SEAT TUBE SLIT QUESTION

[greenstiles]

Hello this is a pic of my new no name ti frame......should the base of the slit really have a nice big round hole at the bottom.thought this was to stop the tube cracking when tightend ???? or will it be ok.if not how easy is ti to drill !

http://i257.photobucket.com/albums/hh20 ... arf006.jpg

 

[mattbrown]

just design, my STS and RTS dont have the hole at the bottom

 

[greenstiles]

Phew ! that's ok then..........

found this pic

http://www.flickr.com/photos/18bikes/50 ... otostream/

 

[danson67]

Greenstiles,

The best protection against this:

Or this:

:shock:

is a good fitting seatpost which is long enough to overlap the top tube junction.

Ideally the seat tube slot would look something like this:

The longer edge of the circle and the absence of sharp corners reduces stress at the bottom of the slot immensely...
but Ti is a pig to drill as it work hardens like stainless steel, better to file or grind it into a nicely rounded profile like your second picture

All the best,

 

[dyna-ti]

Something like a dremel to grind away a bit would be ideal as they have shaped grinding stones[maybe something like a cone shaped one :? ]
Alternatively a round hand file,one of the tapered ones is what you should use.Just work on the bottom of it till it starts to take shape.

WARNING
If you're using the dremel or any similar powered tool then you must stop every few seconds[Yes,seconds :shock: 5 or so]to prevent the cut edges from heating up as they are as thin as they are.
You will be working with a tapered tool so the cut will have a very thin leading edge,that edge will become brittle if overheated or allowed to become red or burn in any way.
Water cooling spray[from the chemist] or just plain water will do to cool it down but dont try to skimp or rush anything.Take your time,it should be done in under 1/2h.

The best protection against this

Riding on the nose of your saddle can cause this.

 

[BerthaPog]

The original pic looks like the slot has a rounded bottom, so the stress risers of sharp angles shouldn't be there. Think of it as having a round hole drilled at the end, exactly the same width as the slot.

 

[silverclaws]

It is interesting that frames still have the slot at the back of the tube, just where it can receive loads of water and trail crap from the back wheel and there increase the likelihood of stuck seat post due to corrosion and dried out abrasive particle 'glue'

But stop drilling is a good way to stop cracks and possibly prevent them from happening in normal circumstances, it is regularly used in the aviation industry on air frames.