Honestly I’m not sure where this micrometers crap all came from. If you look at really old videos/photos of fab shops or talk to really old time builders, they would do things like put the whole frame in some wood blocks and wrestle the dropouts until they lined up with some other wood blocks, or file the dropouts until the wheel looked straight (no joke, this was SOP forever). There was no surface plate stuff and no micrometers or anything fancy and those bikes rode great.
There’s a great video from the 40s (they make their own spokes and tubes!) of bicycle manufacturing in the UK. The whole thing is worth watching (would be a good OSHA-violations drinking game), but if you want to see the “alignment” stage, it’s at ~5:13 or so - the “holder” shown is used to check the alignment of the dropouts, which you can see a worker take about 1 second to do if you watch carefully.
At some point someone decided being obsessive about alignment was a selling point and then I guess it snowballed. There’s nothing subjectively or objectively better about a frame that is straight to .5mm vs 2mm, even if you could measure it, which you can’t.
Walt, what you say is pretty much bang on but the problem is you get someone like me who is just trying to build the best bikes I can and one of the variables I can control is alignment and the tolerance of misalignment. I’m a sensitive rider I can feel when a rear contact path is not tracking directly behind the front. I wish I didn’t but my arse can tell every time and it’s unsettling. So while building a bike with looser tolerances can work and is good enough to do the job it’s not something that satisfies me. I enjoy getting head tubes within 0.2mm over 450mm,. It’s satisfying and I take pride in doing the best I can.
Daniel, the surface plate for me is more than just a check for bike center lines. I use it for everything. Jig set ups and calibrating, checking straightness of material and tools. It’s my workshop datum for a lot of things.
As I said at the beginning, everyone has their own standard that makes them happy. If you value trying to make things as straight as you possibly can, that is a perfectly valid goal.
Just remember that it’s only possible to get things so straight because of measurement errors inherent in the process, and that until recently sub-mm alignment “problems” weren’t something anyone worried about on even the highest end bikes.
@Daniel_Y I like the idea and sentiment but it’s going to be very difficult to have any kind of standard for alignment even if we all agreed upon the numbers and participating. Maybe if we all used the same measurement system and had the same flat plate, but it’s all over the map in what people use and how they measure. There would be no testing of any sort or way to verify.
This starts down the road of the Framebuilder’s Collective or whatever the group was that several years ago. I don’t think they got very far but i believe they were wanting to put some rules into effect that simulate a “certification” in framebuiding so when new builders wanted to join the fold they had some guidelines and expectations outlined. Maybe I’m fabricating the details but I think that was the intention.
I can’t imagine how this would all work, we’d need a governing body of some sort to make sure everyone abides? Seems unlikely…
If you aren’t careful you’ll miss it!
It’s also wild how they do everything to the frame including paint and only then put on the “rear stays” (seatstays) at the 15min mark.
It really is a fascinating movie to watch. We all need white lab coats for when people visit the shop.
Yes, this sort of thing always turns into a crap-throwing contest where everyone loses. If someone says they align to .005" over the whole frame with lasers calibrated by NASA or some such, then everyone else is afraid to look bad by saying they only align to some lower standard and the people who built their first bike and just used a piece of string and their fingers start to think their bike that rides great has something wrong with it.
Forks aren’t straight. Wheels aren’t straight. Saddle rails/covers/padding aren’t even. Most bikes have a whole heavy drivetrain on one side and a much lighter set of brakes on the other so even if they were perfectly straight you’ve already built something unbalanced. Your feet/cleats don’t fit on exactly the same spots on the pedals.
When you go to face your BB shell and head tube, you inevitably have to reference the first facing cut off something (threads, unfaced end of the head tube) that also isn’t flat/straight.
And humans aren’t even symmetrical! I’ve got a bigger and longer right leg than left, and one foot that’s 1/2 size bigger than the other and I’m nothing unusual at all. I bet the right side of me is 100g or more heavier than the left side.
The reality is that I don’t think I’ve ever ridden a decent quality production or custom bike that didn’t turn how it was supposed to and ride fine with no hands. Heck, I’m not sure I’ve ridden a Walmart bike that didn’t do those things.
So the standard is “you pick how straight you want to try to get” but it’ll almost certainly be fine even if it’s your first try and the flattest thing you’ve got is a formica countertop. If you find it personally satisfying to pursue perfect straightness that’s great, but it’s not necessary. We built toys for adults, not centrifuges.
Totally agree, there is undoubtedly an art to framebuilding that can’t be described by tolerances. I think that is one of the things that separates a custom frame from production bike
Maybe “guidelines” is a better choice of words. To me, the “standards” I am proposing are just to give people a goal to work towards and some realistic expectations for what is achievable. I want bring more people in, rather than intimidate and exclude people with unrealistic numbers!
