anything > or they may be covering up a bad design fault. Taking what you see on a > plastic assembly and using it on a metal assembly is bad practice. Happens > all the time, and now we are all used to it. Reminds me of Phillips heads > which Henry Ford put into service specifically because they cam out and > strip the cross so as not to mess up sheet metal. Or the QWERTY keyboard > designed to exercise out littler fingers, not to promote efficient fast > typing. This s*** just happens > > Returning to battery terminals on EV's: > I haven't seen all the various battery connection means. Some may suck and > need something to keep them from loosening. None of my batteries are like > that. If you have all flat metal in your battery terminal stack, and your > screws can be torqued well, then you don't need any lock washers. But, > each battery type and EV needs to be taken as a separate case. > > I redid my pack of 38120s. These have a stamped metal cap on each end with > t tapped hole. These were not torqued to even half what they should have > been, came loose with barely finger tightness. I took them all apart, got > rid of the lock washers (they have a tool large ID so there is an area of > unnecessarily high stress between the screw heads and the flat washer). > This is nit picky, but I have no reason to cut corners. Then I put them > all back together and tightened them using an inch pound torque wrench > because is has small enough resolution to do a good job on the M5 screws. > I am annoyed that they are Phillips screws and might replace them with > socket head cap screws later. I used some little SS SAE washers that are > not the best choice. > > I have a pack of 40Ah Thundersky cells. these have aluminum pads with a > tapped holes for terminal contact. I am going to get some screws that are > long enough to get good thread engagement all the way to the bottom of the > tapped holes. These did not have lock washers installed, but properly > sized flat washers. I didn't pay attention to if they were torqued right. > It is hard to tell, and it was all coming apart anyway. I will torque > them to the correct torque for aluminum threads. > > Another pack I have is 19650 cells (like fat AAs with flat ends) which have > no screw fasteners at all. These have strips of stainless laid across the > ends and resistance welded to the cell ends. They are series strings to > get the voltage, of numerous parallel cells to get the capacity. I like > this for cheapness. They may be assembling the packs with welding robots - > or they could anyway. The bad part is if a cell goes south, it is hard to > replace. > > As has been noted, the current does not travel the bolt and threads, but > goes through the flats where the terminal, strap or bus bar contacts the > battery terminal - I think a thread locker is probably fine to use if one > is are hesitant to torque fully. But it is unnecessary if you have full > thread engagement (>1.5 times the bolt diameter) and torque properly. Just > torque it. A lock washer is simply not an effective means for anything in > a metal joint. > > > On Fri, Jan 10, 2014 at 5:05 AM, Evan Tuer <evan.t...@gmail.com> wrote: > > > On Thu, Jan 9, 2014 at 9:27 PM, Michael Ross <michael.e.r...@gmail.com > > >wrote: > > > > > > > > Please explain what I got wrong here. > > > > > > > > The real world? According to you, there is no reason for ANY sort of > > locking washer or nut to exist. > > > > > > That's clearly not the case. Even in your > > Toyota, there will be plenty of fasteners Loctite'd in, probably a few > > Nylocks, perhaps even a few castlated bolts lurking somewhere. > > > > The battery terminals we work with are not ideal either, though I > maintain > > the environment is not bad enough to warrant Nord-Locks or anything that > > extreme. YMMV. > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: < > > > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140110/9b80a1c2/attachment.htm > > > > > _______________________________________________ > > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > > For EV drag racing discussion, please use NEDRA ( > > http://groups.yahoo.com/group/NEDRA) > > > > > > > -- > Put this question to yourself: should I use everyone else to attain > happiness, or should I help others gain happiness? > *Dalai Lama * > > Tell me what it is you plan to do > With your one wild and precious life? > Mary Oliver, "The summer day." > > To invent, you need a good imagination and a pile of junk. > Thomas A. Edison< > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> > > A public-opinion poll is no substitute for thought. > *Warren Buffet* > > Michael E. Ross > (919) 550-2430 Land > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google > Phone > (919) 631-1451 Cell > (919) 513-0418 Desk > > michael.e.r...@gmail.com > <michael.e.r...@gmail.com> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140110/dcddc853/attachment.htm > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Marcus Reddish -------------- next part -------------- An HTML attachment was scrubbed... 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