Cell terminal bolt torque - you might be wrong!

[HRTKD]

What if you attach the (short) crowsfoot at right angles to the torque wrench?

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Not being an mechanical engineer, I can't give you a definitive answer. My common sense tells me that anything that extends beyond the torque wrench's normal connecting point will affect the torque applied. In other words, if you normally wouldn't exceed 35 in/lbs, you may have to dial it down to 33 in/lbs. I simply don't know the fudge factor required for this. Given that we're dealing with very small amounts of torque in the first place, this could get ugly.

The inability to accurately gauge the required torque is one reason I have avoided using a grub/set screw.

 

[ArthurEld]

I stripped one of mine. Wa wa wa ?
The thread that came out was literally as thin as a piece of thread.
That tells me the holes are tapped too big. I noticed a lot of the holes feel sloppy.
I guess I'm going to have to permanently loctite all my studs in.
Now my 2 spares are both down.
I'll get a Helicoil kit and try to avoid drilling into the jelly roll.

 

[fafrd]

I am going into work tomorrow with all of my torque wrenches and testing them against standards.

One thing is to let you learn what the right torque feels like.

I thing a screw driver with the right bit might be best. Something that requires you to work hard to apply a lot of torque.

I was using a Philips screwdriver to ‘snug’ for all my insertions until this last one with the torque wrench (which felt obvious to me was far more force).

 

[fafrd]

I stripped one of mine. Wa wa wa ?
The thread that came out was literally as thin as a piece of thread.
That tells me the holes are tapped too big. I noticed a lot of the holes feel sloppy.
I guess I'm going to have to permanently loctite all my studs in.
Now my 2 spares are both down.
I'll get a Helicoil kit and try to avoid drilling into the jelly roll.

Bummer. I’ll be interested to see what you think of the Helicoil.

I have a drill press but it is small and I was not thinking about the cell height. It either won’t fit at all or I’ll need to find a very, very short bit.

Checking for play with an M6 bolt (by hand) may be a good way to identify any other vulnerable threads before they give up the ghost...

 

[Gazoo]

I stripped one of mine. Wa wa wa ?
The thread that came out was literally as thin as a piece of thread.
That tells me the holes are tapped too big. I noticed a lot of the holes feel sloppy.
I guess I'm going to have to permanently loctite all my studs in.
Now my 2 spares are both down.
I'll get a Helicoil kit and try to avoid drilling into the jelly roll.

I think you noticed the photo I posted of my silver thread. If you use loctite consider using the primer as suggested in the instructions. I did not and should have but so far the studs are all good with the exception of the one I stripped. I think JB Weld might be a good option for a thread locker?

 

[HRTKD]

I stripped one of mine. Wa wa wa ?
The thread that came out was literally as thin as a piece of thread.
That tells me the holes are tapped too big. I noticed a lot of the holes feel sloppy.

Or your screws/bolts are too narrow? Could you feel any play in the fastener when inserting into a terminal without anything else attached to the terminal?

Given the issues with stripping, I would be reluctant to put any torque on the fastener/terminal until the thread locker was dry. Otherwise, the thread locker just acts as a lubricant. In this case, I'm thinking of a grub/set screw, not the usual screw or bolt.

 

[ArthurEld]

I think JB Weld might be a good option for a thread locker?

I was wondering the same thing
I saw the chunk of aluminum that came out of yours. Mine was literally like a fine wire. I'll see if I can find it and take picture.

 

[ArthurEld]

Bummer. I’ll be interested to see what you think of the Helicoil.

I have a drill press but it is small and I was not thinking about the cell height. It either won’t fit at all or I’ll need to find a very, very short bit.

Checking for play with an M6 bolt (by hand) may be a good way to identify any other vulnerable threads before they give up the ghost...

I have a little HF drill press and I can move the adjustable platform out of the way if I have to.
I put in helicoils before but not on such a shallow hole. I am fairly sure I will have to cut off a piece of the helicoil.

 

[Gazoo]

I was wondering the same thing
I saw the chunk of aluminum that came out of yours. Mine was literally like a fine wire. I'll see if I can find it and take picture.

Mine is a fine wire too. If you look closely it looks like a compressed spring. I have not had the heart to stretch it out. It's a sentimental thing..

 

[Hedges]

Not being an mechanical engineer, I can't give you a definitive answer. My common sense tells me that anything that extends beyond the torque wrench's normal connecting point will affect the torque applied. In other words, if you normally wouldn't exceed 35 in/lbs, you may have to dial it down to 33 in/lbs. I simply don't know the fudge factor required for this. Given that we're dealing with very small amounts of torque in the first place, this could get ugly.

The inability to accurately gauge the required torque is one reason I have avoided using a grub/set screw.

