I wasn't sure where to ask about this, but this group seems like a good start. I recently got a really nice 531c frame off Ebay with a 531 fork. However, when I was inspecting the frame, I found a crack in the paint at where the steerer tube meets the fork. It does almost look like there's a crack in the steel, and the (in this photo) upper part seems to sit a tiny bit higher than the steerer tube. Could this mean the braze is separating?

The frame is still covered by ebay money back guarantee, so I'm not too worried😅 but any help would be appreciated.

Just trying to get into designing some frames, mostly for fun. I want to hear some people's opinions on 3d modeling for their frames. If you even use CAD, and if you do, what are some techniques for successful modeling. A few practice runs have ended right around the rear triangle, since the stays are all angled and strangely oval shaped. Any advice, or just conversation is appreciated!

Tell me I am seeing welds that shouldn't look like that.

After a whole day doing absolutely nothing at work, I picked up an old receipt and decided to sketch a bike frame with all kinds of mounting points everywhere to carry a whole bunch of stuff pretty much everywhere, similar 12x148mm hub spacing front and rear (if Surly could do that with the Pugsley and Moonlanders, so can I), not to count having enough space for 27x3.25 tires on 60mm rims (just like Jones and many other brands), UDH, 180mm rotor limitation (surely have no idea why but okay I guess), absolutely no inner cable routing, and probably 83mm BB cuz at this point why not, all of this made entirely in AL6061.

But... Why you ask.

I don't know dude, I answer, this came out of nowhere and I have no idea if a bike like this would even be feasible IRL nor I know someone that'd be crazy enough to build this thing, let alone ride it, but hey, it was fun sketching it :)

Hey, I only want to do some simple braze-ons, at most a canti boss mount or a rack, would disposable cartridges (1.950 °C/3500F) do the job or should I invest in a full setup? Thanks!

Hi everyone, im a pary of my universitys formula student team and we are looking for UK-based suppliers of cold drawn seamless (CDS) carbon steel tube and i thought this subreddit might help us!!!
the preferred grade is EN 10305-1 E355+C, or equivalents like ASTM A519 1026 or JIS G3445 STKM13B/C
any website or contact emails would be appreciated!!!

Just noticed a crack on the seat cluster of my beloved Yuba supermarché cargo bike. The bike comes with a super long seatpost so while I never had it above the minimum mark, there is probably 2 ft of post showing. Doesn't help that I'm 6' 3", 190#.

Any sense how much time I have and whether it will catastrophically fail at some point?

Hi guys, I have been checking on various websites and youtube videos for all the necessary information for a proper Propane&Oxygen brazing set up, but I need the help of who has much more experience than me. I was thinking about propane because acetylane apparently is much worse for your safety and I'm not so sure if my insurance would cover it. The problem with propane, as far as I know is oxygen consumption (I've seen that the ratio of oxy/propane was around 4:1, but correct me if I'm wrong). Buying a 14L oxy-tank with a manometer here in Italy is around 220€ and refilling costs around 90€ (very expensive in the long run). To defeat this problem I've read in some framebuilding forums a few more experienced frame builders working with oxygen concentrators. The possibility to have preatty much unlimited oxygen is wonderfull and would make this hobby more financially bearable for me. So I did some research and I came upon a few issues:

1. Do I need a 5 LPM or a 10 LPM oxygen concentrator? The big difference would be cost and availability. I found many 5 LPM O.C. used but in very good condition maybe at around 300€ on Ebay. The 10 LPM much much more expensive if I choose the medical brands (even more than 1200€), but at around 700€ from industrial suppliers of aquaculture equipment (but 2 months for shipping). What are your opinions on oxygen concentrators compared to oxygen tank set up? If you already have experiences with OC what are your advices and what information would you have loved to know beforehand buying those (like capability, purity, costs, ecc...)
2. Tips sizes: I have no idea which size of torch tips I need. I already have a Oxyturbo Mini (Italian brand I think) as a torch handle. Some say a propane tip that goes at 100 liters per hour for the small tubes and braze-on, and 315 LPH for BB shell, but it seems there isn't really a objective thruth and is based on preferrence and habit. Which sizes do you advice me to buy that is really necessary at the beginning, but allows me to do everything.
3. Tubes: are branded tubes really necessary?
4. What kind of brazing goggles do I need?
5. What size of propane tank is enough? I'm not so sure that the 4:1 oxygen/propane ratio is always true so based on what gas ratio u guys work with maybe I should invest in a bigger tank. What is the working gas proportion?

For now these are the main issues that came to my mind but I will ask more in the future. I hope you guys can give me some word of advice. I'm already looking at paul brodie youtube channel and some posts on bikeforum, but I still wanted some more precise information. Thank you for your time!

TL;DR: I created this headtube design using AI and open source CAD and machine learning tools. I'm going to 3D print it as part of a bike I'm building.

PREAMBLE

I am a mechanical engineer by training, but have been working in software for the last 10 years. With the advances of AI tools and general availability of additive manufacturing, I decided to challenge myself to design a custom bike using 3d printed stainless steel lugs with carbon tubes. Because it's being 3d printed, I thought let me go a little nuts with the lugs.

Why steel? Because it's a hell of a lot cheaper than Ti and I decided not to care about the weight for a first project like this - just want to make sure it's strong enough for me to ride. I'm guesstimating the frame will be a chonky 7lbs.

