Originally Posted by
flatlander_48
OK, first know that I do not work for 3T or any other bicycle or bicycle-related company.
When you design a bolted connection, I think 2 things are important: for the situation that we're discussing, it would be generating enough clamping force and leaving the bolts in tension when you're done. I don't know how they would determine the clamping force. You can calculate a theoretical value, but you would need to verify that by physical testing as parts have tolerances, surface finishes can vary a bit, etc.
Once you know what clamping force you need, how many screws will you use to get the clamping force?
By what magic do you determine the clamping force necessary for the stem to correctly hold every single after market handlebar that might be mated to it?
Often you can use a small number of screws, but your clamping force would not be evenly distributed. The screw manufacturers can tell you the strength of a given screw size (and head design) and what torque you need to develop realize that full strength.
The key to this is knowing the required clamping force. Deciding how to configure the bolted connection comes aafter that.
And therein is the flaw in your thinking. You can't know the clamping force because the stem manufacturer doesn't have all the data.
So, the torque value that you get from the screw manufacture does have a safety factor. I don't know offhand how much.
So you have no idea if the max torque specified is within the tolerances of your torque wrench, so you have no way of knowing if your wrench will overtorque the connection.
Regarding assembling a stem and handlebars, I would put all 4 bolts in and lightly tighten in and X pattern. The next step would be to repeat the X pattern and torque to the appropriate setting. If this is what you meant by "sequentially", then we are in agreement.
Actually, I intentionally specified an incorrect scenario to make it clear that blindly following torque specifications will NOT guarantee that you are safely assembling parts.
So, what happened to the bolts in the origional situation? I would suspect either poor quality or the bolts OR misformed or mismatched threads that worked to bind up the bolt with the tapped hole.
I don't think there's sufficient data to come to that conclusion.