keeping the frame straight while modifying???

[El C]

I have no jig so that´s a fail #1 but how do you keep it straight without?
Eyeballing?
Front is pretty decent but the rear wheel will not center, what ever I try. It´s always offline after welding...
That scooter body does NOT make it easier...

 

[LukeTheJoker]

I use the string method if eyeballing it isn't working.

Run a string from one rear dropout around the headtube and back to the other dropout, then measure each side of the seatpost to the string to make sure the measurements are the same.

 

[Captain Awesome]

String method or makeshift jig out of wood. Clamping the major junctions

Be surprised at what you can do with some 2x4's, a drill and clamps

 

[LukeTheJoker]

String method or makeshift jig out of wood. Clamping the major junctions

Be surprised at what you can do with some 2x4's, a drill and clamps

And you can use a known straight frame to set your reference points on the "jig" too!