I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?

Grant

On Mon, 18 Feb 2008 18:45:29 GMT, Grant Erwin
wrote:

I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?

Grant

Clamp tube to bench. Set height gage for 1/2 tube dia. Scribe both
sides of tube.

"Don Foreman" wrote: Clamp tube to bench. Set height gage for 1/2 tube
dia. Scribe both
sides of tube.
^^^^^^^^^^^^^^^^^^^^^^
Or: Measure tube circumference accurately. Set mark half-way around. To
check accuracy, do it again the other way 'round. If the two marks do not
agree, go half way between them.

You could check accuracy on Don's method by turning the tube over, just in
case your height gauge setting isn't spot on.

On Feb 18, 1:45*pm, Grant Erwin wrote:
I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?

Grant

1. Wrap a sheet of paper around the tube, aligning the edges where
they overlap to square it. Mark the corners of the inner layer on the
outer layer. Remove the paper, connect the marks and cut the line.
Fold the paper in half and crease it. Put it back on the tube. The
crease is one line, the abutting edges are the other.
You'll need to use a Legal or B size sheet.

2. Stand the tube upright on paper and trace the circumference. Lay
the corner of another sheet over the drawn circle and align the corner
with the line. Mark the circle where the two edges of the top sheet
cross it. If you were careful a line between the two marks is a
diameter. Cut out the circle and slide the paper over the tube.

3. If your first line on the tube is near the end, you can use the
center finder head on a combination square to locate the second one.

Jim Wilkins

Leo Lichtman wrote:
"Don Foreman" wrote: Clamp tube to bench. Set height gage for 1/2 tube
dia. Scribe both

sides of tube.

^^^^^^^^^^^^^^^^^^^^^^
Or: Measure tube circumference accurately. Set mark half-way around. To
check accuracy, do it again the other way 'round. If the two marks do not
agree, go half way between them.

You could check accuracy on Don's method by turning the tube over, just in
case your height gauge setting isn't spot on.




Place two tubes side by side and secure together - duct tape works ok.

Use a big magic marker to color in a fat line down the length of the tube.

Slide a hard straight edge down the length to scrape off a narrow
straight line.

Rool 'em over.

Do it again.

Grant Erwin wrote:

I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?

Grant

Got it, thanks. I was mitering a 45 degree cut, then rotating one piece
to make a 90 degree bend. All done, looks OK too (it's just for a barbecue).

Grant

On Feb 18, 6:32*pm, Grant Erwin wrote:
Grant Erwin wrote:
I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?

Grant

Got it, thanks. I was mitering a 45 degree cut, then rotating one piece
to make a 90 degree bend. All done, looks OK too (it's just for a barbecue).

Grant

I clamp angle iron to pipe with U bolts before making miter cuts.
There's no layout except marking the length because the angle squares
it in the saw vise, and I have flat clamping surfaces to align the
pieces for welding.

To attach a piece of angle at the other end parallel with the first
one I clamp a piece of bar stock on crosswise and level them both or
align them by eye.

Jim Wilkins

I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

OK, here's an odd idea: Take two files, and clamp them both to a bar,
maybe 6" apart, so they are both perpendicular to the bar. Rest the
bar on the tube, and turn it at an angle from perpendicular until both
files contact the tube, then drag along.

I have no idea how well it would actually work, though. :/

--Glenn Lyford

Don Foreman wrote:
On Mon, 18 Feb 2008 18:45:29 GMT, Grant Erwin
wrote:

I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

I know how to draw one line down a tube, but I am looking for a good trick
to locate the other line.

Ideas?
Grant

Clamp tube to bench. Set height gage for 1/2 tube dia. Scribe both
sides of tube.

THAT'S the kind of ingenuity I like to see. :-)
...lew...

On Mon, 18 Feb 2008 16:24:15 -0800 (PST), wrote:

I have a 4" tube which I want to scribe lines on. The two lines will be
parallel to the tube axis and should be exactly 180 degrees apart, i.e.
on the opposite sides of the tube.

OK, here's an odd idea: Take two files, and clamp them both to a bar,
maybe 6" apart, so they are both perpendicular to the bar. Rest the
bar on the tube, and turn it at an angle from perpendicular until both
files contact the tube, then drag along.

I have no idea how well it would actually work, though. :/


This depends on the edges of the files being exactly 90 degrees to the bar;
especially tricky with files that have a curve to their edges.