this is gonna be a collective thread for my bike builds. I don’t have any real experience machining/brazing/whatsoever, so please feel free to share your thoughts and feedback.
This all started, when I was looking for a gravel-frameset, and couldn’t find any that has the right proportions for me (I’m ~201cm tall with 101cm inseam). So I started designing the frames, that I eventually want to build. I have plans on doing a roadbike, a tracklocross, as well as a xc-mtb, however my first frame is gonna be a (rimbrake-) gravelbike.
I designed it around 50mm tires, but I should have clearance for up to 60mm. I’m also planning on building a unicrown fork for this bike.
For tubing I’m using Columbus Zona for everything, with a 36mm HT, 35mm DT, and 28.6mm TT and ST.
Since I don’t have any power-tools or jigs, I’m hand-filing everything. I don’t really have a good Idea yet, on how I’m gonna assemble everything when the tubes are ready, but this is a problem for future-me. Right now I finished the ST, HT, and (mostly) the TT.
I’m very happy with the ST-BB miter and the ST-HT, only the upper end of the HT-TT miter needs some more work. I don’t use templates right now, so getting this miter somewhere near acceptable was a big pain, especially to avoid rotation from the ST to the HT.
I would love to get some feedback, especially on the miters. I will keep posting updates, I want to get the bike somehow finished during the next month, since I want to go bikepacking in June. We will see…
Those mitres are all basically perfect. Even your “bad” one is perfectly good enough (although you might as well tweak it a bit while you’re at it). I’ve welded much worse than that on some of my early frames and it was absolutely fine (and didn’t cause any distortion which is the thing people are worried about).
The less good news I have for you is that those are the three easiest mitres But I think you will be fine. I do the TT last so I can sneak up on the right length on what I consider the slightly easier tube. No problem doing that with the DT instead, just bear in mind that you don’t want to end up making it too short when titivating the mitres. If your TT is a fraction too short already it doesn’t matter. But obviously everything has to fit together at the right angles.
And don’t forget to drill some vent holes. Various theories about water drainage but wherever you stand on that, you do need somewhere for hot gases to escape.
I also do the bottle cage holes before joining the tubes together because access is easier.
Nicely done. Many of us started exactly like this. One thing I found very helpful was Paragon’s tubing blocks. 2 on each tube holds the centerlines straight. You may have other ideas. This was #3 I think and as you can see I had invested about $50 in a slab of marble countertop remenant for ‘precision’!! Haha
I then held them in my vise and tacked the joint.
Tight miters will help ensure the frame is as straight as possible and those look pretty good. Not having a machine and tools it just takes a bit longer and there is a lot of fitting, 2 files strokes, fitting, 1 file stroke, fitting, swearing, 4 file strokes, fitting…I’m sure you figured that part out!
I would figure out the joining part sooner rather than later. TIG or brazing each have a learning curve - especially if you’re teaching yourself. I think for a new person, with all of the braze ons that a gravel/bikepacking bike has, brazing is going to be better. You can braze the whole thing and only learn one technique (and set of equipment). If you TIG the joints, you’re still going to want to braze the braze-ons so, effectively you’ll need to ‘master’ both techniques and have welder and torch/tanks. That will be hard (time and money), on your own, in 6 weeks!! TIG’ing braze-ons in the middle of a tube with a wall thickness if 0.5mm is going to be difficult to master in your timeframe. I am sure there are prodigies out there who will argue but, established builders almost all braze the braze-ons (at least in steel).
I’m a big believer in vent holes everywhere (2 per tube) so air circulates to facilitate drying after a wet ride. If you’re brazing, it makes washing the flux out much easier too. I use half inch holes in the head tube and BB shell for each tube - same at the seat cluster. Then in the stays, I use 1/8” drill bit at the dropout ends. Bridges get them too. Some people seal them all up but, I’ve seen more rust out from water being trapped than water washing through. Water will always get in so find a way to let it out. Check back often and don’t hesitate to ask questions! Good luck!!
Adding the braze ons distorts the tubes also. If they are all locked down, then that distortion turns into internal stress in the frame. If the tube is loose, you can adjust the miter to compensate. I initially found this to be a bit nerve wracking. I think it’s hard to conceptualize where they go on a plain tube. Once you have a frame, it’s easier to place them where you want them.
Yes of course. The minimum number of vent holes you need is one, in the HT behind the TT junction, assuming you’re using “hooded” dropouts which are vented. But many people also like to vent everything into the BB shell for water drainage.
Interesting. I do the braze-ons after welding the frame, but the bottle bosses before. As you say, it’s easier then to visualize where you want them. I just basically tack them on with a bit of TIG braze so there should be very minimal distortion.
I have also heard of people complaining of tubes buckling where they had drilled holes during frame alignment. But I think if you need to do such aggressive realignment you’re probably doing something else wrong.
I don’t own an oxy-gas setup and I TIG braze all those little bits (with silicon bronze). After all, on a Ti or Al frame, people are welding around the bottle bosses and things. You could of course TIG weld them carefully on a steel frame as well, but because they’re often going on the thin sections of the tubes, I prefer to use braze.
