In summary, he says that using the lower temps sufficient for silver minimises distortion of the tubes, which means the frame is more likely to remain accurately aligned after it's welded. That in turn means there is less need to bend the tubes into alignment after they cool.
Agreed; there is no doubt the lower temperatures used for silver brazing result in less heat put into the tubes and undesirable results, but there are many other factors that also affect post-braze alignment.
Some of these include brazing sequence, fixturing, technique/experience and tubing and filler composition, even flux (brand, type and water content for mixed powder types or whether the builder uses a gas-fluxer). All affect the amount of time heat is applied to a joint and any undesirable resultant consequences.
I can share some firsthand thoughts on the subject because I've been a hobbyist framebuilder over the last 27 years or so. "Hobbyist" means I build solely for myself and not others, partly because here in litigious America one really needs to be well insured against liability if you build a frame to sell -- even give -- to others. I remember reading about one case here where someone built a frame for a friend who eventually sold it on. The buyer got distracted and rode it into a parked car, incurring injuries. He had no desire to sue anyone but his insurer went back through the line of succession and sued the builder in an attempt to recover their payout for medical bills and were successful in it. The original builder was unable to prove a negative and refute the insurer's claim that faulty workmanship -- though unproven -- might have been contributory and had to sell his home to pay the court-ordered judgement. When my frames are no longer useful to me, they are scrapped so they cannot be used by others, limiting my liability and responsibility to only myself.
I currently own 15 bikes. I am of average dimensions for my age cohort in the US, so all the ones I have purchased have been used or new production frames that fit me well (and identically) with only minor adjustments in stem reach and seatpost adjustment. The frames I have built were not available commercially and have included full-suspension, small-wheeled Folders and recumbents. Unusual angles mean they are comprised mostly or wholly of fillet-brazed joints that use/require higher-temperature bronze/brass as a filler because lower-temperature silver does not build the large fillets necessary for lugless construction.
It is hard to beat the economies of scale and overall accuracy of mass-production frames that are backed by generous warranties. These come out overwhelmingly well-aligned and can generally be counted on to hang together for the covered warranty period. There have been some notable quality exceptions I will avoid mentioning here by name, but it is in the interest of large-scale makers, their insurers, and their dealer networks to have their frames be well-aligned, hold together, and be safe for the buyer/end user. Historically, the vast majority of brazed large-scale steel production frames have been joined with lugs and brass filler. Over the last 35 years, this method has been largely superceded by TiG welding which requires little/less/virtually no post-join cleanup of the joints, making it a more efficient form of mass production. To better withstand the greater localized heat (welding actually melts the steel tubing at the joins, where brazing melts the filler), tube butts are adjusted in length and thickness and tubing alloys are optimized for the methodso they are more heat-tolerant.
All my own frames were accurate to within a measured 0.1mm (my standard for what I considered "spot-on") in all dimensions upon cooling and required no post-braze cold-setting or alignment. This was due to careful mitering and layup, my heat-compensating fixturing and my brazing sequence that ensured the tubes did not pull/distort to one side or another. Despite long, hard use, none cracked or broke. All of my practice joints held up to destructive testing -- the tubes failed before the joints when clamped in a vise and beat on with a hammer or levered on -- and the same for the completed frames.
Quality tubesets are not cheap. Back when I began, a really nice tubeset started at USD$300 and the "fiddly-bits" -- bottom bracket shells, brazed-ons and droputs could easily add as much to the cost if they were limited-production investment cast items. One of my Folders used a vintage Phil Wood-produced unbutted elliptical tandem keel tube as the main frame spar, a very rare tube even then and I paid dearly for it. It gave me fits because it was not symmetrical in cross-section, causing a lot of headaches in mitering and fixturing but ended up perfect for the application.
Because my framebuilding was a hobby and tubesets were expensive, I tapped a friend who owned a used-bike shop for crash-damaged frames so I could harvest the good sections of high-quality tubing from production bikes. What a surprise to find some well regarded, high-quality framesets were made very poorly at the lugged joins. Because I built my unusual frames with lugless construction I didn't need lugs, so I used my electric bandsaw to cut the tubes in the still-butted end sections just outside the lugs to I could see if the builders achieved full braze penetration at the lugs. Some bikes did not use mitered/fish-mouthed tubes! Instead, the tubes were either cross-cut square at the ends or the tubes were mechanically bent/dented into rough "v"s to better approach the mating tube inside the lug, leaving the lug walls as the sole bridge between tubes(!). One frame had what looked like a paint flaw at the edge of the lower head lug' it turned out to be the end of the downtube, barely inserted before brazing. For those who haven't built frames, it is desirable to have joints that are mitered so carefully to be nearly light-tight before brazing so capillary action can draw the heated filler into the join. Despite these flaws, the original owners regarded these as some of the best riding bikes they'd owned.
At the other end, not every custom builder gets it right. A chiropractor friend of mine contracted for three custom randonneur frames from three different builders, some of which had placed well at shows. All had glaring flaws for which the buiders were loathe to take responsibility. She asked me check them with my laser alignment rig and in my fixtures. One had a fork badly out of alignment with one leg longer than the other at the crown. When she complained the builder grabbed a fork off a show bike, repainted it poorly and shipped it to her badly packaged with resultant shipping damage. Another failed to leave the proper clearance/didn't dimple the ends of the seat- and chainstays so she was unable to shift into her top cassette cog. Yet another made expensive custom racks that when mounted conflicted with the tops of the tires. She finally found a builder who not only accommodated her need for a transporter/bakfiets, he did a stellar job and was accommodating and pleasant with no need for redress.
