I'm going to seal my seat stays, but have a quick question. I'm using a socketed dropout and capping it, so the stay will be entirely closed off once I've filled in the vent holes. Can I do this before I attach it to the side of the seat cluster and the rest of the dropouts?

Basically: will heating the tube to braze it to the rest of the bike cause dangerous/problematic pressure buildup if it's sealed off?

Thanks!
Jim

Close the vent holes after you are done brazing.

The socketed dropouts that I've used have had a vent hole below the socket. Once your stays are finished and brazed at the dropout and the cluster, use a bit of brass rod (I picked up a couple of feet of 1/4" brass rod at Home Depot for a few bucks). Cut about a 3/8" length, bevel one end and "squash" (flare might be a better term?) a bit of the other end. Hit your vent hole with a 1/4" drill, flux, push the plug in place, and braze it up. I flare the one end so that you don't accidentally push the plug into the hole too far and lose it, which I did once File it up and Bob's your uncle.

or just braze it shut

My sequence is usually: 1. cap seatstay; 2. braze dropout side & seat cluster side; 3. braze vent hole shut.

If there is no vent hole and you are brazing to the tube's interior, the hot air will want out and might interfere with the filler flow. It's possible to braze without a vent hole (just like you do went filling the vent hole) but you have to be quick and it might leave some tiny pinholes.

I like to clean out (soak and flush) the SS before joining to the rest then seal off the vent holes. Andy.

At this time I vent the top and bottom. I know many seal them, but I like doing it like I do. Same for my forks. If you're going to seal them, make sure they are sealed.

I'm not sold on sealing up tubes, so sometimes I hide a pair of vent holes under the brake bridge. I've also drilled the vent in the hood in Paragon's Wright dropouts.

https://www.flickr.com/photos/smudgemo/5968855056/

I have never sealed vent holes either. I don't see anything wrong with it, but I just never did it. My commuter has lasted 30 years and seen a lot of nasty salt without issue.

Just make sure your painter knows of the hidden vents, and is motivated to work around them. A painter I know of (is still in the business) didn't do due dillegence with a frame I sent him, used a soak tank, filled up the stays with fluid, didn't drain fully, painted any ways and the result was a mess. then there's the painter who used a sand blaster but forgets to mask off the brake holes in the bridges (where one can hide a vent hole to the stay) or inside the seat tube (where a fast back stay could vent) and during the clear coat the sand trickles out...
Sure the painter is "on the hook" but don't we want the guy who makes out frames look really great to the public a happy camper? Andy.

I forget to mention who should control the placement and sealing, or not, of vent holes. Your painter. Andy (in case it wasn't obvious)

No dunking with my PC guy AFAIK. The place I started going is a block from work, and on my last job they blasted the canti brake mounts in addition to leaving grit in the frame that I found later. I wasn't thrilled and I'll have to spend some time making them aware of what I'm expecting (at least with respect to what they tape off. I imagine hidden holes are not as much of an issue with a single shot of powder, but thanks for the heads-up. One of these days I'll feel like my work is worth investing in paint.
-Ryan

Hmm... I guess my main question is really: is it unsafe to heat the tubes after they're sealed?

I want to seal the stuff when it's nice and hot and dry in there... but don't want to heat the whole tube an extra time to ensure there's no more water in... so it seems to make sense to seal the tubes right after I attach the seat stay top and bottom. The only drawback is that I'll be adding the brake bridge later after I've checked alignment, etc.

Do I have to worry about pressure buildup in the sealed seat stay tube when I put that bridge on (it'll have it's own vents)?

Thanks,
Jim

No worries in heating a sealed tube. Yes the pressure will rise but it's totally benign.

Cool! Thanks all! Also, thanks for the procedural advice, it'll be helpful.

I'm doing my own powder coating (techshop has a giant oven... it's awesome), so I don't need to worry about painter issues other than my own ;-)