Best lockwashers for M6 grubscrews?

fafrd

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To all of you who have converted the soft aluminum female threads in your EVE 280Ah cells to male threads using M6 grubscrews (threaded studs), what type of lock washer did you choose to secure assembly?

I know there has been some chatter about using Belleville washers rather than split lock washers for more uniform (and calibrated) distribution of force and I’m curious to know whether anyone has put that into practice.

I’m also interested to understand what specs for a Belleville washer would make it appropriate for this application (of holding down lugs/busbars onto 280Ah terminals).

Since we are aiming for ~35 inch-lbs of torque, I suppose we’d want a washer that reaches at least twice that at it’s point of maximum force near half-deflection.

Has anyone done the conversion of 35 inch-lbs of torque on an M6 thread to the specs we’d need on a 1/4”, 5/16”, or 3/8” Belleville washer?

And on that last point of diameter, and configuration in general, interested in thoughts on what would be best.

After playing with Belleville washers for a 390kgf fixture, I’m actually concerned enough about interaction of the edge of the washer with threads that I’m thinking larger than minimum would be better. Among other things, a larger diameter hole is going to distribute the force over a larger area.

So my thoughts are:

-terminal is 15mm diameter so I want a washer whose central hole is at least 10mm so the force is applied over a large area (and the washer is nowhere near the grubscrew threads.

-Belleville washer placed upside-down (cone-up), followed by a large M6 flat washer (larger OD than the Belleville so it completely covers the outer edge).

-M6 nut tightened down until 35 inch-lbs (or a calibrated number of 1mm M6 turns if you trust your washer specifications more than your torque wrench.
 

Gazoo

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Serrated Flange Nuts. Use 35 inch pound torque (= 700lbs clamping force) = done. No washer needed.

One thing to think about are the BMS terminals. Mine are currently under the nuts and I will be either soldering them to the busbars or putting them under a second nut when I redo my pack. I am leaning towards a second nut. Since the voltage reading will be the same and the balancing current of my BMS is tiny, it will not be a problem. And the second nut will add a bit of assurance the other nut will come lose, although I think that would be very unlikely.
 

fafrd

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Serrated Flange Nuts. Use 35 inch pound torque (= 700lbs clamping force) = done. No washer needed.

Link?

So 35 inch-lbs of torque on an M6 thread translates to 700lbs? Assuming that is correct, it’s going to mean a very meaty Belleville washer..,
One thing to think about are the BMS terminals. Mine are currently under the nuts and I will be either soldering them to the busbars or putting them under a second nut when I redo my pack. I am leaning towards a second nut. Since the voltage reading will be the same and the balancing current of my BMS is tiny, it will not be a problem. And the second nut will add a bit of assurance the other nut will come lose, although I think that would be very unlikely.
Going with my ‘inverter Belleville washer covered by a 6mm fender washer approach, you can either place the BMS terminals between that fender washer and the nut or, if you are worried about the nut twisting the terminals as it is torqued, you can add another small M6 washer on top.

I suppose if you are concerned about resistance between BMS sense wires and lugs/busbars, you want them directly on the busbars/lugs, but since no current is flowing, I’m not sure that I’d critical (and best solved with a seperate attachment/connection if it is (as you suggest),
 

ArthurEld

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I'm just using flat washers. If my batteries were mobile I'd use lock washers or serrated flange nuts.

It's kind of a pain using washers. Serrated nuts are easy but they gouge the busbars.
 

fafrd

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I'm just using flat washers. If my batteries were mobile I'd use lock washers or serrated flange nuts.

It's kind of a pain using washers. Serrated nuts are easy but they gouge the busbars.
Cool, so for stationary application, you think torqued force of the nut on a flat washer is enough to maintain torque.

No concerns about the impact of temperature cycling (I suppose that can result in some change of the effective clamping force, but no reason for the nut to turn / loosen)?
 

fafrd

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Got it. I was concerned enough about stainless galling on stainless grubscrews that I’ve invested in brass nuts, so those are not an option for me...
Link to the calculator, I thought you saw it? It was @cinergi who found it.

Thanks. So that’s where 741lbs comes from (35 inch-lbs on an unlubricated stainless M6 thread).

So we’re looking for a Belleville washer that has several thousand pounds of force at full deflection (way stronger than the Belleville washers being used for 300Kgf compression fixtures).
 

