Ring Torque Specs

Discussion in 'Miscellaneous Sako parts' started by ColColt, Nov 11, 2013.

  1. ColColt

    ColColt Well-Known Member

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    This has probably been brought up before but I couldn't find any info. What are the torque specification for mounting the Sako rings? I have a rifle coming in a few days that has a scope on it but may change it out and wasn't sure what the torque in inch/pounds should be.

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  2. misako50

    misako50 Sako-addicted

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    ColColt- The reason you haven't found the information here is because it hasn't been covered. All things considered, scopes are not created equal so there is no constant like a set amount of torque for the scope mounts. Scope mounts are not created equally either. Some scope tubes are real susceptible to crushing while others can stand up to some over tightening. If you are using Sako mounts in the vintage era, there are some good general things you need to know. Let us know what you plan to put on and be aware that the older Sako rings come in at least 26MM and 25.4MM. -Misako
     
  3. ColColt

    ColColt Well-Known Member

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    Looking at the scope it looks to me like someone didn't get the rings evenly tightened. So, I may try to do that properly but wasn't sure about the torque. If I decide to swap it out it will be with a Leopold VX-2 target scope 6-18X. Both of these scopes have a 1" tube.
     
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  4. kevinlg

    kevinlg Well-Known Member

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    It appears that the front top ring half.....has been reversed.
     
  5. ColColt

    ColColt Well-Known Member

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    How can you tell that and does it matter? OK, I see what you mean. They indent on the front one is on the side shown whereas the indent on the back top ring is on the other side. Which is right?
     
  6. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    The little index marks appear on both top and bottoms of the rings on the right hand side only and are very slightly in different places on the front ring and the rear ring. This allows you to not only turn the ring top the right direction, but put it on the ring bottom it is matched to. The rings are drilled to a pretty close tolerance, but these older ones are hand machined, or at least partially so. Swapping the ring tops or turning them the opposite direction may not give a well-matched fit and can put stress on the scope, or perhaps cause ring marks. The person who mounted the scope in the photo apparently paid no attention to these index marks.
     
    Last edited: Nov 11, 2013
  7. ColColt

    ColColt Well-Known Member

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    That's one of the reasons I was seeking torque specs for those rings. I know on Leopold they're about 21 in/lb but wasn't sure about these. I figured I'd probably have to remount the scope or replace it.
     
  8. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    The Leupold rings use just one screw per side and it is, I believe, a #8 screw. The Sako uses two smaller screws per side, which are metrics and closer to a #6. So, whatever the proper torque for the larger screws you would want to use a lesser amount for the smaller ones. Typically, an amount which does not risk "buggering" the screw slots is about right. I've never seen a scope tube damaged with properly mounted Sako original rings.
     
  9. ColColt

    ColColt Well-Known Member

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    You may be right but it seems to me the Leopold base screws are #8 while the rings are #6. You don't want to get ham handed with those little jobbies!
     
  10. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    My caliper measures the Leupold single ring cap screw diameter at .162", while the Sako double ring cap screws measure .135". Not sure what "numbers" these correlate with, but that will give you an idea of the difference, along with some idea of the difference in how much torque should be applied to each.
     
  11. tslans

    tslans Well-Known Member

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    If any one is interested.

    The limiting factor of the torque that can be applied is the yield stength of the screw - the force at which the screw starts to stretch not its ultimate tensile strength when it breaks.

    Here is a handy source for calculators: http://www.engineersedge.com/calculators/torque_calc.htm

    The Sako ring screw has a diameter of about .138 inches. I used steel with yield of about 50,000 pounds to to make the screws that I sell. I used a clamping force of 300 pounds per screw at a safety factor of 80% of the yield strength, and calculated the force at diameter at the root not the outside diameter to come up my recommendation of 6 to 8 inch pounds of torque.

    The Leupold #8 screw has a major diameter of .164 inches. At their recommended 21 inch pounds of torque there is about 640 pounds of clamping force per screw or 1280 for two screws. 1280 pounds divided by the 4 screws on a Sako ring is 320 pounds of clamping force per screw. Input 320 pounds into the calculator and the major diameter of .138 of the M3.5 Sako ring screw yields a torgue of 8.8 inch pounds for each of the Sako ring screws. Rounding down for a 80% safety factor yields 7 inch pounds.

    tslans
     
    Last edited: Nov 12, 2013
  12. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    Tracy: Great explanation, technical yet understandable.

    As an aside, there are some very precise applications in which screws (or bolts) are actually torqued until they stretch a certain amount. I was told by a credible airplane mechanic that the rod bolts on an airplane engine are not torqued to a certain tightness, but rather are torqued until they stretch to a certain length as measured with a caliper. Considering the strength of the steel they're made of, that's tight!
     
