Direct Mount braze-on

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I thought my most recent frame would fit a traditional front derailleur but turned out I was wrong. I’m close to never running a front derailleur ever again…but if I’m gonna make frames for friends I’ll have to learn.  This must be why many builders keep if safe with ‘regular’ chainstays of 17.5″ — those will fit any type of derailleur and any tire size pretty easily.  So anyways, I was somewhat forced to create my own direct mount braze-on for frame #6.  The chainstays are just under 17″ (429mm).  Frame 5, which I got built up this weekend with X9 2×10 setup and Avid Elixir 5’s, has 435mm chainstays and the low-mount SRAM front der barely fits with a 2.4″ tire (i’m talking 5mm of clearance…maybe).

So above are some pics from Saturday. Making this lil braze-on took me WAY longer than it probably should have.  Thanks go to Walt for his recent writeup on the “how to…” of DIY direct mounts. (Paragon makes a nice mitered or un-mitered brazeon but I guess that machine is broken so they’ve been out of stock for a long long time.)

I used a hacksaw to cut a small 25mm x 14mm-ish piece of 4130 plate steel that’s too thin to tap threads into.  So I silver brazed on a nut to the backside and threaded it with a M6 x 1mm tap.  Then, i used a short piece of extra 16mm seat stay tube to braze onto the plate, encapsulating the nut on the back. After this was all done, I used the 10″ round file to quickly file down the tube to the right amount of offset on the seat tube.  This took some guess-work as I wasn’t sure exactly how much offset it needed but with a little protractor I was able to get it right at 66 degrees (Shimano says you need a 66 – 69 degree angle between the centerline of the chainstay and the bolt-center of the direct mount braze-on). The “fixture” I used was just a piece of steel from the hardware store drilled to be 155mm on center of the bottom bracket to the center of the direct mount bolt.  With some ‘spacers’ (chainring bolt and washer), I was able to get it snug up against the seat tube so I could use the heavier silver to stick it on.  Soak, clean, file, clean, and so on.  We’ll see how it mounts up when Heyride builds it up today…being the first time I’m crossing my fingers it fits!

 

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