TiHabanero

Cut up a Schwinn World Sport circa 1987. Found that the top tube/seat lug junction is pinned. No other tube junction on the frame is pinned. In a production setting is there a reason to pin one tube on the frame, and no others?

unterhausen

It depends on their processes. But I'm not sure why they wouldn't pin at the front too. The joint I had trouble with occasionally with the fixtures at Trek was the seat tube/bb. Seat tube would slip.

Cynikal 

I would guess that they pinned the seat tube junction( both lug and seatstays ) to be able to braze the joint once.

unterhausen

that would make sense, but he said seat lug top tube, which doesn't include the stays. We need pics

Cynikal 

I guess didn't explain well, it was in the pre-coffee haze of the morning. I can see using pins to hold the top tube/seat tube while the seat stays are getting prepped, then brazing at one time.

unterhausen

what is your process of assembling that part of the frame. I do seat stays last thing, because before that you can still align things. Put the seat stays on, and nothing moves without everything moving.

Cynikal 

My process is the same as yours, seat stays are the last major assembly completed for the same reasons. But this is a production frame and I assumed that production processes are different than what I do in my garage.

TiHabanero

Must have been done to simplify the production process as noted in above posts. I have built jigs for production of widgets, but never frames, and I have designed production processes and physical layouts to produce widgets, but never frames. Building one-offs is one thing, and quite simple, but to do one after another is a different game. I'd like to tour a production facility some day, just have to get to China to do it!

squirtdad

here is old video on production