Torque wrench woes

[RocketRacing]

The veterans will know this, but i figured i would share, as I am on the learning curve.

About a year ago i invested in a pro torque wrench set. I always use carbon paste. I always follow torque specs, and lean to lower end of specs. I adjust 2-4 bolt pieces a bit at a time. I never left the wrench pre-loaded.

I got lazy and used the torque wrench to loosen bolts. I never verified accuracy.

Torque wrenches can loose “up to 10%” of accuracy in the first year. You are not supposed to loosen bolts with torque wrenches (says the internet, fwiw) and doing so can alerter torque wrench accuracy.

This week i snapped a bolt on a stem. I immediatly ordered a new torque wrench (park tool, goes to 2nm). The stem was fine (bolt replaced), but my (freshly cut) carbon steerer had clamp marks. Lucky for me, no cracks, so it is fine.

I checked my carbon saddle, it was ok. My handmade carbon post... cracked and crushed. It is being sent for repair. My new eebrakes... seem to be fine.

None of this stuff is cheap if you get my drift.

I tested the old torque wrench for the new... the old one set at 4nm, was making more like 6nm. So imagine what 5 and 6nm was doing!

Check your torque wrench accuracy. Don’t loosen bolts with it, and go as low on the torque as is tolerated. Just because you can go to 5-6nm, don’t do it if you don’t need to, because who knows how accurate your torque wrench really is.

That is all

[adilosnave]

Well now I'm scared!! How can you check for accuracy?

[caballero]

Be sure to buy a quality tool !

I knew of a shop that prided itself on building 5 figure machines but would often have customers reporting cracked bars, posts, seat clamps etc.. which they in turn put back onto the customer.

Turned out the dodgy, bought on the cheap torque wrenches were massively under reading. They never made their customers right though.

[bikeboy1tr]

Seems strange that the bolt snapped as stem bolts are normally 5mm or 6mm diameter and it would normally take some pretty good torque to snap a 5mm bolt. The kind of torque that would make you say wow this is way to much for carbon clamps on carbon steerer tubes. I would guess that the bolt was defective or had some previous fatigue of some sort. Most times I dont use a torque wrench and have never had any issues. I also believe that you would have to overtorque assembled parts by a good bit before they fail. Perhaps the seatpost was not able to withstand the rated torque it should have.

[C36]

Well now I'm scared!! How can you check for accuracy?

In industry, yearly calibration is a minimum and a quick internet search should allow you to find places to send for calibration, worse case a industrial hand tools dealers (mean real hand tools -Facom for example-, not the Mickey Mouse bike brands ) either should be able to do or provide places to have it done.


Envoyé de mon iPhone en utilisant Tapatalk

[Bigger Gear]

I have a PRO torque wrench as well. I've used it quite a bit, but I also have the older Park beam-type that is for 2-8 N-m. I can use the Park to keep track of the PRO and I have found the PRO consistently is less torque applied for the set value. For example, 5 N-m on it is usually about 4.5-4.8 on the Park beam. Not sure if Park still makes the beam. Feedback has a new compact torque wrench that is also like a beam, in that it relies on a spring and can be zeroed by the user. These tools are not as elegant as a click-wrench but as long as the indicator points at zero with no load they are pretty accurate.

Going forward for the OP, it is also a good idea to get a "feel" for torque and not rely 100% on the wrench. Between bicycles and motorcycles I've been pulling wrenches for more than 40 years and in general I only use the torque wrench for the final movement of the bolts. I can reliably tighten a M3 or M4 bolt to around 4.5 N-m just by using the same wrench and keeping my operation angle with my hand and arm consistent. I think it is good to be able to feel the torque, especially in the event where a click wrench could indeed have a random failure. When I'm using the PRO click wrench, I definitely don't have the same feel for the torque.

One of these days I'll break down and by the Effeto Mariposa but not just yet....

[RocketRacing]

Feel is key. I had a decient “feel” and my brain kept saying “gee, does it really need this much force?” My mistake was trusting the torque wrench for the final adjustment, and not my gut until it was too late. But i think mis-calibration creeps up on you... it is not as if one day it went 50% off spec. Or maybe it was always off... and i just got lucky till now. But i suspected it migrated over time.

[RocketRacing]

Fyi, big boy toys Snap-On 1/4th torque wrench that does about 1nm to 27mn with a 0.1nm resolution is about 500usd.

https://store.snapon.com/Standard-Model ... 42510.aspx

Q: how do you spot a proper weight weenie?
A: when his/her torque wrench costs more than his lightweight bike.

But there is something to be said... do you trust you exotic carbon frame/fork or bars/post to a 60$ torque wrench. And there i thought Pro would be solid.

[bikeboy1tr]

Anything that has the word, Snap-On usually means big $. Proto is another quality tool and not normally as expensive like the Snap On. Actually I made the mistake just the other day of torquing a left hand thread and then realizing that they dont click off when set for loosening. Fortunately I stopped before getting carried away and stripping something expensive (CeramicSpeed BB). Guess I better get that wrench calibrated. Like Bigger Gear says its good to have a feel for these things before they get Fubar.

