'Default' torque settings - do they exist?
jps - 23/7/18 at 03:53 PM
Is there such a thing as a set of 'standard' torque settings which I can use for bolts where there isn't a Haynes manual/manufacturers
recommeneded torque value?
E.g. in the absence of any other value to use, an M10 8.8 bolt can be torqued to 50lbft (or whatever the value would be)
I have Googled and found lots of tables that seem to be exactly what I need - but just posting here to be sure!
jwallbank - 23/7/18 at 05:25 PM
Hi,
Have a look at the following, gives the basic explanation and formulas to calculate if required, but provides a list of general toque setting for
metric & unc/unf threads. If you've not come across Norbar before, they make torque wrenches so should know what they are about.
http://www.norbar.com/Portals/0/downloads/TorqueValueGuide.pdf
Sorry, tried to insert as a link but failed!
John W
macc man - 23/7/18 at 05:29 PM
I would say experience and common sense would be best as you need to take account of the material you are
tightening into eg alloy. I rarely use a torque wrench as you can feel when a bolt is at the correct torque.
More critical parts such as on an engine would best be torqued up.
Bluemoon - 24/7/18 at 08:38 AM
quote:
Originally posted by jwallbank
Hi,
Have a look at the following, gives the basic explanation and formulas to calculate if required, but provides a list of general toque setting for
metric & unc/unf threads. If you've not come across Norbar before, they make torque wrenches so should know what they are about.
http://www.norbar.com/Portals/0/downloads/TorqueValueGuide.pdf
Sorry, tried to insert as a link but failed!
John W
Handy table and use that myself. Just note how the values change with bolt coatings... as they are figures for 90% of the yield so changing to
oil/coatings will cause you to over tighten and fail if you don't adjust the values. Doing by feel for non-critical bolts is probably good
enough, and once your "tuned in" will let you know when you have gone too far. Counterfeit Chinese bolts are out there and a will
fail/stretch before you expect.
Dan
[Edited on 24/7/18 by Bluemoon]
balidey - 24/7/18 at 07:16 PM
The linked photo is from my 'Ref' book.
https://www.cromwell.co.uk/shop/cutting-tools/reference-and-data-books/engineers-data-reference-book-nov-08-v2/p/CAT8490356A
https://ibb.co/iY1kdo
[Edited on 24/7/18 by balidey]
coyoteboy - 24/7/18 at 10:20 PM
Mini rant alert...
You can't use tables because they only account for one situations (i.e. nut and bolt). The female thread is, in most automotive cases, the most
likely to be stripped and that's the one you know the least about (material strength, thread engagement, thread quality etc). Tables are a recipe
for disaster (as someone who tried to implement a table-based design strategy in products with highly trained personnel and regularly calibrated
tools, I would say I had about the most control over the situation possible and it still went wrong 
). I defy anyone to "feel" the right
torque for any situation, especially in the presence of rust/oil/grease/water etc - the only thing you could feel is the plastic yield plateau of a
high tensile fastener, which feels about the same as the plastic yield point of the female thread in an alloy casting, for example, at which point
it's buggered. The correct load for a joint is the torque it was designed to, not the maximum torque the fastener can achieve, and there's
dozens of examples of places where maxing out the torque can warp joints.
Get the design torque, or accept the risk your level isn't OTT or too low.
jps - 25/7/18 at 08:36 AM
quote:
Originally posted by coyoteboy
Get the design torque, or accept the risk your level isn't OTT or too low.
Really i'm thinking about situations where I don't know the design torque, and there is no way (that I can see) to establish it.
E.g.( but not the only instance) - the bolts which hold my wishbone (polybush and crush tube) to the bracket on my chassis.
I would rather have some sort of figure to work towards for some of these than just guess completely.
coyoteboy - 25/7/18 at 10:44 AM
But in that case you have a nut and a bolt, so you have the standard tables?
As I say, without knowledge of the joint (if it's not a nut/bolt combo) you just don't know and there's no way of knowing, so just take
a guess and hope from your intuition.
As it is, there's very very often chances where you will just crush the brackets and totally overload the joint without going near the bolt
table/limits. This is engineering I'm afraid, without wanting to sound harsh.
[Edited on 25/7/18 by coyoteboy]