Funk unicorn

[Swede]

Re:

Thanks for the advice.

The caps should be bonded to the top of the leg, so doing it again shouldn't reduce any of its functionality i.e. it would be the same as it came from the factory.

I assumed the grooves were there to hold the bonding material that was used previously?

 

[syncrosfan]

When it comes down to bond strength the surface prep is way more important than grooves (threads in this case). When bonding metals in professional industrial applications the surface prep is paramount. Usually they use a special etching kit that peps the surfaces at the microscopic level (much more important that something as heavy-handed as grooves). Bottom line: the better the surface prep, the stronger the bond. For hobby applications sanding the surface should do the trick. De-grease the parts with acetone, then de-grease them again, then sand, then clean again a couple of times with acetone then bond rather quickly (don't let too much time for an oxide layer to from that will compromise your bond strength). And wear gloves absolutely no greasy fingers touching the areas to be bonded. I guess those guys at Funk back then were't exactly experts in those matters they most likely too a "good enough" approach to the engineering and testing of those parts.

 

[Swede]

Re:

I've had a quick look online and I've found a company in the UK that sell the industrial Loctite products. I'll give them a call in the morning and see if they can offer any advise.

In the meantime... Anyone got any recommendations for lubrication (grease) that's elastomer friendly?

 

[Retro Spud]

I’ve got to say for those of us on the outside looking in, your problems - Challenges with the front end are making this thread even more interesting than it already was !

 

[Swede]

Re:

I’m nearly a year in and I’m still working on the frame and fork! Hopefully in the next few weeks that will be done and I can move on…

Part of me is impatient to get it done but another is secretly pleased that it’s throwing up so many challenges; otherwise why would we do this?

I got the headset race sorted using a local machine shop. If you’re interested; follow this. I think I might use them again as the rod that the elastomers slide on to is quite rusty in the other leg and might be better to replace than repair. It’s sitting in a bath of Oxalic acid at the moment, so I’ll decide later once it comes out.

 

[Swede]

Re:

I've had a bit of time to look into the options for bonding the two parts together and there are literally hundreds of options, which makes it very difficult to make the right choice when you're new to this. I've tried calling a few companies that sell this sort of thing and they won't offer any advice/guidance. Understandably, there are too many variables that will affect the final performance and consequently they just refer you back to the technical literature...

You don't seem to be able to buy Loctite 9430 in the UK but I have found a company that sells and number of structural adhesives and I've listed a few below that could be a option.

Is tensile strength the key parameter to look at when selecting the right product? This figure is based on an ISO standard and therefore it's about as good as it gets. I did see some data showing that you achieve lower bonding strengths when sticking anodised parts together (I believe the legs have been hard anodised).

 

[Swede]

Re:

Some more web based research identified a two pack epoxy adhesive with a tensile strength of 60MPa (8720psi) which looked pretty good plus I managed to talk to their technical support team over the phone .

After explaining what I was trying to do a very helpful chap at Robnor ResinLab confirmed that PX628HP was a good choice as the aluminium to aluminium lap shear adhesion was exceptionally good and this would be critical for this repair. He also advised that removing the hard anodising would give a better bond strength.

£39 later and a few days for postage a 50ml cartridge, dispensing gun and nozzle arrived... Let's get started

 

[Swede]

Re:

After 48hrs I reassemble the fork and it all seem to be working fine

 

[Retro Spud]

Nice

 

[jez-4-bikes-max]

Well done!