Carbon fiber and torque wrenches

antfly

If I recall the video showed a carbon frame being squashed in a vice and when it was released it just popped back to it's original shape.

desweller

IME of training people in industrial assembly areas, most will use a torque wrench incorrectly anyway. Plus they are notoriously unrepeatable; 10 to 15% R+R is not uncommon.

You could get most of the way to avoiding involuntary damage by selecting tools with the right length of handle IMO; stick to short handles for low torque items, breaker bars for high torque ones. Never met anyone who could put 90Nm on with a 6" wrench!

mfin

Most 4 or 5nm settings... get a Ritchey Torque Key, try it, try it on a bolt that doesn't hold any Carbon parts first. When you've done that, its pretty obvious that things don't need what that torque key will tighten to, and its easy to test with an allen key to then know the feel of what to tighten something to.

Torque wrenches on Campag ultra torque chainsets are a waste of time too IMO, when you've done it with a torque wrench it becomes apparent that the tightness is 'f**king tight'.

Anyway, there's no way in hell Id tighten a stem onto carbon bars with the full whack of a torque key.

...anyway, like people have said, if you're someone mechanically minded and sympathetic to the materials you will normally know what to do anyway without a torque wrench, and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

dennisn

mfin wrote:

........... and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

Never used the stuff. Never had a seatpost or bars slip. To me it's a solution for a problem that doesn't exist, and a somewhat expensive solution. Just what the makers want you to buy. It gives people the sensation that they are doing something technical and therefore is worth any price. To top it off it would appear that whole bunches of people have bought into it. Exactly what the manufacturer's want. :roll:

antfly

Just because it hasn't happened to you doesn't mean it doesn't happen, I never had a carbon post that didn't slip. It cost a few quid and works, it's not expensive.

mfin

dennisn wrote:

mfin wrote:

........... and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

Never used the stuff. Never had a seatpost or bars slip. To me it's a solution for a problem that doesn't exist, and a somewhat expensive solution. Just what the makers want you to buy. It gives people the sensation that they are doing something technical and therefore is worth any price. To top it off it would appear that whole bunches of people have bought into it. Exactly what the manufacturer's want. :roll:

Well, seeing as you've never used the stuff... if you try it you will find the parts fit together already gripping to a good extent, its obvious when you use it. But you haven't used it so you wouldn't know.

For carbon seat posts on carbon frames you'd be a bit daft not to use it. One slip and you've got a nice scratched seatpost. You're just speculating on something when you haven't used it and have no experience of it.

dennisn

mfin wrote:

dennisn wrote:

mfin wrote:

........... and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

Never used the stuff. Never had a seatpost or bars slip. To me it's a solution for a problem that doesn't exist, and a somewhat expensive solution. Just what the makers want you to buy. It gives people the sensation that they are doing something technical and therefore is worth any price. To top it off it would appear that whole bunches of people have bought into it. Exactly what the manufacturer's want. :roll:

Well, seeing as you've never used the stuff... if you try it you will find the parts fit together already gripping to a good extent, its obvious when you use it. But you haven't used it so you wouldn't know.

I'm not the type to buy stuff because I might need it. I've never needed it so I'll leave the buying of what I consider useless stuff to the rest of you. Buy all ya want. Stock up on it if you must. Remember, it's a bicycle we're talking about, not a rocket ship. I realize that most people need to feel and talk like they are working on some highly technical project but in the end it's still just a bicycle.

mfin

dennisn wrote:

mfin wrote:

dennisn wrote:

mfin wrote:

........... and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

Never used the stuff. Never had a seatpost or bars slip. To me it's a solution for a problem that doesn't exist, and a somewhat expensive solution. Just what the makers want you to buy. It gives people the sensation that they are doing something technical and therefore is worth any price. To top it off it would appear that whole bunches of people have bought into it. Exactly what the manufacturer's want. :roll:

Well, seeing as you've never used the stuff... if you try it you will find the parts fit together already gripping to a good extent, its obvious when you use it. But you haven't used it so you wouldn't know.

I'm not the type to buy stuff because I might need it. I've never needed it so I'll leave the buying of what I consider useless stuff to the rest of you. Buy all ya want. Stock up on it if you must. Remember, it's a bicycle we're talking about, not a rocket ship. I realize that most people need to feel and talk like they are working on some highly technical project but in the end it's still just a bicycle.

