Is this the case for a seat tube reamer?

[fpavao]

Hello,

I'm building my 17th frame for a friend and it's the first time I'll use a seat tube with a thickness of less than .9. It'll use a 28.6 OD columbus cromor for 27.2mm seatposts. I'm using brass brazing and a straight gauge .9 top tube.

Anyway, it seems like something went wrong on the tt/st junction. The inside of the tube seems a little lumpy where I brazed, to the point where it interferes with the seatpost. Not sure how that happened, might be too much heat (unlikely) or on cold setting. I build in subassemblies and had to do some realignment.

I haven't tried a 27.2mm seatpost yet as I don't have one on the shop right now, but I've tried a 26.8mm and it catches a bit, not very drastic, but some force needs to be applied for it to move. I can feel the lump with my fingers also.

What should I do? The frame is not ready, only front triangle. I don't have a reamer and buying one was not on my plans right now. The guy I'm building for is my friend so if something goes wrong it's no big deal, but he wanted to use a carbon seatpost and I'm pretty sure the way the frame is now that'll be impossible.

Still amazed by how a thin walled tube needs care unlike the heavier stuff I was using.

Thanks.

[afwalker]

Sounds like normal to me (14 frames). I've had to ream all of them so far.
Without a reamer, just use a half round file and get it smooth.
For carbon, it should be pretty smooth I would think, a flex hone is what I finish mine with.
Flex Hone, Cylinder Hone 29mm
cheers
andy walker

[EnginCycles]

Hello,

I'm building my 17th frame for a friend and it's the first time I'll use a seat tube with a thickness of less than .9. It'll use a 28.6 OD columbus cromor for 27.2mm seatposts. I'm using brass brazing and a straight gauge .9 top tube.

Anyway, it seems like something went wrong on the tt/st junction. The inside of the tube seems a little lumpy where I brazed, to the point where it interferes with the seatpost. Not sure how that happened, might be too much heat (unlikely) or on cold setting. I build in subassemblies and had to do some realignment.

I haven't tried a 27.2mm seatpost yet as I don't have one on the shop right now, but I've tried a 26.8mm and it catches a bit, not very drastic, but some force needs to be applied for it to move. I can feel the lump with my fingers also.

What should I do? The frame is not ready, only front triangle. I don't have a reamer and buying one was not on my plans right now. The guy I'm building for is my friend so if something goes wrong it's no big deal, but he wanted to use a carbon seatpost and I'm pretty sure the way the frame is now that'll be impossible.

Still amazed by how a thin walled tube needs care unlike the heavier stuff I was using.

Thanks.

Wrong tube and process. That tube needs a lug or a sleeve. It will break eventually. Once reamed you have minimum to no tube left.

[steve garro]

Wrong tube and process. That tube needs a lug or a sleeve. It will break eventually. Once reamed you have minimum to no tube left.

Drew is right - if you ream it out you will be reaming brass out.
Save yourself time, money and bad client interactions when that puppy cracks - you know all the TT/ST/DT/SS cluster cracks you see?
Well this is why.
You need an externally butted ST or a sleeve.
No two ways about it.
- Garro.

[Andrew R Stewart]

Fillet or lugged? (Brass can mean either). What's the wall at the top of the ST (or did i miss that)? How long did you spend brazing this joint? Did it seem that you had to heat one side a bunch longer then the other?

Drew is correct (of course) that a thin wall fillet joint willikelyli warp and/or fail easily. This is why sleeves and externally butted STs are made. But if it's lugged there still can be warping and/or brass that got over the end of the ST and inside.

Just about every frame I've built (39 now) have needed some sort of inside the ST clean up. Some only needed a honing (Flex hones are great, not too costly and available through QBP via your LBS). Others needed a reaming. I got an adjustable reamer years ago and use it after completing all the brazing (as attaching the seat stays can add to the distortions) but before cutting the binder slot. Icreepreap up to the amount of reaming that is needed to fit the correct post. Most all the time this is very little actual removal. Just recently I got a spiral reamer (a Silva) and have begun playing with it.

So without more specific info I'd say you have an experiment at worst and the common need to ream at best. Since this frame is for a customer i think you should start over (maybe with a bit more practice) and then return to this main triangle and complete it as a tester. Then you can ride it and/or cut it apart to see how well other joints went too.

Either way you need to figure out what happened before repeating the same methods or design. If you're building for others you really need to be both well tooled and good at what you do. Oh, and have insurance (you do, don't you?). Andy.

[fpavao]

Thanks for the replies.

It's fillet brazed and .6 thickness on tt/st junction. So, everyone agrees that's not proper? I've seen some bikes like this around, although none with more than 10 years, probably. They seemed pretty tough to me, so I didn't think it would be a problem.

This is bad...

[steve garro]

Thanks for the replies.

It's fillet brazed and .6 thickness on tt/st junction. So, everyone agrees that's not proper? I've seen some bikes like this around, although none with more than 10 years, probably. They seemed pretty tough to me, so I didn't think it would be a problem.

This is bad...

You need a tube like the HOXPLATST5 that HJ sells - at least you are only into it for a front triangle!

What you are describing is not acceptable, I couldn't make that work & I can braze pretty well......

- Garro.

[fpavao]

You need a tube like the HOXPLATST5 that HJ sells - at least you are only into it for a front triangle!

What you are describing is not acceptable, I couldn't make that work & I can braze pretty well......

- Garro.

