# How to bend chainstays a little bit before welding to frame



## Mark_BC (Sep 19, 2012)

Hi I am building a steel bike in my 2 week frame building course. It is a fat bike and we have the chainstays for that. But they are shaped go to 170mm axle spacing and I want 135mm spacing so I need to bend them a little bit in the latter half back of the tire. How do I do this without kinking? I have seen the sand method with a tube bender or rolling press. I'd rather not spend $500 to just bend the stays 2 cm, does anyone have any tips?


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## Walt (Jan 23, 2004)

Um, what do your instructors say? Presumably they should be the ones you ask first...

You can use an arbor press, mill vise, anything that can squeeze stuff, plus a wooden form/mandrel. For small amount of bend on small tubes, you probably don't need any sand or cerrobend or anything like that. Practice on some scrap first (or just plan to ruin a set of chainstays and muck around until you figure it out - they're cheap). 

-Walt


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## Mark_BC (Sep 19, 2012)

He is worried it will kink. But we will both think about it over the weekend. Thanks for the ideas. These chainstays are expensive but we could practise on cheaper ones.


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## BenCooper (Feb 25, 2013)

Chainstays are unlikely to kink with that kind of bending. I use the Hammill benders for stays, never a problem, and I don't fill with anything. As long as you have a decent former with 8-10" radius should be fine.

But yes, experiment first.


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## Meriwether (Jul 26, 2007)

I bet you could put the right sized tube blocks and cradle it in a vice and smush it a bit flatter on the rear bend. That is what you need yes, *less* bend not more? 
What chainstays are these? Do they have others in stock up there that may fit better? 



Sent from my iPad using Tapatalk


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## Mark_BC (Sep 19, 2012)

I think this is it. You can see how they bend outwards towards the dropout, I want to basically straighten out that bend so it will fit 135mm, not 170mm which it does now.


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## Live Wire (Aug 27, 2007)

no, you won't need to bend anything. The BB miter will determine where the dropout end falls.


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## Mark_BC (Sep 19, 2012)

Live Wire said:


> no, you won't need to bend anything. The BB miter will determine where the dropout end falls.


If I mitre it to end at a 135mm dropout then the biggest tire it will take is a Big Fat Larry. If I bend it then I can fit the fattest tire out there (Lou). I'll need some kind of a thin sheet chain guard to keep the chain out of the tire which should be easy. But I'll have to bend the stays if I want the biggest tire.


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## Eric Malcolm (Dec 18, 2011)

Most of us here are usually bending a tube, so your query is in the opposite direction - you want to straighten it out a little. I find most tubes will tend to be easier to return to a straightened piece than the other way. The bend looks rather relaxed, so it should do what you want it to. I would put it between 2 blocks of softwood and squeeze it gently in a vice. The stays will be springy, the only way you will find out is to give it a go.

Eric


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## Walt (Jan 23, 2004)

1: Those are very easy to remove the reverse bend on - but be careful about crankarm/heel clearance problems.
2: Those are cheap, get an extra set and practice first.

-Walt


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## Walt (Jan 23, 2004)

Mark_BC said:


> I'll need some kind of a thin sheet chain guard to keep the chain out of the tire which should be easy.


I'm confused by this. Can you explain what you mean?

-Walt


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## Mark_BC (Sep 19, 2012)

Walt said:


> I'm confused by this. Can you explain what you mean?
> 
> -Walt


Think of a plastic acetate ruler. That general shape of plastic and I'll attach it to the chainstay somehow, like bend it and wrap it around and bolt it on, then the plastic will go up vertically, maybe at a forward angle, right where the tire is closest to the chain. This will keep the chain out of the tire. If plastic I'll probably have to continue it on up and around to brace it on the seat tube somehow but if metal it might be strong enough to not need support on the top end. But metal will be noisier.


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## Walt (Jan 23, 2004)

That is a really, really terrible idea. Best case it'll make tons of noise, worst case it'll derail the chain all the time and/or wear out/break/jam everything up. 

If you want to avoid chain/tire interference, you need to look at offsetting dropouts, going to wider spacing, or a smaller tire. Period. Trying to push the chain out of the way with a ruler (or anything else) is not going to work.

Did your instructor sign off on this plan?!? I'm sort of baffled by a lot of these questions if you're getting professional instruction.

