cheap insurance atmo -

here is an exposé, lesson, safety net, and more, rolled into one atmo. i have been brazing up forks on and off for two days and had about 10 in the bag when the last unit was loaded in the fixture. i prefer doing some things one at a time, and other things en masse. data point - en masse does not mean in massachusetts. since i have only been back to work for a week or so, i decided to light up all the blades. typical me, self-absorbed and shit, i was smarting all along the way with how well it was going despite my hiatus from the bench, and also reveling in how tight the tolerances and brazing lines were coming out. when i got to this last guy, i had the second-guess thing descend on me; mister second-guess is a guy you don't wanna meet when you make a frame, and especially when you are making a fork atmo.

when i completed the assembly task and washed off the flux, i noticed that the linearity reading using the M+L table told me that the center-line of the tips, though at a nice 101mm OLD width, was over to one side of the steering axis by nearly 2mm. that falls outside of my comfort zone with respect to what i would willingly align into spec. but, to borrow a phrase that pal CPG often used, "but that's just me". i guess if it was a B model (sic) or a team frame, i might have leaned on it and showed the fork who's boss, especially since it was the last pair i was gonna braze for a while. but second-guessing won me over and i decided to sacrifice the fork in the name of low budget R and D. for me here at the new presidential palace, that means destroying the fork and seeing how far i can bend anything bendable before something appears truly broken. in short, despite the alignment issue, i want assurance that the brazing will stay intact until i can't push and pull any longer.

the pic set on flickr was loaded in order. i shot close-ups and at regular distances so you could see what i saw. the long and short of it is that once the tip width got to near 12", i couldn't get the blades any further apart for fear of tearing the bench out of the wall, or breaking my elbows trying. the entire sacrifice was done with the steering column firmly clamped in the bench vise. only after i got to the 12" mark did i begin to see a slight blem (i used MS paint program to make it clearer for you to view. notice the red marks on some of the later images.) that could be considered the beginning of brazing shear. NOTE: this only appeared when the front fork tips were nearly a foot apart from each other. when i was done strong-arming the sucker, i sawed the blades off and tried to take some pics of the inside fillet, or whatever it's called.

for the record, i used a straight gauge 1.6mm steerer, columbus SL blades, and BAg-7 (56 percent silver alloy) brazing rod. this fork, while it was out of spec after cooling, probably could have been safely pulled into alignment for the 1-2 millimeters needed and not really sweated the consequences. but seeing it come out post brazing a whopping 2mm over to one side raised a red flag here. hey - what color did you expect it to be?

cheap insurance atmo.

ALL PICS APPEAR HERE ATMO
ps there will be 51 images in all so check back...

thanks for posting this. I saw one of your posts mentioning that you do this if there is any question and it really clicked with me.

Cut those dropouts just right and you can make 2 rad bottle openers from that fork. Paint 'em red and sell them at your NAHBS booth next year.
Thanks for sharing the pics too, btw.

yer f*ck-ups are better than my first runs.

'course, you've built many thousands more frames than myself.

this all only happened because uconn women lost last night.
there's some bad juju in the air atmo.

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Originally Posted by pruckelshaus

yer f*ck-ups are better than my first runs.

'course, you've built many thousands more frames than myself.

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Yeah, next time you screw up one that's my size send it to me and I'll dispose of it.

thanks for posting this series. as i'll be doing this test fairly soon, does it make a difference to bend the blades side/side or front/back?

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Originally Posted by myers

thanks for posting this series. as i'll be doing this test fairly soon, does it make a difference to bend the blades side/side or front/back?

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dunno. but intuitively, i'd say that using brute strength it's be a lot harder moving blades forward/back than it is
side/side if what you wanna see is how much effort it takes to wrinkle a tube, break a bond, or similar atmo.

Awesome destruction series! Thanks for the lesson ATMO- Chris

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Originally Posted by e-RICHIE

dunno. but intuitively, i'd say that using brute strength it's be a lot harder moving blades forward/back than it is
side/side if what you wanna see is how much effort it takes to wrinkle a tube, break a bond, or similar atmo.

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What you did was pretty good. If you want to go real pro-like you should mount the steering post like it would be in a frame, put a dummy axle in and pull both blades at the same time in the same direction. If your not superman, you will need a hydraulic press. I would also measure the applied force and corresponding deflection. That makes internal failures visible. But, that might all be overkill.:blink1:

If you ever need real numbers, I have used EML
They can do most of the CEN tests and their prices are not bad. The fatigue tests can be enlightening.

I have been drawing up fixturing to mount bike parts on one of my fatigue machines.

Hey e-Richie,

Cool stuff... such a shame to see those nice shorelines being sacrificed... =(
I'm curious, do you have a certain sequence when brazing up forks? Clockwise, inside-outside, upside-down... stuff like that. Is there a tendency for the blades to spread out or contract inwards after you're done?

Thanks,
Hansen

more builders should do this stuff
I mess up a fork each year or two
and I am so mad I myself I give them a hurl out the back door at the crows outside
but next time I will have to get the camera out and do some autopsy pics

It is a good thing that Richie shares these pics with builders

If anyone has examples of QC like this that they're going to trash, I am interested and will reimburse for shipping, etc. thanks.

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Originally Posted by suhacycles

Hey e-Richie,

Cool stuff... such a shame to see those nice shorelines being sacrificed... =(
I'm curious, do you have a certain sequence when brazing up forks? Clockwise, inside-outside, upside-down... stuff like that. Is there a tendency for the blades to spread out or contract inwards after you're done?

Thanks,
Hansen

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i am tired - so let me post to this on thursday atmo.
later.