Pinning

[apbrey]

Hey all,

I'm excited to see this new mentor forum. I'll try not to make too much of a nuisance of myself asking you all silly questions.

I've got a question for builders of lugged frames. When and why do you choose to pin? Is this decision based on the specifics of your frame fixture or materials? Do you consider pinning to be essential for building a straight frame, or is it merely a safeguard against tube creep? Do you pin the whole frame, or just select sections or joints?

Alex Brey

[Eric Estlund]

Hi, Alex-

This conversation has been had several times and in great depth on the old Framebuilders list serve (now Google group). There are some in depth conversations over there that cover most of your questions. Do some reading, and if you have some specifics on the techniques you read there fire back.

[apbrey]

Will do, thanks!

[apbrey]

So, what I'm getting is that there are two main reasons why people pin. In the case of tubes that are constrained on both sides (like the top tube), it sounds like the pins serve as tacks that you can't accidentally melt.

In contexts where a tube is free to move on one or both sides, it sounds like pins serve to manage the effects of heat expansion. Since things expand when heated, the pin establishes a point away from which all expansion projects. Rather than altering the position of the joint that you're presently brazing, pinning pushes the effects of heat expansion to the other side of the workpiece. That way, when the side that you're brazing cools down, it has actually been brazed in its intended location.

Is this more or less the idea?

I'm also getting that a good contingent of lugged framebuilders out there don't pin at all. I wonder if a good quick tack can fix things in place before heat expansion becomes much of a problem.

[e-RICHIE]

I add pins as part of the setup process, in conjunction with the fixture and all the parts on it. When a main triangle (or rears, etc) is ready for heat, I don't want anything under load. So, part by part, joint by joint, I drill the holes and consider the pins as dowels. Then, when all pipes are cleaned and fluxed, I can replace them in the fixture using a minimum of clamps or spring pressure, the pins through the aforementioned holed acting as self-centering devices allowing all centerlines to be respected. When the pins are hammered in, the frame design and linearity are exact, yet no pipes are being clamped.

PS Adding this thought according to my opinion:

The point being that combining material and fixtures produces an enemy. It's your job to tame the enemy. The enemy wants to win. But you have to be a Kissinger and negotiate a common ground. Heat + Metal + A Fixture + The Human Condition = War. Fine framebuilding is always a compromise.

[apbrey]

Ah, that makes sense. The fewer forces trying to push the tubes around the better. Pinning holds everything together in an unstressed state. So when you go to heat them, the tubes have a bit less to be angry about.

Thanks again for taking the time to help me out.

[Curt Goodrich]

A counterpoint- I never use pins. I tack in the jig. Zero ill effects and very repeatable. Pins work. Tacks work. Don't overthink it. Try both techniques. Find what works for you. Rinse and repeat.

[Eric Estlund]

A counterpoint- I never use pins. I tack in the jig.

I'm in the same boat. Works for me.