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Thread: Repairing a cracked seat tube slot...forever.

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    Default Repairing a cracked seat tube slot...forever.

    This repair highlights a couple of issues that are important to pass on;

    1.) For new builders, you need to understand that most seat tube stock IS NOT prepared to be slotted into a frame and built off of. The majority of standard tubes are too light in wall thickness to support the stress of a leveraging seat post and the mechanical weakening that comes with slotting. You must address the problem by one of three options; using an externally butted seat tube designed with a thicker wall for the post insertion butt, using an external sleeve that is brazed over the seat tube and then built off of ala early Groves/Ritcheys etc, or turning down an internal sleeve that is pressed into the seat tube to provide additional strength. Without it, you will most certainly develop a lateral crack extending from the slot around the tube much like this example.

    2.) If you are going to perform a repair, do it right. When this frame cracked, a repair was attempted to correct the situation, obviously by a builder who has little experience/understanding of mechanical stresses and how to address them. In this case, the lateral crack from the seat tube slot was simply brazed over top of with silver, a band aid to please the customer for the moment and obviously not for the long term as no attempt was made to limit the extension of the problem or to support it for future use.

    3.) The disadvantage is that you will need to step down a seat post size, but with the availability of posts, finding just the right one should not be an issue.

    With the paint off, here you can see the crack has extended through the silver patch...
    DSC02241.JPG
    The game plan for this repair is to remove the poor silver patch, clean up the tube, fabricate an internal sleeve to improve the tubes ability to sustain the stresses of riding, and then to limit and clean up the cracked area.

    I started off by cutting off the seat tube top as close to the top tube as I was comfortable with, keeping the cut straight and parallel. I also removed all the silver patch that was applied and drilled out the end of the crack to stop it's forward progression. In progress in this pic...
    DSC02242.JPG
    Using a machinists square and a file, I then worked around the tube insuring all aspects were as flat as possible.
    DSC02243.JPG
    I then cleaned up the inside of the tubing with a bit of a barrel sander, lightly applying pressure so as to keep the ID constant.
    I then got to work on the new sleeve insert, cutting the selected tubing in the cold saw. As this repair will rely on an internal sleeve, I has to choose a piece of tubing that would allow me to keep the OD the same as the original seat tube, have a great enough wall thickness to turn down the wall for the insertion portion so that it still adds strength to the section, and have an ID that will accept a current seat post size...quite a few variables to consider.
    Once cut to rough length, the sleeve is squared and deburred in the lathe, then I began to turn down the OD to fit the ID of the seat tube...
    DSC02246.JPG
    Here you can see a quick dry fit to insure I have the tolerances correct before pressing into place...
    DSC02248.JPG
    The piece is then taken out, everything chemically cleaned then pressed into place...
    DSC02249.JPG
    A thorough cleaning to get rid of the balance of the mill scale, a wipe with acetone again, and it's time to weld the two pieces together.
    DSC02252.JPG
    I then drilled and slotted the front aspect of the extension for the compression duties. I am a firm believer in slotting the front of the tube. Why you ask? Well, it never made any sense to me to place the weakest point of the tube, the slot, at the rear of the tube where a majority of the stress from the seat post leverage was concentrated. By moving it around to the front, it allows a uniform dispersal of stress in the rear of the tube.
    Some of you may ask why I did not slot the extension prior to pressing it into the tube, an act that would have been easier outside of the frame. Well, I've been caught once or twice having the insert turn just a skoosh when pressing into the frame and then been stuck with aligning the slot, no small task with the pressure fit of the sleeve.
    DSC02253.JPG
    Something to watch out for if attempting this type of repair, you must have good heat control with your tig torch so as not to burn through and cause irregularities inside the seat tube that will cause interference with your seatpost. Tig bead is a bear to try and ream out, so control is the name of the game. Here you can see just a slight heat shadow on the inside...no distortion present.
    DSC02254.JPG

    The interior of the tube can then be reamed to insure a perfectly round diameter and a final once over to cosmetically insure all is good and it's ready for paint.
    DSC02256.JPG

    cheers,
    rody
    Rody Walter
    Groovy Cycleworks...Custom frames with a dash of Funk!
    Website - www.groovycycleworks.com
    Blog - www.groovycycleworks.blogspot.com
    Facebook - https://www.facebook.com/pages/Groov...s/227115749408
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    Default Re: Repairing a cracked seat tube slot...forever.

