Cracked Ti frame

[danson67]

IMHO the best solution would be to avoid any more welding...cut it down and refit the clamp.
There might be a little more stress on the relieving hole at the bottom, but at least you won't have the crack in the back of your mind.
A longer clamp covering the crack well would also be fine if you can find something appropriate/suitable.

It could be welded, but it is now a very thin part of the frame with a weld start on an edge. Not easy without getting bad distortion, build up of weld material or burn back of the original metal. Ideally it would be completely degreased and cleaned and run with a back-purge through a heat-sink, which also seals the slot, to avoid distortion. Usually the seat tube bore would reamed out post weld (while still 360 degrees round), before cutting the clamping slot.
With the slot now there, the back of the weld would need to be ground out close to size, then reamed with a clamp in place set at the right size. The outside may also need filing back in order for the clamp to fit.
This all reduces the thickness of (weaker weld) material left at the site of the crack, but doesn't reduce the stress it is subject to.

These days more prudent builders would use a 0.089"/2.25mm wall insert at the seat clamp 31.8mm OD/27.2mm ID), press fitted then welded onto a 0.035"/0.8mm wall seat tube to prevent the weakness and distortion in this area. You can see the weld around the seat tube here on this Moots:


All the best,

 

[xerxes]

Re:

A + C with something like this perhaps: http://www.chainreactioncycles.com/bran ... p-prod8213

 

[legrandefromage]

I have to point out that I'm not Dan's agent.

Or am I?

 

[reanimation]

Re: Re:

A + C with something like this perhaps: http://www.chainreactioncycles.com/bran ... p-prod8213

This is what i bought for my DMRs but also had one on a Genesis for looks.
With this topic I'm wondering if I should consider one for my Kinesis decade Virtue build, or stick with the tried and tested Hope clamp/Thomson post combo that wored for the previous owner.

 

[danson67]

I'm not Dan's agent. Or am I?

Maybe, Mark...but your 10% won't keep you in beer tokens so far

All the best,

 

[02gf74]

Like this 121559892649 on ebay
18.5 mm ih height. Ot maybe one if the slotted ones.

That CR clamp looks agricultural.

 

[dyna-ti]

Thanks for the answer ,something to think on :?
What do you think to the idea of a sleeve around the outside, like a seatclamp but obviously a cut ti tube, basically wrapped around and the style that requires just a bolt.

Just a thought on what you were saying on whats left after grinding it all back or flush was that how would an internal shim be then affected ? especially it it was in there as the welding is done :?


PS
Thanks to everyone else

Like this 121559892649 on ebay
18.5 mm ih height. Ot maybe one if the slotted ones.

That CR clamp looks agricultural.

Cheers. Ill add that to the others to look at when or if i review the options.

 

[danson67]

Just a thought on what you were saying on whats left after grinding it all back or flush was that how would an internal shim be then affected ? especially it it was in there as the welding is done :?

Do you have an internal shim at the moment? Doesn't look like there's one.
If you're suggesting welding an internal shim in, you've only really got the top edge of the tube to weld. It might work, but there would be a lot of stress on a small fusion weld.

Possibly worth bonding an internal sleeve in after (or instead of) welding to strengthen the area. Just make sure that it is a decent length. Reaching well below the seatstay joint, maybe 80mm long or so.
What's the current seatpin size?

If you have already got a sleeve fitted, it will be too grubby to weld reliably. Best remove it and start again with a new shim.

All the best,

 

[dyna-ti]

Putting the finger into the tube i can feel the tube ends maybe 60mm down. This be butting ? or a 2nd tube inside,welded around the top edge i dont know. it does have hols through where the other tubes are welded in maybe indicating it was fitted prior to welding the top tube etc in place
It means the top 60mm of the seat tube is about 2.3mm for the walls., no idea what it would be below this shim, or butting end or whatever it is.

Musing a bit here
I at first was thinking that the size of the clamp has been the cause.maybe deeper should have been fitted, though that said its not a normal thing to see deep clamps on anything, ti especially
Measuring in through the bottom of the slot it reads (cheapo) 29.33mm/29.89mm so say 29.5mm and subtract 2.3mm wall thickness leaves us 27.2 approximately. That is the size of the post, clamp is 31.8mm with is the outside diameter of the tube so everything works together as it should.
Crack was level with the bottom of the Hope clamp :? implies that bit at least had room to move or flex :?

I think if a longer clamp was fitted and the area would be less likely to flex,though i think pivot would be a better descriptive thanks to the way 60mm down it opens up.

Internal shim or butting doesnt go down far enough :? The entire top must be flexing at the point the clamp tightens.

Lowering the height the seattube protrudes might prevent that, in that it could stiffen it.
Problem is the whole area is the same dimentions so if the flexability is an issue it may just crack below that.

More musing
If the lower section of the tube was prevented from moving there would be no flexing on the upper.
Problem there is it would need a very very long post which would need to drop as low as a frame bolt hole and a fixing go through from there. Self tapping might do it but 2 threads have a habit of pushing eachother apart and fitting such could deflect the post and put the top top junction of welding under constant pressure :?

Shim to the same internal at present but much further down to support the bottom of the post and prevent it from swinging and thus flexing the top at the fulcrum that is the seatclamp.


Musings over solution found ,bodge brain engaging.


Now im kind of kidding here but ...

Remove bottombracket.
Heavily grease seatpost and cap the end with something.
Fit seatpost to half an inch or so lower than normal.
Using a long hose fill the top end of the seatube with expanding foam.
Allow to harden
Remove post,just to make sure it comes out
If the problem is the end of the seatpost flexing and thus putting flex on the protruding section of the seatube then filling the gap should give the end of the seatpost nowhere to flex to :? Correct ?

Now if the expanding foam was replaced with something with a bit more density, then this bodge could do the trick
Go down in the annuls of bodging history did someone say ?

 

[WD Pro]

Expanding foam has far more 'give' than I would expect movement in that area, and it sounds like a right bodge ...

If it helps you identify how it's made, this is a press fitted / fuse welded shim :





It's very neat around the slot and the joint edges. Sorry the pictures aren't better / closer - they weren't actually for details of the shim ...

WD