Holding strength vs. compression. You do not need to squash your tube in order to hold it. </div></div>
Yes, actually you do. That’s where the force of friction comes from. You can have 100% contact but with no force to the normal you will have no force of friction and the scope will be free to move.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Here's a guy who makes a single split ring that is somewhat nonconventional</div></div>
I wasn’t talking about those rings. Those rings operate in a completely different manor than the Larue mount. Completely different.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">The bottom screws on the single split rings like Larue and Warne don't really serve the function of holding the scope. </div></div>
Bingo. But the hinge in the ARC ring does. It reacts with the same force as the screws on the other side. Completely different.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Only the top 2 screws impart any real holding forces on the scope.</div></div>
Exactly. And whatever clamping force they develop, the scope only sees that minus the amount of force used up bending the rings and prying at the screws on the base.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">I don't agree with the bold. </div></div>
Draw a free body diagram and balance it. Then you will. There is nowhere else for the force to go. Any fitment issues resulting in localized areas of increased pressure (note the different direction) will not change this. They can’t.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> however, the strap clamp type solution posted by Salmonaxe (the ARC rings) is a better solution for the following reason.</div></div>
Again, I wasn’t talking about those rings at all. They work completely differently and are a very good setup. However:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> results in 4 point contact, not full clamping force. This means that for an equal amount of axial friction force imposed by the rings, the contact points must be under significantly higher load due to the reduced contact patch. </div></div>
First, as stated above, even in cases where the “4 points of contact” is occurring, this does not reduce the total clamping force on the scope tube. It can’t.
Secondly, without getting too far in the weeds here, please keep in mind that the “4 points of contact” occurring at all requires specific assumptions about fit-up and relative stiffnesses of the assembly which are often not the case.
But again, I was not commenting on the ARC rings as they have nothing to do with the original subject and I believe they are a very nice design. People should not encounter the slippage with them that is sometimes encountered with the vertical split mounts that we were originally talking about.
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Thanks for clarifying the points you were making. The equal forces of friction result in higher contact pressures because of the reduced contact patch with the deformed shape.
I should clarify my point about the clamping force. It goes into clamping the tube, however it ends up driving the corners into the scope tube from the elastic behavior of the materials. The rigid body behavior balances out cleanly like you said.
My verbage choice was poor in the post you're referencing.
The fitment issues of the scope rings is one problem to worry about, but even with a diametral tolerance mismatch that causes problems the elastic behavior of the split clamp design creates small, localized regions of high contact stress.
High contact stresses are evident when the scope has clamp marks on it that correspond to where the split line of the rings is.
The clamping force is focused into that region and is causing a number of issues, in the worst cases the plastic deformation is so bad as to render the internals of the scope useless.
I just checked it again to verify since it's been a while since I wrote the initial review on these months back, and indeed the freebody balances out as it must. But that is a rigid body behavior and it assumes equally infinite stiffness of the parts in contact.
Look at a small region of that freebody, my main point about the "4 points of contact" is really 4 small patches of contact driven by the corners of the scope cap rotating under the induced moment from the screw forces to drive the cap diameter smaller and therefore cause high contact stresses. This is where the rigid body assumptions break down and the elastic behavior drives the analysis.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Secondly, without getting too far in the weeds here, please keep in mind that the “4 points of contact” occurring at all requires specific assumptions about fit-up and relative stiffnesses of the assembly which are often not the case.</div></div>
If you'd like to discuss more via PM's or email I'd like to as I see certain stiffness issues but not ones which would preclude the behavior I described above to neutralize the stiffness assumptions to get away from a snowman shaped deformation pattern. Would you mind discussing it more?
The stiffness issues that I see are this:
High aspect ratio tubes (large OD to wall thickness ratios) are very soft in localized radial contact.
The clamp shell on a traditional mount has a very stiff local region near the clamping screws.
Large forces are in play with a soft scope body and a stiff contacting point.
Even if the same materials are used the load path from the scope ring to the scope body in the radial direction is extremely poor.
Rigid body behavior would have no difference in the various forms of clamp design, however, the elastic behavior is driving it I think.
I suppose it does boil down to your statement here:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">
Exactly. And whatever clamping force they develop, the scope only sees that minus the amount of force used up bending the rings and prying at the screws on the base.</div></div>
The efficiency to which the screw torque is transmitted into axial load and then into frictional force via contact pressures is the defining trait between the various designs.
I thought you were talking about the ARC rings in addition to the various split clamp designs and the over-arching comparison wasn't making sense in my head.
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making an epic quote</div></div>
and by epic quote I mean how many quotes can be stacked on top of each other before Snipers Hide implodes and the girl from "the ring" comes out of my screen and kills me?
