Tandem Tom

I have noticed that there are vent holes on the chain stays. Are they necessary? As a real novice here it seems like the BB would be more than adequate.

Andrew R Stewart 

I can think of one reason right away. Two points of entry/exit makes for better flush out and drying. Also related is how they hold their frame/sub assemblies during this. Andy

pwyg

If you want the frame to last yes. There should be a hole at each end of every tube and the most critical one exiting the bottom bracket. These holes need to be big enough to avoid being filled with grease and crud at the BB, so make them 3/8” minimum, I like 7/64 in the stays and fork. On the stays and fork as high as you can and through a reinforced point preferred. Many will argue against venting and sealing up a frame but moisture is insidious and will build up over time in frames and slowly corrode them out and faster if water is allowed in and not a way out. Others will jump on the frame saver band wagon but that is not a long term solution and it is better to build it right than with a patch.

Andrew R Stewart 

I believe Tom is using lugs and a socketed BB shell so there's a big "hole" for the chain stays and the BB shell. I think his question about adding an additional vent hole near the drop out is a good one.

For a home builder who takes their time I don't think there's a big advantage to a lugged shelled bike also having a chainstay vent hole near the drops. Still a vent in this case won't hurt either. When I was building with lugged shells I evolved to having that extra vent during the build then plugging it before paint.

With a filleted (or I guess welded) shell/stay I'll put about a 1/4" hole in the shell towards the lower point that is still within the stay end. A second hole is done near the drops. After finishing all this second hole gets plugged, the shell's hole stays open. I am also placing the TT and DT vents, done at both their ends, fairly low on the joint to better allow for drainage. The shell gets a drain hole at its 6:00. Andy

pwyg

I should let you talk to a customer of mine that brought in his custom tandem for a few modifications and I had to call him back an tell him his tandem was trash due to the fact the 1/4 vent holes in the BBs were plugged and caused the internal corrosion that killed his tandem. Dozens of black pin holes through the paint in all the lower tubes.
Holes should be as I stated before at each end of all the tubes. Regardless of lugged lugless construction if you want the frame to last. Of which the most critical is a hole or cutout in the BB shell.
Due to my predecessors I have extensive experience with internal corrosion. This is one aspect of the industry where it has failed both in the production and custom parts of our industry. If the frame is only ridden in “nice” weather then it will not be an issue. If it is a work horse or will be ridden often and in all conditions then precautions must be taken. You only have to step out of this industry and look at others to see my point. That is were I will end it.

Tandem Tom

Again my thanks for your replies!
As this is only my 2nd. frameI tend to have a number of questions.
On my first I "plugged" the holes with brazing rod. I also flooded the interior with Frame Saver.
So if I am understanding correctly the idea is to leave them open so the frame can "breathe"?

TiHabanero

My experience with internal frame corrosion differs greatly from what others have stated here. The first frame I built was in 2001. I commuted 30 miles a day in all weather including winter on salted roads using no fenders. Frame tubing was 70's era 531. Lugged construction with no vent holes and no treatment to the internals of the tubes. Around 15 years later I hit the bike with a car and ruined the rear end. Removed seat and chain stays and replaced them.
The removed stays had only a patina of surface corrosion much like a bare tube gets sitting on the shelf.
Perhaps I am lucky or something, but I have not had corrosion issues inside frame tubes on any of my commuter bikes. Keep in mind the roads around here are heavily salted during the cold months and corrosion of components is something I have observed, but not internals of frame tubes.