Dag nam it

Wrath Rob

Took the Comtat to Swift Cycles today to take advantage of their £10 service deal. Just heard back form them and it appears that the rear wheel, which I know isn't true, was so out of true that it has been rubbing against the drive side chain stay and worn a groove into the carbon. Apparently the groove is deep enough to be structurally suspect and therefore unsafe to ride :shock:

Unfortunately they can't do a rebuild (using the old Boardman frame) until late Feb. So short term I think I'll be riding one of the other bikes, which isn't ideal. I can then take some pics of the damage and see if its repairable, plus have a chat with my LBS (who sold me the frame and also recently had the rear wheel off to fix the free hub) to see if they can recommend something.

Bugger.

notsoblue

Bad luck! How did you not notice that rubbing though?!

dhope

Ow, that's bad news.
Did they comment on the tarty white mudguards?

sketchley

Bugger indeed.

How did it rub enough to damage the carbon fibre? It might of taken the lacquer off and maybe the paint off too, but to rub carbon in this way seems extreme. I would get second opinion. Are you sure they are not trying to sell you a new bike? A £10 service sounds like a loss leader to me.

nicklouse

it does not take much to wear though a frame.

Ben6899

Sketchley wrote:

Bugger indeed.

How did it rub enough to damage the carbon fibre? It might of taken the lacquer off and maybe the paint off too, but to rub carbon in this way seems extreme. I would get second opinion. Are you sure they are not trying to sell you a new bike? A £10 service sounds like a loss leader to me.

Can I add to this?

I suffered some tyre rub on my Felt Z35 that came fitted with 25s - fork and chainstays. The lacquer and paint are damaged - slight groove, but there is no carbon weave visible. Now this doesn't constitute a second opinion, but you need to remember how much lacquer and "cosmetic" weave some of our bikes have overlaid onto the structural carbon.

jzed

:shock: would it not have caught on the brakes first before catching the frame?

Must have been slowing you down (I've used that excuse before).

Wrath Rob

I'll be picking it up later for a closer inspection. However, their mechanic said that there was some evidence of cracking too, which suggests that structural integrity is suffering. I'll be getting a 2nd opinion at the LBS. And adjusting my FCN as a result

Ben6899

Wrath Rob wrote:

I'll be picking it up later for a closer inspection. However, their mechanic said that there was some evidence of cracking too, which suggests that structural integrity is suffering. I'll be getting a 2nd opinion at the LBS. And adjusting my FCN as a result

Aah, if there is cracking then that's a different story - that shows a weakening of the frame ove time, I would suggest.

DonDaddyD

I have to say the OP is taking rather well...

Ben6899

DonDaddyD wrote:

I have to say the OP is taking rather well...

I disagree. Swap "rather" for "very".

jzed

Chinarello innit

daviesee

Ben6899 wrote:

DonDaddyD wrote:

I have to say the OP is taking rather well...

I disagree. Swap "rather" for "very".

OP wants a new frame :P

veronese68

Can't you put a plaster on it? By which I mean rub back the paint and lacquer and lay some carbon fibre matting over it and apply resin. Using one of these:
http://www.carbonology.com/kit-no-2-the-tube-repair-kit-size-b-p-240.html?sesid=g36646ltp2ai95b46qbemi3fu1

Wrath Rob

daviesee wrote:

Ben6899 wrote:

DonDaddyD wrote:

I have to say the OP is taking rather well...

I disagree. Swap "rather" for "very".

OP wants a new frame :P

I'd be lying if I said the though hadn't crossed my mind :P

However, my cycling fund is going to purchase a powertap wheelset and not a new frame so the timing isn't idea. Must not look at Enigma website.....

In all seriousness, its pretty annoying. I'm fortunate that I've got another bike (or 2) to ride but its going to cost me money to repair the frame, if it can be repaired, or money to rebuild the bike onto the old frame if it can't. Cost is likely to be £100 upwards no matter what solution I go for. And I might be a bike down at the end of it.

rick_chasey

Wrath Rob wrote:

Must not look at Enigma website.....

I'll save you the trouble.