What do you mean by "couldn't make that work & I can braze pretty well"? Is brazing the problem (heat distortion) or is the wall too thin for a safe joint without a lug or reinforcement (i.e., not even a tig welded frame could have a 28.6 x .9/.6 st)? Or both maybe.

[Amaro Bikes]

What do you mean by "couldn't make that work & I can braze pretty well"? Is brazing the problem (heat distortion) or is the wall too thin for a safe joint without a lug or reinforcement (i.e., not even a tig welded frame could have a 28.6 x .9/.6 st)? Or both maybe.

Steve means that even himself with good enough brazing skills wouldn't be able to make such a st tube thickness work as it's too thin and will always create a weak point. Even with a TIG welding procedure and heatsink help would be a too thin section for such a big stress area (tt-st-ss) and most recommended scenario is to use at least a 0.9 thickness on tig and even thicker (sleeves/lugs) on brazing.

Reaming is just a the final touch for this situation, where small thickness means even the slightlest reamed section will result in less than 0,5mm tube wall, which is future trouble... and there's no money enough to pay good sleep nights.

[steve garro]

Steve means that even himself with good enough brazing skills wouldn't be able to make such a st tube thickness work as it's too thin and will always create a weak point. Even with a TIG welding procedure and heatsink help would be a too thin section for such a big stress area (tt-st-ss) and most recommended scenario is to use at least a 0.9 thickness on tig and even thicker (sleeves/lugs) on brazing.

Reaming is just a the final touch for this situation, where small thickness means even the slightlest reamed section will result in less than 0,5mm tube wall, which is future trouble... and there's no money enough to pay good sleep nights.

What he said.
Reaming is to remove the curly-Q's from vent holes and such & then you give 'er a quick flexhone and the seatpost should slide without friction or grit.
Here's a freebie: Make your seatpost compression slots wide and put a pucker hole at the end ;)
- Garro.

[fpavao]

Ok, thanks for the help and clarification. Clearly not a case for reaming.

I'll look into what can be done.

[EnginCycles]

I'll look into what can be done.

The recycling bin is what can be done. Seriously IT WILL BREAK!

[fpavao]

The recycling bin is what can be done. Seriously IT WILL BREAK!

How long do you think it'll take to break? I'm thinking of finishing the frame for myself. Or maybe take the tubes off and add a sleeve.

Yes, I'm that cheap and I don't want to scrap the tubes.

[steve garro]

How long do you think it'll take to break? I'm thinking of finishing the frame for myself. Or maybe take the tubes off and add a sleeve.

Yes, I'm that cheap and I don't want to scrap the tubes.

Why do people ask advice if they ain't gonna take it?
- Garro.

[edoz]

What they really want is validation of their bad ideas.

[Amaro Bikes]

Why do people ask advice if they ain't gonna take it?
- Garro.

Receiving advice from such experienced people like you, Drew, etc, is an incredibly valuable gift. Once we realize we've done something wrong, best step (after blamig ourselves from previous blindness) is to learn from it and improve thanks to such a gift as your advices. Ignoring it is like driving full speed to a dead road.

[fpavao]

Sorry if I'm sounding stupid. The thing is these tubes were really expensive for me (college student, now unemployed) and it's a pain in the ass to get them here in Brazil.

I'm not going to finish it like this but the frame is not going straight to the trash, I just want ideas of what to do with it. Even if it's just for hanging on the wall.

[veryredbike]

Sorry if I'm sounding stupid. The thing is these tubes were really expensive for me (college student, now unemployed) and it's a pain in the ass to get them here in Brazil.

I'm not going to finish it like this but the frame is not going straight to the trash, I just want ideas of what to do with it. Even if it's just for hanging on the wall.

In that case, finish it for practice then hang it on the wall? It means using other tubes that you could have saved for the next frame though. I'm planning to cut up my first frame when I finish my current one. I know my brazing was terrible at that point so I'm going to cut away one half and grind the other right down to the center line to see exactly what was up. The rest goes on the wall. Mostly it's because otherwise I know I'll be tempted to keep riding it until something happens.

[Curt Goodrich]

While I agree with what others have said that you used the wrong tube and will lead to problems later. Given your stated desire to "save" money you could keep the frame for yourself and ride it. When it cracks (notice when not if) you can then practice doing a repair. When this cracks it likely won't be dangerous immediately. This is not like a cracked fork. This frame should not be pawned off on somebody else. Or you could do the repair now by just replacing the seat tube but the frame still should remain yours.

[Rody]

Fpavao,

Here's what needs done.

Cut out the seat tube above the bottem bracket and just below the top tube.

With the seat tube removed, mechanically cut/grind way the remaining stump of the seat tube from the bottom bracket and any fillet, down to clean metal.

Carefully cut away the remaining seat tube from the top tube and file down the fillet to as close to the top tube as possible without getting into the base metal.

Detail sand the area with emory cloth to finish up the areas.

Then create a new seat tube with an externally butted top section (thicker than the rest of the tube), a sleeve that fits over the new tube, or an insert that is joined to a new tube.

File the top tube coping to match the new dimension of the seat tube.

Fixture, tack, check alignment and braze.

The seat tube is truly the spine of the entire frame and needs great attention to detail. Here is a blog post on how I make mine...

Groovy Cycleworks 330-988-0537: Creating the spine of the frame...

Steve uses a sleeve, and his process can be seen here...

coconino cycles custom bicycles 928 774 7747 www.coconinocycles.com: Building a mountain bike Coconino style.

Best of luck,

Rody