Monday, January 22, 2018

Bicycle Stem Repair 3

Previously on Scrap Attack:
We built this stem upgrade which cracked after 9 months of use
Building the stem upgrade
Then, repaired it with a second tube
Repairing stem upgrade the first time
And now:

After 2 years using the repaired setup, it cracked again.  It probably didn't help that I left that sharp corner instead of welding all the way around the connection.
At first I was considering just re welding over the crack like last time, but upon closer inspection, I figured it would just crack again in another few years at the part where the stem contacts the head tube.
That, and I was still not satisfied with the handlebar height, I felt it could be even higher and closer.
To avoid having the stem crack again, I decided to machine a new stem base (like I did with my other bike here).  This way, the parts of the stem that endure the most stress would be thicker than just reusing the original stem as before.  I still reused the top 2/3 of the stem upgrade since they didn't seem suspect to breaking, the remainder of the tubing used was leftover from the seatpost ultimatum since that was some thick stuff.  Here I measured and lined up the new handlebar location on a piece of cardboard.
Starting with some 1" round stock to make the stem base from.  Drilling a pilot hole.
Then a larger hole.
Instead of drilling all the way through and making a separate cap like with the other bike upgrade, I decided to counterbore one end to accept the socket head screw, and leave some extra material on top have more space to to weld to.
Turning the outside of the bottom end to 7/8" to fit the head tube.
Milling the angle for the wedge.  This one was measured to be 35° unlike the one for the other bike which was 20°.
Comparing the new stem base with the original that was cut off.
A view of the counterbore.  I drilled out the top part a little more to save some weight, and make the wall thickness more closely match the 2 pieces to be welded (for more even weld penetration).
Lining up all the new pieces.
Now setting them up to weld on some bricks.
After welding.  I used some 6011 rod for the first pass since that gets good penetration, then 6013 for the filler passes.
Then some white paint.  Blends in with the wall pretty good now.  I figured white would a great color for an item that I would want to emphasize how dirty it gets.
One consideration I forgot to add during welding was a cable stop for the front brake.  To account for this, I turned an aluminum cable stop with a groove for a hose clamp to attach to the stem.  Another thing I noticed, since it rained shortly after this was completed, was that the bolt was tightened down so good that water would pool in the top of the counterbore.  To prevent this, I inserted a conveniently sized rubber stopper that I had lying around from another project that never happened.  Looks like the law of scrap alchemy also applies to accidental purchases and manic shopping sprees as well!

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