Cafewanda

@ Rick Chasey . Just wicked.

sketchley

or

SimonAH

Veronese68 wrote:

Can't you put a plaster on it? By which I mean rub back the paint and lacquer and lay some carbon fibre matting over it and apply resin. Using one of these:
http://www.carbonology.com/kit-no-2-the-tube-repair-kit-size-b-p-240.html?sesid=g36646ltp2ai95b46qbemi3fu1

No, you can't. This stuff worries the snot out of me (also had the same thought when the carbon frame on rollers, fix it in the kitchen thread came up).

A patch like that may restore some sideways compressive strength to a carbon tube, but will add next to zero torsional strength. Your tube may look better but in any force scenario that matters you have done no more of a repair than actually using the elastoplast of the analogy.

When carbon tubes fail it is usually catastrophic. I wouldn't ride any frame that has had any significant damage repaired in this manner.

Wrath Rob

RC and Sketchley, you are evil. But I'd already had a sneaky look at the Burls website

Just realised I'm likely to be on the SS tomorrow, which means my FCN is getting lower. This is going from bad to worse!

dhope

Wrath Rob wrote:

Just realised I'm likely to be on the SS tomorrow, which means my FCN is getting lower. This is going from bad to worse!

What time do you hit Embankment btw?

tgotb

SimonAH wrote:

Veronese68 wrote:

Can't you put a plaster on it? By which I mean rub back the paint and lacquer and lay some carbon fibre matting over it and apply resin. Using one of these:
http://www.carbonology.com/kit-no-2-the-tube-repair-kit-size-b-p-240.html?sesid=g36646ltp2ai95b46qbemi3fu1

No, you can't. This stuff worries the snot out of me (also had the same thought when the carbon frame on rollers, fix it in the kitchen thread came up).

A patch like that may restore some sideways compressive strength to a carbon tube, but will add next to zero torsional strength. Your tube may look better but in any force scenario that matters you have done no more of a repair than actually using the elastoplast of the analogy.

When carbon tubes fail it is usually catastrophic. I wouldn't ride any frame that has had any significant damage repaired in this manner.

Easy enough to add a patch that takes torsional load; just need to align the fibres appropriately.

Back when I was sailing seriously, we used to repair broken carbon masts overnight. That was quite a lot harder because aswell as making them strong enough we also had to preserve the bend characteristics (an over-stiff section being bad news). A bike is much easier, because (within reason) you can build in a safety factor by overengineering the repair. I'd probably do something a bit more elegant than just adding a few layers of plain weave, but it's not rocket science.

SimonAH

Ok, you've intrigued me and perhaps I've jumped to an engineering conclusion (so happy to be educamated) however...

The strength in a carbon fibre structure lies in the strength of the fibres and at any load point a crack has to rip them if they are placed in a direction perpendicular to the crack formation. This is the reason for using woven matting as it pretty much ensures that at least some fibres will always be in that orientation, also adjacent fibres assist each other in the same way that the short bits of hemp friction together to allow a huge long strong rope to work as one structure. The lay-up process is very similar to laying fibreglass in that wet resin layer is placed upon wet resin layer until the required thickness is achieved. This ensures that the resin is effectively contiguous through the thickness of the material and the fibres act as one structure.

When you place a patch onto an existing tube you are placing wet matting onto (admittedly roughened) substrate, but the adhesion between patch and substrate will be little better than mechanical shurely? There will be a laminar interface as no chemical welding between patch and previously hardened resin?

If the patch is a full wrap around the circumference of the tube then fair enough as it will have torsional strength in it's own right (which is, I'm willing to bet, what you did with the masts?) but if it is just a plaster then the stress will be transmitted along the strong undamaged tube exerting enormous leverage at exactly where you have your patch. This patch will then ping off like a pringle along the much weaker interface layer between patch and original tube and leave you skittering along the road in a tangle of broken carbon....?

So, full wrap yes. Plaster abso-no unless you can tell me why I'm wrong footed here.

itboffin

I like pringles who has the pringles?

cjcp

How do you apply a wrap to a chainstay?

tgotb

SimonAH wrote:

Ok, you've intrigued me and perhaps I've jumped to an engineering conclusion (so happy to be educamated) however...

