Heat Treatment of Unknow Aluminium Alloy

[Sub MandrelParticipant @submandrel]

Even as I start to type this I know what a stupid idea it is, so think of it as a thought experiment, not a real plan…

 

I’ve got ancient Halson Inversion forks on my mountain bike. They have been battered by heavy landings and skill-free riding and they have bent where they leave the fork crown. this summer the bend was properly noticed, and seems to be getting worse surprisingly they still work freely, but with less than 1/2″ of trail the bike is very twitchy, and I worry about work hardening and a snap.

 

So they have to go. But I couldn’t help wondering if they could be saved.

 

 The forks are glued into the crown. I wondered if it would be possible to remove them with gentle heating, then straighten the tubes under a decent amount of heat. They are an aluminium alloy of some kind, very strong and tough (no sign of cracking although they have bulges at the bend). I wondered if it would age harden on its own?

 

No! I must not be stupid enough to try this, and machining 10″ of perfect interanl bore for new tubes is beyond me.

 

So I’ll have to save up for new forks

 

Neil

[Sub MandrelParticipant @submandrel]

[Axel BentellParticipant @axelbentell]

 Not unthinkable you have hardend spots where they´re best or bulged, can not be mended. They are made by cold forming.  When they crack they crack good, thats aluminiums downside. Steel gives fair warning. But it´s hard to give advice w o seeing parts live of course.

[Axel BentellParticipant @axelbentell]

best=bent

[John OlsenParticipant @johnolsen79199]

Attempts to straighten bent motorcycle forks were always regarded with a great deal of suspicion when I was riding back in the seventies. The general opinion was ” you can’t bend things straight”.

 

Now making new tubes should be possible, although it will depend what machinery you have. You might want to line bore the internal bore, with a between centres boring bar for instance. If your lathe is not big enough for that, you could use a setup like I used for my steam launch main bearings. I made a boring bar that ran in a pair of pedestal bearings, bolted to a flat table. The engine bedplate was bolted down between them, and by traversing the rotating bar through the bearings the bores were machined. In my case the bar was rotated by an ordinary electric drill. The fine feed for the traverse was arranged by using the table of my mill drill to mount the work, so that by winding the handle on the table the job and the pedestal bearings moved. The drill was held down on a nearby workbench and drove the boring bar via some rubber hose couplings. Very crude, but capable of doing a good job.

 

You would also have the problem  of making sure you had suitable material.

 

regards

John

[adyParticipant @ady]

If you’ve hammered them enough to bend them then only a proper new set will do.

 

Not worth the risk doing otherwise.

 

If you crock yourself it can still be an issue decades later.

Edited By ady on 08/09/2010 23:07:57

[John Stevenson 1Participant @johnstevenson1]

Posted by John Olsen on 08/09/2010 22:30:29:

Attempts to straighten bent motorcycle forks were always regarded with a great deal of suspicion when I was riding back in the seventies. The general opinion was ” you can’t bend things straight”.

 

 

regards

John

 .

 

John, if you are talking about the steel fork tubes we used to straighten these all the while and very successfully.

We used to push a piece of plastic waste pipe over them as close a fit as possible given the limited sizes to protect the chrome, then lob them into a big powered set of sheet metal rollers.

 

Start up and let them run giving a tweak at each end every so often until they couldn’t go no further.

Used to take about 10 minutes per leg and because of the rolling action they came out dead straight.

 

There used to be a big pile of them stood against the roller on a Monday morning !!

 

John S.

[Sub MandrelParticipant @submandrel]

Thanks for not being rude guys

 

Some nice ideas/stories there!

 

The tubes have the bearing surface on the inside and are slotted for a brace that keeps the smaller lower parts in line (hence “Inversion”). Miy 7×12 mini lathe hasn’t got along enough bed to bore out new ones.

These forks are so old the ‘elastomers’ (you can’t get them anymore) are all squashed so If fitted the best to one side and replaced the other side’s with clutch springs and alloy centering spacers. Performance is now fairly poor so it’s time to kiss them goodbye – I already worryt when braking ahrd at high speed.

 

I’m surprised by how cheap some of the resonable forks are on ebay. I’m not as ‘radical’ as I was 15 years ago and my main interest is keeping the bike light, so light forks with 50-100mm of travel will be great.

 

Neil

[Author]

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