Latest bodge-idea - this one may actually happen

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Latest bodge-idea - this one may actually happen

83 posts & 33 voices | Started 1 year ago by cynic-al | Latest reply from cynic-al

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cynic-al - Member

I'm thinking of adding a rear disc mount to a ti audax frame. It has 2 rack mounts about an inch apart and I'd plan to bolt it to these then epoxy it to the seat-stay further up to triangulate it a bit and stop it "doing an Ellsworth".

I'd use 6mm steel plate, bolted inside the stay, which mates perfectly to my plan of mounting the disc 6mm closer to the hub than normal.

Any ideas as to whether epoxy would be strong enough? I guess I could wrap it in CF but I'd like to keep it as neat and reversible as possible.

Ideas, jokes, even al-haterz welcome.

Posted 1 year ago #
5thElefant - Member

Wouldn't making a clamp make more sense than epoxy?

Posted 1 year ago #
momo - Member

Disc brake might introduce too much torque for the rack mounts to cope with, other than that, cracking idea.

Posted 1 year ago #
scaredypants - Member

you can skid the rear wheel of a road bike so bloody easily that I can't see there being
a) much force for stays to deal with
b) much point

Posted 1 year ago #
cynic-al - Member

clamp - better mechanically, but heavier, uglier, more hassle.

It's for using it off road, and we've done the "riders that don't use discs on road bikes think it's a stupid idea" argument many times.

Posted 1 year ago #
TandemJeremy - Member

As you were told before epoxy will have very little strength in this sort of situation. Flat plate glued to round tube does not work. The loads on the rack mounts will be far higher than it was designed for, you are putting loads thru the frame in directions it will not have been designed for. You are talking about massive forces - thousands of newtons with shock loading as well.

Posted 1 year ago #
anotherdeadhero - Member

Ages ago I managed to find a much neater adaptor than the A2Z, which just coweled the inside of the dropot face, and had a little threaded stop you could screw down to the seat stay to transmit the forces to the frame.

In the end I managed to track down a Hope dogbone.

Make on of these:

Then spray paint it so it looks less naff.

Mudguard eyes/rack mounts will just get ripped right off, seriously.

Posted 1 year ago #
scaredypants - Member

we've done the "riders that don't use discs on road bikes think it's a stupid idea" argument many times

yeh, but the "riders who think it may be appropriate to bodge on a disc mount to a primarily road/hybrid frame (and then pretend it's a cross frame)" is a variant I'm new to

Posted 1 year ago #
cynic-al - Member

TJ have you thought this through? Who said the brace will be flat? How do you know the loads on the rack mounts will be higher than designed for if the brace is securely glued to the stay? Certain folk have commented that domestic epoxy can make very strong bonds. Any forces on the stay would be mostly along its length - in whihc direction is have massive strength.

Frame builders do weld disc mounts on to frames, remember?

scaredypants - Member
yeh, but the "riders who think it may be appropriate to bodge on a disc mount to a primarily road/hybrid frame (and then pretend it's a cross frame)" is a variant I'm new to

So what?

Posted 1 year ago #
Dancake - Member

I made a mount that looked a lot like anotherdeadhero's post.

Took a few goes to get the angles right but it worked like a charm in the end.

I personally didn't "need" a disc brake but I I hate those 'orrible v brake things myself. - You can get a brand new bikehut hydraulic disc brake and disc from Halfords for 30 quid now and you will probably never use it enough to touch it again (I have one of these)

*good time to reserve online and take advantyage of a 3 for 2

Posted 1 year ago #
TandemJeremy - Member

Yes al I have thought this thru - and its a stupid idea. Frames with disc tabs are built with them in mind. Teh forces will hundreds of times higher and will be in directions not designed for plus you get shock loadings.

~I can't be bothrered argueing with you as you will not believe anything I say. Just do it and film the results please.

Posted 1 year ago #
scaredypants - Member

So what?
so that's why I joined in - you piqued my interest

Posted 1 year ago #
cynic-al - Member

TJ, are you saying something akin to the pics above, but a little shorter, and with a long contact patch for gluing or wrapped in CF, will break?

~I'd listen more if you backed it up with experience, knowledge or facts...can you do so?

Posted 1 year ago #
cynic-al - Member

Jeez, I just spotted the double-sharksfin action going on there.

chapeau!

Posted 1 year ago #
racing_ralph - Member

Al - just pay the **** money and buy the right frame for the job for **** sake

Posted 1 year ago #
hilldodger - Member

I'd listen more if you backed it up with experience, knowledge or facts...can you do so?

http://www.wikipedia.org/ http://www.google.co.uk/

Posted 1 year ago #
cynic-al - Member

RR this is way more fun and cheaper!

Posted 1 year ago #
anotherdeadhero - Member

al, stop being such a **** tard

Posted 1 year ago #
cynic-al - Member

I'll never stop ADH :love:

Posted 1 year ago #
STATO - Member

Dont glue anything, it'll never work; the force on the stay is not just direct compression, as the braking surface is not inline with the stay (imagine looking at it from the back) there will also be a twisting force which will just crack the glue.

Plenty of options shown here (http://forums.mtbr.com/showthread.php?t=314985) tho many would not be sensible for a thin tubed road frame. Concentrate on the ones which bolt to the axle and use the v-boss if you want to be succesful, tho if your dropout is strong enough then the example posted above would work.

