The head tube is off by this much.
I know my miters are sound, and my bowing has been marked and taken into consideration so I know it's just a matter of (usually) that I simply tack heavier with my left hand - I tack from my chair of course, so I tack with both hands. Sometimes it's spot on from the get-go, but it's no big deal, and I'll make it fine with out bending or cold setting the tubes. Read on.
See all the arrows on the frame in sharpie? (you may have to click on the image) they are where I will place additional tacks to "pull" the frame into near perfect alignment.
The size of the tack, it's location, the amount of filler applied and how hot you make the tack all influence the amount of pull the tack will have on the structure.
I have done really nice tight clean fabrication so I know it "wants" to be straight, I just have to accommodate it to let it be proper.
Like these two tacks I'm going to lay, which have great pulling power - careful!
Click on the picture and you can see the tacks.
Everyone has their own ideas and sequences for alignment, some theory and some factual, it's best to find a repeatable sequence which allows you repeatable results.
Waiting for that to cool I have cleaned up the chain stays a bit, it's easier before you tack them on. Again - clean everywhere you will be joining inside and out with 80 grit and 91% alcohol.
See where this is going? the inside tacks are where the chain stays go, and the vent holes are being drilled.
I have one tack - the one you can see - holding on the left chain stay, it's always a few file strokes shorter every time due to the deflection from mitering both stays at the same time in my Anvil chain stay fixture in which the dropouts were brazed as well. Then, you match the right stay to the left and check the clearances for the chain rings and tire and then tack both stays on good and solid at 12:00, 6:00, 3:00 and 9:00.
Checking to make sure the dropouts are parallel to each other - good to go!
......And, making sure that the center of the hub is centered to the BB shell and the rest of the frame. good to go.