rosefarts

I got the idea in my head that I could build my next gravel bike. I wouldn't go completely nuts, essentially copying the geo of my Voodoo Wazoo but adding a little bit of toe/tire clearance. I'd be closely comparing it to the published specs of the Ritte Satyr and Ritchey Swiss Cross. I wouldn't build a fork, I want carbon.

Questions in no particular order.
1. Is there a manufactured lugged T47 bb setup? If not, is it possible at all to build a frame for 700x45 without a super long rear triangle?
2. I see Columbus tapered head tubes but no 1.5" lugs for the bottom half. I suppose this could be fine with careful mitering and no lug, but it sure seems like a great place for extra metal.
3. For 142mm/thru rear triangle spacing (it's just 135 with a different interface really), I am not seeing much. Plenty of disc mounts but the thru axle dropouts I see look like they must be welded. I kinda wanted a tinker toy build.
4. Since lugs are standard but geometry is not, with hand filing etc, are they adjustable or does building with lugs limit you to traditional geo?

I haven't spent any money yet. I'm just trying to figure out how big of a project this will be and if it is even realistic considering what I want and my own skill.
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I don't know if it makes a huge difference but it would be a 1x mechanical shift build.

unterhausen

I am currently doing a lugged gravel build. I'm building a fork though, because there are no lugs for anything bigger than 1 1/8" steerers. My current gravel bike has a 1 1/8" steerer and it works fine. My design is long reach/short stem for my own reasons, turns out everyone else came to the same conclusion at the same time for different reasons. Synchronicity.

It's not a tinker toy build. First thing I did was blacksmith the bottom bracket so s-bend stays would fit. I have seen lugged builds for short chain stay and 2.25" knobbies. I don't believe in short chain stays myself, but it certainly is an interesting challenge. I'm told the regular s-bend chain stays work up to about 50mm tire with no issue. I think the columbus flat mount stays will clear much wider tires, although I probably won't end up using the pair I have on the current build.

I am thinking about doing a fillet brazed version with tapered head tubes.

dsaul

I can't think of a way to make building a frame more difficult than trying to build an off road frame with lugs. I know it seems like building with lugs makes things more plug an play for beginners, but that only works for road frames that fit into the traditional lug angles and bottom brackets. Any off road frame is going to be much easier to build with fillet brazing or TIG welding.

As for fitting a 700 x 45 tire, I would say the shortest chainstays I would attempt is 435mm with a 68mm bottom bracket. At that size, you have to be concerned with clearance between the tire and the seat tube, as well as chainstay clearance.

This frame has 430mm chainstays and a 700x40 tire. Another 5mm of tire would be very close to the seat tube and I don't think I could squeeze a wider tire in there and still have clearance for the chainrings.

rosefarts

Dsaul.

I am not interested in ultra short chain stays. I may have erroneously thought you'd need really long ones to fit a 45mm tire on a 68bb. Isn't this exactly what press fit was supposed to be for? Wider BB. It'd be 1x with something like a 38 tooth chainring though, so probably not a problem.

My Voodoo has 68bb and 135 spacing and can run 45s no sweat, so maybe I'm overthinking it.

I did find some T47 bb shells online, same net effect as pf but threaded.

I guess as a beginner, I'd be worried about alignment and strength. Especially considering how hard I hammer my current gravel bike. That's why I thought lugs might help. Maybe they're not needed.

Possibly a dumb question here.

Are fillet joints mechanically held in place prior the torch work? Is there an internal sleeve or something? I don't know how there could be on most joints, but it seems like some miters just wouldn't be enough to hold it all together.

unterhausen

That's exactly why I'm doing it, more difficult. I disagree that lugs make frame construction easier anyway. I suppose that's because I have no fear of fillet brazing. Fillet or TIG certainly would solve a number of problems.

dsaul

I don't think lugs makes it easier, but I think that beginners mistakenly feel like lugs will hold things in position, make up for bad fit up and/or add a level of security to questionable brazing.

unterhausen

There is some truth to the structural advantages of lugs in the face of poor mitering and other faults during construction. Not sure about brazing, lugs can fail quite spectacularly if poorly brazed (or even if well brazed and something goes wrong). I have seen pictures of separated lugs/tubes where the builder got full penetration. Not sure what's up with that.

