Torque spec for thread in cantilever boss stud
11-14-22, 01:14 PM
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Torque spec for thread in cantilever boss stud
I have a Kenesis aluminum fork and steel M10 threaded cantilever brake boss studs. What would be a good torque value when installing?
11-14-22, 01:17 PM
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WOW... Oddly this is a hard question... **********???
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11-14-22, 01:24 PM
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I'm not sure but I am curious about differences in cantilever post length. Also, if the post is too long, I saw a Cyclus tool recently that "faces" the ends of cantilever posts down. Has anybody seen something like this?
11-14-22, 01:25 PM
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Maybe the torque spec is attached to the brake and not the fork.
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11-14-22, 01:41 PM
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Snug it down. If it loosens up, then tighten a tad more next time. Rinse and repeat as needed.
11-14-22, 05:50 PM
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Short answer -- 8-9 nm dry or 6-7nm lubed*, but please read on before taking this as gospel.
Screw torque specs depend on the screw diameter, thread pitch, and material. Do a search for "metric screw torque specs" or similar and you should find the info you need. Note, that the torque spec are very different based on the actual material involved.
A better understanding comes from understanding how treads work. Screws stay tight through friction. The amount of friction depends on tension within the section from the last thread to the head. So proper torque is about tensioning that section of the bolt so it'll exert continued force on the threads. The ratio between torque and tension depends on the slope of the thread helix and the material friction.
Since it's about tension and elongation, the material is very important, and the published data will be the MAXIMUM for each material. What would snap a brass bolt, won't be enough to properly tension a high strength chrome-moly bolt. Working from that max. you might go lower if for example a high strength bolt is threaded into aluminum. So, assuming the folks who designed Canti brakes and the studs know what they're doing and spec'd tge right bolt size, you can use the published specs as a guide. Also consider things that might change the required torque such as lubed vs. dry threads, use of a traction compound of some kind, etc.
Using the above as a guide and understanding that it's about tensioning the bolt, you can let your hands guide you. As you tighten a bolt the torque will be low until it begins to bottom. Then it'll rise as you take up any slack and compress the assembly, rising still higher as the bolt begins to tension. At this point the torque will begin to rise very quickly as the bolt stretches, and you'll feel the "wall" . That's the proper tension, the bolt is under decent tension, but has plenty of room before snapping. That room is critical because the application can add load on then bolt, taking it from highly loaded to overloaded if you went too far.
FWIW- we shouldn't forget that folks have been tightening bolts for eons without special tools to measure torque, and except for critical applications we should be able to continue to do so.
*assumes typical commercial grade (60,000psi) steel bolt.
Screw torque specs depend on the screw diameter, thread pitch, and material. Do a search for "metric screw torque specs" or similar and you should find the info you need. Note, that the torque spec are very different based on the actual material involved.
A better understanding comes from understanding how treads work. Screws stay tight through friction. The amount of friction depends on tension within the section from the last thread to the head. So proper torque is about tensioning that section of the bolt so it'll exert continued force on the threads. The ratio between torque and tension depends on the slope of the thread helix and the material friction.
Since it's about tension and elongation, the material is very important, and the published data will be the MAXIMUM for each material. What would snap a brass bolt, won't be enough to properly tension a high strength chrome-moly bolt. Working from that max. you might go lower if for example a high strength bolt is threaded into aluminum. So, assuming the folks who designed Canti brakes and the studs know what they're doing and spec'd tge right bolt size, you can use the published specs as a guide. Also consider things that might change the required torque such as lubed vs. dry threads, use of a traction compound of some kind, etc.
Using the above as a guide and understanding that it's about tensioning the bolt, you can let your hands guide you. As you tighten a bolt the torque will be low until it begins to bottom. Then it'll rise as you take up any slack and compress the assembly, rising still higher as the bolt begins to tension. At this point the torque will begin to rise very quickly as the bolt stretches, and you'll feel the "wall" . That's the proper tension, the bolt is under decent tension, but has plenty of room before snapping. That room is critical because the application can add load on then bolt, taking it from highly loaded to overloaded if you went too far.
FWIW- we shouldn't forget that folks have been tightening bolts for eons without special tools to measure torque, and except for critical applications we should be able to continue to do so.
*assumes typical commercial grade (60,000psi) steel bolt.
Last edited by FBinNY; 11-14-22 at 06:19 PM.
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11-14-22, 06:28 PM
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Many of the removable (thus threaded into a welded on base) brake boss use a thread locking compound to add extra insurance from a boss loosening from its base. Andy
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11-14-22, 06:43 PM
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most of these that i've removed are Tighter than the hubs of Hades... i've Spread/ruined a 9mm trying to get one out in the past.... it was in a steel frame and Old.. Let the Blue Locktite do it's job. FBinNY quoted a brake arm retainer bolt torque specification for a 6mm metric fastener, Not a Mounting post spec. Remember that you are mounting the post into Aluminum so going insane on the torque will NOT be good... is it a Coarse thread? It should be, going into aluminum...
So.. A drop of Blue Locktite, put the post in Tight but not Crazy tight... then let it set up overnight.
To guess at a torque spec, i'd say 15 lb/ft... 20N-m
Last edited by maddog34; 11-14-22 at 06:58 PM.
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