# Bottom Bracket Warp



## Drewbis1 (Feb 9, 2013)

After welding the bottom bracket shell in the jig, the ends of the BB moved up less than .25mm each. The BB shell is still perfectly circular, and I can hand thread in the drive side of my "fit up BB" without any problems. You can notice the slight warp when you put a square, or any strait edge to the bottom of the BB shell, and you can rock it just a little bit.

In the first image, you can see the gap on the non-drive side is different on the top vs the bottom. You can see it more in the second image.

I went to a couple bike shops to see if they would have advice as to chasing and facing the BB shell. Most of them seemed hesitant as they don't normally deal with raw frames. They said their tooling is more directed towards aluminum frames that just have to be re-chased. My concern is the amount of thread that is going to be taken out to make the two cups thread in square to each other. I found one mechanic who didn't seem to think it was that big of a deal, but he did admit, he doesn't know much about frame building, so didn't know how to combat these issues.

How do you frame builders deal with BB warp? Is chasing/facing worth it, or is this frame going to the scrap bin?


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## afwalker (Apr 26, 2012)

Did you have a heat sink?
If you take the rubber off this from HF, it'd at least help in the future.
Medium Tail Pipe Expander
or the full monty is here:
Heat Sinks
cheers
andy walker


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## Drewbis1 (Feb 9, 2013)

I did not have a heat sink...

My friend has the Anvil frame jig. I had it clamped in there thinking it would hold it in place well enough. It was also being purged to help keep everything cooler and cleaner on the inside.


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## afwalker (Apr 26, 2012)

I'm just getting starting tiging frames, went to the metal guru class where we used the jig to tack, then took it out and aligned it, then tig'd out of the jig with heat sinks.
Blog « Metal Guru « Lessons in bicycle manufacturing
The HF deal is $13. We did not purge the heatsinks, but they make ones that can. The warp is worse than some colors you cant see on the inside. They're probably some discussion on purging, if it makes any difference.
cheers
andy walker


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## Walt (Jan 23, 2004)

Chase it and face it and the BB will square up to the faces of the shell. You're fine, BB's always distort some. 

-Walt


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## DWF (Jan 12, 2004)

No fixture can prevent distortion and even if it could, as soon as you removed it from the fixture, SPROING!

Distortion is the by product of heat used during the joinery. Here's how you prevent or minimize it:

1. Don't lolligag during the joinery. Get in and get out fast & minimize the heat input to the exact amount required to complete the joint competently. Fingies have a bigger problem with distortion because it takes them so long to get the joinery done. Over-applying filler metal causes problems too. 

2. Use components of suitable thickness relative to your expertise. If you're a Fingy and using the Pargaon BB shells, use the 1-9/16s rather than the 1.5s which have highly relieved IDs. Same goes for seat tubes and head tubes. Err on the side of thickness when while you're learning. Goes for all tubes actually. If you're using less than 9./.6/.9 tubes you're just begging to compound your problems.

3. Complete your joinery in quadrants. Do not just weld one tube at a time or all the joints at a specific area. Weld a joint quadrant here, then weld a joint quadrant there, then other over there before going back to where you started. BB's are easy for a Fingy to heat soak because there are so many joints there. Allow it to cool before starting the next joint.

4. Heat sinks are for pussies & my personal feeling on them is that if you need one for normal frame construction you're probably using tubes thinner than your skill level and/or joinery procedure calls for. That said, they will help reduce distortion at the risk of localizing stresses at the joints. Smoke 'em if you got 'em.

5. Like I tell folks in the seminars: your first frames are going to be both better & worse than you expect. Everybody's is. If your first frames are aligned within a pinch of millimeters without bending them on the table and they ride straight, you're doing awesome. Bask in your awesomeness but temper it with the realization that no matter how good you get, every frame will have some flaw even if you're the only one who can see it. This is the way it's supposed to be.

As far as chasing & facing; it'll clean up fine. If you're going to build frames, you're going to need tools to complete the job. Taking them to a bike shop to have them finish the job for you is lame. Invest in quality reamers, facers, and skip tooth BB taps.


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## RCP FAB (Jun 15, 2011)

:eekster:

There is so much win in that post, I can not even begin to describe it.