-Walt


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## dr.welby (Jan 6, 2004)

How exactly are you going to clear a Lou with a 135 chainline? A Lou is ~110mm and 135 single speed chainline is 52mm. That's 3mm interference without including the width of the chain or your plastic deflector.


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## Mark_BC (Sep 19, 2012)

I'm not pushing the chain anywhere. The guard is simply there to keep the chain from hitting the tire if it bends to the left during hard riding. I don't anticipate much chain wandering anyways since I won't be using a derailleur which contributes to sloppiness. So I might not even need this chainguard, we'll have to see. But it would be good for keeping mud and snow out of the chain since the tire is so close to it.

My instructor is a little baffled by my questions but I think this bike will work, I see no reason why it won't. There are a lot of advantages to going with a 135mm symmetrical fatbike and I'm surprised no one has tried. The only disadvantages are that you can't run a regular cassette in the back which I never intend to do again anyways because derailleurs always cause trouble and are not dependable. The other challenge is making sure the chain stays out of the tire which shouldn't be too difficult with a bit of planning and experimentation on a chainguard. Also the chainline will be a bit angled but no different than what you'd get running a normal cassette and triple chainring setup; chains are designed to run at a slight angle.

The benefits are 1) true front/back wheel swappability (not possible with 170mm), 2) none of the offset headaches like with the Pugsley, 3) you can run narrower 29" wheels if you want to since the wheels are symmetrical, 4) much easier and cheaper to find compatible hubs (not willing to fork out another $1800 for a 170mm Rohloff which will not fit any of my other bikes, when I already have a 135mm one as well as an Alfine). This will be my expedition tourer and I want it to be able to take any kind of wheel depending on where I'm bikepacking -- Bud/Lou type tires for winter or desert fatbiking adventures, or narrower 29" tires if I go somewhere that fat tires aren't needed or wanted due to the attention they attract.

It won't be swappable with a 150mm hub if I ever use shocks up front but oh well.


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## Mark_BC (Sep 19, 2012)

dr.welby said:


> How exactly are you going to clear a Lou with a 135 chainline? A Lou is ~110mm and 135 single speed chainline is 52mm. That's 3mm interference without including the width of the chain or your plastic deflector.


It works, I have the full scale drawing in front of me, my computer is sitting right on it as I type! I drew in the tire, the rear Rohloff chainring and the front Raceface fatbike chainring, drew a line between and it works. The Lou will fit with about 3mm of clearance. If I instead put the front chainring on the outer crank position then there is 7mm clearance to the tire but that gives a more angled chainline which isn't good for the chain but may work. In that case the Big Fat Larry has a full centimeter of clearance!


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## dr.welby (Jan 6, 2004)

Since we're talking chain guard things you should look at the old Cleland bikes:

Cleland Bikes - Evolution

For everyone else, there's some thread amnesia going on:

Symmetrical 135 mm fatbike


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## Walt (Jan 23, 2004)

Yeah, it's not going to work with anything huge tire-wise. I have done plenty of 83mm shell fatbikes and for crank clearance reasons, your max tire is about 100mm. Period. Do you have the cranks in the drawing? Because a typical ~165mm Q factor crank needs a max chainstay span of at most 125-130mm. Each chainstay is going to be ~15mm diameter/width, so you're at 105mm of space. 

OP, good luck.

-Walt


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## Walt (Jan 23, 2004)

Here's a photo (third photo on the post) of what you get with an 83mm shell/61mm chainline, 28t ring, and a Nate. I don't see a practical way to do a whole lot better than this on clearances.

Waltworks Bicycles: Kevin's low-Q fatbike complete!

-Walt


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## Mark_BC (Sep 19, 2012)

Lots of clearance between crank arm and chainstay (~7mm). I am using a 100mm BB, not 83mm. It is a wide Q factor but I am used to it now, done lots of riding on it already on my Pugsley with no problems. It all works, even for Lou!


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## Walt (Jan 23, 2004)

Ah, got it. Yes, that will work. Sorry, didn't understand that part.

Smoosh those stays! And post some pictures!

-Walt


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## Chad_M (Jul 11, 2013)

Sounds like a cool plan for a bike. I 2nd some pictures.


