FAO doubters II (carbon brake mount & potential FLAME-AGEDDON content)

crispedwheel – Member
45 mins between ‘going out for a test ride’ and posting again. Did it last longer than the rear, or did you just not use the front brake? Attention-seeking whore aside,

Seems to work fine on a stoppie-tastic test ride, I thought I’d let the thread run a bit before telling y’all.

I could easily not have bothered posting this up, and I knew I’d get the piss taken, but it’s a bike forum, and I guess I thought someone might be interested in someone who’s actually trying to make bike bits. But hey! I guess no one will be interested in my next project….the ultimate mtb!

Ultimate = Last.

Alas, for you, this might be too true 🙂

disc rotation only matters a tiny ickle bit on very muddy rides. Cack will collect at the top of the spokes on the dis, that’s all….slightly affectng braking power.

So did it work?
edit, ah so it did…for now 😉 keep an eye out for cracks at the top of the fork leg, that’s where the bnding moment will be greatest, that’s where it will fail.

Eh? Quote me in full please – you missed off ‘I’m enjoying these threads btw’ from the end of that. Precisely because, you know, it’s about bikes and modifying them. Glad to hear it’s working so far.

For compression (if there’s a next time) you can try insulating tape, wound sticky side out (so it sticks to itself). Get it really tight and prick lots of holes in it so the excess glue can seep out.

I need to see video of this being used. Without it I’m convinced that this is just an incredible troll 😉

Seriously though, good job on putting it together. I love seeing homegrown projects, especially bike or car related. If you don’t try it out you’ll never know if it works.

Mmmm….nice finish 🙂

I see you’ve upgraded to a spork this time.

Nice one richmars. I’ve ordered proper epoxy and everything, it’s all going great!

Oggles I did shoot a video…it’s of me coming to a stop, too dull even for me to post!

Well you can’t argue with innovation

but I’m still imagining forces in the forks further up…..

Al, to apply compression and get a good finish use some electrical tape with lots of pin holes adhesive side away from the component. Wrap it round and squeeze out the excess resin. You really, really do not want to much resin in the carbon windings.

Ta. I spiralled the string and it seemed to squeeze a lot of epoxy out.

What you need to get a good finish and strength is peelply it lets excess resin through and compresses the carbon/glass. Kevlar added to the mix might be a good idea as it will hold together in the event the carbon fails.

BTW I only play at this composite stuff you might want to read up on this stuff as a failure on the bits you are experimenting with could bugger you right up

Thanks mikeypies, I’m aware of the consequences of failure.

Survived an emergency stop today already!

thing is, in the short term it’ll probably be fine, but unless its done properly then you’ll never REALLY know if it will last or not.
I personally wouldn’t want to be spending the whole ride worrying about whether my face would require reconstructive surgery at the end of the ride.

Survived an emergency stop today already!

I think this is what worries me.

I wouldn;t like each brakign experience to be a ‘Well I survived that!’ one. I just want to brake and stop, knowign that someone actually calculated the forces involved and then tested (to destruction) the resulting item.

Good luck to you Al and you’ll probably be fine.

I think a lot of people on here over-estimate how much calculation and engineering goes on in the creation of mountain bike bits. Testing, yes. But we all know the vagaries of that.

That said, I’m not sure brakes would have been my first choice of MYOG, but good on you for trying.

so 3 days later is it still working or has it done a Buemi?

Didn’t go so well.

Mount snapped off and I went under a bus.

I’m posting from purgatory.

TJ is talking endlessly about rotational helmet injuries on one side of me, Fred is moralising on the other, Junkyard is guffing on somewhere else…

Seriously it’s been fine but I’ve run in today and rode the Pomp home so not done too many miles since then.

Good effort on the home brew stuff. Surely as long as the mount is able to hold and thransfer the force unto the steerer end, then it’s not going to be all that different from normal rim brakes where they place all their forces.

Al I just think it is a daft thing to do,is done poorly [ certainly aesthetically] and is risky to the point it is dangerous and possibly very dangerous/serious.
MMM now I think about it I should have encouraged you from the start 😉

Thanks and agreed – it’s just they can place higher stresses along the blades.

Fingers crossed!*

*(I’m only coming out with this to wind the usuals up)

Junkyard – Member
Al I just think it is a daft thing to do,is done poorly

How so? Do you know how many layers of carbon I’ve used? What type of carbon?

Etc etc you don’t really know do you.

I think it’s cool to be that into bikes that you wanna try modify or make yer own stuff, rather than splurge loads of cash on the latest thingy. Bikes aren’t that complicated. Interested to see how it holds up.

Didn’t go so well.

Mount snapped off and I went under a bus.

I’m posting from purgatory.

TJ is talking endlessly about rotational helmet injuries on one side of me, Fred is moralising on the other, Junkyard is guffing on somewhere else…
😆

I am very sceptical. You’ve certainly solved the problem with braking forces encouraging front wheel ejection, but there is absolutely no sign of any of the thought processes or calculations that a real engineer would apply to a prototype. (Is there a prior thread?)

I hope you get away with it, but from where I am sitting, if I had to place bets on your personality I’d be calling you an eccentric fool.

I’d like to think it’s a wind up and the picture is a mock up. Video by a third party of the bike and yourself in stoppy action or it didn’t happen.

Etc etc you don’t really know do you.

and you have not subjected it to industry standard testing either so you dont really know either
cant be arsed al best of luck but it is foolhardy IMHO

i’m assuming this is a bodge hand layup of unidirectional CF? Is the resin stable in high humidity? Have you applied a weave to the outer layer, for impact integrity?

finally, do you have a good dentist?

Of course I don’t know JY, but no one else here does either.

Hans – wasn’t planning any tropical riding. Unidirectional? Pah!

Foolhardy – I accept that, if it fails and I hurt myself I will post up so you can mock, I’m a decent sport like that, modest too.

Wade – will upload a stop (not stoppie)

well, it’s damn humid in the UK too. Unless of course you solely ride in the Gobi.. Just curious, what material(s) did you use? And how did you do it?

Are you using continuous fibres or chopped mat? How did you cure it without over curing the leg already?

It sounds like such a bad idea and i can think of a dozen ways it can fail… i hope it doesn’t though.

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?

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?

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 😎

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 😆

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 tbh

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.

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.

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.

I appreciate your concern and encouragement!

Wait till you see the other crap I have planned!