A new dawn (DIY brake mount and CARBON CATACLYSM content)

is it really worth the effort when these are less than £70 ?

why spend money on those when the he has a cutlery drawer close to hand.

is it really worth the effort when these are less than £70 ?

****ALERT ALERT****
XX CHROMOSOMES DETECTED
****ALERT ALERT****

Slightly puzzled. If those forks were designed for rim brakes, will the fork leg be able to cope with the braking forces applied at the bottom? So is a snapped fork leg just a matter of time?

So is a snapped fork leg just a matter of time?

he kept his teeth when the last bodge job/carefully engineered solution failed 🙂

Al, out of interest, would the squeezing of the CF / Resin worked better using a vacuum pump and a bag around it?

Yes, but he only had a roll of insulating tape. 🙂

Greek track teams bikes for the Athens games were made using the ‘reverse insulation tape’ method of consolidation and cured in the back of a car on a sunny Greek day. At the time, they were considered to be more than adequate for the job at hand 😉

Was that in the first Olympics 😉 Point of order… Track bikes don’t have brakes…..

cured in the back of a car

maybe they misunderstood what an ‘autoclave’ was?

Airbag on the handlebars…just in case like

Was that in the first Olympics

Nope!

Point of order… Track bikes don’t have brakes…..

Irrelevant, to the point that the consolidation method Al is using is perfectly fine, provided the engineering of the joint itself takes into account the effect that the method has on the resulting material strength. Other factors are, of course, at play here… 😉

When he is ready for his first test (crash) can someone please follow him and film it for our amusment – it would be a nice addition to the midweek movies.

A far cry from those massive DH vids and giant jump vids we are tired of watching.

bristolbiker – Member
<snip> provided the engineering of the joint itself takes into account the effect that the method has on the resulting material strength.

Uh oh….. 🙂

Just take a hammer to your teeth/face. It will have the same effect.

I will, as ever, provide a video of the test ride, hopefully tomorrow.

“Show us the spoon”
“Show us the spoon”
“Show us the spoon”
“Show us the spoon”
“Show us the spoon”
“Show us the spoon”

But seriously… well done 8)

Oh and I did put the insulating tape on inside out!

Hmmmm, what will be the failure characteristics ?

Possible theory: If the joint fails in one go with the front lever applied then the caliper will rotate with the rotor and I guess detach from the brake hose if the hose is short or fixed to the fork leg. Otherwise the caliper could remain on the rotor until it collides with the rear of the fork leg…

Shouldn’t you have used a non crushable spacer?

Like Oak?

Spooky

I’ve been considering lashing up a rear mount for my SS you previous adventures with composites had me considering something similar to what you’ve got there, attaching a PM adaptor to the stay and wrapping it…

My other thought was to try and create a bridge between the seat and Chain stays which integrated a pair of 51mm IS mounting hole and applied load to both…

Ignore the doubters Al, perseverance is a sign of greatness

I feel some garage time coming on…

Like Oak?

or a couple of fish knives?

That sir, is marvelous.

it seems to me the pull will tension the carbon wrap (to follow) which is how carbon works – rather than try to compress it.

But if you put the mount on the back of the fork (on the left leg) the carbon would be under almost no load at all – all the load would be taken by the spacer under compression. Now granted balsa may not be up to that (though weight for weight it is an excellent material), but it would be quite simple to use something else which would take the load (possibly just a carbon wrapped block of balsa, though a stronger bit of wood would probably be simpler).

Which brings us on to the other point – carbon works just fine in compression, provided (just like any other structural material) it is properly supported to prevent it buckling. How else do you think those carbon forks of yours support the load? The strength requirement to prevent the buckling is far lower than the strength requirement to support the load, and can quite adequately be provided by the epoxy resin bonding the carbon to whatever it is attached to – hence how sandwich constructions provide good bending strength (where one side is in tension, one side in compression). As mentioned above, a carbon wrapped block would provide very good compression strength. The only reason the outer carbon wrap wouldn’t do a good job of providing this compressive strength is that you’d be relying on the epoxy bond in tension and shear – the alu mount would likely separate from the carbon.

is it really worth the effort when these are less than £70 ?

go away and think about what you’ve just said.