    Thanks for sharing this Rody!

    It's great to see such a wise approach to frame repairs
    Andrea "Gattonero" Cattolico, head mechanic @Condor Cycles London


    "Caron, non ti crucciare:
    vuolsi così colà dove si puote
    ciò che si vuole, e più non dimandare"
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    Default Re: Repairing a cracked seat tube slot...forever.

    Classy.
    Is that a Grove or a Brodie?
    Nice job, R.
    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com
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    Default Re: Repairing a cracked seat tube slot...forever.

    This is a great post, thanks for doing it. Now if I only I had a lathe! It's seems ridiculous that anyone would try to braze a crack like that, might as well just put some duct tape or jb weld on it, would have about the same longevity as that little puddle of silver.
    Miles - Alameda, CA
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    Default Re: Repairing a cracked seat tube slot...forever.

    Thanks Rody!
    Mike Anderson
    Wellytown
    Nooooo Zeeeland
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    Default Re: Repairing a cracked seat tube slot...forever.

    Rody - your expanse of knowledge and willingness to share it constantly amazes and impresses me.
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    Default Re: Repairing a cracked seat tube slot...forever.

    Definitely a creative solution. Thanks for taking the time to put the tutorial together.
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    Default Re: Repairing a cracked seat tube slot...forever.

    I felt bad that the original post in the general session closed before I could get an answer in, just short on time.

    Steve, the frame is neither a Grove or Brodie; an east coast builder who is not as active as in the 90's, the builder really is not important as shit eventually breaks, this was just an object lesson.

    This is actually a repair from 2009 that I mined out of the blog for reference. Some day I need to add to my web page an instructional area with stuff categorized for reference, there is so much info buried in the blog but it is tough to find it if you are not me :)

    cheers,

    rody
    Rody Walter
    Groovy Cycleworks...Custom frames with a dash of Funk!
    Website - www.groovycycleworks.com
    Blog - www.groovycycleworks.blogspot.com
    Facebook - https://www.facebook.com/pages/Groov...s/227115749408
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    Default Re: Repairing a cracked seat tube slot...forever.

    Nice post Rody (no pun intended). Thanks for sharing

    One thing I would add regarding irregularities on the back side of the weld when welding in/around a seat tube: If you have the ability to purge the tube when TIG welding, DO IT. You still have to have good heat control, (back purging is not a crutch for heat control), but it will really aid in the job and help to ensure a good clean back side of your weld. In addition when you need to ream the inside of the seat tube, the job will be that much easier and you will also extend the life of your reams. This also applies to the head tube and bottom bracket.

    I guess you could call that "Sugar Free".
    Kristofer Henry : 44 BIKES : Made to Shred™
    www.44bikes.com · Flickr · Facebook · Instagram
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    Default Re: Repairing a cracked seat tube slot...forever.

    Quote Originally Posted by fortyfour View Post
    If you have the ability to purge the tube when TIG welding, DO IT.
    An absolute for new fabrication and another necessary factor for repairs... thanks for kicking in Kris.

    Repair work is most troublesome as years worth of contaminates are present despite your best effort to clean them away. The above was cleaned with multiple abrasives and acetone, purged, and welded quickly and smoothly. Still there is the occasional micro volcanic eruption when something nasty gets pulled through the puddle and pushed to the outer edges.

    Repair work such as this really walks the line between making the situation better or quickly spiralling into a mess that is difficult to recover from.

    Put the odds in your favour and prep/clean/purge/control heat/move fast to get the job done right.
    Rody Walter
    Groovy Cycleworks...Custom frames with a dash of Funk!
    Website - www.groovycycleworks.com
    Blog - www.groovycycleworks.blogspot.com
    Facebook - https://www.facebook.com/pages/Groov...s/227115749408
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  11. #11
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    Default Re: Repairing a cracked seat tube slot...forever.

    Quote Originally Posted by Rody View Post
    I felt bad that the original post in the general session closed before I could get an answer in, just short on time.
    I closed that thread because it appeared to be a consumer asking about how he could
    fix the issue, rather than how some of us would in a time/cost no object world atmo.
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