Dennis, you're really something sometimes. IF you used it, you would be able to tell how much more gripped the surfaces are. Now, when a sachet of the stuff costs £3 and is enough to assemble all the bits on a carbon bike and it ensures against a seatpost that might cost £100 from slipping down and being scratched forever, then its a no brainer, a bit like you ironically

dennisn

mfin wrote:

dennisn wrote:

mfin wrote:

dennisn wrote:

mfin wrote:

........... and carbon assembly paste for seat tubes etc is magic stuff anyway, wouldn't be without some of that in the toolbocks.

Never used the stuff. Never had a seatpost or bars slip. To me it's a solution for a problem that doesn't exist, and a somewhat expensive solution. Just what the makers want you to buy. It gives people the sensation that they are doing something technical and therefore is worth any price. To top it off it would appear that whole bunches of people have bought into it. Exactly what the manufacturer's want. :roll:

Well, seeing as you've never used the stuff... if you try it you will find the parts fit together already gripping to a good extent, its obvious when you use it. But you haven't used it so you wouldn't know.

I'm not the type to buy stuff because I might need it. I've never needed it so I'll leave the buying of what I consider useless stuff to the rest of you. Buy all ya want. Stock up on it if you must. Remember, it's a bicycle we're talking about, not a rocket ship. I realize that most people need to feel and talk like they are working on some highly technical project but in the end it's still just a bicycle.

Dennis, you're really something sometimes. IF you used it, you would be able to tell how much more gripped the surfaces are. Now, when a sachet of the stuff costs £3 and is enough to assemble all the bits on a carbon bike and it ensures against a seatpost that might cost £100 from slipping down and being scratched forever, then its a no brainer, a bit like you ironically

Use whatever you like on your bike. Means nothing to me if you think you need this or that. If you believe the hype then by all means buy away. And by the way, I've got a carbon seatpost that's been in and out of various frames for the last 10 years. It's scratched to hell and back, and low and behold it still works. I know you want to believe that you're working with aerospace materials and that your bike is as technologically advanced as a Mars lander but....

desweller

Hairspray works just as well. Much better value!

yaya

Most damages done by over-tightening are sheered threads in alloy or snapped bolts

I have a 3T Arx stem with one half of a titanium bolt stuck in it, waiting for me to find the time and the tools to pull it out. This happened when using a torque wrench at the correct settings, all other bolts are fine

I once snapped a seatpost collar on a carbon frame/ carbon post. Again using a torque wrench, the frame (at the time at least) was fine (now it's in the shop getting its BB shell mended)

Use your common sense ,use a wrench if you can but use it carefully!

mfin

dennisn wrote:

And by the way, I've got a carbon seatpost that's been in and out of various frames for the last 10 years. It's scratched to hell and back, and low and behold it still works.

Great, Ive got a couple that old and they don't have a visible scratch on them above the collar, and never will. Most people like to look after their expensive stuff. You're coming from a completely different angle here, but no problem that you just don't get the logic.

ricky1980

Runtothehills wrote:

ricky1980 wrote:

Not quite - carbon fibre is very strong and stiff along the fibre direction but is very weak perpendicular to it: when it's crushed across the fibres it tend to then fail very easily along the fibres as well, especially as when it's crushed the matrix fails which means the load distribution between fibres is shot.

As you say it's also brittle which means it's very susceptible to stress concentrations. If something made from aluminium/steel is overtightened or unevenly tightened so one side is stressed more than the other the material will yield plastically and sort itself out- CFRP won't, it'll just fail.

first of all, the carbon layering is not uni-direction...although they use Uni-directional carbon sheets but they are layered at varies angles to create a tube that can resist bi-axial bending as well as bi-axial shear...so no in real word composite should exhibit strength in both principle axis as well as out of plane resistance.

secondly, brittleness is a description relates to stress and strain characteristics of a material, if a material fails i.e breaks, shortly after achieving UTS then it is brittle, if it yields i.e. elongates/deforms when the stress is applied pass the UTS then it is undergoing plastic deformation and it is not consider brittle...so a material's brittleness has nothing to do with it is more susceptible to stress concentration.

all materials are susceptible to stress concentration, stress concentrations for a number of reasons, due to imperfection during fabrication, due to geometry of shapes and forms...

matt_n-2

antfly wrote:

If I recall the video showed a carbon frame being squashed in a vice and when it was released it just popped back to it's original shape.

That would merely be the matrix (resin) material suffering plastic deformation from which it can return to its previous form.

It's more than likely that the actual fibres, which provide the majority of the CFRP's properties would have fractured and therefore no longer be up to the job.

Quite often CFRP's fail but are undetectable to the eye as the fibres have failed within the matrix, often the inner surface, with the exterior surface appearing fine.

