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Thread: Vent Holes and Rear Triangle Alignment

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    Default Vent Holes and Rear Triangle Alignment

    Good Morning,

    Two questions in one when someone has a moment.

    When Tig welding steel frames, is it necessary to drill vent holes in the headtube for TT/DT as well as in the seat tube for the seatstays?

    Also, any tricks to getting the rear triangle all centered/squared up. I cut the chainstays and seatstays at equal lengths and equal miters and try to get the chainstays welded in the same distance from the outside edge of the bottom bracket, but always seem to have to do some cold bending adjustments to get my dummy wheel rolling true and center within the frame. Perhaps there are other variables that I am not factoring in, but was hoping for some suggestions.

    My process right now: I have been tacking in the chainstays first, starting at the bottom bracket and then tacking to the hooded drops I use. I then check alignment and finish weld these before moving onto the seatstays.

    I am using a dropout alignment tool and a dummy wheel that I have trued and dished, and is as straight as I can get it!


    Thank you!
    JD
    JD Reich

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    Default Re: Vent Holes and Rear Triangle Alignment

    Vents: Vents are good. Especially when you start using a full argon purge (not required for steel but it sure is nice). They're also nice if you need to soak your frame to remove flux for braze-ons . . . water gets in and out.

    I've struggled with the rear triangle as well but am getting close to an acceptable result: I tack at about 1:30, 4:30, 7:30 and 10:30, check alignment, and run my beads to try to pull everything back into alignment. A faster pulse setting has helped me control stuff as well.

    I don't like cold setting things. Others have mentioned that the frame just has built in stressed and will eventually work itself out of alignment down the road. One one of my first frames I was trying to cold-set a tube and buckled it — a pretty great motivator to get me to dial things in at the torch side.
    elysian
    Tom Tolhurst

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    Default Re: Vent Holes and Rear Triangle Alignment

    Vents: You can do it with just one side, but is highly recommended to get a complete circuit for the air circulate, I guess you're asking considering it might restrict the amount of water going "down" on DT and SS, but reality is it will work much better in terms of avoiding dump/rust if you make as big as possible vent holes in both ends, think about a room where you have the door and all windows wide open, opposite to a room with almost everything close, which one will be more humid? you got it.
    Beside the dump/air circulatio, the complete circle on vent holes will make for a properly made purgue cycle with inner gas all over the frame, and will also help to make the framesaver coating all over inside the frame, as will move freely and easy, hope it makes sense.

    Alignment: If you're talking your first frames and not enough tig practice, most likely you might have two issues, one the heat distortion due to welding and maybe not tight enough miters, but apart from that, I would recommend to tack the whole frame together and do not weld through sub-assemblies, if you tack the complete frame and then weld it as a unit it's easier for the frame to keep alignment as each part compensates the other. Anyway, even if you prefer to go through sub-assemblies, main thing is to make as tight miters as you could, if miters are dead tight, then alignemnt would be ok if you make your welding properly (gaps on the miters will make the tubes to "move" as if trying to close these gaps). Get as much practice as you could with simple tubes, forget frames yet, just get your hand files and tig torch and make as many angle miters and welds till you have it dialed, then move on into frames and you'll be able to focus on frame specific questions rather than just welding or mitering matters.

    Cheers

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    Default Re: Vent Holes and Rear Triangle Alignment

    Good Morning,

    Thank you Tom and Aimar for your insights! I'm seeing that there are many benefits to vent holes, not only during the tig process to let gas escape but also once I start backpurging and for cleaning and final prep with framesaver...I appreciate those thoughts!

    I do assume that the alignment issue I have is with the tig process; mainly not getting in and out quick enough and getting those miters super tight. I have been foot pulsing with my old everlast welder and have found that I most likely still putting too much heat into the metal and not getting my miters tight enough hence the movement. Ideally I'd like to get things tacked, and then do a few smooth single passes on opposite sides to keep the tube straight. I'm sure as with anything, time and practice will show me how to get a tube to move in the direction I need with heat, or not move at all throughout the process! ;)

    Thanks again for the help and suggestions!
    JD Reich

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