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Epoxy Disc Tabs

Old 10-10-07, 09:56 AM
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arrasmithf
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Epoxy Disc Tabs

Let me just say that even as i post this, I have decided to try it, but i am curious as to what other members might think, especially an engineer's prospective,and not just a professional, but a backyard homebrewer with experience in fabrication as well.
I have an '86 giant rs930(my favorite commuter) that i am in progress of upgrading to disc brakes. The progress is going well and I have completed the rear, but i am having budget issues, so I have considered another option which i feel would be sufficient to complete. In order to do the front, I was going to need to change the fork, and since there is only a few forks that would fit, my options are limited, as well as i would need to spend excessive time and money to acquire a new headset, stem, spacers and dialing in the fit. I have my setup dialed in perfectly so i would rather not mess with it. I first considered having a metal fabrication shop welding the tabs to my existing fork, and though i think this would be best, then there would be large paint repair area i love the color of my bike( deep plum) and the paint is in excellent condition so i dont wwant to deal with matching or changing the color.

Here is the plan. Having some experience with Epoxy, i am considering taking the adapter attached, and epoxying it to the fork, which is something i could do myself, there would be little down time, and if I f*** it up, then no harm, no serious money blown, and save until i can change the fork. I am pretty comfortable with epoxying and have made some serious repairs with it, so i have high confidence, but lets hear from all you experts out there as to concerns about this modification.
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Old 10-10-07, 10:50 AM
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you would have to make sure that you epoxied it in the correct position, at the correct distance from the dropouts. i gotta say that i think this is a terrible idea which could result in serious injury.
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Old 10-10-07, 11:06 AM
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No! Absolutely not! This is not a job for epoxy. This requires brazing the mounts to the fork. Either buy a new fork or get a frame builder to do it for you.

Do it right or be sure your medical insurance will cover your trip to the emergency room.

BTW, although adding the mounts will require repainting the fork, if you paint the fork black, it should look good with your current frame and you won't have issues with matching new paint to old.
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Old 10-10-07, 11:14 AM
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Epoxy will be a very expensive approach when it fails and you and/or the bike are damaged. It will fail, and most likely the first time you really need to stop. As others have posted, do not do this.
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Old 10-10-07, 11:14 AM
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Originally Posted by OneTinSloth View Post
you would have to make sure that you epoxied it in the correct position, at the correct distance from the dropouts. i gotta say that i think this is a terrible idea which could result in serious injury.
Ok, have anything specific or just what you have put into above. The issuesyou mention I think fall into what would be considered a proper installation.

I want to add that I have used an aftermarket adapter for the rear(A2Z universal) and after properly installing, it has worked excellent without any problems this season, with the Disc brakes performing better than any brake i have used in the past. This adapter clamps over the rear dropout and holds in place with 4 small bolts + the skewer. I would guess that a basic epoxy metal which is rated for 4000 psi, will easily match/exceed the clamping force of that adapter clamp.
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Old 10-10-07, 11:22 AM
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Originally Posted by supcom View Post
No! Absolutely not! This is not a job for epoxy. This requires brazing the mounts to the fork. Either buy a new fork or get a frame builder to do it for you..
Ok, so you agree that welding new mounts to existing fork is acceptable? i haven't ruled that out as an option, but i thought the heat might cause distortion.

A few questions about epoxy to any who might be an expert in the field.
1. Don't they glue airplanes together with this stuff now?
2. How is epoxying a tab to the fork any different than having a carbon fiber fork, which is basically fibers suspended in epoxy resin?
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Old 10-10-07, 11:37 AM
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the figure below is from a data sheet for Super Glue metal epoxy. Anyone know the force that gets applied to the fork when a 200Lb individual hits the brakes on bike equipped with 6"rotor on a 700c wheel. How does the figure below compare to the shear strength of the two 5mm bolts that are holding the calipers to the mounts?