Posted 1 year ago #
brakes - Member

plate with disc mount attached to axle at one end, then put a connecting rod from the other end of the mount and attach it to somewhere on the bike which can take the load, like the BB area?
something like a floating caliper arrangement that you get on DH bikes

Posted 1 year ago #
clubber - Member

I'm not sure I'd trust a rack mount to take the load - I'd be looking to clamp one end at the dropout as it'll be much more secure.

As to the other end on the seatstay, that might work though in the past I've seen stays get bent by adaptors that worked in a similar way. I'd suggest a wide, profiled section in contact and held in place with jublilee clips or a clamp. I did something similar years back but it clamped to both the seat and chainstays, near the d/o. It worked fine.

Posted 1 year ago #
nicko74 - Member

I have no experience here, and personally never found it tricky to lock up a rear wheel with v's, but wanted to pipe up anyway....

It doesn't *sound* like it'd work, as the rack mounts aren't fitted with that kind of force in mind - I'm guessing on the audax frame they're fairly low profile, compared to the thickish plate of a disc brake mount.
And the people saying the epoxy will be poxing useless also have a point...
Still, they said man would never be able to fly to Mars and, well, so far they're right, but let us know how you get on.

Posted 1 year ago #
brakes - Member

never found it tricky to lock up a rear wheel with v's

you can skid the rear wheel of a road bike so bloody easily

modulation? rim wear? working in the wet? self-adjusting?
there's more to braking than locking up the back wheel, you could do that by sticking your hand in the spokes

Posted 1 year ago #
cynic-al - Member

The rack mounts are in the dropout which is 5/6mm ti. I like clubber's idea though, it would be easy to adapt the hub.

Posted 1 year ago #
scaredypants - Member

modulation? rim wear? working in the wet? self-adjusting?
there's more to braking than locking up the back wheel, you could do that by sticking your hand in the spokes

modulation probably better with rim brakes, esp in the dry. Rim wear minimal for road (remember it was an "audax" bike in the OP though Al did subsequently say it would go offroad).
wet: bah, not with half decent pads - though in mud, definitely !

Posted 1 year ago #
cynic-al - Member

scaredypants - Member
modulation probably better with rim brakes, esp in the dry.

Not in my experience (5 years running discs on road bikes)

Rim wear minimal for road (remember it was an "audax" bike in the OP though Al did subsequently say it would go offroad).

I've gone through a rim per year when training.

wet: bah, not with half decent pads - though in mud, definitely !

Wrong again!

I guess you've never used disc brakes on a road bike? Durrrrrrrrrr

Posted 1 year ago #
GW - Member

b) much point

+1

Posted 1 year ago #
cynic-al - Member

Got cantis on your off road bikes then?

Posted 1 year ago #
scaredypants - Member

one last try at a reply

Wrong again!
I guess you've never used disc brakes on a road bike? Durrrrrrrrrr
Bugger me, you're right Al - my cross bike has discs on it though

Discs on the front of a roadie, maybe. On the back ? Nah. On the back AND needing a crap bodge ?

Posted 1 year ago #
Junkyard - Member

i suspect you could make something that worked though I would want a few frames and designs to test. I can see no way in which glue will work as it is not really designed for the forces as it sticks one object to another. Welding makes two pieces one piece by melting the two together so they are the same piece of metal. If you do a tear test the weld will usually be stronger than the actual metal [even spot weld]. You will not achieve that with glue.
Bolting somewhere would be better but I am not certain as to the forces and what it will do but do not use glue whatever you do. It would be MUCH cheaper to glue frames than weld them but they dont becuase it does not work well.

Posted 1 year ago #
cynic-al - Member

Scaredypants I guess I have different reasons for using discs to you (this is for cx use)

Junk nor sure if you understand my proposal - it's entirely different to joining tubes...which they have done with glue (and lugs) anyway

Posted 1 year ago #
Junkyard - Member

I do understand but went of on one about welding.
You want to attach a disc mount using epoxy which i consider to be a "glue" as it sticks stuff together - I am sure it is technically a bit different though to an expert. I dont think this will be strong enough for the forces and if it is it will not exactly be reversible therefore I would bolt or weld rather than epoxy which i consider to be stronger in the first case and reversible in the later.
lugs

the end of the tubes are inserted into the lugs and subsequently brazed with a silver or brass filler metal. The lug greatly increases the strength of the joint by distributing the molten filler metal over a larger surface area via capillary action
have they really used lugs and just glue for frames? I dont know have they?

Posted 1 year ago #
cynic-al - Member

You're not an engineer, are you?

Nor been into bikes that long?

Posted 1 year ago #
TandemJeremy - Member

there have been motorcycle frames built with tubes lugs and glue

Very carefully controlled gaps and large areas of contact. Completely different scenario to what Al is proposing which shows how little he understands about engineering. If you were attempting to glue a sleeve on a tube with very carefully controlled tolerances in might work - I have done this myself in a much lower load situation.

With the off centre forces, the magnitude of the forces and the shock loading and the small area of contact that does not go right round the tube it will not work

Bolting onto the brake mount and wheel spindle might - or it might just bend the tube

Posted 1 year ago #