It's the tapered end of the nipple in to the tapered bore of the caliper that does the sealing. You just need to nip it up, so it doesn't come loose.
Is it the case that the compression is present in the case of a standard bolt and a bleed nipple, just at different points along the thread? The compression occurs at the far end of the bleed nipple whereas with the bolt, the compression happens just under the head? But it's still compression in both cases? And the thread in both cases contributes with it's own friction resistance? Or maybe it's mystical faeries that supply the resistance that requires a certain degree of torque to overcome?
Now, what you need to ascertain whether it's a 55deg or 60deg thread, pitch, dia. and the coefficient of friction of the materials being used.
i have worked with people like this. take an age to do anything. very good at spending other peoples money. i
There is tension in a bolt......that's why they are called High or Low Tension..........The bolt becomes under tension as the bolt head touches the bolting surface.........if compression exists (IE joining two plates together), it is because of the action of tension. There isn't any head on a bleed nipple that makes enough contact to cause tension..........it is the compression of the nipple end into the seat that prevents it from coming undone.
Belt it with a 14lb hammer Ive a Zeus guide and a rather lovely Moore and Wright thread gauge. Plus I have Moore & Wright micrometers, dial gauges, depth gauges and I once had a wonderful surface table. But alas I left it at my old house. I forgot it. Went back 6mnths later and it'd been skipped! Oh woe. All I need is a brown lab coat. I am a nerd.
There can be no lasting compression without friction (or a constant tightening force), in the cases we are discussing. Or else the bolt or bleed nipple will simply undo itself, regardless of how you torque it. The amount of torque required to lock the thread is roughly the amount of compression required to produce friction sufficient to prevent movement in the thread. The "compression at the nipple end into the seat" applies force along the thread, to create the friction (along the thread) to stop the nipple undoing itself. This force is in the opposite direction to the one supplied by the bolt head mating to the bolting surface, but in every other respect it acts the same way and performs the same function as in the case of nipple compression. If the thread is slippery, with oil or other lubricant, the torque required to lock the bolt will be greater than in the case of a dry thread ... mmm ... nipple compression ... I've been looking for an excuse to type "nipple compression" and "lubricant" in the same post.
Whether you call it friction in conjunction with compression, as the tip of the nipple comes under compression, what force is being applied to the nipple in the thread? It's an equal and opposite reaction.....IE compression, because the tip compression is trying to force the nipple out (which is plainly obvious when overtightened and the threads strip) therefore the thread is also under compression.....because the two compression forces are equal and opposite, the forces are working against each other, therefore it cannot come undone. Stuff the lubricant............if there is brake fluid swimming around the thread, then it is almost certainly going to lead to corrosion........and when I do up the nipples on my brakes, I always run a tissue taper down into the holes when finished to soak out any excess fluid.....so I can check for leaks and avoid splashes on paintwork etc.
Use your hankie...........your missus says you always get a clean one when you go out into the garage...........:wink:
Al, we are arguing more or less from the same page. I'm just pointing out that without friction, compression won't work on its own. You have to have both. The thread of the bolt pushing up from the end of the nipple (where the seal is) will push the nipple, or the head of the bolt will pull the bolt, up out of the hole, in either case - that equal and opposite reaction you correctly mentioned. Friction acts to prevent the two threads sliding past each other, counter-acting the force that drives the bolt out of the hole. More compression means more friction, and to achieve that friction you need to tighten (aka torque) the nipple or bolt sufficiently (whether by nipping, guestimating, finger-tight-spannering or torquing according to the manual).
This debate has gone too far regardless of the physics..... ......I refer the honourable gentleman (and the dishonourable ones) to the second post in this thread (or if you like, the / my first answer)....it was a simple question.......all it needed was simple answer, which he got.