I “averaged” @anon91558591 and @DEVLINCC standards, since I think that represents the full spectrum of framebuilding
Guideline
Tolerance
Comments:
HT Angle
0.25deg
2.2mm over 500mm
HT offset
2mm
measured at bottom of headtube
Dropout Offset
1mm
Dropout parallelism
.2 deg
Not sure how to measure this
Offset at saddle
1mm
750mm saddle height is the “average”
BB offset
.5mm
Does anyone have any comments or thoughts on these guidelines?
Most of your standards are below what can accurately be measured even with nice tools.
Remember to not conflate precision and accuracy. You can use very precise tools (ie micrometer), but if you’re measuring something based on BB/other tubes on the frame that we know are imperfect, you are not actually making accurate measurements.
Otherwise, yes, your standards will result in a bike that rides just fine.
I am thoroughly enjoying this discussion! @anon91558591 deserves a lifetime achievement award or something for his contributions to the education of so many aspiring frame builders - and the information just keeps on flowing!
I wanted to share an alignment anecdote. An early frame of mine (personal bike, not customer) has a seat tube that angles toward the drive side a bit. I know this came from an imperfect miter at the ST/BB subassembly, which is the very first connection I make. I unwisely thought I’d be able to chase the problem away over the course of building the front triangle, but once I got it built, the seat tube was still leaning to that side. Cold setting was an exercise in futility (now I know better). After adding the chain stays and aligning the dropouts, the dumbest thing I did was to put the frame back in the fixture before tacking the seat stays. When everything was locked in the fixture it looked great, but out of the fixture the seat tube pulled everything back towards the drive side, making the left seat stay closer to the tire by a couple mm. Looking at it drives me nuts, but having figured out what happened is so valuable. AND it rides great - doesn’t bother me in the least when I’m on the bike. I really do agree with the sentiment that most bikes are going to ride like bikes and the best we can do to make them straight, whatever technique that may be, is probably enough. But the important lesson I learned is to get those miters tight!
The Park dropout tools are great if you’re building a QR bike and plan to be super sloppy with joining the dropouts. I own some of those damn things, they’ve been gathering dust for a good decade and a half now. Make me an offer.
In all seriousness, those were mostly used to assess/fix damaged dropouts back in the day. It’s not a tool you will need as a framebuilder these days.
AFAIK there is no TA version. Even if there was I’m not sure you could effectively align TA dropouts. For TA you have to get it right first try, or use the Syntace system (no knock on the Syntace system, it’s great).
Seatstays always go last after all aligning is done. Once they’re on, you are stuck with whatever you have.
If you don’t use your alignment table for a whole bunch of other stuff, that tool Paul uses is super simple to make and saves a lot of space! It also makes it a lot easier to check each side.
But yeah…get the miters good and plan your welding/brazing sequence seems to be the best place to start regardless.
I adore Paul Brodie, but that alignment tool is really not the best.
Themain problem is using the BB as a datum. The shell gets really distorted by welding or brazing and also has a pretty small surface area compared to the distances being measured.
The other problem is checking to a part of the down tube rather than the steer tube axis. It doesn’t matter where the DT is as long as it connects the BB and HT. What matters is alignment between the wheels and the steering axis.
Is a photoset of the original version of the tool I make showing how I check alignment of frames.
The key take aways are:
the head tube centerline is the datum!
This gives you a virtual center plane to check everything else from.
twist or whatever of the main tubes is easy to check with the “V” part of the tool.
Centering of the dropouts is done by the stepped part of the tool.
Jamie Swan wrote a nice article for BQ about checking alignment this way. I first heard about it as the Bontrager method?
Hahn Rossman
What an amazingly informative thread, thanks everyone for your contributions!
Would anybody care to drop a short explanation of your methods for front triangle alignment through braze sequence/heat manipulation? How do you correct a twist you see developing?
As a newb that’s been obsessively watching Paul Brodie’s videos as I go along my current framebuild I thought I’d just clarify, it looks like Paul basically only uses his alignment tool to ballpark alignment in the early stages of his builds, and explains why it’s fine for this purpose during his build method in the following video (he accounts for BB shrinkage after the BB-DT fillet). You can also see him cold setting a frame on his alignment table using the headtube as the centerline.
The long and short of it is basically: make good miters, then swap sides of the frame as you go (ie do the driveside of the DT, then the nondrive, then the driveside of the toptube, etc). You can and probably will tweak that based on your preferences/results but that’s the basic idea.
Seems to me like a decent method if you’re using tubing diameters that will move, but I’m a big time novice so I can’t speak from experience