[RocketRacing]

Seems strange that the bolt snapped as stem bolts are normally 5mm or 6mm diameter and it would normally take some pretty good torque to snap a 5mm bolt. The kind of torque that would make you say wow this is way to much for carbon clamps on carbon steerer tubes. I would guess that the bolt was defective or had some previous fatigue of some sort. Most times I dont use a torque wrench and have never had any issues. I also believe that you would have to overtorque assembled parts by a good bit before they fail. Perhaps the seatpost was not able to withstand the rated torque it should have.

That is my point, the parts should not have been seeing the torques they saw. What i thought was on spec was going over spec. The bike was new to me, so how many times did i torque, remove and retorque with part/fittment changes? Each time I may have been doing added damage by being over spec a few nm.

The issue is not that the part is being crushed. I think carbon can take that punishment to a high degree before it fails, as long as the force is uniform. The issue is the clamp design, and what happens when the clamp ends are pulled too close together by the bolts (by high torque).

A clamp is designed to clamp a small range of diameters in a circle of specified diameter. If you exceed that diameter by clamping too hard, the metal ends of the stem by the bolts get too close together, and the inner part of the stem begins to cut into the carbon. They start with harmless bite marks, but progress to failure with sufficient torque, and repeat insult.

My stem/steerer was a one time thing. My lbs lets me torque all my “exotic lightweight parts” because they know i am careful with all the specs, and using a torque wrench. The steerer was cut last week. The “bite” marks are only where i clamped the new position. Thus my theory that something went off on my wrench... and maybe faster than a gradual process.

Back to the stem bolts... they had been on and off a lot due to me setting my position, and adjusting, readjusting. Metal fatigue is real and the bolt broke in the space between both clamping ends. As you force those ends too close together, not only does the stem ends bite into the carbon, but the straight path that the bolt takes to connect both sides of the stem now begins to need to bow. A bowing bolt that is also asked to twist, as asking for failure. Maybe not today... but some day. Mine literally exploded.

Being a weight weenie stem, my bolts were of a thinner type than most oem stems. One could say fragile (chro moly). But I will say that this probably saved my carbon fork. The bolt broke before serious damage was done to the steerer.

Water under the bridge. Ironically when i got my bike, the oem carbon post had evidence of crushing (no cracks). A bike shop employee owned it, and i was surprised he would let that happen. Maybe he didn’t let it happen and had a similar issue to me...

[bikeboy1tr]

Seems strange that the bolt snapped as stem bolts are normally 5mm or 6mm diameter and it would normally take some pretty good torque to snap a 5mm bolt. The kind of torque that would make you say wow this is way to much for carbon clamps on carbon steerer tubes. I would guess that the bolt was defective or had some previous fatigue of some sort. Most times I dont use a torque wrench and have never had any issues. I also believe that you would have to overtorque assembled parts by a good bit before they fail. Perhaps the seatpost was not able to withstand the rated torque it should have.

That is my point, the parts should not have been seeing the torques they saw. What i thought was on spec was going over spec. The bike was new to me, so how many times did i torque, remove and retorque with part/fittment changes? Each time I may have been doing added damage by being over spec a few nm.

The issue is not that the part is being crushed. I think carbon can take that punishment to a high degree before it fails, as long as the force is uniform. The issue is the clamp design, and what happens when the clamp ends are pulled too close together by the bolts (by high torque).

A clamp is designed to clamp a small range of diameters in a circle of specified diameter. If you exceed that diameter by clamping too hard, the metal ends of the stem by the bolts get too close together, and the inner part of the stem begins to cut into the carbon. They start with harmless bite marks, but progress to failure with sufficient torque, and repeat insult.

My stem/steerer was a one time thing. My lbs lets me torque all my “exotic lightweight parts” because they know i am careful with all the specs, and using a torque wrench. The steerer was cut last week. The “bite” marks are only where i clamped the new position. Thus my theory that something went off on my wrench... and maybe faster than a gradual process.

Back to the stem bolts... they had been on and off a lot due to me setting my position, and adjusting, readjusting. Metal fatigue is real and the bolt broke in the space between both clamping ends. As you force those ends too close together, not only does the stem ends bite into the carbon, but the straight path that the bolt takes to connect both sides of the stem now begins to need to bow. A bowing bolt that is also asked to twist, as asking for failure. Maybe not today... but some day. Mine literally exploded.

Being a weight weenie stem, my bolts were of a thinner type than most oem stems. One could say fragile (chro moly). But I will say that this probably saved my carbon fork. The bolt broke before serious damage was done to the steerer.

Water under the bridge. Ironically when i got my bike, the oem carbon post had evidence of crushing (no cracks). A bike shop employee owned it, and i was surprised he would let that happen. Maybe he didn’t let it happen and had a similar issue to me...

Oh okay that really does explain everything then and yeah I agree the clamps on the stem will distort terribly with overtorquing and deforming the bolt. Bolt materials of different sorts will have their own torque ratings dependant on diameters and then of coarse on application. And like you say the bolt breaking probably saved you much agony and expense on carbon forks. I guess calibration of tools is a good ideal. I know for industry to keep their ISO ratings calibration is something that needs to be done on a regular basis.