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## shiggy (Dec 19, 1998)

Drewbis1 said:


> After welding the bottom bracket shell in the jig, the ends of the BB moved up less than .25mm each. The BB shell is still perfectly circular, and I can hand thread in the drive side of my "fit up BB" without any problems. You can notice the slight warp when you put a square, or any strait edge to the bottom of the BB shell, and you can rock it just a little bit.
> 
> In the first image, you can see the gap on the non-drive side is different on the top vs the bottom. You can see it more in the second image.
> 
> ...


Less than 0.25mm? Really? Not a problem. At all. Will not even notice it in use.


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## Drewbis1 (Feb 9, 2013)

Thanks for the heads up on the HF heat sink. And thanks to all for your replies...

@ Walt, thanks again for your expertise. You may remember my seat tube dilemma that was suited for lugs.... I was hoping this tube set didn't get effed as well.

@ DWF, I just shite myself laughing at some of your post. I'm not really an aspiring frame builder, just wanted to make myself a frame since my last steel bike was folded when I got hit by a bus. If I decide to make a living out of this, I will definitely purchase the proper finishing tools. And somehow, this being my second frame (first frame was scrapped due to a .6mm seat tube), it is perfectly aligned. I don't have a dedicated alignment table, but my less than scientific methods are all reading that the HT and ST are in line with each other, and level with each other. The dropouts took some muscling, but they're good now, and the wheel that I fit in there rolls nice and straight. Only have the seat stays to go.

Again, thanks everyone.
Cheers.


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## afwalker (Apr 26, 2012)

Thanks Don,
Didn't know paragon had different thickness BB shells, thicker is better for me at this stage of the game! I'll still use a heat sink, just for kicks, I'm not as good a welder as you!
Might as well do everything I can to help myself.
cheers
andy walker


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## Meriwether (Jul 26, 2007)

DWF said:


> 1. Don't lolligag during the joinery. Get in and get out fast & minimize the heat input to the exact amount required to complete the joint competently. Fingies have a bigger problem with distortion because it takes them so long to get the joinery done. Over-applying filler metal causes problems too.
> 
> 2. Use components of suitable thickness relative to your expertise. If you're a Fingy and using the Pargaon BB shells, use the 1-9/16s rather than the 1.5s which have highly relieved IDs. Same goes for seat tubes and head tubes. Err on the side of thickness when while you're learning. Goes for all tubes actually. If you're using less than 9./.6/.9 tubes you're just begging to compound your problems.
> 
> ...


What in the world is a Fingy...?

My favorite is #5. Especially the last two sentences. Putting that one on speed dial.

DWF, you need a blog like Sadoff's http://overopinionatedframebuilder.blogspot.com/2012/12/the-mark-of-master.html?m=1. Would be really fun to read The Over-opinionated Toolbuilder.


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## BenCooper (Feb 25, 2013)

F***ing New Guy ;-)

Tacking in quadrants is a good way to minimise warp - along with the usual stuff about minimising heat and getting good tight miters. Tack it so it can't move so much, then fillet.


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## Meriwether (Jul 26, 2007)

BenCooper said:


> F***ing New Guy ;-)
> 
> Tacking in quadrants is a good way to minimise warp - along with the usual stuff about minimising heat and getting good tight miters. Tack it so it can't move so much, then fillet.


I probably shouldn't ask, but what are the various framebuilding "classes" and when does one graduate...? 

IMO welding in quadrants helps with alignment more than warpage. Tight-arse miters and good heat control via speedy passes (and maybe pulsing) helps the most with warpage but it all matters of course. Everyone experiences a bit of warpage and heat sinks help minimize it. But I'm a Fingy ***** so what do I know.


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## calstar (Mar 26, 2013)

*Meriwether: "What in the world is a Fingy...?"*

From the Urban Dictionary: Urban Dictionary: fingy's

_*fingys *

1.) A shortened term for FISH FINGERS 
2.) A shortened term for Finglands Buses
"What shall I have for tea tonight?" 
"Fingys!"

"What bus is this?" 
"A fingys one."

_Still doesn't make a lot of sense, must be some nuance lost in this definition.

Brian


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## DWF (Jan 12, 2004)

Fingy or FNG is a term from my years working on the Ice where you were either a Fingy or an OAE. Fingy is ****ing New Guy, a term of endearment really, and everybody is one at some point in time.