The bad thing about lugs is that it can hide extremely problematic brazing. Best to have the problems out in the open so you know not to ride the frame.

dsaul

Press fit and T47 were not designed to allow wider tires. Most of the press fit and T47 bottom brackets are the same widths as standard english threaded bottom brackets. The main reason for Press Fit was so a metal bottom bracket didn't have to be bonded into carbon fiber frames. T47 was mostly to get the benefit of the larger bearings of press fit, without the creaking and poor fit issues. They actually make it more difficult to fit a wide tire with short stays, because the bottom bracket is a larger diameter and therefore closer to the tire. They do have the benefit of not having to notch the downtube around the seat tube with smaller tube sizes, so there are some benefits. T47 bottom bracket taps are way more expensive, as are the available bottom brackets, so I have no desire to use them.

Fillet brazed frames are tacked together with the torch and filler material in the same way that a TIG welded frame is tacked. We use various methods of holding the tubes in place for tacking in the fixture. For welding, I use magnets to hold the tube in place for tacking, although the only tubes that really need it are the top tube and seat stays. Magnets don't work very well with the heat from torches, so I use spring clamps to hold tubes in place for fillet brazing

guy153

As dsaul said, no, but you need a spring clip or small magnet or two. But he means for when you have also have the frame in a jig. Without a jig it will all just fall apart.

As for strength do a few test joints and break them. This can't prove your joining method is good enough but can prove if it isn't.

Alignment does have to be to a very high standard compared to most fabrication projects but there are various tricks to getting it right I'm sure we can help you with!

unterhausen

I think in a test where you try to rip apart a joint in a vise, the results can be misleading. Bike frames don't fall apart that way, they fail in fatigue. If they break when you put them in a vise, there definitely is a problem

guy153

Yes that was my point really. It can show if there is an obvious problem but can't prove there isn't one.
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rosefarts

It seems like my first step is to find a junkyard bike and chop it up, then use it to teach myself how to fillet.

​​​​​Basically take one size of bike and turn it into a much smaller one. Seems like a way to test whatever jig i make, mitering, and brazing. Then toss it in the trash.

Another more expensive but more fun practice project would be to get one of the $150-170 tubeset kits on eBay and build a complete bike from it.

Edited to add. I totally agree with the person who said 1 1/8 is enough. The issue is availability of forks

unterhausen

I feel like there have to still be 1 1/8" forks out there. Might be steel. There certainly are production bikes still coming with them, although those tend to be aluminum.

I searched and there are a ton of them. Maybe not exactly what you want though, I didn't really check for that.
https://www.google.com/search?q=grav...hrome&ie=UTF-8

It might be more fruitful to just get some lengths of 4130 and fillet them together. A couple of inches for each piece of the joint is enough. Or ask for offcuts.
I lament the disappearance of straight gauge bike tubing. That was a bargain.

guy153

Yes an old bike is a good source of practice material. If you're anything like me you will need a bit more practice than just resizing it once though. An entire bike almost completely reduced to 1" coupons got me to an acceptable level of TIG capability. I don't know about brazing with gas but I should think about the same amount of practice needed.

unterhausen

Someone recently posted a video of a motorcycle guy doing the "stack of dimes" method of brazing and now I'm going to practice that with my tubing scraps. If I feel good about it, I might do a bike that way. I'm also making bike stands for my garage out of old bikes. I feel perfectly competent to make a fillet bike, but I haven't done it for years and warming up a bit would be a good idea.

rosefarts

So here is where it all stands.

I got a montgomery ward junk bike today. Lugged head, bb, and seat tube. Brazed seat stays. Crimped dropouts.

I'll do unspeakable things to this frame over the winter, hopefully ill get a sense of my jig setup and the nuance of fillet joints in the process.

I got a book about frame building. Reading it now.

Time isn't always on my side, so this might take a minute. Got a pinched nerve in my back making riding literally impossible temporarily, so maybe I can make some progress.

I'm sure I'll update once I hit a few snags.