How to repair threads? (HELP!)

Frank in Thailand

making mistakes so you don't have to...
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I have a problem.

Due several changes in my setup almost all threads are lost.

Hardest hit are my 152Ah cells, I used the bolts that where delivered with the cells at start..
Now I know: Only threaded rods!

Still, with threaded rods, 4Nm is a lot of force.

I've cleaned all recognisable threads and used epoxy to give them a tat more strength.
That works, sometimes.

For those who are stripped, I went to 8mm.
Drilling is easy, I took out the tip of the drill, it's not needed when making a hole bigger.

This prevents to drill too deep.

6.5mm isn't much material to work with.

And while I epoxied all the M8 rods out of precaution, some of them aren't strong.

I have 3 taps to use, last one should go to the bottom, it doesn't.

2.5mm isn't threaded...
2 rounds are tapered, not straight.
M8 is 1.25, so 2.5mm not used.

add that manually tap will wiggle some, especially at start.
you lose a mm there.

that leaves 2.5mm usable thread..
not a lot :-(


Screenshot_20210430_034527_com.lazada.android_edit_1393856621730541.jpg
Perhaps adjust a normal M8 tap?
They are flute, but can be cut halfway, then its full threaded.

It really sucks.

I can feel if/when it goes wrong.
A good thread feels like iron on iron, massive hold.
A bad one feels like it has a spring under it, you are tighten it, but the torque doesn't really increase the way you expect with that 1/4 or 1/2 turn.

When they are above 4.x Nm, I let them be. 4Nm is enough for the connection. (Is the terminal and bus-bar are clean, free from oxidation)

So what's next for solutions??
Go to M9?
Or M10?
Probem stays the 6.5mm material,that only become a larger problem with the thicker stud size.

Helicoil could be an option if there are helicoil bottoming taps available in Thailand, on-line.

I have helicoil for M6.
The Incerts are to long, that's fixable. (10mm)
The thread cutter I have for my helicoil is through hole (flute), not a blind one!!

Blind hole/ straight taps are a real problem.

I know Thailand is somewhat third country left behind with many engineering tools.
I even needed to get the ox-guard from US...

Living off grid with no power isn't fun.

I need a locally available solution.
China / USA takes too long time.

options please!!
 

Frank in Thailand

making mistakes so you don't have to...
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Thanks, I haven't, but could have made the video myself :)
I know how to tap
.
Just not blind holes that need all 6mm available threaded!!

The aluminium is really soft.
The drilling I do by hand in the drill stand, no motor needed!!

Tapping in the stand a problem due the dril stand want to pull up, something I can't disable.

So I do by hand.
Most of them go really well.
Not all.
Not all is +/- $100,- lost per not OK tap.
That is a large problem.

Through hole, I have tapped hundreds.
And all available taps I've.ever seen available for customer have flute.
None real bottoming tap.

YouTube video's on bottoming/ straight taps have without flute.
Sweet unobtainable toys.
Aka, can't be bought, can't be used.
Unless I start machine shop and invest a few hundred thousand dollars....
Then throw in a laser welder and someone to operate.....
Unobtainable toys...

How to make straight taps if you can't buy them??
 

Northernchateau

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Worth, NY
1st Don't use thread rod purchase Brass Set Screws and brass nuts. Strip them out before a hole.
2nd What you need is called a Bottoming tap. It will have the least amount of lead threads.
3rd The taps you see without flute is a thread forming tap. Not right for this application as it has too many lead threads.
4th When tapping aluminum use a light oil like WD-40
 

Frank in Thailand

making mistakes so you don't have to...
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1st Don't use thread rod purchase Brass Set Screws and brass nuts. Strip them out before a hole.
2nd What you need is called a Bottoming tap. It will have the least amount of lead threads.
3rd The taps you see without flute is a thread forming tap. Not right for this application as it has too many lead threads.
4th When tapping aluminum use a light oil like WD-40
Yes, thank you.

Last year, when I started the warning about using the supplies brass bolts wasn't there yet.

My results are one of the reasons it's now advocated in this forum.

The results are what they are, and I can't turn back the clock.

Forming taps are supposed to provide 25% stronger taps then cut.

Bottoming taps aren't available in Thailand.
Thrust me, I've tried to find for months.
If you can send me one, please do.
I will pay for the costs.

I know how to tap.
Tapped several thousands of holes.
With machine and by hand.

Aluminium bottom tapping is a totally different ballpark!!

Helicoil sometimes work.
Not always.
My next option is M8.
That's a challenge with 6mm of soft material.

I have thread Incerts that might work.
Screenshot_20210501_205543.jpg

It will reduce the stud to M5.
Haven't tried it yet, but gets incerted in M9

Alterative could be Loctite thread repair.

Sadly not available in Thailand.
I need help to buy it from USA, or pay +70 for $20 product :-(
 

Frank in Thailand

making mistakes so you don't have to...
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Last edited:

Northernchateau

Solar Enthusiast
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Thanks (I think??)
I'm not sure what I need to do with it.
Please explain.

Bolt strength isn't usually the problem.
The weak aluminium thread is.
Even the weakest bolt in the list will tip the thread out on the terminals.

Edit: probably cross post from the other thread.

I replied there :)
At this point put a thread insert in the post, use brass set screws and DO NOT over tighten them.
Also Do Not bottom the set screw off in the post.
 

Frank in Thailand

making mistakes so you don't have to...
Joined
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Messages
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At this point put a thread insert in the post, use brass set screws and DO NOT over tighten them.
Also Do Not bottom the set screw off in the post.
No brass stud available here.
Twisting motion is extra stress on the weak threads, besides this, it's really difficult to have the exact length bolts!
In a parallel and series you have double and sometimes tripple busbars.
Each needs its own bolt.
Then adding BMS and other toys, is a lug or a few lugs, what need also their own bolts.

I strongly advise never to use the brass bolts shipped out by the seller
Especially if you think you might need to redo th setup a few times.

Studs, scrub bolts, headless bolts, all the same product.
And once they are in, you never need to stress the threads :)
Yes on pulling force
No on twisting stress.

Still, the aluminium is as soft as lead, and 6mm isn't a lot.
Several re installation, is several times 4Nm torque.
That's a problem for the soft aluminium.

And no, not overtighten.
I have a Torquemeter.
4Nm is enough.

Lost thread..
You feel.
It's "elastic", rubbery, not solid mass.
The ones that feel solid it's hard not to have 5Nm!
They twist, till they don't.
No movement, almost no phase between tightening and being tight.
From 2.5 (normal Torque shown during fastening) to +4Nm is almost instant. It doesn't have much "spring" (what's the correct word in Englis?)
I twist slowly, have one washer between nut and busbar.
It twists till it "bites" with a healthy thread, and often I see 4.5-5Nm reading on my meter.
I do need to mention that I epoxied the studs, so your handling feeling might be different in clean aluminium.

Sure, probably in solid iron, one can make really tight.
But that's not needed here.
4Nm is enough for clean terminal and busbars.
 
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ed1380

Solar Enthusiast
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Apr 10, 2021
Messages
107
Bottoming taps aren't available in Thailand.
Thrust me, I've tried to find for months.
use a grinder to remove the tapered threads from a normal tap. now you have a bottoming tap

img_5a1b10fbddbc2.png

YouTube video's on bottoming/ straight taps have without flute.
Sweet unobtainable toys.

when you say tap without flute. what do you mean by flute?
 
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