I don't tack in quadrants, centerline of the frame (12 & 6) or on the long axis of the adjoining un-mitered tube only for the front triangle. If you tack on the side of the tube, it will pull the tube in as it shrinks that will give you a gap on the opposite side. That is bad. If you insist on tacking the sides, do so only after the centerline miters have been completed & cooled. All you really want to do is to draw the crotch of your perfectly formed, tight fitting miter, snug against the adjoining tube. A tight miter and a strong tack in the proper place will draw the tubes together and will minimize misalignment from joinery. You want your tacks to work for you and not against you. For you tig guys, the fewer tacks means the fewer lumps you have to deal with as you weld the bike which means your final product will look better...and less lumpy.


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## TrailMaker (Sep 16, 2007)

DWF said:


> I don't tack in quadrants, centerline of the frame (12 & 6) or on the long axis of the adjoining un-mitered tube only for the front triangle.


OK;

FNG requests clarification.  This appears to suggest a more intuitive, less formulaic or regimented technique, and is perhaps based on the joint in question. You do not tack in 4 equidistant spots, at 12 & 6, or 3 & 9. The last part I'm not sure how to interpret at all. Where and how do you tack, both in flame and TIG? For those of us who have not and will not build dozens of frames from which to glean experience, this is invaluable info.


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## BenCooper (Feb 25, 2013)

To be honest, I'm not rigorous about exactly where I tack - I tack enough to hold the frame together while I fillet freehand. My jig is also not the fanciest, and I don't have fantastic access all around. So at the BB, the DT gets tacked at about 1.30, 4.30, 7.30 and 10.30, but at the HT it's tacked at 12, 4 and 8. 

I generally also tack opposites - so at the DT I do 1.30, 7.30, 4.30, 10.30. On the theory that it pulls one way then pulls back. I also have sequences for doing the fillets. Dunno if they actually make a difference, but my frames come out straight so I'll keep doing it ;-)


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## DWF (Jan 12, 2004)

TrailMaker said:


> OK;
> 
> FNG requests clarification.  This appears to suggest a more intuitive, less formulaic or regimented technique, and is perhaps based on the joint in question. You do not tack in 4 equidistant spots, at 12 & 6, or 3 & 9. The last part I'm not sure how to interpret at all. Where and how do you tack, both in flame and TIG? For those of us who have not and will not build dozens of frames from which to glean experience, this is invaluable info.


The idea is to always draw the adjoining tube into the crotch of the mitered tube. So, looking down the long axis of the frame, the clock locations for tacking are:

TT/HT, the TT/ST, and the DT/HT - 12 & 6 with the first tack being where it draws the tube more tightly in the adjoining tube, so 6 first on the DT/ HT & TT/ST; 12 first on the TT/HT. Savvy?

ST/BB & DT/BB - 3 & 9.

CS/BB - 3 & 9.

The rest depends on the configuration of the DOs & seat stays but again it's with the idea that you want the tack to pull the tubes tightly into the deepest part of the mitered tubes crotch.


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## TrailMaker (Sep 16, 2007)

So...

- First, you want to tack the most acute angle of each of the first three junctions, on the vertical center line of the frame (12 or 6, depending), because they by their nature will fillet to some degree, and therefore draw the hardest

- Then, you want to tack the BB housing on a horizontal plane (3 & 9) in order to try and maintain it's perpendicular relationship to the frame's center line.

Each of these points also happens to be in the center of the "valley" of the miter.


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## mrblint (Mar 10, 2021)

I hope you don't mind if I resurrect this old post since it is exactly about a question that came up for me recently and you all seem to have much hands-on experience. I haven't welded any frames myself and have taken only an intro welding course. But I did buy a frame recently that arrived with visible distortion in the BB shell. My question, from a buyer's perspective, is how much distortion is too much distortion? Is there a point where demanding a replacement frame is reasonable? Is there any way to measure the degree of thread misalignment to assess whether the amount of metal that needs to be removed by chasing, to bring the left and right axes into alignment once again, is likely to result in threads that will get prematurely eroded from repetitive slight rocking motion inside the shell, or in premature bearing wear, or in a creak when pedaling?


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## JackOfDiamonds (Apr 17, 2020)

Do you have some calipers to measure it? We can make a swag if you post pictures or measurements. Do you mean it's just out-of-round, or is it welded into the frame crooked (like the right side is higher than the left or something)?

BB threads are about 0.025" deep, or about 0.6mm. I would say if the BB is oval to the point where the difference between the two axes is half of that or more, you have a problem. If it's less, then just have it chased. But I just made that up.


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