Roger Bloom

I知 just about to finish my first frame and am wondering some thoughts on putting in a chainstay bridge. I知 not planning on using fenders. The stays are oval . I知 more concerned if they are structural .
thanks in advance for the input.

unterhausen

they aren't structural. One issue with bridges on a steel bike is that putting them in almost always pulls the dropouts together. Heating the outside of the stay will ameliorate that.

Does your bb shell have a cross brace between the chainstays?

Roger Bloom

It does . There is a thin piece bridging the two chain stay sockets.

unterhausen

that thin piece was intended to replace a bridge.

There are reasonable ways of mounting fenders without a bridge. I have considered making a one sided attachment.

Andrew R Stewart 

No fenders and a cast in web between the chainstay sockets to me say no bridge is needed. Eric's suggestion for fenders of a one sided stub having the fender mount is cool, but best done before the stays are brazed to the shell as to avoid uneven drop out pull in,

We'd like to see photos of your complete frame, especially close ups of details that you have worked through. Andy

Roger Bloom

Thanks Andy, I plan to once it痴 finished. I hope by then I値l have the requisite number of posts to I can add pictures.

fietsbob

kick stand plate also serves as a chain-stay bridge..

I own 2 bikes with no chain-stay bridge on their frames..

Roger Bloom

The thought did cross my mind

apollodriver

would you mind to share some images with us. This is a very important topic.

mikeread

I have built two frames with no chain stay bridge. I did some googling at the time and concluded that they are not needed except for mounting mudguards.

Fitting a chain stay bridge is an extra chance for a cock-up or to cause distortion and miss-alignment, so being a beginner it seemed sensible to leave them out!

One of the frames had the little bridge on the BBkt shell which didn't seem to do much other than to hinder getting a good chain stay fit. So I cut that out too.

Both frames ride great :-)

TiHabanero

My daily rider has no chain stay bridge as well as the frame I built this past winter. They're good for mounting fenders, but not much else. This last frame had the web between the CS sockets, and I removed it because I found it to be ugly in a way, not clean.

guy153

+1 that you don't need them although somebody said on one of these forums that if you have a disk brake maybe they will stop some twist. But I've made an MTB with a disk brake and no bridge and it's fine. I'm about to put one on another frame now (for future fender options). Going to leave a dummy axle bolted into the dropouts and I'm doing it before the SS go on. They always pull the CS together. The dummy axle will help, but without SS I can easily put the CS back where they're supposed to be. I think in the recent videos Paul Brodie also put the CS bridge on before the SS.

I just TIG braze them on. They aren't structural and with TIG brazing the actual tube isn't melted and experiences very little heating if you keep moving and get the rod in there.

unterhausen

Putting them on before the seat stays is a good idea. Make sure the chainstays are aligned properly first.

guy153

I got it all perfectly aligned (well as good as I can measure it anyway). Then brazed in the bridge with the dummy axle bolted in. Waited for it to cool right down, took out the axle, and it had gone from 131mm spacing to 125 but both sides the same and no up or down. I cranked it out with a threaded rod to 160 (in several steps because I wasn't sure far to go) which sprung back to about 133. Then I just squeezed it by hand back to 131. So it's all good. But I'll check it all again before putting the SS and then the SS bridge in. It will probably need bending out again after the SS bridge. I might try winding the dummy axle out to maybe 135 or so and hold it all there while the SS bridge goes in.

guy153

If the hole being a bit off-centre bugs you, how do you think I feel? As you can see the HAZes are pretty small from the TIG brazing.

unterhausen

I guess witch wanding with tig isn't that easy.

guy153

Is that where you heat things up a bit to bend them? Without SS it's very easy to just ease the CS to where you want them by hand. I've also learned from Brodie that the easy way is just to put the BB shell in a vice. I used the threaded rod to make sure both sides were being pulled evenly but I think would have been just as easy to have simply pulled on it. Was very easy to push back.

