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Jun 25, 2020 19:44:08 GMT
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There are loads of sites which list the standard torques for a given bolt material and thread, as said above the torque is usualy based on the bolt not the nut a standard height nut being deep enough to shear the bolt before failing. If the nut is a significantly weaker material such as alloy I would suggest using a 1.5 height nut, for a stainless nut on a steel bolt I would just use the standard torque, idealy suspension bolts would use some sort of patch or nylock feature as well so if the joint does relax it clonks around rather than falling to pieces.
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Jun 25, 2020 20:51:05 GMT
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Just did a small test in my workshop. Took a M10 8.8 steel bolt and a A2-70 SS nut and torqued it to 58Nm with my torque wrench and no problem. Repeated it 5 times with the same nut and no problems. After releasing the tension, i could simply remove it with my fingers. Had a look at the nut and there is no deformation of the thread. Off coursr this a simple test with 1 bolt and nut but i would not hesitate to use it on my cars and motorbikes
Peter
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Jun 25, 2020 21:10:01 GMT
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For my bolts I don't have a specific torque - as I designed the bit's I just built them extra strong My shock absorbers all have 1/2" bolts as well, they again are all double shear so I's guess that 30Lbs/ft was a perfectly good torque rating on them. Suspension arms are a sleeved urethane bush, the bolt clamps the sleeve against the double shear mounts and the urethane revolves around the sleeve. So again I'd guess something like 40 to 50Lbs/ft would be about right. So for the clever helpful people who know about load ratings - what is the load rating fo a mild steel 1/2" UNF nut compered to a stainless 1/2" UNF nut? (both on 8.8 or 10.9 steel bolts). A bit of Google searching has found 1/2" x 20UNF nuts in both grade 2 and grade 4 stainless - grade 4 is more expensive so I assume that is the better grade but neither list torque loadings. The Grade 2 are DIN 985 std but the grade 4 are not standardised. You mentioned double shear but i doubt this as there will be a sleeve or a metal bush inside the rubber of your shockabsorber eye and if so, it is no longer a shear load but a bending load which makes the construction much stronger.
Peter
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Last Edit: Jun 25, 2020 21:10:41 GMT by petervdv
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Jun 25, 2020 21:35:47 GMT
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Hi Peter, thanks for the advice & torque PDF link. You are right in the bending load assumption - all suspension fixings are fitted between two metal plates which we commonly call double shear here, we call single shear as only one side being fixed - like a stud with a washer etc. I think I'll talk to my local bolt supplier and try a couple of stainless nuts and see how I get on. kevins - yes all nuts are nyloc nuts. Interesting & educational thread.
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jonomisfit
Club Retro Rides Member
Posts: 1,751
Club RR Member Number: 49
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Jun 25, 2020 22:29:03 GMT
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After some comments / questions earlier in the thread about fatigue of stainless vs other material of bolts I've been trying to find some fatigue life curves. (S-n curves)
I've found some for 304 stainless but can't find any for equivalent of 8.8 bolts. I've found notched and un-notched medium carbon steel, but not any for material thats been hardened.
Mostly out of interest to see if there is much of a difference.
If I find anything I'll put it on.
Good to see some empirical results.
Generally I find it pretty difficult to strip threads on full nuts. Unless it's Cheap at which point all bets are off. The male part goes first, either shears or strips it's threads.
Any mated threaded parts I've designed have generally followed the principle of I want the male part to fail before the threads strip. It's quite exciting when a blind female thread gives up on loaded parts. Bolts there's at least some potential to see something is amiss.
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I'd be interested if anyone can answer whether it's ok to use a stainless nut on a 8.8 steel bolt +1. This is actually something that i have been looking into recently from a corrosion standpoint.
It comes back to the galvanic corrosion table, the anode should be the part with less surface area.
So with a stainless nut and steel bolt the nut would be the anode and the bolt would be the cathode.
Because your anode which is the high risk part is stainless it wont corrode as easilly but could cause slightly faster corrosion to the bolt.
But if you were to reverse the setup and used a mild steel nut on a stainless bolt then your anode is now mild steel and will corrode much faster.
So never use a mild steel bolt to hold on stainless steel part but a stainless bolt into a mild steel part has the potential to corrode faster but will generally be ok.
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Badger
Part of things
Posts: 250
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Jun 26, 2020 11:18:54 GMT
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Nuts are an interesting one which people tend to overlook a bit in the bolt/threaded fastener conversation. I'm a little rusty on this, but typically in a "matching" nut and bolt pair - e.g. grade 8 nut, grade 8.8 bolt - the nut will be slightly weaker to allow a small amount of thread deformation and so allow better distribution of the load as otherwise the first threads will take a much higher proportion of the load. Using a weaker nut will reduce the amount of torque which can be applied before the threads strip, and in turn the amount of preload which can be applied. Preload's a bit of an odd one as well - torquing bolts is often an extremely inaccurate way of achieving a set preload as there are so many variables - operator experience, tool calibration, tolerance stack, lubrication (whether added, cleaned off or the protective oil), the materials being joined (not just the thread but the material under the bolt head), presence of a washer... loads of stuff. It means that outside of a lab it's pretty difficult to be accurate, therefore most settings will have a large margin of safety built in. Achieving preload by specifying rotation has its own issues as well - the tolerances of parts, how well they fit together before the fasteners are tightened, user experience... Basically it's a pain in the wossnames subject as soon as you start getting into the detail of it! I think I may have gone off on a tangent
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Last Edit: Jun 26, 2020 11:19:25 GMT by Badger
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jonomisfit
Club Retro Rides Member
Posts: 1,751
Club RR Member Number: 49
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This came up on my YouTube feed.
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Aug 19, 2022 13:33:17 GMT
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I'm interested in the questions raised here, especially about bolt fatigue. When a bolt is threaded into a nut, everything is clear. But what about self-tapping screws? A friend built a terrace by the water and used the tek screws from Scrooz for the assembly. I am planning to build a similar terrace. But I would like to know about such a fastener's durability. After all, self-tapping removes the protective coating from the threaded part, and corrosion will take over faster. Of course, a bolt and nut would be preferable, but not everywhere you can screw a nut.
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