Consider a 12" wrench and a 1" crowsfoot making a right angle.
(for length of wrench to have clearly defined value, assume one with a handle that has a pivot in the middle.)

(12^2 + 1^2)^0.5 = 12.04

When using a torque wrench with an extension, what you are doing is applying a torque to one end of the extension (causes identical torque to opposite end.)
In addition, whatever tangential force you apply to handle of the torque wrench (in order to create that torque) is also applied to the extension.

If you use a 12" torque wrench connected in-line (not right angles) with a 6" extension, and torque wrench reads 10 foot-lbs (10 lbs at 1 foot), you're apply 10 ft-lbs torque to the extension. In addition, you're applying 10 lbs at 6 inches on the extension, another 5 foot-lbs, for a total of 15 foot-lbs.

Calculated in a different way, you're applying 10 lbs at 18 inches from the bolt, for 15 foot-lbs.

With a right angle extension, still have the torque but the force isn't tangential. With 6" extension it is still at a significant angle off radial. With a 1" extension, the force is essentially all radial, so does not alter the torque on bolt, which is essentially the same as reading of torque wrench (certainly within its tolerance for accuracy.)

The other point with torque wrenches is that radial loading on the bolt adds friction, alters clamping force for a given torque. So use an extension (e.g. 3/8" drive 6" long) and balance head of the wrench with your other hand. That way, no radial load on thread.

 

[ArthurEld]

Or your screws/bolts are too narrow? Could you feel any play in the fastener when inserting into a terminal without anything else attached to the terminal?

I went and checked with other screws I have from a reputable US supplier. No luck.

Given the issues with stripping, I would be reluctant to put any torque on the fastener/terminal until the thread locker was dry. Otherwise, the thread locker just acts as a lubricant. In this case, I'm thinking of a grub/set screw, not the usual screw or bolt.

If I do use permanent thread locker I will follow the instructions and wait until it is completely dry.

I don't have to rush to fix this one since it's a spare. But it stripped so easy that I'm afraid it will happen again. Or that it already has happened part way on other holes.

I am using grub screws.

The shadow makes it look bigger than it is. But I guess it isn't that thin for such a tiny screw.

 

[Luthj]

I bet they used an oversize drill to make tapping easier. My cells were very well tapped, and an excellent fit for the M6 studs.

 

[fafrd]

I bet they used an oversize drill to make tapping easier. My cells were very well tapped, and an excellent fit for the M6 studs.

So I spent a lot more time inspecting my threads including the one stripped thread and I just may luck out.

First, when I compare an M4 bolt that I purchased compared to the bundled all-in-one (permanently preattached washer and lock washer below nut head and above threads) SS M6 bolts that came with my batteries, I get play of 1mm wiggling lightly-threaded bundled SS bolts while the newly-purchased bolt has less play (~0.5mm), so the bundled SS M4 bolts may be undersized, exacerbating the problem.

I get 4-3/4 turns from first thread grab to light contact with the bottom and I can see what looks like 5 threads down the side of each hole.

The upper 3 threads of all of the terminals I torqued to 4Nm / 35inch-lbs yesterday are noticeably worn compared to the lowest 2 threads and compared the the upper 3 threads of the cells which have never been torqued (though the upper 3 threads of those bevel-torqued terminals do show some wear versus the lowest 2 threads).

So first, every time you thread and unthread stainless bolts from these soft aluminum terminals, you are weaa as rung down the aluminum threads.

Second, bundled hardware may be undersized which will increase wear and the liklihood of stripping threads.

And third, bundled hardware will often only use the top few threads, leaving the lowest threads pristine.

So the main lesson learned for me is if I purchase any more cells, the first thing I will do is inspect threads and then loctite in an M6 grub screw.

And the other point as far as my stripped thread is that the lowest 2 threads are still intact and pristine and even better, my new M4 bolt grabs a full 4-1/2 threads, so I’m hoping I can loctite in an M6 grub screw and it will hold.

That stripped terminal has a visible aluminum lip that now extends up past the terminal surface so it will need to be cleaned up, but seeing the 2 pristine threads at the bottom makes me hopeful the thread can be salvaged without retapping.

A quick question for those of you that have attached M6 grub screws - is there a reason to back off 1/4 turn after touching the bottom? Is it to provide some safety margin in case the grub screw gets turned further when tightening down a nut?

This one thread has so little fully-intact thread left that I’m considering going all the way to the bottom to maximize holding force of the threads I have left (and seeing to the wear on the upper 3 threads in all of my terminals is making me consider bottoming-out all of my grub screws).

Not going to claim victory yet but I’m a lot more optimistic than I was yesterday...

 

[Luthj]

If you are using loctite, you don't need to back off the bottom.

 

[fafrd]

If you are using loctite, you don't need to back off the bottom.