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## Mark_BC (Sep 19, 2012)

Not too much to show yet but here it is in the jig. I tacked it up and brazed the top tube to the headtube and am now brazing the BB. I discovered that I like brazing.










I will use these Paragon dropouts. They are stainless so we will have to bend the tabs at an angle and my instructor will tig weld those to the stays. The good part about this is that it requires very little bend in the stays to do that because the bent tabs space them outwards.

I also discovered something interesting about these dropouts. You can take the insert off and put it on the outside of the frame part of the dropout and they still work fine. Then the dropout spacing becomes 163mm.... So I realized that if I machined out my own inserts I could make some with 170mm spacing.... I could have a bike that does both 135mm and 170mm.


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## dr.welby (Jan 6, 2004)

Mark_BC said:


> Then the dropout spacing becomes 163mm.... So I realized that if I machined out my own inserts I could make some with 170mm spacing.... I could have a bike that does both 135mm and 170mm.


I'd mock it up to make sure your chain, small cogs, and disk don't rub on the dropout and frame.


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## Mark_BC (Sep 19, 2012)

dr.welby said:


> I'd mock it up to make sure your chain, small cogs, and disk don't rub on the dropout and frame.


The disc is OK but the smaller cogs will rub so I won't be able to run a normal cassette but it will be possible to do something. I could make an Alfine fit if I machined the axle slot a little lower. Just an interesting observation, not something I'm seriously planning at this stage.


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## dr.welby (Jan 6, 2004)

Yeah, just sayin' from experience it's sometimes better to have a bike that does one thing right instead of ending up with:


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## Eric Malcolm (Dec 18, 2011)

I will use these Paragon dropouts. They are stainless so we will have to bend the tabs at an angle and my instructor will tig weld those to the stays. The good part about this is that it requires very little bend in the stays to do that because the bent tabs space them outwards.

I also discovered something interesting about these dropouts. You can take the insert off and put it on the outside of the frame part of the dropout and they still work fine. Then the dropout spacing becomes 163mm.... So I realized that if I machined out my own inserts I could make some with 170mm spacing.... I could have a bike that does both 135mm and 170mm.[/QUOTE]

I like how you think, it would seem that you will need to check the chain/cog clearance and disc clearance on the other side so they don't interfere with the stays - particularly if you swapped to the 170mm position. I refer to the disc to lock-nut change. The drop-out won't change and the fitting will be good, but you have the stays to clear now.
Same for when the chain comes off the sprocket to the Chainwheel. If you can resolve those issues, all good.

Eric


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## Mark_BC (Sep 19, 2012)

Eric Malcolm said:


> I like how you think
> Eric


It seems like a real opportunity for some company to offer this, they'd just have to refine the dropouts to work both 135mm and 170mm with none of the clearance issues, probably do-able. There would be a large market for this considering how expensive IGH's are. Why get a new bike or Rohloff every time you want to switch between a derailleur/cassette setup and IGH?


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## dr.welby (Jan 6, 2004)

It's been done with none of the frame clearance and chainline issues.

edit: That piece won't work with bolt-on axles but it's the right approach.


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## Mark_BC (Sep 19, 2012)

Interesting welby.

I have good news and bad news. The good news is that it will work fine with a Rohloff. Using the small front chainring gives almost a straight chain line and it clears a Big Fat Larry but only just. If I put a Bud on then I will have to use the middle or large chainring.










The other good news is that it shouldn't be too hard to switch to 170mm if I wanted to run a regular cassette. The brake rotor clears the stays. I'd have to machine a new dropout insert and drop the axle about 5mm for the freewheel to clear the dropout, and the outermost cog would have to be replaced with a low profile spacer. If I designed my own dropouts I could do it so you don't have to drop the axle but then I'd need to build another bike...

The bad news is that in all the hurry to get the bike done in the 2 weeks I forgot to check chainring clearance on the chain stay! So stupid, can't believe I forgot that. The large and small chainrings fit but there is no way the middle one is going to. The stay would have to come in about 3mm, which will still leave enough clearance for a Bud. So what I might do is sometime later if I want a light fun trail bike which uses a cassette and derailleur (the Rohloff is kind of heavy in the back end and more suited for touring) get a torch kit and remove the stay from the BB but keep it attached to the dropout, then position the whole bike in a press and straighten out the chainstay a little bit which should move it over towards center. The mitre will be off then but with so much brazing I don't think that will affect strength. I'll also put a Bluto up front which has that clearance problem with the down tube... oh well, maybe I'll just build another bike later on to address these issues, I am inspired by engineerjoe's cheap building methods. (Excuse the brazing blobs, I was in such a hurry the second to last day and it needed so much heat there to melt the braze.)