  13. ColColt

    ColColt Well-Known Member

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    Seven inch/pounds doesn't seem like much at all. You'd think Sako would have provided, as Leopold does, some specs as to how tight their rings/mounts should be. I've read that the large thumb screws for the base should only be hand tight...plus maybe a slight turn of about 1/8-1/4 turn with a screwdriver but I hadn't read of the rings themselves. I feel sure I'll be taking those rings off and positioning them properly as well as checking the alignment whether I use the Leopold 16X now on the rifle or another.

    I located the instructions for the Leopold mount and rings and they indicate for the medium rings, which is what I have, a diameter of .770". their #6 screws torque is 22 inch/lb and the #8 is 28 inch/lb. These figures are for the base. The rings are #8 and torque value is 28 inch/lb. Since the base screws were #8 I noticed the ring screws were smaller so they had to be a #6.
     
    Last edited: Nov 12, 2013
  14. gunner620

    gunner620 Well-Known Member

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    ColColt, the original Sako split ring screws will break if over tightened. The screws that tslans had made are in my opinion better than the original screws from Sako. The torque spec. given 6-7 lb. in. will hold the scope securely given the rings have not been modified. As far as the large clamping nut goes, since the rings clamp on the tapered dovetail recoil tends to tighten them. Over tightening the clamps can also damage the rings. In the past one of our members suggested this method (use a penny file a notch with a round file (this will allow the penny to clear the threaded stud and seat in the slot) use what ever tool you wish to hold and tighten the nut,when the penny starts to bend they are tight enough. This method works for me. Jim
     
  15. ColColt

    ColColt Well-Known Member

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    From the photos I'm surmising these are original ringmounts. I don't know how knowledgeable the fellow was that mounted the scope, however. Judging from the fact h e got the rings turned wrong I won't know until I get the rifle. I sure don't want to bend or over tighten things but I think they do need checking.
     
  16. tslans

    tslans Well-Known Member

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    The Leupold torque recommendations are for grade 8 steel 150,000 tensile, 130,000 yield. Plug 22 inch pounds in the calculator and the result is 800 pounds clamping force per screw - 1600 for 2 screws / 3200 for 4 screws. The screws that I had made used 75,000 tensile, 50,000 yield steel. Cut the torque in half to 11 pounds and the 4 screws on the Sako rings yield the same clamping force as the Leupold recommendation. And, you don't want to stretch any bolt past its yield stength to the point where it is permanently stretched. It is weakened and will eventually break. That is why I used a safety factor and recommend 6 - 8 inch pounds. We also reduced the probability of popping off the head by machining a chamfer on the edge of the head of the screws to reduce the need for high torque to properly tighten the clamp because of the interference with the fillet at the bottom of the counterbores on the clamps. To further reduce the chance of breaking off the head we machined a fillet where the shank meets the head. As designed with the 75,000 tensile steel the screw should tolerate being tighted to 10 - 12 inch pounds of torque.


    tslans
     
    Last edited: Nov 13, 2013
  17. emmerth

    emmerth Well-Known Member

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    tslans, you are the man. I just checked the torque on a set of rings that I recently installed (without the knowledge that you provided) and they were all approximately 10lbs and I thought I torqued them pretty tight when I did the install. I guess it depends on the tool you are using. Mine was a small screwdriver set (the one with different size tips that you swap out). I think anything past that and you will strip the ring out (which I have done or was damaged before me by previous owner).

    In reference to the large clamping nut, I use the penny method that gunner mentions and have never had any issues.
     
  18. ColColt

    ColColt Well-Known Member

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    That is most interesting. I have a suspicion that one or two, possible all those screws on those rings may be buggered up. Do you sell those screws you mentioned? The old ones may indeed need replacing. My Wheeler "Fat Wrench" doesn't go down to 6-8 inch/lb but rater 10 but I think you can set it a bit below 10 which should give around those specs mentioned.
     
  19. tslans

    tslans Well-Known Member

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  20. stonecreek

    stonecreek SCC Secretary Forum Owner SCC Board Member

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    Tracy's screws are first class and seem superior to the original Sako screws. I've broken a couple of Sako screws (back in the years of my devil-may-care youth) which seemed to be somewhat brittle. Fortunately, my more mature self was able to drill out the broken screw and salvage the rings. I've had Sako rings come to me with stripped threads in the ring bottoms, and with drill-out holes rethreaded to a larger diameter. I've also had Sako rings come with horrrrribly buggered screw heads and screw threads which looked like they were fired with potassium chlorate primers and never cleaned. Tracy's screws have restored at least a couple of fine old Sako ringmounts to working condition for me dozens of other Sako shooters.
     

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