Filed In: Process
Father/Daughter Project - Part 8
Wednesday, December 11, 2019 | Chris Blandford
Moving forward. Steps for today:
12. Check Frame Alignment
13. (Align Frame if Necessary)
I only recently purchased my little alignment table. Up until my last couple frames, I’d been relying on my fixtures and the various string/straightedge/frame-alignment-gauge methods to check alignment. The classroom at UBI housed a full-size BB-tower style alignment table; in both of my courses it served as a very heavy coffee table.
I think the attitude there is that if you use good fixturing and processes, an alignment table isn’t really necessary. I think I understand the wisdom in that. One of my favorite walk-around-town activities is one-eyed-squinting at the rear ends of production bikes that I see locked up to racks. Yikes. At least in terms of alignment, the bar isn’t set very high. And really, I don’t know enough about bikes to know whether any of it matters or not. Especially for the types of bikes that I build and ride.
So, I “align” my frames to a level that my perfectionism will accept. Which--given that I’m new to making bicycles--is a pretty loose tolerance. I’ve put a couple of my scrapped frames on my little table and felt the amount of force that it takes to move a head tube even a half-millimeter. A triangle made out of tubular steel is shockingly strong. In essence, I’ve quasi-decided that: A. if something needs mild correction, it isn’t worth me yanking the hell out of my frame to correct it; and B. if something needs major correction, I should probably just start over. So--as of right now--“aligning” my frames is really just a way to gain a little feedback as I go along. I'll nudge dropouts, but that's about it. I use the alignment process as a tool for improving the work on my next frame, not as a way to correct my current incompetencies. I hope that makes sense.
With that said, here’s what I check and how I check it. (Note: I didn’t take photos of this until after I’d finished the fillets, but I checked the frame before I started filing. Nevermind the shine for now!)
First, I face the BB shell with my Park Tool facer. The Paragon shells are supplied .5mm long, which I’ve found to be about perfect for the amount of distortion I get at the BB while brazing. Taking off .25mm from either side results in a full, fresh cut around the BB.
Once faced, I re-scribe the BB centerline onto the bottom of the BB, using my calipers. Then I mount the frame onto the alignment table. I use a little surface gauge/scratch/probe/thing and set it to meet the centerline. Then I compare this height to the height of the axle center.
Next, I set my previously-mentioned Compass gauge to the height of the surface scratcher. I use this gauge to check my head tube and seat tube ends.
On the table, I found that my head tube was off-center by about 1mm, to the drive side. My axle center was off about 1mm as well (but to the other side). The head tube showed no twist, though, and the seat tube was fine. I make mental notes.
Next, I take the frame off the table and clamp it in my vise. I throw some Park H-tools into the dropouts and check for parallelism. (I’ve never had even a slight problem here, for whatever reason.) Then I place a true wheel into the dropouts. I check (using a straightedge held against the head and seat tubes) the top of the rim for center (keeping in mind that my head tube is off-center and so this reading will be skewed). I also check the distance between both chainstays and the rim. And finally I check the dropout spacing. Everything here jived with the readings on my table. If they didn’t, I’d have to figure out what was off (other than what I already know to be off).
Finally, I step back and do the fling-the-wheel and one-eyed-squint thing. Better than most bikes I see on the street, which is good by me.
I make the conclusion that the dropouts need moving 1mm each, back to center. I’m going to leave the head tube alone for now, and check it again after I tack the mixte-style stays in place. Mostly out of curiosity.
With the dummy axle in place, I give the chain stays their 1mm… nudge.
Once more on to the table and then I call it good.
If you’re curious, I did put the little sample Cleary bike up on the table, too. Let’s just say that I’m happy with how my frame compares. Or that--more likely--none of this mattered. Like, at all. Especially on this little bike.
Like I said, feedback and perfectionism appeasement.
That’s it. Next I’ll finish the main fillets and begin working on the seat stays.