Torque Question (involving NF and Spuhr)

[RedBreast21]

Most people here are probably familiar with Spuhr mounts. 6 screws per "ring", and from 21-25 in-lb per screw. I have I 6-8 Spuhr mounts and have never had any issues (and shouldn't for what they cost). However, I recently picked one up (30mm, 1.89") and mounted a NF NX8 1-8 in it.

I mounted it as I always do, using a FixIt Sticks torque limiter, and started in the middle two screws on each ring to resistance/alternating and then torque to spec. Then I move to the outside 4 screws and do the X pattern alternating to resistance and then to torque. Here's where my question comes in . . . once you torque those outside screws the middle ones are now looser (obviously) and I continue to torque down until all 6 screws are limited by the limiter. Is the torque somehow additive? If it's tightened to 21 in/lb and then you go back over it again after it's been "loosened" by tightening the outside screws on the rings, does that mean it's now MORE than 21 in-lbs?

Now here's the why: after mounting the optic (at the range) and zooming into the targets at 500 yards, things were very, very blurry. I brought it home, set it upon my tripod and looked off my deck into the surrounding hills and confirmed that it wasn't some weird thing at the range. I emailed and then spoke to NF and they said "sure, send it back in", but then I started thinking. What if it's the mount? So, I took off the front "ring" and the image was clear again. I then completely removed the optic, made sure it was 100% centered (the turret housing relative to the rings) and retorqued the rings. The blurriness had returned.

So, I grabbed the a much lower torque limiter and tightened it down just to snug and the image is clear again.

Knowing what I know about NF, it's hard for me to believe there is anything wrong with the scope body such that it's out of round. But the same is true of Spuhr, too.

What are your thoughts? I always think I'm not an idiot, but I consistently prove myself wrong. I'm wondering if this is one of those times.

 

[Cutout]

I hope you mean "inch pounds" and not "foot pounds."

 

[Taylorbok]

I hope you mean "inch pounds" and not "foot pounds."

if he's using fix it sticks it's inch lbs.

I use MDT and ARC mount's. The MDT I go over the screws several times until they are all limited by the limiter and never had an issue. The ARC only has one bolt so it get's torqued once and then double checked. That ARC mount is tittie's BTW and don't think I'll buy anything else again.

 

[Arc Light]

The torque value is not additive, if you set it to 21 in-lbs that's what the screw will be torqued at, no matter how many times you go over the screw. If you lubed the threads and didn't reduce the torque by say 25%, then you'll get more clamping force vs dry threads and could cause damage to the scope or mount.

I've never used Spuhr mounts, but 21-25 in-lbs on the screws seems excessive to me. I've never used more than 15-18 in-lbs on dozens of rings and mounts and never had an issue with an optic moving. I would start at 15 in-lbs and see if the scope moves.

 

[Cutout]

 

[RedBreast21]

I hope you mean "inch pounds" and not "foot pounds."

Yes, lol. I'm so used to typing "FPS". I just edited to clarify.

 

[Cutout]

Yes, lol. I'm so used to typing "FPS". I just edited to clarify.

Lol, I get it. Just making sure.

 

[RedBreast21]

The torque value is not additive, if you set it to 21 in-lbs that's what the screw will be torqued at, no matter how many times you go over the screw. If you lubed the threads and didn't reduce the torque by say 25%, then you'll get more clamping force vs dry threads and could cause damage to the scope or mount.

I've never used Spuhr mounts, but 21-25 in-lbs on the screws seems excessive to me. I've never used more than 15-18 in-lbs on dozens of rings and mounts and never had an issue with an optic moving. I would start at 15 in-lbs and see if the scope moves.

I did not lube. As @Cutout noted, Spuhr calls for 15-25 INCH/lbs.

 

[koshkin]

Conical head screws in Spuhr mounts occasionally werak havoc on optics. They pull the ring halves laterally when the machining is not perfect. That creates shear stress on the scope tube. Most of the time Spuhr mounts work fine, but as far as expensive mounts go, I have seen more problems with Spuhr mounts that with all the rest combined and not by a small margin.

ILya

 

[1911hombre]

Didn't it used to be that Spuhr wanted the user to apply rosin on the scope tube "if you encountered slippage" or some shit?? Or maybe a chunk of beer can shim, I forget. Oh, and if the threads strip, just go ahead and use the next bigger self-tapping screw. FFS. I like good mounts but Spuhr seems so.... Diva. I also believe the conical head screws by virtue of that design are inconsistent in regards to stretch vs. observed torque, which may be the root of some of their problems.

 

[hafejd30]

My 7-35 atacr is torqued to 25 in lbs in my spuhr with blue loctite. No issues with the rings or scope

When the crossbar on the pic rail cracked I wasn’t happy. But the new one has been mounted several times and is still in one piece

The NX8 may be a thinner tube. Try 15-18 lbs.

 

[chevy_man]

It still baffles me people pay spur money only to get a sub par product. The number of products that are half the price and have fewer issues, spur has great marketing!