The first fork I made was a segmented fork with TIG welds with TIG braze on top (for the fake fillet braze look). It looked quite nice but the brazing heated it more than I was expecting. It would have helped to have left something bolted in while brazing it but I didn't and and it ended up quite a bit twisted. I managed to get it straight again by welding a piece of angle iron to the top of the steerer (which was going to get cut off anyway, as they do), holding that in the vice, and twisting the blades with long piece of square tube. This worked but only after I also heated the blades up a bit with a MAPP torch. Not red-hot but enough to leave them a bit black afterwards. I don't have oxy-acetylene. The trick was to heat it, twist it a bit past where you wanted to go, and then hold it there for a bit while it cooled down some.

I have seen people correcting warps in thick pieces of sheet metal with a TIG torch on YT but definitely not something I'd want to try on a bike frame! The TIG torch tends to want to behave like a plasma cutter at the best of times.

I then found that the V-brake posts were way too far apart. I'd made the blades nice and wide for huge tyres but it didn't occur to me that you can't just do that. So I just started over and made a narrower fork with none of the same mistakes and it turned out really well.

Andrew R Stewart 

This is all part of the learning process. how to set up the construct to end up with the dimensions you want given your process. As mentioned it's common to set drop out widths a few mms wider to allow for after joining close up. With canti bosses I fined there's less closing up of the drop outs then when adding bridges. Likely due to the bosses being on the back side of the stays and thus the heat isn't as one sided WRT the stay as with a bridge. I attach the bosses after the rest of the frame/fork is done. Andy

guy153

Well I experimented with the idea of TIG-brazing the seatstay bridge in with the dropouts pushed slightly open. But even a change of 1mm at the dropouts completely alters the fit, which I guess is obvious really. I filed (well I used an angle grinder with a worn-out flap disk don't judge me) the bridge to fit nicely with a wheel and tyre in the frame so I could actually put the brake caliper in and check it was all in the optimal place for that exact caliper. The bridge did pull the dropouts back together but not by much and it was easy to get them back to where they were supposed to be. CS bridge before SS is definitely the way to go.

The frame is finished now and came out really well. I'm waiting several days for the spray.bike paint to fully dry out indoors before putting automotive 2K clear on it. This makes a nice shiny finish that's fairly tough but experiments and opinions on the internet concur that if you don't wait for the underlying paint to dry completely and utterly then it will be sealed in for ever under the clearcoat in a still slightly-soft state. This makes the whole thing much less resistant to bashing as the soft paint doesn't support the clear which can kind of cave in.

unterhausen

Doesn't 2k automotive clear still contain isocyanates?

guy153

Hopefully. I should probably spray it on as many projects as I can before they ban it. I heard it was pretty nasty so have got a respirator mask and only use it outdoors. I already used one can on the CF-hybrid bike which has 2K clear over selenious acid cold gun-blue. He wanted a raw finish and this was as raw as I was prepared to go It came out looking really nice actually. Let's hope it actually offers some protection.

unterhausen

I don't think isocyanates are going to be banned, could be wrong. Dupont did kill and disable a lot of people in Bhopal with it though. And the other place they make it is in Charleston WV, which has the same topography as Bhopal, which is bad because it traps the chemicals close to the ground.

Some people tolerate it okay, some people tolerate it until they don't. And some people get asthma-like symptoms right away, many times it's fatal. Since I was one of the first bike painters that used urethane clear on a bike, nobody knew the dangers. I wonder if my asthma isn't related to that. I wouldn't hesitate to use it with the proper precautions. That's expensive though.

Looks like California wants to ban them, so maybe they will eventually be banned everywhere. Hopefully there is a less problematic substitute

guy153

Usually the less toxic substitutes don't work as well hence my flippant reply. I've heard also with epoxy it's fine until one day it starts giving you flu-like symptoms and after that it always does because you've lost some kind of resistance to it or your body has decided it's an enemy. This is from people who use buckets of the stuff to glue boats together layer by layer.

But I do consider that stuff strictly outdoor-use only which is why I now need some nice weather. I figure the frame is ready for clear-coat when the new paint smell has all gone away.

unterhausen

I first became aware of the dangers because of people that spray truck liners. They typically didn't use PPE at all. But, as you say, most people would eventually develop problems and the occasional newbie worker would get sick immediately or even die from exposure to it. Those of us that are just painting a few bikes probably could use a substitute, but there is no volume in the sales to people like us. Even a car body shop wants the stuff to be dry almost right away. I could live with waiting a week.