I agree this looks like a tubing defect.

I'm surprised OP can't find a builder for a Keirin-type frame. They're a bit simpler to make than a road frame and much simpler than a rando frame with racks, a dozen braze-ons, internal routing, etc... That said getting the clearances tight and leveling the track ends can be tricky. I once made a frame with a dimpled ST and spent HOURS figuring out the the correct sprockets, chain/chainstay lengths combo to achieve a pleasing clearance.

BTW Kalavinka sells beautiful lugs and ends that fit the Keirin aesthetic.

If you know of a framebuilder in the United States or Canada who is interested in building and painting a keirin frame for that specification of components and with that severe of a geometry, let me know... I haven't been able to find one and I am actively searching. I listen to framebuilding podcasts and subscribe to framebuilding YouTube channels... All I have heard is "I won't build a track frame..." Prove me wrong: Who is willing to build a steel track frame?! I am a customer waiting to buy your product!

And it isn't that I literally "can't find a framebuilder"... It is my experience that Rinsei-san at Rinsei Lab is producing the most well-built and beautiful keirin frames in the new era... The only two bikes I have built up now are a 2018 and a 2019 Rinsei Lab, and I absolutely love these frames: They are both wonderful and Rinsei-san is active in documenting his process.

Though it would be lovely to have a bike frame built with these considerations in a more local context... Buying secondhand keirin frames from Japan is a roll of the dice—understandably. I'd love to find someone who'd be interested in building something like this for me in a native tongue.

Though, again, if you know of someone in the United States or Canada who is keen on building a keirin frame: Let me know! I am a potential customer... And holy hell: I spend enough money on keirin frames every year not to be startled by the price of it

Mr Fattic, sir... I do want to build my own frame(s). Especially as the designs I wish to create seem esoteric to the western hemisphere these days (brazed steel lugged frames).

I am in Wisconsin and am already attempting to figure out how to make my way towards your classes... The things and attitudes I have seen constructed by your former pupils has astounded me... I wish to be put on that path—sincerely.

Though I do not have a lot of money and I am still trying to figure it out... Otherwise I would have already contacted you or your staff.

I apologize for contaminating the framebuilding forum as a non-framebuilder... I have just come to believe that you guys have all the answers

I think this was the best place for this thread. Or I probably would have moved it.

My understanding from some cursory research (I'm not an expert on Keirin racing!) is that to be a true 'Keirin' bike, it has to be made by a certified builder of specific sized tubes and lugs so, you're right, no one in the US is likely certified and therefore it wouldn't be a Keirin bike. However, replicating the geometry and particular fitment requirements of a keirin type bike shouldn't pose any builder a challenge. I have made several framesets for local velodrome racers and the velodrome Juniors Program and some are using NJS parts. I don't think there are any specifics that most any builder couldn't meet. I'm now curious and want to go do research into these certifications (which I really should do before commenting on them!).

You don't mention how tall/heavy you are or how you ride your bikes but the limitations of a true Keirin bike may actually be your problem. You say you've broken several in the past year. My guess is that for a Keirin racer who makes money racing, replacing a frame every few crashes isn't a problem (as with all high level racing) however that same rate of failure isn't very useful for the rest of us. The specific rules for Keirin are for a standard diameter tubeset which is a bit outdated. As TiHabanero mentioned, I made a frameset for his son from a special set of 70's Columbus PS track tubing (which is standard diameter ). Ti's son is a tall, strong guy and 1" top tube and 1" steerer aren't sufficiently strong for him to race on. The top tube had also previously been nicked by a saw at some point in the past 50 years so it had to be replaced anyway. As the goal was specifically to use this tubeset, I used the 28.6mm DT for the TT and used a new DT with appropriate diameter and thickness and then increased the headtube to 1-1/8" to stiffen up the whole front end. Those tube diameters also require different sized lugs that wouldn't meet any NJS rules. This may take it too far outside of a 'Keirin' bike for your taste but it may be required to support your riding style, volume and type of riding you do.

The geometry of a Keirin racer is the same as a typical track bike (or close enough) and there are many builders of those and most would adjust the geometry to suit your needs - within reason. There is no reason to stick to the outdated dogma of a controlled racing series that requires a bike that isn't suitable (as you have proven) for normal riding. We have access to much better materials and techniques in the real world that you should take advantage of.

Having said all of that, I actually have a few full sets of Ishiwata (pre-cursor to Kaisei) 019 tubing that are just sitting here gathering dust.