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

Assuming you have a drill press or drill guide that allows vertical
drilling, and assuming that you have at least a few feet of table, there
is a solution, for VHF and up anyway.

Take a small piece of plate or board and mount a rod the same diameter
as the holes you are drilling vertically from it. The accuracy here is
going to set your ultimate result. If you are off 1 degree and use the
device as a reference 10 times during the drilling, you will have a 10
degree twist, although there is a simple way to reduce that error.

Drill your first hole. Now use the device and the new hole to hold the
boom in place and slide along your table to position your drill at the
next hole. Move the device to the latest hole drilled as you run out of
table. To reduce errors from imperfect vertical on the device, rotate
it 180 degrees between each move.

I have used this method to drill 39 element holes for a 31 foot 432 beam
with almost perfect results on an 8 foot table and just a drill guide,
not a drill press. It can be used across boom diameter boundaries,
which it was in this case, with a bit of care.

tom
K0TAR