For painting I think I'll use Tremclad rust paint to save money, I've spent enough. It won't stick as well as a proper paint job but the good part is that if it scratches it's only $5 for a touch up can.

My helper


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## Walt (Jan 23, 2004)

Do you have clearance at the down tube for your fork crown?

First frames always have some funkiness. Ride the snot out of it and then do another one!

Where was your class, btw? 

-Walt


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## Mark_BC (Sep 19, 2012)

Walt said:


> Do you have clearance at the down tube for your fork crown?
> 
> First frames always have some funkiness. Ride the snot out of it and then do another one!
> 
> ...


Lots for the Moonlander fork. I haven't measured for the Bluto but I highly doubt it. I guess I could put in a Bluto fork anyways and I just won't be able to turn it very far. Just put some plastic pipe on the tube to protect it and somehow protect the fork.

Agree, I'll ride it a lot to get a feel for the geometry.

It was from Paul Brodie at the University of the Fraser Valley.


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## Mark_BC (Sep 19, 2012)

Also I have a question: how important is it to get the mitres perfect for brazing? It takes either expensive precise tools or a lot of hand filing to do this and it doesn't seem to me to be important if it is all going to be encased in braze anyways. The joint strength comes from the braze not where the tube ends. It obviously is necessary for tig.


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## Eric Malcolm (Dec 18, 2011)

Firstly, you can easily file down that blob of braze and tidy up the finish. So no big deal there. 
Second, what a good excuse to build # 2.
Third, accept the chain-wheel error, get it right on the next frame. It will be a lot of work to correct. It is beyond an indent.
Four, Yes, you gotta do the mitres, sorry, that's how it is. O/K? 

Well done to get as far as you have. 

Eric


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## briderdt (Dec 14, 2012)

Could you crimp the chainstay for clearance? Looks like it might be a b!tch with the bridge location, but it's an option.


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## Mark_BC (Sep 19, 2012)

We already dimpled it but to make the middle chainring clear I'd have to crimp it so far it would probably lose strength. The small chainring works fine which is good for now. I'll just use the Rohloff and if I want a cassette I'll run 1X7 or something, no biggy, fatbikes aren't meant for speed.


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## todwil (Feb 1, 2007)

Would a 30t middle ring clear Im just assuming when you say middle its a 32t ring?


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## Mark_BC (Sep 19, 2012)

Yes I have a 33t ring but there's no room even for 30t. I may try dimpling it some more which will weaken the stay but there's a bridge tube right there on the inside to help stiffen it up. I took it for its maiden ride today on some knarly North Shore trails and it is pretty stiff.

Climbing, it is really good, super good at technical climbing. The ultra low gearing probably helps with that. But going downhill, there are some issues... On technical stuff when I really squeeze the brakes the wheel just does not want to steer, kinda scary. Not sure if that's because of the huge Knard tire I have on which was petty low pressure. Maybe my trail is too big? The headtube angle is 69.5. When going down tamer downhill sections if I turn a little bit it wants to keep turning more. ANy ideas what is causing that?

This is a great bikepacking setup but it has some issues as a techncial fat trail bike, I think I'll just plan to build a new frame at some point when I get everything sorted out: bent down tube to take a Bluto, no rocker dropouts (not needed if I run a chain tensioner), shorter chainstay length (currently 440-460, would be nice to have it around 430), fix that issue with the middle chainring not having clearance, solve the steering issue.

The 135mm spacing isn't causing any troubles except on the climbs the dropouts were slipping and the tire was twisting into the chain. I really like 135mm fat rear spacing, I could fit a Lou or larger tire in there no problem. I could run a dingle or even a partial tringle and if I use a Singleater chain tensioner to keep it tight, changing gears would be a breeze. I might even be able to run a rear derailleur if I limit it to 4 cogs.


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