CFRP when used in bike applications are not particularly resistance to impact damage and I'm sure the areas hit by the hammer would feel like soggy wood due to fibre failure.

keef66

Re the carbon paste: for me it was a solution to a very real problem. Carbon post in an alloy frame. Tightened the clamp bolt as much as I dared but still it kept slipping down. Smear of carbon paste (free sachet from Epic who had supplied the bike) and it's rock solid with only moderate tightening of the clamp bolt.

I've since bought a tub so I can periodically remove, clean and reapply.

dennisn

keef66 wrote:

Re the carbon paste: for me it was a solution to a very real problem. Carbon post in an alloy frame. Tightened the clamp bolt as much as I dared but still it kept slipping down.

For me, this ask's the question of why would you buy something that you are paranoid about working with?
Also where did this paranoia come from? Why were you afraid to crank down on the seatpost bolt? If you thought it was that fragile how could you possibly trust it to support your weight or withstand a good pothole hit? Or was it because you had to have it, reguardless of the dangers, because it was, well, it was carbon and it's what you're supposed to have?

In other words I simply don't follow why anyone would put a fragile item on a bicycle? Especially a fairly expensive item?

pkripper

dennisn wrote:

keef66 wrote:

Re the carbon paste: for me it was a solution to a very real problem. Carbon post in an alloy frame. Tightened the clamp bolt as much as I dared but still it kept slipping down.

For me, this ask's the question of why would you buy something that you are paranoid about working with?
Also where did this paranoia come from? Why were you afraid to crank down on the seatpost bolt? If you thought it was that fragile how could you possibly trust it to support your weight or withstand a good pothole hit? Or was it because you had to have it, reguardless of the dangers, because it was, well, it was carbon and it's what you're supposed to have?

In other words I simply don't follow why anyone would put a fragile item on a bicycle? Especially a fairly expensive item?

But isn't that the point everyone is making - treat it properly and it's almost certain to be fine. Treat it improperly and the risk exposure is likely to be increased.

meesterbond

yaya wrote:

I have a 3T Arx stem with one half of a titanium bolt stuck in it, waiting for me to find the time and the tools to pull it out. This happened when using a torque wrench at the correct settings, all other bolts are fine

Glad it's not just me... there's an ARX Team Stem currently sitting on my S5 which I'll be replacing with an ARX Pro tonight after the bolt sheered off when the torque wrench was showing about 3 N/m

First time I'd used the torque wrench too so I assumed it was my cack-handedness... maybe not!

mfin

pkripper wrote:

But isn't that the point everyone is making - treat it properly and it's almost certain to be fine. Treat it improperly and the risk exposure is likely to be increased.

You can't reason with Dennis. Using a product that addresses a very real problem and that costs £3 a sachet or £5 a tube that'll last loads of bike builds is not something he understands.

He might try drag this out 50 pages like the Lance thread by repeating the same complete guff though.

dennisn

pkripper wrote:

dennisn wrote:

keef66 wrote:

Re the carbon paste: for me it was a solution to a very real problem. Carbon post in an alloy frame. Tightened the clamp bolt as much as I dared but still it kept slipping down.

For me, this ask's the question of why would you buy something that you are paranoid about working with?
Also where did this paranoia come from? Why were you afraid to crank down on the seatpost bolt? If you thought it was that fragile how could you possibly trust it to support your weight or withstand a good pothole hit? Or was it because you had to have it, reguardless of the dangers, because it was, well, it was carbon and it's what you're supposed to have?

In other words I simply don't follow why anyone would put a fragile item on a bicycle? Especially a fairly expensive item?

But isn't that the point everyone is making - treat it properly and it's almost certain to be fine. Treat it improperly and the risk exposure is likely to be increased.

Tell me where I'm wrong here. You buy this seatpost because it's showoffy, blingy, pretty, and it's what you're supposed to have? You buy it thinking, or should I say knowing, that it's fragile and needs special care and special tools? You believe any scratch could destroy it? You're afraid to tighten the seatpost bolt? You then use this post to do a job that most likely has tremendous forces, stresses, and pressures even though you're afraid you'll damage this thing by tightening a bolt? How does that work? You keep telling me that this thing needs special care and then you use it for what has to be one of the most stressful jobs on a bicycle?

Runtothehills

ricky1980 wrote:

Runtothehills wrote:

ricky1980 wrote:

Not quite - carbon fibre is very strong and stiff along the fibre direction but is very weak perpendicular to it: when it's crushed across the fibres it tend to then fail very easily along the fibres as well, especially as when it's crushed the matrix fails which means the load distribution between fibres is shot.

