JB MacDonald wrote:
I know how to find the center of a pipe, using a vee block, but my
question is how do you scribe a line from one end to the other , so the
first hole is in perfect alignment with the last hole .. take for
example a 20 foot pipe , or tubing . If we had a 20 foot layout table
fine , clamp pipe down and use a height gauge to scrib a line the length
of the pipe. if you do not have a line you could get a twist(miss
alignment) but what can a person due that does not have a 20 foot layout
table . Maybe I am being to critical

Two methods I have use:

1) "Chalk line", available at any hardware store. Stretch line tight
down the center of the top of the boom (as viewed from above) snap!

2) Lay a 20 ft board, which is 1/2 dia of boom, next to boom and scribe
line down the top of the board on the boom.

I am sure there are other ways ...

JS