Process pics – seat tube collar for 31.6 dropper post

Just getting back to blogging about fabricating some stuff but been busy with other things lately.  I’m done with Scott’s fatbike fork with an good amount of bling (brazons) for fatty loaded touring goodness and the use of a Dyno hub with internally routed wiring.  I’ll post something on that fork soon once it gets painted and i can take some glamor shots.

I’ve started on Russell’s slack-ass all-mountain 29er.  In usual fashion, I run before I can walk so stuff takes me three times as long as it should.  Russell’s build has a 34.9 bent seat tube (True Temper 1/7/1 Supertherm) with a collar so he can use a new internal cable-routed 31.6 dropper post (no doubt a blog post on that cable routing later on…), an arched and ovalized top tube, and arched seat stays attaching to Paragon’s Rocker dropouts.  The geometry is similar to the Kona Honzo where it’ll have a 68 degree head tube angle and a 120mm X-Fusion fork.  Chainstays will be at most 416mm effective length (16.4″) with the Rockers all the way forward and he’ll be using an XX1 crankset with a 32t ring and a 10spd cassette in the back. It’s going to be tight with clearances…!

Here’s some photos of the collar making sans lathe.  Kinda hard to get faced/square collars without a lathe and the horizontal mill almost cut it but ended up failing.  So I just laid a fusion pass on a 65mm section of 1.375 x 0.65″ tubing without a ‘step’ to hold it in place. Worked fine but I’d rather have a step!

this looked so promising…
No, not the approved methodology. Can’t get the right angle with this vise for the cutter, and definitely not rigid enough and the mill doesn’t spin fast enough. FAIL!
slotting the collar
take 2 with a new collar but not trying the insert this time.
facing  the collar
The cold saw got it very close to being square, but just took a few thousands off to be sure. No lathe, this is as good as I can get it.
flat plate alignment
This is why i love my flat plate. So many uses for lining stuff up, fixturing with magnets, tacking while on the plate, etc etc.  Just wish it was supersized!
fitted collar
Pretty close, not a perfect fit though. I then ran a small fusion tack on top, then flipped in place and tacked and then did the other sides before fusion welding it all up.
fusing the collar
mitered in fixture.

I use that tube block near the BB the whole way to make sure it’s in phase from bender to the BB miter using the vise on the vertical mill. Also helps draw the tube centerline after bending for water bottle boss placement.

2 thoughts on “Process pics – seat tube collar for 31.6 dropper post

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  1. If this was something you *had* to have squared up, you can try something like putting a Dremel with a carbide burr into the mill vice. You don’t have to be move the stock fast because you’ve got plenty of cutting speed behind the tool bit.

    The downside, and it’s significant, is that you’re either throwing lots of metal filings or, if using an abrasive wheel, grit, all over the place. I have a stash of canvas scraps to cover the machine beds. You also want to wear gloves because the carbide filings in your hands are the worse things ever.

    1. I had never thought of that, but makes total sense if you can securely hold the Dremel mostly square and in place without hurting it…hmm….i like it! Since I took those pics last weekend I’ve got my main tube mitering fixture on that mill i may have trouble fitting it all on that table. Worth a try though and definitely cover it all up beforehand. I just need a little bit off to square it so shouldn’t be that much grit.

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