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Old 2nd February 2010, 10:33 PM   #1 (permalink)
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Bolt torque into aluminum?

For socket head screws tapped into aluminum to hold brackets (i.e., not machine screws you use the screwdriver with), how much torque would you apply to a 1/4x20 bolt?

1/4x20 is usually 10ft-lbs, so that's what I did; then removed 4 of them to sharkhide the area, then put it back and all were stripped (boooo =( ). Then I researchd and it says for aluminum reduce tq values by 40%

So that's around 5-6ftlbs or so.

I knwo ya'll will say "snug with the socket", but is 5-6ft-lbs snug enough for a 1/4 or 5/16 (what I ended up drilling the stripped 1/4s out to)?
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Old 2nd February 2010, 11:54 PM   #2 (permalink)
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Re: Bolt torque into aluminum?

If you don't have too many brackets, you may want to heli-coil your mounting holes. This solved a lot of problems.
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Old 3rd February 2010, 12:01 AM   #3 (permalink)
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Re: Bolt torque into aluminum?

it's only 2 brackets that's I'm using the socket heads on. I thought of heli-coiling them .... after I finished drilling them out to 5/16
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Old 3rd February 2010, 08:02 AM   #4 (permalink)
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Re: Bolt torque into aluminum?

Reduce torque and use an Anti-Seize compound on the threads.. You may not have stripped the threads, but actually had them gall and seize on the bolts.
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Old 3rd February 2010, 10:30 AM   #5 (permalink)
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Re: Bolt torque into aluminum?

Alex, try gently running your tap through again. Use anti-seize as Randy suggested.
I torqued mine to 8 ft/lbs. Made many brackets and this is what works for me.
Use a heli-coil as necessary. I had one tapped hole that gave me the same problem.
Chased it out with the tap & it worked fine.
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Old 3rd February 2010, 01:39 PM   #6 (permalink)
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Re: Bolt torque into aluminum?

~everything~ that's gone into the frame has been anti-seized....gobs and gobs of anti-seize everywhere, heh.

I think maybe my inch/lb tq wrench may not be accurate anymore (it's a $30 cheapy one because I couldn't find a quality inch/lb one that wasn't super expensive). I tried chasing (and then re-tapping) the 4 holes, but that didn't do any good.

Good thing it was only a handful I used allen-headed socket bolts on and not the screwdriver/machine screws =)
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Old 3rd February 2010, 03:17 PM   #7 (permalink)
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Re: Bolt torque into aluminum?

Sounds like heli-coil or nutsert time...
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Old 3rd February 2010, 05:03 PM   #8 (permalink)
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Re: Bolt torque into aluminum?

yea, my 1/4'' tq wrench (in/lb) definately was messed up. I always got the feeling something waas wrong with it, but I wasn't going to pay $60 to calbrate a $25 wrench .... so i bought a new industrial strength one; $150. Much much better (my 30 to 100lbs and 40 to 250lbs are both high quality as well, so no worries there)

So basically using the torque values and not accounting for

- buggered up torque wrench
- anti-seize would lower torque value a bit
- threading into aluminum would lower torque value a lot more
- stainless steel bolt

= I screw myself. hehe, lesson learned, as usual


Btw, in an effort to outhink myself, what I've done now is, instead of using 5/18 stainless steel socket heads (i couldn't find any zinc plated ones locally unless I wanted to pay $50 for a 100pack), i replaced them with 5/16 machine screws, like I'm using ot hold my rubber insulated clips for brakes/electrical. mUahahahaha, can't over-torque those with my screwdriver (unless I tried using a drill to do it, lol!)

Quote:
Originally Posted by molleur View Post
Sounds like heli-coil or nutsert time...
Nah, i just drilled the 1/4x20 to 5/16x18
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Old 4th February 2010, 02:53 AM   #9 (permalink)
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Re: Bolt torque into aluminum?

Okay, all buttoned up! It took me 3hrs today, but I found a place that carried plated machine screws in 5/16. Man, those are hard suckers to find, but worth it - install with a screwdriver means Alex can't screw it up and over-torque them, muahahaha

You can't even tell it should have been 1/4; infact, I meant to do 5/16 all the way. Yep, yep, no galled/stripped threads here, it was all part of the master plan





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Old 4th February 2010, 08:12 AM   #10 (permalink)
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Re: Bolt torque into aluminum?

Great solution you Alex.
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