Yes, I’ll use Loctite. I want this to be ‘one and done’!

what length grub screws are you all using?

it seems like I’ll need a minimum of 15 or 16mm if I want the freedom to attach 2 busbars and/or lugs leaving space for a nut, washer and lock-washer, but I’m thinking of going with 20mm to have more margin.

I found some aluminum grub screws but they are slotted rather than hex and I don’t yet know the cost.

These yellow-zinc costed hex grub screws only come in 23mm (at least from this outfit) but I’m not overly-concerned about height and the price seems reasonable ($0.51ea w/o shipping): https://www.belmetric.com/m6x10-coa...p-10727.html?zenid=c3gjqt75i3j03cm013igt00u96

Widest availability for stainless but I’m thinking reducing whatever marginal risk I have of galvanic corrosion within the aluminum terminal may be a higher priority to me than lowering post height by a few mm...

Anyone know if there is anything to be concerned about with ‘yellow zinc’ as opposed to the grey/silver type?

 

[Luthj]

Zinc is zinc. I used 20 mm length.

 

[Gazoo]

A quick question for those of you that have attached M6 grub screws - is there a reason to back off 1/4 turn after touching the bottom? Is it to provide some safety margin in case the grub screw gets turned further when tightening down a nut?

In my case the grub screw came up when I noticed it was stripped. When you tighten the nut it puts upward pressure on the grub screw. I did back the grub screws up a tiny bit. And going by my photo of the loctite visible on the grub screw that lifted out, I believe all of the threads were engaged.

I am using 20mm stainless steel grub screws. I don't think there are any corrosion worries within the terminal since the loctite will seal everything?

If I was in your situation I would consider using the original JB Weld on that one terminal's grub screw. Loctite bonds to the threads and doesn't act like glue where there are no threads. Curious as to what others think about this. I have been able to get 3nm torque on the stripped terminal I used JB Weld on. Not sure yet if I can get more. And not sure if I need to.

 

[fafrd]

In my case the grub screw came up when I noticed it was stripped. When you tighten the nut it puts upward pressure on the grub screw. I did back the grub screws up a tiny bit. And going by my photo of the loctite visible on the grub screw that lifted out, I believe all of the threads were engaged.

Meaning the final thread in the terminal did not go as far down as the first thread on ghe

I am using 20mm stainless steel grub screws. I don't think there are any corrosion worries within the terminal since the loctite will seal everything?

Well that’s a whole other aspect to consider. Whether loctite or JB Weld, if sealing the threads means galvanic corrosion cannot be an issue even if the environment is moist, I may go stainless.

If course there is also the exposed threads to consider. My busbars and/or lugs are zinc-plated copper, so if zinc-plating to stainless has a higher probability of galvanic corrosion than zinc-plating to zinc-plating, that’s another reason to go with the zinc-plated grub screws.

I just read something about yellow-zinc and apparently it is a non-issue, but it also made mention of ‘white rust’ that can occur in zinc-plating. That seems to be primarily caused by salt so hopefully a non-issue for me.

I know corrosion on the exposed threads is better than corrosion on the threads in the terminal, and that the grub screw can just be replaced if that happens, but especially if I’m using JB Weld on my grub screws, they will be pretty much permanent and cannot be replaced (hence why I’m so hung up on the best choice to preserve them in my sometimes-moist environment).

If I was in your situation I would consider using the original JB Weld on that one terminal's grub screw. Loctite bonds to the threads and doesn't act like glue where there are no threads. Curious as to what others think about this. I have been able to get 3nm torque on the stripped terminal I used JB Weld on. Not sure yet if I can get more. And not sure if I need to.

Is the only downside to JB Weld that it is permanent? If JB Weld is stronger than Loctite and I want my grub screws to be permanently mounted (like the new welded terminals), I’m thinking why not use it on all terminals (especially since the first 3 threads are worn)?

 

[Hedges]

... if I’m using JB Weld on my grub screws, they will be pretty much permanent and cannot be replaced ...

Is the only downside to JB Weld that it is permanent?

I'm not a mechanical guy, but I attempted analysis of JB Weld strength for repair of these 6mm screws in terminals. My math showed it could hold the specified torque, but not a whole lot more. (posted by me somewhere on this forum).

I think the studs that are JB Welded in could be jacked out. Use a sleeve (so nut doesn't climb onto JB weld) and an appropriate nut (something other than stainless, if that's what he stud is, to prevent galling.) Just restrain the stud with Allen wrench and crank the nut with higher torque, probably 8 to 10 Nm. That should shear the JB Weld bond and any threads that might be left. (Change out sleeve for a longer one as the pulling process progresses.)

 

[BiduleOhm]

My busbars and/or lugs are zinc-plated copper

Zinc plated copper? you're sure? I'd bet it's tin platted copper.