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Filed In: Process

Father/Daughter Project - Part 7

December 09, 2019   |   Chris Blandford

All right, time to tack and braze this little frame together.

For today:

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9. Tack Frame in Jig
10. Quick Alignment Check
11. Braze Frame Free of Jig
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To tack the frame together, I begin by applying blue flux to the tubes and loading them into the jig. I apply a full coat of flux--enough to last through the tacking and the brazing. I also flux about an inch up into the ends of the mitered tubes. Using the same 203 tip, a neutral & rumbling flame, and 1/16th bronze rod, I tack the tubes together along the frame’s centerline. Here’s my tacking sequence:

In short: obtuse angles first--from the BB up and around to the seat tube, and then acute angles--back down and around. The general thinking here is that tacking the obtuse angles first will minimize any pull-apart on the opposing side of the miter, as the bronze will pull the tubes more “into” one another. For chain stays, however, I tack the outside (acute) sides first, then the obtuse sides. This is done to minimize suck-in at the rear dropouts and to keep the rear spacing as designed. (For this little bike, I’m waiting to connect the top tubes along with the seat stays, mixte-style. So, I skipped tacks #3-6.)

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Filed In: Process

Father/Daughter Project - Part 6

December 04, 2019   |   Chris Blandford

Over the long holiday weekend, I had Mathilda down in the studio with me a bit. She’s a wiggly almost-four-year-old, so the patience for my show-and-tell is a little short. That said, she’s been enjoying seeing the progress made on her bike, and asks to see the little frame each time we head through my space down to the garage. She also really loves squishing stuff in my vise. I keep having to tell her that we will not be squishing her frame. She only seems mildly disappointed.

Onward:

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6. Miter Chainstays
7. Drill Vent Holes
8. Tin Seat Tube to Bottom Bracket
9. Final Fit & Prep for Brazing
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I miter my chainstays in the same way as my main tubes. However, there’s one extra (semi-backwards step) that I take here. Back in BikeCAD, I now retroactively make the computer drawing match my chainstay hand drawing. All I care about here is the miter template. So, now that I have a chainstay miter angle (from my hand drawing), I can make the BikeCAD version match. It takes 30 seconds--and I don’t care about the overall shape of the chainstays in BikeCAD, just the diameter and angle. Once done, I print the templates, tape them onto the tubes, and set their distance from the rear axle (which is taken from my hand drawing). Trace, hacksaw to rough length, tin snip, and file.

These used to give me fits. I’ve found, however, that thinking of the chainstays as a single unit--instead of individual tubes--has helped me with their mitering quite a bit. Once I get the individual chainstays mitered, I place them onto their dummy axle--together--and lightly clamp them in my vise. Just a light swipe or two with the file--across both tube ends at once--saves a lot of tail-chasing in the jig.

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Father/Daughter Project - Part 5

November 29, 2019   |   Chris Blandford

Moving on to the chainstays.

Steps for today:

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3. Tab Dropouts; Slot Chainstays
4. Braze Dropouts to Chainstays
5. Finish Chainstay Ends
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Before I dive in, one thing to note. For the first couple frames I made I did things one step at a time, with a sort of process tunnel vision. Now, however, I tend to do things whenever it makes most sense in the overall build. An example of this is with the chainstays. Previously, I would’ve brazed the front triangle together before even touching a chainstay or dropout. Now, however, I work on these as separate sub-assemblies of a larger whole, prepping everything in anticipation of finally joining stuff together.

Anyway. I begin by laying my chainstays on top of my overview drawing. I include the tire, chainring(s), and crankarm in these drawings, and check that the chainstay will clear all three. I also check that the outer diameter of the dropout end isn’t wider than the tab on the dropout. It’s a bit of a balancing act to choose the most appropriate chainstay (to this point I’ve only bought pre-formed stays--I haven’t bent my own) and get it ideally positioned. Once satisfied, I trim the dropout end of the stay to length and rough-cut the BB ends to length. Then I lay the chainstays on my surface plate and run a straightedge across their tops, scribing a “top” line onto both.

Tool note: I use my Anvil fork jig as a makeshift chainstay jig. A while back, I made a crude little adapter that fits in the steerer tube holder of this jig. It holds the BB ends of the chainstays in place while I work on them, kinda like a crappy chainstay mitering fixture. (I miter out of the fixture, but the jig is helpful for getting everything in its place.) I use the fork rake measurement and a little math as a makeshift BB drop/rise indicator.

Next, I put a tab on the dropout. For chainstays, I’ve been making these 8-10mm deep. I check the internal diameter of the small end of the trimmed chainstay, and take off an equal amount of material from each side of the dropout (hacksaw first, then files), so that the tab fits into the stay.

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