As you say it's also brittle which means it's very susceptible to stress concentrations. If something made from aluminium/steel is overtightened or unevenly tightened so one side is stressed more than the other the material will yield plastically and sort itself out- CFRP won't, it'll just fail.

first of all, the carbon layering is not uni-direction...although they use Uni-directional carbon sheets but they are layered at varies angles to create a tube that can resist bi-axial bending as well as bi-axial shear...so no in real word composite should exhibit strength in both principle axis as well as out of plane resistance.

secondly, brittleness is a description relates to stress and strain characteristics of a material, if a material fails i.e breaks, shortly after achieving UTS then it is brittle, if it yields i.e. elongates/deforms when the stress is applied pass the UTS then it is undergoing plastic deformation and it is not consider brittle...so a material's brittleness has nothing to do with it is more susceptible to stress concentration.

all materials are susceptible to stress concentration, stress concentrations for a number of reasons, due to imperfection during fabrication, due to geometry of shapes and forms...

Ok materials 101

1- True the lay up is not unidirectional but there are no fibres running through the thickness of the tube so for the forces here that's irrelevent. The tube will be of the order of 1mm thick; there's no way you can put fibres running through the thickness of that. The clamp essentially puts a compressive pressure force around the outside of the tube, overtighten it and you crush the fibres at right angles to the fibre direction (all the fibre directions) leading to the problems I mentioned. When you talk about biaxial bending and shear (you missed torsion by the way) that's in the handlebar's frame of reference. Think about the frame of reference of the tube wall and you'll see what I mean.

2-Stress concentrations are a much bigger problem in a brittle material. In the region of a stress concentration a ductile material will deform plastically when the stress is above the yield stress. The load then gets re-distributed until everything's in equilibrium and the structure is fine. For a brittle material it breaks, no load redistribution and the whole thing fails. Think of what happens if you tighten the bolts for an alumimium bar so the forces in the bar are just past the yield stress, the bar will deform locally until the stresses have dropped and the bars survive. Do the same for a CFRP bar and watch it fail completely.

Stress concentrations are also the reason you can't bolt glass, CFRP etc together (ok technically you can but only if you don't want to load the componant) - the bolt is never the same size as the hole so the actual force is put onto a tiny portion of the edge, a huge stress concentration. For steel, aluminiumand other ductile materials you can bolt them as it plastically deforms in that area and look, no more stress concentration (apart from those around an ideal bolt hole, much lower).

mike6

Much as it pains me, I think Dennisn has a point here. If he can use a carbon seatpost, for years, in a number of frames with no carbon paste, then why use it? I have a lightweight carbon seat post in a Ti frame and I have not used paste, with no problems, so I don't feel the need. Each to there own.

dennisn

I would be willing to bet that any reputable carbon seatpost manufacturer(Easton, Ritchey, whomever) who makes higher end product puts ALL their new designs through, what I like to call, the ham fisted knucklehead stress test. They take the post, put it in a frame, tighten the seatpost bolt until it strips or breaks, examine the post for damage, and if there is any it's back to the drawing board. These companies know that they can't put out a product that might break because of this scenario, which is bound to happen many times over. Lots of us knuckleheads out there.
Now IF you bought your post from Ed's Carbon Fiber Seatpost Company and Bait Shop then you might have cause for a bit of concern when tightening that bolt.

ddraver

It's pretty simple dennis. Carbon is strong in some ways and not strong in others. Just as concrete is strong if you crush it but weak if you pull it apart. Does nt stop people building homes, bridges and office blocks out of concrete though.

pkripper

dennisn wrote:

pkripper wrote:

dennisn wrote:

keef66 wrote:

Re the carbon paste: for me it was a solution to a very real problem. Carbon post in an alloy frame. Tightened the clamp bolt as much as I dared but still it kept slipping down.

For me, this ask's the question of why would you buy something that you are paranoid about working with?
Also where did this paranoia come from? Why were you afraid to crank down on the seatpost bolt? If you thought it was that fragile how could you possibly trust it to support your weight or withstand a good pothole hit? Or was it because you had to have it, reguardless of the dangers, because it was, well, it was carbon and it's what you're supposed to have?

In other words I simply don't follow why anyone would put a fragile item on a bicycle? Especially a fairly expensive item?

But isn't that the point everyone is making - treat it properly and it's almost certain to be fine. Treat it improperly and the risk exposure is likely to be increased.

