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I am putting together a motorcycle from OEM and custom made parts.

I have parts from 6061 and 7075 aluminium and TiAl6V4 titanium and I am putting bolts in sizes M6, M8 and M10 (some fine and some coarse thread).

I would assume that recommended torque depends on thread dimensions (e.g. M8 fine thread with a length of 16mm) and the alloy. Given that, I assume that there is a certain range of clamping force I can achieve that moves closer to the yield point as the clamping force ramps up.

Is there such a thing as a table or online calculator where I can get recommended torque values for these bolts or maybe see what torque results in 80% of the yield point (where 100% = stripping the thread)?

ChopperOnDick
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  • The torque needed also depends on what the joint / parts do... if it is just a dust cover then not much, but if it is a major suspension arm fixing subjected to cyclic loading and lots of stress then the torque needed is much higher. – Solar Mike Jan 19 '24 at 12:08
  • You are right @SolarMike - I think the question for choosing a bolt starts with what is the alloy I am clamping something to, and what clamping force do I need? Dust cover requires less clamping force than suspension linkage hence I can choose a smaller bolt size and/or less torque. – ChopperOnDick Jan 19 '24 at 12:44
  • Generally approach the problem from clamping force, and add overestimated torque required to overcome friction in the threads. If this exceeds the thread's (check shear for both bolt and nut sides) capabilities then you need more bolts or bigger bolts – Abel Jan 19 '24 at 12:48
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    Machinery's Handbook has this – Tiger Guy Jan 19 '24 at 17:32
  • Recommended torques are for the application, not the for bolt. You should be torquing not to the bolt specifications, but to the application specifications. Then you get a bolt that can tolerate at least that much. – DKNguyen Jan 19 '24 at 19:10
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    @TigerGuy Thank you - I just found a pdf of the 29th edition and as you say there's a whole section devoted to "torque and tensioning in fasteners". I will give it a read - many thanks! – ChopperOnDick Jan 19 '24 at 21:27

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