HRTKD

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I'm not using ANY washers! Seriously. No flat washers, no lock washers, no thread locking crud.

I had to take apart a bunch of my system this weekend to put on heat shrink tubing. The tubing was on backorder when I originally put in the system and I couldn't wait for it to arrive. I had camping to do! I checked all the terminals on my two batteries this weekend. Not one of the OEM screws (provided with the battery) were loose. I mean not one of the screws needed to be adjusted. They were all right on the money.

My batteries have well over 2,000 miles on them since September, going down rough dirt roads for quite a few miles. If anything was going to shake loose, it would have happened already.
 

fafrd

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I'm not using ANY washers! Seriously. No flat washers, no lock washers, no thread locking crud.

I had to take apart a bunch of my system this weekend to put on heat shrink tubing. The tubing was on backorder when I originally put in the system and I couldn't wait for it to arrive. I had camping to do! I checked all the terminals on my two batteries this weekend. Not one of the OEM screws (provided with the battery) were loose. I mean not one of the screws needed to be adjusted. They were all right on the money.

My batteries have well over 2,000 miles on them since September, going down rough dirt roads for quite a few miles. If anything was going to shake loose, it would have happened already.
So for a stationary install, I think your experience suggest just a nut on a 1/4” lug or busbar torqued to 35 inch-lbs could hold just fine.

Is that the the torque you used?
 

Rocketman

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Here is a tip I saw from the Jeeping world & figured I would pass it along.

After you get everything exactly tight - take something like a fine Sharpie marker and put a straight line down over the nut, washers(if any) and onto the bus bar. Then you can see in a glance if the nut has started to vibrate/move (loosen).

If you ever pull it apart - acetone or finger nail polish remover will wipe off old sharpie marks on metal. then redo.
 

HRTKD

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Here is a tip I saw from the Jeeping world & figured I would pass it along.

After you get everything exactly tight - take something like a fine Sharpie marker and put a straight line down over the nut, washers(if any) and onto the bus bar. Then you can see in a glance if the nut has started to vibrate/move (loosen).

If you ever pull it apart - acetone or finger nail polish remover will wipe off old sharpie marks on metal. then redo.

I'll have to do that. Easy to do.
 

noenegdod

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My application is mobile so that is what I keep assuming. For a stationary applications where the joint will not be exposed to vibration, using a lock washer is pointless. If however you are looking for the ultimate in vibration proofing you would look to a nord-lock washer. These do not address thermal cycling however which I think is a much greater concern for most.

To deal with thermal stress, I linked to an article in a power transmission publication that deals with belleville washers and how/why you would use them. You can find it in this thread that was characterized as "mangled" but hopefully it can be brought back on track:

 

MattiFin

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Forgot to mention: belleville washers are also available in serrated version.
 

ArthurEld

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Cool, so for stationary application, you think torqued force of the nut on a flat washer is enough to maintain torque.

No concerns about the impact of temperature cycling (I suppose that can result in some change of the effective clamping force, but no reason for the nut to turn / loosen)?
No, I think it is unlikely that they will loosen.
HRTKD took his pack off roading and his didn't loosen.

The most likely thing to cause loose terminal nuts is weak threads. And lock washers aren't going to help when the threads tear out.

I have 200 lock washers in case I change my mind.
 

Oranjoose

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Beginner question: is the 35 in-lbs rating for the post, the nut, or both?

I was thinking about putting the provided posts in my EVE cells and nylon nuts on the posts, in order to prevent the posts from moving, leaving the nylon nuts there indefinitely. From there, I'd put my ring terminals and flange nuts on top of the nylon nuts.

The idea would basically be to make it so that I don't have to worry about overtorqueing or stripping the battery terminals while I swap around nuts, busbars, and wires. Does this sound reasonable?
 

Just John

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Beginner question: is the 35 in-lbs rating for the post, the nut, or both?

I was thinking about putting the provided posts in my EVE cells and nylon nuts on the posts, in order to prevent the posts from moving, leaving the nylon nuts there indefinitely. From there, I'd put my ring terminals and flange nuts on top of the nylon nuts.

The idea would basically be to make it so that I don't have to worry about overtorqueing or stripping the battery terminals while I swap around nuts, busbars, and wires. Does this sound reasonable?
The current should not flow through the high resistance posts, the busbar should be making contact with the terminal, then any ring connectors, then the nut. The post and nut are to make this connection tight, not to block it.
 
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