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I don't want to excite anyone too much with this topic but... I need a glue.
It's for sticking an experimental power meter to an aluminium crank, so basically aluminium to aluminium. The two surfaces don't match perfectly (although I'm capable of making sure they're properly prepared and free of oxide and oil and stuff) but can be clamped together while an adhesive sets / cures.
I know very little about different kinds of epoxy and most of the Serious Ones only seem to be known by product codes, whereas lots of the easily available ones (Araldite, Gorilla Glue, JB Weld) don't seem to be popular with the fabricator forumites I've found in a few minutes' Googling.
So I'm hoping to consult the collective wisdom of STW. I'd appreciate any useful advice.
Would this not be a job for Sugru? Tech doc here:
When I had to stick an aluminium insert into a carbon frame I used the first stuff on this link (VM100). I don't see why it wouldn't work for ally to ally. It is incredibly strong, like nothing I have ever used before.
https://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/structural-adhesives
If not then I am sure you can find something else suitable from that website. Or give them a call and see what they say.
How much stress is there on the joint, and what happens if it fails?
It might be worth considering a thin coat of a non-viscous epoxy, applied immediately after cleaning, to bond with the surface and avoid oxidation. Allow that to cure, lightly sand it and than use a gap-filling type like JB weld.
Short answer - red araldite.
Get you surface prep spot on and everything very clean.
The plastic deformation you'll see will be well within the tolerance of araldite under normal conditions.
I can give you a longer answer but it will come back to red araldite - I work on the mechanical properties of epoxy systems, have access to all the industrial materials to formulate and still use that stuff for general purpose. It has enough viscosity to fill any tiny defects.
Is the power meter measuring the strain in the crank? If so, use an epoxy designed for attaching strain gauges.
jonba
...I work on the mechanical properties of epoxy systems...
That's what I like about STW, despite all the BS, there's actual experts lurking... 🙂
OK, now I have a question. Is there any reason these days why we should not be building lugged bicycle frames with adhesives instead of brazing?
The Athertons do.
eddiebaby
The Athertons do.
I was thinking more the traditional lugged steel classic style, ie get the lugs & tubes for a tradtional braze up job, but use an epoxy instead.
Been meaning to do it for years but hated the idea of wasting expensive tubes if it failed.
Araldite - job jobbed
No reason not to glue a lugged frame together. I did with carbon lugs and tubes, so a 'conventional' looking carbon frame. You just need a jig to hold it together as it cures, but no different to welding/brazing.
The Special Products division of Raleigh did it to the main titanium triangle of MTB tubes in the nineties.
For most everyday purposes, the epoxy in a double tube from Poundland is quite good enough.
OK, now I have a question. Is there any reason these days why we should not be building lugged bicycle frames with adhesives instead of brazing?
Plenty of non-structural bits of modern cars are glued. Structural is a different story.
The chassis on the Lotus Elise is bonded aluminium, which is pretty structural. Bits of plane wings are held on with double sided tape. Again structural.
I'm currently liking "Bob Smith Industries QUICK-CURE 5", it comes in a decent sized bottle and bonds crazy well to everything I've tried so far (Carbon, Aluminium, PETG carbon filament 3d printed parts, wood), on my test piece I broke the clamp before it failed, red epoxy failed at about 25kg, the clamp failed at 40kg (By no means scientific as it relies on bathroom scales and a 3d printed clamp squeezing it to cause shear force across the joint). They do slower cure "stronger" ones but I can't see how that would be needed by anyone.
How about one of the thicker 3M Gopro sticky spots? They're like....WELL sticky...
Folks hang cameras off them and get up to all sorts of radicalness.
Bits of plane wings are held on with double sided tape. Again structural.
I've never heard of double sided tape being used for structural joints in aviation land.
Can you point us towards an example of a type constructed using double side tape?
Back to the classic steel lugged bike frame.
There's not much surface area compared to later bonded frames.
What epoxy is recommended for that?
And how does it compare to the strength of a brazed joint?
Ok, slight mis-remember. They use 3M tape for fixing scuff strips to wing flaps. Still outside in the wind, and extreme temperatures.
We use 3M VHB tape and it's pretty good
No worries. Was expecting a school day moment!
Thanks for all the replies! And sorry for the delay - yes, as richmars suggested, the power meter contains strain gauges so needs to be very inflexibly attached to the surface, to measure the flex in the crank. However, it also could do with being not brittle, because I'd prefer the power meter to stay in place if I'm riding through gravel or other stuff that would throw debris up at the cranks / BB area of the bike.
Red Araldite sounds good - looking at Farnell's product information... is it yellow?
What adhesive did you use to stick the strain gauges? Cyano or one of the other glues that need pressure / warmth? If cyano, you need to make sure the gauge is very well sealed from moisture or they will debond after a while.
Back to the classic steel lugged bike frame.
There’s not much surface area compared to later bonded frames.
What epoxy is recommended for that?
And how does it compare to the strength of a brazed joint?
i'm pretty sure it was araldite 2015 - which also used in structural aircraft joints.