Tell me where I'm wrong here. You buy this seatpost because it's showoffy, blingy, pretty, and it's what you're supposed to have? You buy it thinking, or should I say knowing, that it's fragile and needs special care and special tools? You believe any scratch could destroy it? You're afraid to tighten the seatpost bolt? You then use this post to do a job that most likely has tremendous forces, stresses, and pressures even though you're afraid you'll damage this thing by tightening a bolt? How does that work? You keep telling me that this thing needs special care and then you use it for what has to be one of the most stressful jobs on a bicycle?

Nope, I bought the carbon seatpost because the designers have engineered a degree of flex (and hence comfort) into it, due to their understanding of and corresponding layering of the carbon itself, and it is that I'm seeking to harness. I know that it *can* be fragile if damaged excessively or used for purposes outside its original design specification [e.g. i wouldn't put my road carbon seatpost on my downhill bike]. I also know that designers / manufacturers probably do put a massive safety margin in their designs as we're all different shapes and sizes. But I also know that they've specificied torque settings, and I can adhere to them, and in doing so I can reasonably expect the product to have a long and successful life in the use for which it is designed.

And i'll say it again. Should I not adhere to these settings, there MAY [not necessarily WILL] be an increased risk of premature or catastrophic failure - your bike, your face, your bones etc - you choose the level of risk you're willing to accept.

Runtothehills

pkripper wrote:

dennisn wrote:

Tell me where I'm wrong here. You buy this seatpost because it's showoffy, blingy, pretty, and it's what you're supposed to have? You buy it thinking, or should I say knowing, that it's fragile and needs special care and special tools? You believe any scratch could destroy it? You're afraid to tighten the seatpost bolt? You then use this post to do a job that most likely has tremendous forces, stresses, and pressures even though you're afraid you'll damage this thing by tightening a bolt? How does that work? You keep telling me that this thing needs special care and then you use it for what has to be one of the most stressful jobs on a bicycle?

Nope, I bought the carbon seatpost because the designers have engineered a degree of flex (and hence comfort) into it, due to their understanding of and corresponding layering of the carbon itself, and it is that I'm seeking to harness. I know that it *can* be fragile if damaged excessively or used for purposes outside its original design specification [e.g. i wouldn't put my road carbon seatpost on my downhill bike]. I also know that designers / manufacturers probably do put a massive safety margin in their designs as we're all different shapes and sizes. But I also know that they've specificied torque settings, and I can adhere to them, and in doing so I can reasonably expect the product to have a long and successful life in the use for which it is designed.

And i'll say it again. Should I not adhere to these settings, there MAY [not necessarily WILL] be an increased risk of premature or catastrophic failure - your bike, your face, your bones etc - you choose the level of risk you're willing to accept.

What he said. Carbon is not fragile against the forces you're putting on it by sitting on the post (also the design will almost certianly be governed by stiffness not strength) but is vunerable to clamping forces. Think of the kevlar in a bullet proof vest, it can withstand the impact of a bullet but is much less use against a knife which is less force but put in the wrong place.

dennisn

ddraver wrote:

It's pretty simple dennis. Carbon is strong in some ways and not strong in others.

That applies to just about everything.

dennisn

pkripper wrote:

I also know that designers / manufacturers probably do put a massive safety margin in their designs as we're all different shapes and sizes. But I also know that they've specificied torque settings, and I can adhere to them, and in doing so I can reasonably expect the product to have a long and successful life in the use for which it is designed.

Is it possible that part of the reason for the torque settings is so they can charge more for the product by making it appear more hi-tech than it is?
Take a look at the bottoms of high end(high priced) cycling shoes. There is an extremely fancy grid of lines with all sorts of markings on them. Looks extremely hi-tech. But is it really?
I don't think you can discount the effect of items looking hi-tech on the buying public. A few fancy lines and numbers with letters after them, that most people don't understand, and you've just added more than a few dollars to your product asking price. People want to think that they are hi-tech capable and anything that gives them the sense that they are working on something that the average person doesn't understand will help sell that product.

ddraver

dennisn wrote:

ddraver wrote:

It's pretty simple dennis. Carbon is strong in some ways and not strong in others.

That applies to just about everything.

Well I hope you use no materials whatsover then as non of them are engineered to be strong in every possible way you can think of...

imposter2.0

dennisn wrote:

Take a look at the bottoms of high end(high priced) cycling shoes. There is an extremely fancy grid of lines with all sorts of markings on them. Looks extremely hi-tech. But is it really?

No - it's just a series of fancy lines. A bit like a grid reference on a map - it's just a series of fancy numbers. Personally, I used the fancy lines on my shoes to help line up my cleats correctly. You probably looked at the fancy lines on your shoes in the same way as a gorilla might look at a pocket calculator.