Super Glue Metal Epoxy
Shear Strength, Steel: 2500 psi ( 20%)
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Old 10-10-07, 01:41 PM
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Ok, after a bit more research, I think i might get hung up on the spacing actually. I'm still researching though.
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Old 10-10-07, 02:01 PM
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Does your current fork use a 1 1/8" threadless steerer ? If so, you can get a properly made rigid fork with disk tabs for less than 100$, and re-use your old headset.
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Old 10-10-07, 02:28 PM
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Originally Posted by pmseattle View Post
Does your current fork use a 1 1/8" threadless steerer ? If so, you can get a properly made rigid fork with disk tabs for less than 100$, and re-use your old headset.
No, hence the dilemma. 1" threaded headset. there really seems to be one affordable solution, the Dimension Disc fork in 1"threadless, plus changing out all the steering components. That would be the smart solution, and the mainstream one. I am just trying to think outside of the box here. If its completely unsafe/unfeasible then of course I wont do it, but i haven't really heard a solid answer as to why it wont work.

I know it's a crazy idea, but that doesn't mean it won't work, just because it hasn't been done before. A google search for DIY bike projects will find all sorts of wacky sh**, but they seem to work just fine. I saw a blog of a guy who built his own bike from scratch out of building foam and epoxy, plus i personally met a guy on this year's Tour De Cure in MD who was riding a bike made out of BAMBOO for chrissake, bonded together with epoxy, so i just want to know why my idea is so far out there.
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Old 10-10-07, 02:43 PM
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I don't know the difference in bonding strength between brazing and epoxy, but I believe the mount in the attachment is meant to be brazed on...

A frame builder local to me advertizes brazing on items for $30, so assuming this counts a little extra, since it is 2 attachment points, let's say $50-$60... It might be worth the peace of mind to get it done right. Especially since the majority of braking power happens with the front brake...

However, if you can find someone who knows the properties of epoxy well enough to confirm that it is strong enough, and you pay attention to your preparation of the surfaces... then I would trust a good epoxy in this application.
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Old 10-10-07, 03:10 PM
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I live in Baltimore area, Who is this builder, and is he close to Baltimore area? I would like to talk to them as i have certainly not ruled this option out.
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Old 10-10-07, 09:59 PM
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Originally Posted by arrasmithf View Post
Ok, have anything specific or just what you have put into above. The issuesyou mention I think fall into what would be considered a proper installation.

I want to add that I have used an aftermarket adapter for the rear(A2Z universal) and after properly installing, it has worked excellent without any problems this season, with the Disc brakes performing better than any brake i have used in the past. This adapter clamps over the rear dropout and holds in place with 4 small bolts + the skewer. I would guess that a basic epoxy metal which is rated for 4000 psi, will easily match/exceed the clamping force of that adapter clamp.
the mount you puctured is meant to be bolted to existing mounts in order to use a larger rotor on a fork that was designed for something smaller. it actually looks a lot like a ISO -> post mount adapter for a rock shox boxxer.

look, for this to work, you have to figure out the size of the rotor, and where you want the specific caliper you want to use to contact the rotor and then fabricate a mount that fits those dimensions, or find an aftermarket mount that'll work (not likely). Then you'll have to epoxy that to the fork and hope it won't pull away from the fork and land you in the ER.

a brake is a pretty vital part of a bicycle as far as your safety is concerned. do you really want to monkey around with that?

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Old 10-10-07, 10:16 PM
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Just a side note, most manufacturers TIG weld the disc mount, then fill in the gap with brass. Do you think epoxy is as strong as a TIG weld?
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Old 10-11-07, 08:03 AM
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Originally Posted by arrasmithf View Post
Ok, so you agree that welding new mounts to existing fork is acceptable? i haven't ruled that out as an option, but i thought the heat might cause distortion.
No, I don't agree. I suggested brazing them on.
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Old 10-11-07, 09:04 AM
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Originally Posted by fiver View Post
Just a side note, most manufacturers TIG weld the disc mount, then fill in the gap with brass. Do you think epoxy is as strong as a TIG weld?
No, but do i think that Epoxy is strong enough to do the job, Maybe. That's why I am polling. Also, while the mounts are important, I feel that the weakest part in the system is where the two m4/m5 bolts hold the caliper to the mounts. I think as long as i can match/exceed this required force, then it would work

As for the photo of mount adapter that I attached, that was the first thing I thought of that would give a flat surface to bond to the fork, and provide the sideways mounts for my Shimano calipers. If i have to fabricate the thing myself, I think i would try to create something that would clamp over the fork, then i could reinforce with epoxy.
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Old 10-11-07, 09:30 AM
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Originally Posted by OneTinSloth View Post
a brake is a pretty vital part of a bicycle as far as your safety is concerned. do you really want to monkey around with that?