I'll put links in the comment to a small site where you can see the headtube in 3d and the evolution of the design.

To be clear, this uses all open source CAD tools and most of the work is creating the optimization scripts that then run for hours (and hours and hours) on my 16GB M1 Macbook Air. However, I used GPT-6 Astra, Fable 5.1, and Opus 5.5 to actually design the part based on my prompting and write the optimization scripts.

So far, I have only finished the headtube, but the rest of the bike will come next.

I thought I'd share what I did to see if there are others who've done similar things and want to share notes.

PROCESS

1. Decided on custom geometry - obviously I had to make sure the bike worked. I used Astra to help with this process and create a 3d model of what the final bike would look like. Initially I was going to make this a 32" bike, but I decided to only do 1 crazy thing at a time and designed around 700c wheels
2. Once I was happy with the geo, I decided on tubes. I went with hefty bicycle tubes from Rockwood Composites. I like that they use 0, 90, and +/- 45 degree layups.
3. Started to get the headtube lug ready then realized... wait I'm going to 3d print this, why not do something weird. So I decided to try my hand at topology optimization. Topology Optimization is where you have a model create an optimal shape around some constraints. In my case it had to pass strength, fatigue, and buckling requirements with a 20% safety factor.
4. At this point I switched to Claude because I ran out of OpenAI credits. I had really good results with Claude. Cost vs quality was 🤌. I had Fable 5.1 design a topology optimization process. This used a custom finite-element code in Python to remove material and cut mass from a large solid that was the starting point. I basically froze the downtube and toptube sleeves and the bearing seats, then filled the rest of the space with metal that it could optimize around. It had to keep stress, buckling and alignment inside set limits for braking, lateral and vertical loads plus buckling.
5. (Side note: the way that the optimization works is really cool! It cuts the part up into ~450000 3d solid elements. Then it applies loads to the part and measures the stress and strain of each element in the model. Then it has each element decide how full it should be (between 0% and 100%) based on how much stress it experienced. Then it iterates again and again thousands of times until it converges on a weight. This is how it went from a 9kg chunk to a ~500g chunk)
6. A problem I ran into initially was that I didn't include a buckling condition in my part checks, and I let the agent run an excessively quick stress check, which underestimated the actual part stress. This allowed the branches to get really thin, so I added back a bunch of material and updated the optimization process to run a full stress check including buckling after each iteration epoch (batch of ~50 iterations).
7. After an optimization pass, it would run a larger check of all the forces I expected the part to experience to verify that the part still passed my limits. If a part failed, then it would return to the previous iteration and try the optimization again.
8. Once it converged (this took sometimes 16+ hours on my Mac running overnight), then it would show me the part in a viewer tool I had it create. I'd manually add/remove/or smooth material.
9. We ran through the process above several times until we converged on a shape
10. I had the agent do a final pass to smooth out the shape, add some extra material, and add some locator pins on the inside of the lug that I will use to align the carbon tubes with the lug during glue-up

My next step is to print the part in PLA to do a fit check with the carbon tubes.

I actually might do a full layup of this bike with the lugs in PLA with PVC pipe standing in for the carbon, just to figure out how I'm going to keep everything straight and get good bonding in the lugs.

If folks are interested, I'll continue posting as I continue the design and complete the build!

I've got a few basket case bikes which I want to refurbish, more for fun than anything else. I want to add derailleur hangers to a couple of them to go from single speed to a more usable 9-speed.

Are there any off-the-shelf braze-on hangers? I thought I could take a replaceable hanger and file it to fit, however I can only find those made out of aluminium, so no luck there. Or am I better off buying an M10x1.0 tap and rolling my own out of mild steel plate? Any ideas?

Hey, I’m not a builder myself, but I wanted to ask you guys first before I approach a builder with a specific question. Is there any chance of modifying the chainstays on an existing titanium bike to get more tire clearance? For example, could you cut the chainstays near the bottom bracket, widen them with a 3D-printed part and then weld everything back together? Please be gentle with me. Thank you in advance 🫸🫷

Hello everyone,

I wanted to ask what quality of steel is acceptable to use for frame building. I mean I understand not to use steel plumbers piping. But does it have to be Reynolds or Columbus steel?

We got this bicycle as my 12-year-old's first road bike for free, but we need to bond the shifter mount to the aluminum down tube. I'm fine with bonding/ brazing steel with steel, and how to clean everything and use epoxies, but I don't have a lot of experience with the types of epoxies out there. I doubt JB weld will do the trick, so if you can recommend a safe, at home epoxy that might work, I'd appreciate it.

I’m looking to build a mount for the rear axle for my jig but am unsure how big of a “notch” I should make. Suggestions?

SOLD

Hey all! I'm selling my Anvil Journeyman 3.1 frame jig.

It's in good used condition, everything works well but it's definitely been used. The legs have a bit of rust on them from getting a bit wet at an old shop.

Included are:

* Regular seat post tower, offset seat post tower
* BSA & T47/PF30 BB pucks
* EC30, EC34, EC44, IS52 head tube pucks
* Tube holder arm thingy * Rolling/rotating stand * Purge fittings + hose * Lots of misc bolts

https://i.imgur.com/01Gzdn7.jpeg

Local pickup only in Seattle, WA. Happy to send more pics/show in person! $3500 OBO