it was a sheet of CF, wrapped around the leg of an already built fork. All over steel tabs.
So how can it fail then?
Bike Forum
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FAO doubters II (carbon brake mount & potential FLAME-AGEDDON content)
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Posted 1 year ago #
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Posted 1 year ago #
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Well done on getting as far as you have. I realise now that you've used a metal structure within the carbon - did this rest on the original fork and you've then wrapped it on with carbon and resin then?
Possible modes of failure, in my partially educated order of likelihood-
Fork leg shears at upper edge of steel - although the exact location depends on how the original fork manufacturer laid up the fork.
Steel cuts into fork at lower edge due to compressive forces counteracting turning moment of caliper - or whole unit breaks free and moves downward due to inadequate bond with original fork (can't decide!)
Your carbon wrap begins to separate at the upper edge of the steel due to tension forces.I went off and found some papers on carbon/epoxy structural strength, and it seems to be much weaker when not compressed and cured properly i.e. high void space. Which of is probably an insurmountable problem making carbon components at home - I'd think you'd need to spend a lot of money to get the correct equipment, enough to buy a nice Yeti ASR5 perhaps?
Rhetorical question - how do professional bike engineers add disc mounts to carbon forks or even carbon rear stays? Do they do it like this (excepting the problems caused by not using professional equipment)? If not, why not?
Posted 1 year ago # -
Your last point...if I get it correctly...is pretty obvious.
I don't think the bottom of the mount will rotate into the fork.
I wrapped the final Earp layers under tightly wound string-hopefully having some impact on voids.
I may re-do it, applying what I've learnt. I've got a few other projects first
Posted 1 year ago # -
I'm looking forward to seeing what you do next, certainly beats the average confrontational thread on this forum - you are certainly more of a risk taker than I am, and more adventurous.
Nothing was ever achieved without taking risks
Posted 1 year ago # -
i managed to not end up in hospital by sheared forks/brake tabs by not doing this
As far as I am aware even with professional frames where metal and carbon are binded together seems to be the most common area of breakage.
given you have done this and will be applying huge forces [ well if you spped up a bit] and the consequences of a failure are pretty severe I would just have bought some disc forks tbhPosted 1 year ago # -
CA,
Strictly speaking, you should isolate the steel from the carbon to prevent galvanic corrosion, I wrap steel inserts (like a bottom bracket shell) in glass fibre before applying the carbon, but I don't know if this is really necessary. (I sure someone will say it is.)As to doing calculations and working out forces, rubbish. I over engineer everything I make in carbon, with the result that it isn't pretty, nor that light, but it won't fail (and the 3 frames I've made haven't yet).
I do it for the fun and experience of learning new stuff, which I sure is partly why you do it as well.
Keep going.Posted 1 year ago # -
Thanks for your input JY, those points have already been made repeatedly, and believe it or not I did think of them, I think you are missing the point of my project.
Posted 1 year ago # -
I know you thought of them but if i was descending at 30 mph and had to break hard i would want a bit more tham you [ or me] having bodged something to some forks. If it fails it will do so catastrophically when you apply great force. good luck as you note neither of us can be sure it will be safe but if you want to accept that risk I wish you much luck and hope you dont hurt yourse;f
I am not anti bodging or an al hater [ mildly irritated at times]and chapeau for posting this and the other stuff up as you are certainly a sport.Posted 1 year ago # -
I appreciate your concern and encouragement!
Wait till you see the other crap I have planned!
Posted 1 year ago # -
genuine LOL momentPosted 1 year ago # -
TBF it will be more sensible/better executed. I may do some wind-ups though.
Posted 1 year ago #
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