max tightening torque values for screw heads
max tightening torque values for screw heads
(OP)
I'm sure this question has been asked before but I'm unable to find a thread that addresses the question.
I'm looking for a chart or tabulated form that lists the max allowable torque for various materials and drive types for screws. With some of the smaller fasteners we use in products we run into limitations on the amount of torque that can be applied through the drive (typically female hex) long before we reach the yield strength of the fastener. typical materials are 18-8 stainless steel, 316 stainless steel, a-2 stainless, and grade 2 steel.
Does anyone have a good link or table for this type of info?
thanks
I'm looking for a chart or tabulated form that lists the max allowable torque for various materials and drive types for screws. With some of the smaller fasteners we use in products we run into limitations on the amount of torque that can be applied through the drive (typically female hex) long before we reach the yield strength of the fastener. typical materials are 18-8 stainless steel, 316 stainless steel, a-2 stainless, and grade 2 steel.
Does anyone have a good link or table for this type of info?
thanks





RE: max tightening torque values for screw heads
RE: max tightening torque values for screw heads
How many folk in the mechanical (machine design) world actually get to buy fasteners directly from a manufacturer or even reputable distributor?
Sure if it's going to fly or somehow safety critical etc. but much of the rest of industry is stuck with stuff from local hardware distributors or maybe places like McMaster-Carr which have little in the way of supporting data.
rmetzger - so you're OK with just information for the fastener itself, you don't need to take into account the actual joint/mating part?
http://www.thelenchannel.com/1torque.php is a start but I don't think it's taking the head form limitations into account. This one has some of the same data but some extras too http://www.mgtd.ca/Screw%20Torque.htm.
If you come across a good answer I'm sure many folk would be interested.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: max tightening torque values for screw heads
In many of our applications its important to have a fastener that is not easy damaged during product assembly or customer use. Joe Blow in the field using his tools to open a battery compartment isn't going to torque it back down to our spec, but he is going to complain if he damages the screw. Same goes for his brother in law's repair shop that is equally prone to damaging fastener drives. Thus we try to find the best fasteners we can (knowing we'll never know where they came from) that a customer can't easily damage when using their tools and their skill set. Hence the question regarding drive torques for the screw heads.
RE: max tightening torque values for screw heads
I'd feel better about running "Torque to yield, then bust" tests to confirm the spec, and then qualify new batches of screws received, too
RE: max tightening torque values for screw heads
We test head strength during design but it would be good to have a reference to get in the ballpark on paper prior to having to attain parts and begin analysis.
RE: max tightening torque values for screw heads
I created screw torque charts here using Microsoft Excel. We use stainless steel screws. One of our suppliers claims that his English screws have a yield stress of 55,000psi. All other other stress values were higher than this, so this is what I used.
Bickford's Handbook of Bolts and Bolted Joints has formulae for working out stress are on both English and metric screws.
My torque charts seem to work.
If you are stripping sockets...
RE: max tightening torque values for screw heads
*At least two national fastener chains in the USA stock SHCS to this standard, and are what you get when you order stainless SHCS from them.
RE: max tightening torque values for screw heads
Your call.
They practically had to rebuild 2 or 3 of the Space Shuttles just because of this problem - no backup data. And I don't care if you are building F18s or kid's tricycles. - bad bolts, screw, nuts etc. can be disastrous..
I (we) just don't do it with out documentation!!
RE: max tightening torque values for screw heads
For non structural/lightly loaded joints it's difficult to persuade purchasing/operations/management that it's necessary to have aerospace industry levels of traceability etc.
Hell, I can't even persuade myself.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: max tightening torque values for screw heads