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Feckin Eejit!
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Discussion Starter · #1 ·
Puts flame retardant suit on

So the stock sub for my bike is aluminum. I'm just searching for the best way to have a custom tail and keep my weight down.

Is this a valid way to have a steel support on an aluminum frame?


Bolt thru the aluminum into the steel and weld steel bolts to the steel support with epoxy between the 2 metals.

Alternatively, I'm starting to think I should just cut the support and gussets off my OE sub, shorten it all and have someone that can tig put it all back together... So I can have my aluminum.

Yes I'm stubborn.
 

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Can you post a picture of the bike where the subframe will mount? Can you weld some U shaped tabs that will allow you to bolt the subrame to?

Don't use epoxy, it won't help at all. Way too brittle by itself.
 

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lɐʇuǝɯᴉɹǝdx&#4
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With a decent bolt up design you would not need the welding or epoxy. Its not like there's 3 bolts on each side plus weld plus epoxy holding the aluminum sub to an aluminum frame, so why would you need it with steel?

Hell, my custom fork (and pretty much all forks, when you think about it) holds aluminum and steel together with nothing but bolts. Bolts can easily exert a lot of clamping pressure; with a good design, its the friction between the clamped faces, as much as the sheer strength of the bolt, that prevents movement.
 

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hate us cuz they ainus
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Don't use epoxy, it won't help at all. Way too brittle by itself.
That is not entirely true.

Panelbond adhesive is stronger then welding. In most cases when the two pieces are preped correctly the substrate will rip before the epoxy let's go. Most insurance companies won't level let you weld on a car anymore because epoxy is cheaper and stronger.
 

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That is not entirely true.

Panelbond adhesive is stronger then welding. In most cases when the two pieces are preped correctly the substrate will rip before the epoxy let's go. Most insurance companies won't level let you weld on a car anymore because epoxy is cheaper and stronger.
I agree with you, yes there are crazy strong epoxies out there, but something a consumer could get their hands on at a resonable price?

3M Panel Bond states not to use on structural applications:

This product is not intended to bond structural components of a vehicle such pillars, rockers, or frame members
I wouldn't trust any epoxy to hold my subframe, even as a secondary measure.
 

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hate us cuz they ainus
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well shit! neiter one of the ones i use are 3m but they both do say for pro use only. never paid any attention to that i guess.




and yes you wouldnt try to "glue" a cars sub frame together but thats like saying you wanna try to glue the neck tube onto you bike.

i can assure you the skin of any unibody car is very much structural. i actually have a quarter im replacing on the frame machine now. as you can see it is the only thing supporting the top of the trunk





one other big reason why you should at least use some kind of epoxy even if you do bolt it together is galvanic corrosion steel and alu. dont like to be touching each other for extended periods of time
 

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lɐʇuǝɯᴉɹǝdx&#4
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> one other big reason why you should at least use some kind of epoxy even if you do bolt it together is galvanic corrosion steel and alu. dont like to be touching each other for extended periods of time

Yeah, I've heard that. Not sure how I'm gonna deal with that. For most parts I'll be painting the steel, but I've got a couple cases where aluminum slips inside a very tight steel 'pocket', and a couple bolts pierce the whole thing. Its tight enough that the paint might scrape off (or even interfere with the fit). Might just use a lot of grease / anti seize (works for aluminum bicycle seat tubes in steel frames).
 

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> one other big reason why you should at least use some kind of epoxy even if you do bolt it together is galvanic corrosion steel and alu. dont like to be touching each other for extended periods of time

Yeah, I've heard that. Not sure how I'm gonna deal with that. For most parts I'll be painting the steel, but I've got a couple cases where aluminum slips inside a very tight steel 'pocket', and a couple bolts pierce the whole thing. Its tight enough that the paint might scrape off (or even interfere with the fit). Might just use a lot of grease / anti seize (works for aluminum bicycle seat tubes in steel frames).
Plenty of grease and check up on it every so often. The grease creates a boundary layer between the two metals, preventing galvanic corrosion.
 

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Feckin Eejit!
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Discussion Starter · #10 ·
Can you post a picture of the bike where the subframe will mount? Can you weld some U shaped tabs that will allow you to bolt the subrame to?
Main frame is alloy and it's all a bolt on affair.
Heres a shot of the top rails connecting to the frame


Side view


Same bolt is used for upper mount and lower.

one other big reason why you should at least use some kind of epoxy even if you do bolt it together is galvanic corrosion steel and alu. dont like to be touching each other for extended periods of time
So does paint. Unless you're running bare steel against bare aluminum you're gonna be fine. And I'm sure Ahks intends to paint his steel tubing.
Powdercoat is probably the end game. How long would that last? I'm assuming all my weight bouncing on it will add some friction to the bolted joint and rub off the coating. Is there some coating that would bond better and be a better barrier between dissimilar metals?

If I do this design I'd like to either weld the bolts into the bottom rail or weld in nutserts... primarily so I can hide all the hardware.
 

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Is my bike ok?
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Nobody worries about the bolts they use to fasten two pieces of ally with. Like you said, your bike is out together with them.

Steel bolts on alu frame? 0_0

Don't worry about galvanic issues. Its a real thing, but you're fine.

If you are planning hare scrambles in brine water...yeah. Otherwise, just build and ride.

Nutserts might wiggle loose, good call on welding that.
 

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Well it isn't connected to anything. :D

Seriously though I'd add some sort of support for the front of the seat/rear of the tank area.
 

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lɐʇuǝɯᴉɹǝdx&#4
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For a good implementation of a spindly support for a unit with a lot of space under it, take a look at Beucephalis by Loaded Gun Customs. Basically, instead of gussets to prevent fatigue at the connections, they use spherical bearing rod ends (in carbon fiber rods, no less), which allows the joint to flex without concern over cracking the weld (or bolts). Its a fairly common solution for subframe mounting, and a good one both functionally and cosmetically. Would also resolve your upper end connection quandry.
 

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Feckin Eejit!
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Discussion Starter · #17 ·
Someone in chat suggesting that.


Are these just carbon wrapped... or did they use carbon tubes?

I've done some reading on bonding CF to metals and would seriously dig draping some CF on my toy :p
 

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lɐʇuǝɯᴉɹǝdx&#4
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Pretty sure carbon rod- would be simpler than wrapping, and probably cheaper. I'm doing the same thing for my steering links (including red anno hiems); got some 15mmx1mm wall tube, knurled half inch rod just slides in (which will get threaded for my 5/16 hiems - those things they used are huge, probably stronger than the tube by far, and I need actual adjustment; my guess is they just glued the heims in). The carbon I got cost like $60 shipped for 4x1 meter on ebay / alibaba. I can stand one on the floor and put pretty much all my weight on it (as a column) and it might flex a bit, but no buckling.
 

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Is my bike ok?
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What is the best way to join a heim to carbon rod? Seb, I remember seeing your "knurling" on your hossack build, which should work fine. Especially under compression. But are there any other methods?
I'd thought about an end cap. Female threads to accept the heim. Something that slips inside the tube, but also has an outer...cuff?... to dress up the outer edge,too. Maybe a clamp-on type deal? Would get bulky and negate weight savings, though.

Epoxy is ok, but some sort of direct mechanical connection would be cool. Aside from embedding the insert while the rod was being produced my mind can't think of anything. Is epoxy all that is ever done?
 
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