I want to bond metal to metal as I’m fitting an old Syncros seatpost clamp onto a smaller diameter post, for my daughters bike.

The two parts (head and shaft…) are not quite a snug fit so will need a bonding agent to hold them in place and my first thought was araldite, but is there something stronger?

like a super-araldite….

Araldite does come in different types, for different materials, strengths and curing (setting) times. I don’t have a list in front of me but it is available if you look.

But generally the strongest bondings agents will be 2-part epoxies. For high strength you’re going to have to compromise the bonding time and will likely take hours (4+) to cure enough to handle it. So you’ll want a clamp or jig to hold it.

If you’ve got a gap and uneven contact that’s bad, but you’ll absolutely need something with as little shrinkage as possible. Epoxies are pretty good for this.

Also remember that preparation is key. Roughen the surfaces well, make sure it’s clean and grease/dust free.

If done properly you could end up with something approaching the strength of the parent material but this is really unlikely to be the case. Are you sure you want to do this on a seat post? How much would a 2nd hand one cost??!

Seriously, don’t bother. It WILL fail and there is no way of knowing when or how. Serious injury is a distinct possibility

I might be wrong but it sounds as though you just want some sort of shim between the clamp and the tube. Cut up an aluminium drinks can?

yeah I know it sounds bad but it’s actually not as risky as it seems… 😯

The post slides into the head about 2cm so there’s some support there, and a decent surface area for the glue to operate on, and, as I said, it’s almost a snug fit anyway, so the glue should work well in that respect.

The reason is that I need a 22.2mm post with a clamp head, and they aren’t the easiest to find.

The current OE seatpost+seat is a one-piece affair and is glued so it no different to that in effect.

…the shim is another option

I can also drill and bolt it, which would add security.

Are “2-part epoxies” different to araldite Jon

If so, what brand name do they go by?

they are pretty easy to find.

google BMX 22.2 seatpost and saddle clamp

but def drill and bolt it.. I did this as an emergency bodge at a race with a DH post that un-bonded itself in a practice crash – used it for the rest of the season with no issues

they are pretty easy to find

mmmmm

Can we get back on topic…..

there is this

http://www.amazon.co.uk/ARALDITE-RAPID-STEEL-ADHESIVE-STRONG/dp/B000WA9QIU/ref=sr_1_1?ie=UTF8&qid=1292087125&sr=8-1

anything better?

reggie – araldite is just a brand name. AFAIK they’re all 2-parts i.e. you have to thoroughly mix 2 parts. Then it will start to cure and you now have a limited time to position your components. I used Araldite 2011 as shown below. I used lots of it though, so bought a big applicator gun and mixing nozzles, they were ace.

I was getting a little carried away earlier – the stuff I used on my post grad project isn’t ‘consumer’ stuff. You can probably get hold of it through RS or another industrial supplier though.

Araldite selection guide:
http://docs-europe.electrocomponents.com/webdocs/0034/0900766b80034361.pdf

The important thing is the force per unit area. This is in the order of 10-20 MPa (N/mm2) where the aluminium alloy is stronger. Luckily you say you can get overlap, which will be key and give you a much larger bonding surface area than I thought.

That’s actually how my project was held together although I did the sums and needed a much larger contact area than you’ll be getting. The pigot goes inside the carbon fibre tube almost 2 x Diameter. When one of these failed I repaired it by drilling through and holding with lots of screws, which luckily didn’t cause the tube to split.

However you may be able to get hold of one of these and find out the relative strengths of them:

http://www.huntsman.com/advanced_materials/eng/Markets/Adhesives/For_Consumers/Araldite%C2%AE_Consumer_Adhesives/index.cfm?pageID=5902

So, with some overlap it might not fail immediately. With a bolt through it might not fail catastrophically. When it does fail it might not injure anyone.

Some photos would let us have a bit more idea of how badly/quickly it’ll fail!

in a practice crash

why are you practicing your crashing?

JB weld is good, probably similar to Araldite though…

The rapid steel stuff you’ve put a picture up of- may not necessarily be any more suitable than the general purpose (high strength) Araldite.

The general purpose stuff is likely to be 2011 and therefore (longer setting but) higher strength than the metal coloured stuff. It’s a bit of a guess though, unless you can find somewhere that Araldite correlate the consumer stuff to the specific model/range.

http://www.huntsman.com/advanced_materials/Media/Araldite2000PLUS_METALS_A4_ENG_LoRes.pdf

/edit – and it’s worth saying that in my model in the photo above – I had excellent coverage. I machined applicator nozzle holes through the CF tube and grooves in the spigot inside to guide the epoxy and fill the gap up. You can see the epoxy filled remains of the hole if you look closely (just above the right hand most screw). I’d then pump the gun until araldite was squirting out of the ends of the spigot, and then some.