In general, you can buy a production bike off the floor in the moment but must be prepared to wait for a long time -- months to sometimes several years -- for a true custom from a top builder in high demand. Some premier US builders have effectively closed their books to new orders as they have enough business to keep them going until retirement.
I live in Eugene, Oregon USA where some high-quality framebuilders have located as well as two factories, formerly three: Co-Motion, Bike Friday, and (in the past) Burley, who made my tandem. I've toured each of their facilities a number of times and always gained from my interaction as they generously shared their design, build philosophy and even methods. Rob English succeeds Les Lunas as the premier individual/contract painter in the area. Gary Hale for many years built exquisite fillet-brazed touring frames and then recumbents in his human-powered factory. Bruce Gordon built out of his home not far from me in the late 1970s/early 1980s and generously and graciously spoke to the touring classes and groups I led professionally for awhile. Before relocating to the midwest, Eric Estlund was a well regarded custom builder here under the Winter Cycles name. Just two hours north of me, Portland boasts a huge number of custom framebuilders and production parts suppliers including Chris King (of headset and hub fame).
With all these high-quality framebuilding resources available to me locally (and no customs duties or international shipping required), I chose Thorns because they most nearly met my needs and were well built. I'm happy with my choices and the company and would someday like to add an Audax to my stable. Yes, I could "build" a similar frame but for the price and finish, Thorns suit me well for a ready-made product and even with machines, framebuilding really eats up the builder's hands over time. My longterm de Quervain's tenosynovitis means I pay a painful price for any finish work and it has become less and less worth it compared to a readymade solution as time passes.
There's a lot to fitting a bike to the rider's needs and form even when oneself is the builder and end customer. I have learned a lot over the years from owning and riding a variety of bikes, but never more than when I designed and built my own and could see and experience the results of even small changes in geometry and dimensions. There is so much to consider beyond fitting the rider to the "contact points" that can change the feel of a completed frame and the ride is also affected by component choice, tire section width and pressure and weight distribution both unladen and fully loaded (if a tourer). Cycling style is important too; some are high-effort pedal mashers while others are low-effort/high-rev spinners.Each makes different demands in a frame and loads it differently, needs best addressed with different tubing diameters, even frame sizes within a fitting range. Proper rider
fit is paramount. Cycling is a repetitive-motion activity so getting it wrong results in a painful, unpeasant experience or injury with extended use. I don't like pain and over time learned how to adjust my bikes to address the things that hurt me so I can ride 300-400kms/day without suffering undue misery or incurring an injury. Over time, I've come to believe one of the most important dimensions affecting
handling and
bike feel is trail -- a dimension affected geometrically (head tube angle combined with fork rake) and by tire section size/width/sidewall height. For more on the topic, see:
http://thorncyclesforum.co.uk/index.php?topic=4245.msg19567#msg19567 Overall wheelbase, front center and stay length are important too, especially for toe and heel clearance with tires, mudguards and panniers.
In the end, experience and preference determine what one seeks in a bicycle and how happy you'll be. Cost is a factor as well and we're fortunate most people can get a good, comfortable fit with careful selection of frame size/dimension and adjustments made through handlebars, stems, seatpost positioning, crank length and Q-factor/tread. Fitting mass-produced accessories like aftermarket racks and bottle cages is often "good enough" to tailor the bicycle to individual need. Beyond that and fitness for intended purpose and workmanship, we have Art. It is a quality to consider but one can pay dearly to fulfill a vision that is quite apart from function. My beloved Fixie cost me $20 for the now 51 year old handmade frame and nothing for components I drew from my parts bin and a set of used wheels gifted by a friend. My Enduro-Allroad bike frame was sourced as a slightly dented and badly scratched complete bike from a reputable pawn shop and is also equipped with spares from my bin and a choice of two Thorn Sherpa Mk2 forks (depending on whether I desire low-trail or neutral-trail geometry). Another bike's original randonneur frame was custom built to my dimensions by a builder in Japan. It is gorgeous with semi-transparent five-stage paint applied over full chrome and finished with hand-applied coachlining...and the vertical rear dropouts are misaligned by 1mm, an error I corrected by machining and bonding in a custom titanium shim so the wheel will track correclty between the brazed-on centerpull brakes. My tandem was bought used, sound but battered. I made, brazed and TiG-welded the pieces I felt it needed and painted it fully to look like new. Before long I'll modify it further to take a Rohloff in place of the current 3x6 derailleur drivetrain. While I might notice and would surely appreciate the aesthetics and craftsmanship of a top-level custom version of each bike whether made by me or someone else, I doubt I could achieve better function in any of them and for that reason, I'm happy to keep what I have. In contrast, some of my friends have achieved their goals by "commissioning" some truly lovely frames that have seen a fraction of my use and mostly end up decorating the walls of their lounges. It's all good and I'm thankful bikes can be as individual as their owners.
Best,
Dan.