I understand your point, and i don't think just anybody should try this, but at the same time I don't think its rocket science either, plus I'm not expecting my bicycles brakes to be the almighty forcefield. I never expect to do anything but slow down with bike brakes, not stop on a dime. If i wanted anti-lock systems with airbags, I would drive to work, which leads me to the point that to bicycle commute in a big city, one has to be a bit crazy anyway, not to mention I've been a big guy all my life, riding bikes with mediocre to crappy brakes on all my bikes, so It's been a real treat to even have disc brakes in the rear, just because they slow down so well, I think other big riders would agree. Either way, If you have to lock up your brakes, whatever kind they are, you are having a bad day.


With that being said, I am also very confident in my ability to build and make structural repairs, which is why i thought of the idea in the first place. I know this stuff is strong, I have used it previously for many things, even to replace metal that required drilling and tapping to receive bolts. I guess i wasn't asking whether or not that part could or should be done, that part i have made up my mind, I know it can.

Let me re-phrase the question, and put it to someone who is or has worked with a framebuilder in a similar situation. Is it feasible to add disc tabs to a cro-moly fork that didn't have them is the first place? Is there any concern with the fork itself, and if you weld/braze will the heat damage the fork( i considered welding it myself, but if there are special concerns, i may not)? I will test the spacing myslef. I have a disc ready wheel already and 6" rotor, so i will know shortly whether it all will fit.
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Old 10-11-07, 09:57 AM
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Epoxy is NOT strong enough to do this job, period. There is not enough contact area involved and one good lateral bump on the caliper will pop the mount off.

Brazing or welding will be fine. I did not notice if you have a suspension fork; if you do disassemble the left side before applying heat or you will ruin the seals.

Other than that, measure carefully, clamp securely & knock yourself out.
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Old 10-11-07, 10:21 AM
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Originally Posted by arrasmithf View Post
I live in Baltimore area, Who is this builder, and is he close to Baltimore area? I would like to talk to them as i have certainly not ruled this option out.
The builder I know is in Wilkes-Barre, but I know his prices seem to be in line with others ($1,000+ for a frame) so I assume his price for brazing is about right for what you would find if you find a local builder.
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Old 10-11-07, 05:39 PM
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Bilenky is in the Philadelphia area. https://www.bilenky.com/Menu.html

BTW, forks designed for disc brakes are different from those intended for caliper brakes. The loads on the lower fork legs and the bending moments are far different with disc brakes. Even if you got the bracket to stay, the effect of braking on steering and fork flex would be unacceptable. Buy the right fork.
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Old 10-11-07, 05:54 PM
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There is a pretty good taper on these fork legs, its an older road frame. My question answered itself tonight regardless, there is not enough clearance. The rotor rubs on the inside of the fork when monted to the rim, so all that todo was for nothing. Thanks for all the contributions...
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Old 10-12-07, 07:53 AM
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Originally Posted by arrasmithf View Post
Ok, so you agree that welding new mounts to existing fork is acceptable? i haven't ruled that out as an option, but i thought the heat might cause distortion.

A few questions about epoxy to any who might be an expert in the field.
1. Don't they glue airplanes together with this stuff now?
2. How is epoxying a tab to the fork any different than having a carbon fiber fork, which is basically fibers suspended in epoxy resin?
Yes they glue carbon fiber parts together with epoxy but that epoxy isn't any thing like what you can buy at your local big box store. Thousands of hours of research have gone into figuring out those processes and not a single one of them involve attaching a piece of metal that undergoes some pretty significant torque to a preexisting painted surface.

You'll probably also find that disc tabs aren't epoxied to a carbon fork. That part is usually a forged aluminum submember that is then attached to a carbon tube. At least that's the way it is on my Salsa.

This is a very bad idea.
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