And one still failed.

everyone should practice crashing 😉

There’s a company called marine ware who will sell you industrial adhesives.
More than anything surface preparation before gluing…or bonding is the key.
Araldite is a perfectly good adhesive if you get the right one though really it’s just a two part epoxy padded out with filler so people don’t get it wrong when it mixed…the glue is ok often the surface prep isnt

Look for a toughened epoxy they are less brittle Than standard bonding agents

Some photos would let us have a bit more idea of how badly/quickly it’ll fail!

hang on, I’m just cooking tea…

as said, head is from old Syncros post. Black post is 22.2mm.

2cm overlap

Could you machine a matching hole in the black post? The you could slide it all the way in a get lots of contact and a good connection.

Could that work?

Jon, that’s what I thought too but I don’t have a drill bit thick enough (biggest I have 10mm) so temporarily disgarded the idea but it may be worth investing in a bigger one to do it right.

That would effectively double the coverage to 4cm.

What’s key is that it would also increase the moment arm (or rather second moment of area). If you double the height, the (bending) strength has increased x 4, and so on.

It’s definitely worth doing right first time when glues/bonding is concerned. See what you can borrow 😀

right…. new drill bit is in order methinks 8)

Do you have access to a pillar drill anywhere that you can use to make it easier?

yep I’ve got one.

The reason is that I need a 22.2mm post with a clamp head, and they aren’t the easiest to find.

*Runs off to garage with verniers*
Back soon.

Got a nice 25mm one if that’s any use?

it’s a mini bmx that runs a 22.2mm post. The standard setup is a combined seat+seatpost a bit like this:

but I want to run a standard railed seat, hence the DIY. You can get plenty of clamped posts 25.4mm and upwards but 22.2mm posts are pretty thin on the ground, from what I’ve seen (contrary to the comments above). I’ve found a steel silver one here:

http://www.dotbike.com/productsP8453.aspx

but I wanted something lightish and black really. There are also some US exotica but I’m not going down that route for a kids bike.

Silver Haro ones on ebay too..

People seem awfully concerned about a bonding agent failing.

Have they ever considered what holds their stanchions on to the fork yoke?

I would happily use an epoxy for this job.

Jeez don’t you lot watch tv? NO MORE NAILS.

Seriously though:

Have they ever considered what holds their stanchions on to the fork yoke

it’s a press fit isn’t it?

Silver Haro ones on ebay too..

cheers, hadn’t spotted those (silver though…)

I’ve used Chemical Metal on loads of things on cars.

A long long long time ago, I was quite good mates with people who were mates with Keith Bontrager.

Somehow I ended up with one of the early “Titec” posts that he made with them. Carbon with alloy inserts and a bonded head.

The head came loose.

I remember having a lecture at uni (HarryTheSpider was there too) with the one decent lecturer we had (who once told us to look up at a beam, imagine an M8 bolt, and imagine 3 Vauxhall Cavaliers hanging off it as that’s what the tensile strength of an M8 bolt is)… anyhow… this lecturer who said he’d broken one of his wifes plates, and he’d stuck it back together with NORMAL Araldite (Not the RAPID stuff) and (here’s the good bit, especially at this time of year) – LEFT IT IN AN OVEN ON LOW FOR A DAY.

Heat curing the good stuff gives a ridiculously strong bond. And with degreasing and careful assembly, that’s proper “aerospace” quality bonding.

And so that’s what I did with the Bontrager post. Cleaned it. Glued it. Left it sat on a gas wall heater for a couple of days.

It never budged in 5yrs.

HTH

Shameless name dropping!

cynic-al – Member
‘Have they ever considered what holds their stanchions on to the fork yoke’
it’s a press fit isn’t it?

Some are, but others have a bonding agent.

I’ve pressed a few out after heating the yoke and most seem to have had some form of glue there. Maybe it was just old suspension oil, but it has a different smell.

Anyone know?

All the ones I have seen are an interference fit – glue would not work as there is no space for it – the hole in the yoke is smaller than the stanchion – hence the interference fit. ( marzochii call it cryofit)

I haven’t tried it on any alloy stanchion forks yet. I should change my original quote to

epicyclo – Member
People seem awfully concerned about a bonding agent failing.

Have they ever considered what holds their stanchions on to the fork yoke?

They are sitting there with no clamp or glue

🙂

If both parts are aluminium then why not visit your friendly local engineering fabricators and see if they’ll weld the two bits together ?

Have you taken any apart tj?