The strength in a carbon fibre structure lies in the strength of the fibres and at any load point a crack has to rip them if they are placed in a direction perpendicular to the crack formation. This is the reason for using woven matting as it pretty much ensures that at least some fibres will always be in that orientation, also adjacent fibres assist each other in the same way that the short bits of hemp friction together to allow a huge long strong rope to work as one structure. The lay-up process is very similar to laying fibreglass in that wet resin layer is placed upon wet resin layer until the required thickness is achieved. This ensures that the resin is effectively contiguous through the thickness of the material and the fibres act as one structure.

When you place a patch onto an existing tube you are placing wet matting onto (admittedly roughened) substrate, but the adhesion between patch and substrate will be little better than mechanical shurely? There will be a laminar interface as no chemical welding between patch and previously hardened resin?

If the patch is a full wrap around the circumference of the tube then fair enough as it will have torsional strength in it's own right (which is, I'm willing to bet, what you did with the masts?) but if it is just a plaster then the stress will be transmitted along the strong undamaged tube exerting enormous leverage at exactly where you have your patch. This patch will then ping off like a pringle along the much weaker interface layer between patch and original tube and leave you skittering along the road in a tangle of broken carbon....?

So, full wrap yes. Plaster abso-no unless you can tell me why I'm wrong footed here.

What you're missing (not unreasonably) is that epoxy resin makes remarkably strong secondary bonds (ie bonds onto fully-cured substrate). I haven't had a chance to dig out any datasheets, but the secondary bond strength for many epoxies is not that different to the stregth of the original cured laminate. You can test this quite easily by bonding two carbon components and then testing the bond to destruction; if you do the bonding properly, the failure is almost always within the laminate of one of the original components. Don't try this with polyester resin though; secondary bonding using polyester resin is quite poor (though epoxy can be used quite successfully to bond cured polyester components).

If you want to patch a tube, you just need to align the fibres appropriately (longitudinal for longitudinal stiffness, circumferential for hoop stiffness and diagonal for torsional stiffness) and make sure there's a decent overlap onto the existing laminate. The real difficulty with patching a tube in the way you describe is that it's often done to make an invisible repair (ie without increasing laminate thickness). This can be done without weakening the tube significantly, but it's not simple (especially if you don't know the orientation fibres in the existing tube). My approach would always be to make a neat, but visible repair, ie one which increases the thickness of the laminate. This allows you to overengineer the repair, making it easier, cheaper and safer. For something like Rob's issue, I'd probably use unidirectional fibres on the inside of the tube only (ie where the damage is) with a couple of layers of woven cloth at different orientations over the top, and wrapped round the whole tube as much for simplicity and neatness as for strength (because it's a small tube).

As an aside, carbon mast failures tend to be catastrophic (the mast typically comes off the water in separate pieces) so repairs necessarily require a "full wrap". This is a situation where you can't overengineer the repair, not for cosmetic reasons but because you don't want to make the mast any stiffer than it was before...

rjsterry

Intersting. This reminds me of an A-level experiment testing the strengths of various adhesives. The 'winner' was something called Scotchweld - a 2-part epoxy product. The bond between one of those 100g weight hangers and a stout block of wood clamped to a work bench was such that when it finally let go (with a 100kg+ teacher jumping on the end of the rope) it pulled the surface off the weight hanger. Enough metal was still stuck to the wooden block to allow us to pass a current through it.

rick_chasey

TGOTG - what's wrong with having a stuffer mast than designed?

tgotb

Rick Chasey wrote:

TGOTG - what's wrong with having a stuffer mast than designed?

You use mast bend to control sail shape; when you hit a gust (or pull the right bits of string) the mast bends, flattening the sail and depowering it. Change the bend characteristics of the mast and your sail shape also changes...

Another good example of secondary bonding: For our last mast I designed and fabricated some carbon fittings for the wires which hold the mast up (conventional attachments require holes drilled in the mast, which are a potential weak point). They were designed to take a load of 1 tonne, and were glued onto the mast with a contact area ~8cmx4cm.

SimonAH

Whilst interesting, I think the correct response to Rick was 'fnurk'

PBo

SimonAH wrote:

Whilst interesting, I think the correct response to Rick was 'fnurk'

thanks finbar!!