Tig welding seat tubes, wall thickness, and sleeves
02-20-23, 06:57 PM
#1
Newbie
Thread Starter
Tig welding seat tubes, wall thickness, and sleeves
Newbie mistake, I purchased the wrong seat tube. I was originally intending to use a 27.2 seat post. What I thought I purchased was an externally butted 28.6mm seat tube that was 29.4mm with 1.0mm wall thickness at the seat post end, is actually a internally butted seat post with 0.6mm wall thickness at the seat post end, and 1.0mm wall thickness at the BB end. I've read that 0.6mm seat tubes are for lugs which makes sense to me.
Of the two options below, what would you guys recommend I do?
1. Should I weld a thicker walled seat tube section onto the top and size down to a 25.4 seat post, similar to what Moots does:
(I can't post URL's yet, so replace the 'dot' characters with a '.') mootsdotcom/ask-mr-moots-whats-that-weld-on-my-seat-tube/
2. Or should I just cut my losses and purchase the correct seat tube
Of the two options below, what would you guys recommend I do?
1. Should I weld a thicker walled seat tube section onto the top and size down to a 25.4 seat post, similar to what Moots does:
(I can't post URL's yet, so replace the 'dot' characters with a '.') mootsdotcom/ask-mr-moots-whats-that-weld-on-my-seat-tube/
2. Or should I just cut my losses and purchase the correct seat tube
02-20-23, 07:52 PM
#2
semi-retired framebuilder
How about going old school like we all did back in the 90’s, and use an external sleeve that fits onto a 28.6 seat tube?
You can still use a 27.2 standard post this way.
i have a bunch of straight sleeves in my stock, or get one that’s built for the job.
Mark Beaver
Tamarack Cycles
You can still use a 27.2 standard post this way.
i have a bunch of straight sleeves in my stock, or get one that’s built for the job.
Mark Beaver
Tamarack Cycles
02-20-23, 08:36 PM
#3
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First vote is for the "correct" tube. Second vote is a sleeve. Third is a brazed on binder collar and attention to the seat stay attachment. I've never tried a machined extension to the ST as was popular with the early MtBs. Trying to keep the ST and extension coaxial... Andy
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AndrewRStewart
AndrewRStewart
02-20-23, 08:37 PM
#4
Newbie
Thread Starter
Thanks for your suggestion Mark. If I went this route, I'd be welding the top tube and seat stays to the sleeve and then brazing it onto the seat tube? Is the order of operations to weld everything first and then braze the sleeve?
02-22-23, 07:16 AM
#5
semi-retired framebuilder
Back when I last used these, I brazed the sleeve onto the seat tube first then built normally. If you have good heat control you won’t melt through into the braze as these sleeves were fairly thick. (With a thinner sleeve, this could be tricky). The sleeves I used had the seat binder lug cast in, so I usually fillet-brazed the seat stays to it. But I don’t tig weld any more, I prefer the looks of fillet brazing so this is irrelevant now, I prefer to use outer butted seat tubes instead.
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