What tolerance fit for titanium / aluminium.

Afternoon, I'm making some aluminium inserts that need to be a very secure fit in a titanium tube which is 25.2mm ID, 1.6mm wall thickness.

Also looking to use bonding for lubrication on the titanium and for fixing it stronger.

Obviously it needs to be a tight secure fit, but not too tight that the titanium sticks.

What sort of tolerence would you reccomend for the aluminium inserts?

Thanks.

Um, that sort of doesn't make sense! Do the inserts need to be fixed in the titanium or not? And why would you bond for lubrication and fixing it stronger. Am I missing something?

By lubrication I mean to help prevent the titanium galling, hopefully smoother pressing in.

It's a permanent joint.

Chris,

638 Loctite on a sliding fit would be fine, I think.

MichaelG.

Edited By Michael Gilligan on 19/07/2015 16:36:25

Thanks, I happen to have some 638!

I'm recreating these forks in the picture below, it's the aluminium dropouts at the bottom of the forks I want to fit intotitanium legs.

http://www.goatsurfer.com/images/RC30_2ndGen_front.jpg

Nice looking forks, Chris

**LINK** for the convenience of others.

MichaelG.

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P.S. ... Useful document, here

 It may be worth using an activator ... Probably best to try a test piece first.

Titanium is considered inert, and aluminium only weakly active, so 638 may cure more slowly than usual. ... It does no harm to the joint strength though.

Edited By Michael Gilligan on 19/07/2015 17:08:47

Ok thanks.

You you still think a sliding fit?

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Yes ... Shouldn't be any problem,

and [pace, Neil] it will avoid the 'galling' that you might get with anything tighter.

MichaelG.

Very retro Chris!

I finally scrapped my Halson Inversions a few years ago

The elastomers had become unobtainable and I'd managed to kink the tubes below the crown - too many heavy landings =:-0

Neil

Edited By mike mcdermid on 20/07/2015 00:07:42

Edited By mike mcdermid on 20/07/2015 00:08:53

Edited By mike mcdermid on 20/07/2015 00:09:26

Very interesting, Mike

I bow to your wisdom.

MichaelG.

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P.S. ... Just found this Spec sheet for 3M DP420

Thanks, just realised who you are!

The legs are likely to have aluminium inserts in the top down to around the brake boss area to prevent flexing and the tops getting crimped. I have a dropout made now so can calculate how much heavier these titanium ones are compared the the original steel forks!

Mike,

I would be grateful for the benefit of your experience [and I suspect that others would, too]:

Although Epoxy resins are excellent in many respects, I have seen a number of joint failures on Aluminium alloys; and these were [I believe] typically down to inadequate surface preparation. ... We had great success with Araldite 2002, on glass/epoxy [presumably you remember Ciba Geigy 'F-Board'], but results on Aluminium alloys were much less predictable.

Where the joint design permitted; we preferred to use Loctite 638, and found this to be 100% reliable [even with very rudimentary surface preparation] ... and this was why I recommended it to Chris.

Now: Your experience is much more sophisticated than mine, so the question is: How do you prepare the Aluminium alloy surface, to ensure good bonding? ... Chris's forks project would be an ideal example for a 'Tutorial'.

Many Thanks

MichaelG.

Finished now.

Thanks.

Edited By Chris Denton on 27/08/2015 13:43:29