Otherwise the caliper could remain on the rotor until it collides with the rear of the fork leg…

then jamming between spokes and fork locking the front wheel, test ride will no doubt be a slow speed affair, but presuming that’s successful (hell of a presumption) how fast are you going to go in future? how much faith do you have in your bodging skills Al?

perseverance is a sign of greatness

Insanity: doing the same thing over and over again and expecting different results.

just 😆

i look forward to the results of this thread. I also applaud Al for looking beyond the “black magic” of bike design and having a go at it himself

i look forward to the results of this thread.

I think everyone is. Especially with the promise of video evidence 🙂

The only reason the outer carbon wrap wouldn’t do a good job of providing this compressive strength is that you’d be relying on the epoxy bond in tension and shear – the alu mount would likely separate from the carbon.

Yup, that’s why I did it this way.

cookeaa – Member

Spooky

I’ve been considering lashing up a rear mount for my SS you previous adventures with composites had me considering something similar to what you’ve got there, attaching a PM adaptor to the stay and wrapping it…

My other thought was to try and create a bridge between the seat and Chain stays which integrated a pair of 51mm IS mounting hole and applied load to both…

Ignore the doubters Al, perseverance is a sign of greatness

I feel some garage time coming on…

I did similar on my fatbike, shaped the mount to brace against the stays and then wrapped it in place.

Yup, that’s why I did it this way.

You didn’t consider the idea of the spacer being structural – which would be a far better engineering solution?

Yep Al that sounds just like what I’ve got in mind…

The only other thing I was considering was making a Jig plate to line the brace up accurately relative to the Dropout and using Devcon or something similar to position it prior to wrapping, devcon when set can deal with a bit more loading and is easy enough to shape, sculpt and can be dremeled/machined after it has set…

What is the torque applied to a brake mount? I presume it’s a result of the clamping force (which has to be pretty high on a disc) x friction coefficient x the diameter of the disc.

I suspect in a disc brake these forces add up to quite a lot. I’m not sure I’d trust such a solution myself but Chapeau for trying…

cookeaa I use a cable caliper and hub/wheel with a disc attached to line it up -works fine.

aracer – Member
You didn’t consider the idea of the spacer being structural – which would be a far better engineering solution?

Why “far better”?

Not the best I have seen, but full marks for the innovative approach. However, if you really intend to use this things there are somethings you should be aware of (maybe you already are).

Carbon composites, work best in tension, rather than compression and their strength or rather performance will be affected by a number of factors. The braking force is probably going to induce mostly tensile in your bracket, although there could be the possibility of a moment there that could put the lower part of the bracket into compression. If I were you I would be sure to have a fed wraps of continuous fibres which are wrapped around the bracket and the fork leg. How many? depends on the weight of the fabric you are useing (maybe its UD) it also depends on the resin type.

A couple of other things. The mechanical properties of the composite part will be affected by porosity content and resin content. You have tried to get rid of excess resin (i assume) with your tape. (which is not a bad idea) but just so you know, there is a product called shrink wrap. Wrap it around, heat with heat gun and it will shrink to give you a very good compression.

Resin type, what is the cure temperature and what temp do you intend to cure it at? if you dont reach the recommended temp for the right time you will not get the properties. Left in a cold garage to cure=not so good.

Galvanic corrosion, carbon in contact with AL is not so good. Probably ok for the time that this will last (:-) but longer term bonds will deteriorate.

Positioning on fork, well. You are attempting to modify a fork which has not been designed for this. In use you will be applying a significant and sometimes very aggressive and concentrated force, to a part of the fork which is probably highly loaded.

But I guess that anyway you are just doing it for fun and don’t really intend to use it??

But I guess that anyway you are just doing it for fun and don’t really intend to use it??

I’d guess again…

Gulp ! 😯

cheif 9000 I thought you were a physicist?
I think Al is using low temp cure resin which is fine.

Just having a think. The forces on the spacer will be acting in the direction of the blue line. This means the top will be in tension and the bottom will be in comprssion. The balsa will be squished unless the carbon has enough adhesion on the caliper mount to stop it rotating. The chief above my be into fiziks but from an engineering perspective, he’s right.

there is no argument that the forces are not all in tension, but there is more tension than if he had mounted it on the back of the caliper…

Seriously though: if you resolve your blue arrow (which is correct imho) into a horizontal and vertical component then you will have a force pulling to the right of the picture and a force going down. I don’t think there is any compression on the balsa, but I think the downwards force will be appreciable and thats where it will fail.

The best way of doing this would have been to mount the caliper as close as possible to the fork leg, therby reducing the size of the downward component and keeping it mostly in tension.

There’s a bloke here wants to speak to you…..