It doesn’t look as neat as if you silver-”solder” them, which is kind of invisible, but I don’t mind. It looks fine and there’s no reason to hide it
That part I noticed today. I spent around two after work in my garage, just to get the DT-HT intersection. At some point It looked quite promising, but I kept optimizing it, until I made it quite bad again. Especially those big “ears” at a pain to get right (I think it doesnt help, that I am joining a 35mm DT to a 36mm HT, so the ears are really big). Tomorrow I will (hopefully) finish this and the DT-BB intersection. I left plenty of space there to “sneak up” .
The Frame will be bronze-brazed. I initially wanted to go lugged, but they would make everything more expensive and constrain the tubes and angles more than I was willing to sacrifice. (And since I dont really expect this frame to be very good, I didnt want to spent too much money )
Doing the braze-ons before joining the tubes sounds like a smart idea… It seems, like I have to figure out my cable routing soon then.
I have looked at them as well, but their price scared me off. They sell for around 40€ (If they are in stock at all), so I would need to invest around 240€ for the front triangle, and maybe even more, if I decide to build a bike with different tubing at some point.
My current idea for joining the tubes is to use an aluminum piece with a V-shaped groove (and possibly some shims to get the correct height), along with some steel plates to weigh down the tubes and hold them in place while tacking them with a bit of bronze. Afterwards I want to finish them in my bikestand.
However, before I do this I need to finish the miters and braze-ons, so at my current speed it will take until at least mid of May.
Sorry, when I say braze-ons I mean all of them, bottle bosses, cable stops, rack mounts, pump pegs etc. I still think learning TIG brazing and TIG welding (along with all the other fab stuff) within the 6 weeks is going to be challenging. You might be the prodigy I mentioned.
Certainly braze ons and bottle bosses have been added to complete frames for many many years and probably millions of frames. I suspect that was a very common modification in the 70s as braze ons became more popular and people had frames updated. It’s not that you can’t do it. It just adds internal stresses. It’s important to heat the opposite side of the tube from the braze-on to ‘offset’ the distortion and mimize the internal stresses. Even with silver which is lower temp than silicon bronze. I don’t know how you do that with a tig torch…
Yeah, I’m talking about 1/8” vent holes in tubes and then bigger holes in HT/BB shells. I’ve never heard of tubes buckling because of the vent holes. I can’t even think how that could happen given they would be at the ends of the chain/seat stays. Unless you’re talking about for internal routing. Then, it’s obvious if they put them in the thin-walled section and go cranking on it, yes, buckling seems likely. And agreed, there were other problems that should have told them that those materials weren’t destined to be a bicycle! It’s painful to complete a frame (or portion of a frame) and realize it’s just not going to work out. That decision to scrap the work and materials is a hard one but it has to be made. Every framebuilder I have visited has a garbage bin full of those hard decisions.
Not as issue with TIG, especially TIG brazing. The heat input is very low. Much higher temperature and very focused.
Everybody TIG welds canti bosses on (and I weld rather than braze those). It’s fine.
As for learning to TIG in 6 weeks, maybe some people, it took me at least a year before I was anywhere near what you need for framebuilding. But I’m probably on the slower end of the spectrum.
Yes the “ears" are always tricky especially when the diameters are similar as you say! Care is also needed when welding them (but you’re gas brazing I think you said).
Not an issue with TIG, especially TIG brazing. The heat input is very low. Much higher temperature and very focused.
Everybody TIG welds canti bosses on (and I weld rather than braze those). It’s fine.
As for learning to TIG in 6 weeks, maybe some people, it took me at least a year before I was anywhere near what you need for framebuilding. But I’m probably on the slower end of the spectrum.
I have never TIG brazed or used the sif bronze common in the UK. TIG/Sif bronze brazing is higher temp than 56% silver, admittedly the heat is more concentrated. I’d be interested to see what happens when you measure it. Measure the bow of the new tube and then add a braze on and see if the bow changes. You may still decide it’s not an issue but at least then you’re doing so with data. Some people don’t even measure the bow of the tube to begin with so, maybe it’s not an issue.
I haven’t ever seen a custom builder tig canti bosses - not that I have studied the subject exhaustively or anything but anecdotally, I can’t remember seeing it. I know it can be done and I’m not saying either way is better or worse, I just disagree that ‘everybody TIG welds canti bosses’.
Yes point taken re “everyone” tigging canti bosses. What I should have said was that you will usually find them tigged on production steel bikes like all those 90s MTBs.
I could be wrong, but higher temperature usually means less heat. The heat affected zone from TIG brazing a cable stop or something is tiny. A cm or two radius. I’m less familiar with silver-brazing them but although that filler does melt at a lower temperature you have the torch on there for getting on for a minute or so? That feels like more heat than a second or two of TIG at about 30 or 40A.
But I think you will be fine. I do the TT last so I can sneak up on the right length on what I consider the slightly easier tube. No problem doing that with the DT instead, just bear in mind that you don’t want to end up making it too short when titivating the mitres. If your TT is a fraction too short already it doesn’t matter. But obviously everything has to fit together at the right angles.
It’s painful to complete a frame (or portion of a frame) and realize it’s just not going to work out. That decision to scrap the work and materials is a hard one but it has to be made. Every framebuilder I have visited has a garbage bin full of those hard decisions.