Ye ol' chop and slot~~

[drietz]

Reaching out to the experts here, with what I am sure is either a simple or controversial question.

Recently found myself with a frame with a seatmast that is too short (but a top tube that's just right!) and so I'd like to cut it off and insert a post.

I have everything I'll need, including a reamer to bring the ID from ~30.55 to 30.9, except for an answer to this question:

If I want to slot the front of the seat tube (as opposed to the rear, so I can keep the collar facing back and keep stress off of a possibly thin seatpost), how much seat tube should I leave above the weld at the top tube junction? Or, more coherently, how much seat tube extension above the TT should I have? And as a follow up, how far above the weld should I drill the hole at the end of the slot?

Thanks for any and all insight!

Wishing you all a good time all the time,
Daniel Rietz

[progetto]

So the frame has an integrated seat tube that is too short and you want to turn it into an internal seatpost frame, is that the question? You should be asking what strength and longevity are you taking away from the frame by reaming the seat tube down to take a larger seat post than what the tube was designed for. Seat tubes need to have a thick butt or sleeve where you have a top tube, seat tube, seat stay junction. Without it, a crack will develop sooner or later.

Reaching out to the experts here, with what I am sure is either a simple or controversial question.

Recently found myself with a frame with a seatmast that is too short (but a top tube that's just right!) and so I'd like to cut it off and insert a post.

I have everything I'll need, including a reamer to bring the ID from ~30.55 to 30.9, except for an answer to this question:

If I want to slot the front of the seat tube (as opposed to the rear, so I can keep the collar facing back and keep stress off of a possibly thin seatpost), how much seat tube should I leave above the weld at the top tube junction? Or, more coherently, how much seat tube extension above the TT should I have? And as a follow up, how far above the weld should I drill the hole at the end of the slot?

Thanks for any and all insight!

Wishing you all a good time all the time,
Daniel Rietz

[drietz]

Bill, thanks for the heads up. The frame is a Gaulzetti Corsa, and as far as I know, Craig spec'd the seat tube with the possibility of chopping/slotting in mind.

So my original question still stands, and I feel assured in the structural integrity of this undertaking.

[hampco]

I spec my frames with 20 or 25mm of tube above the top tube depending on size and amount of seatpost showing.

Good luck with the seattubeectomy!

[crumpton]

get a campy clamp and slot in the back. the campy clamp acts more like a true clamp and not just a pinch. this will allow you to slot the back while keeping the tube short and looking good. make the slot at least 8mm below the bottom of the clamp and clear of the welds. determine all that before you chop as the joint is gonna dictate the limits.

[progetto]

Assumed it was steel. A corsa is a slightly different situation. Sounds like you are on the right track, Steve and Nick have said the word.

Bill, thanks for the heads up. The frame is a Gaulzetti Corsa, and as far as I know, Craig spec'd the seat tube with the possibility of chopping/slotting in mind.

So my original question still stands, and I feel assured in the structural integrity of this undertaking.

[drietz]

Great success!