Tubing Centerline?

First off thanks for having me on this site, I'm afraid I won't have much knowledge or experience to share with building or flying but I do enjoy reading about yalls exploits and experiences.

I was curious if someone could explain to me how you go about marking the center line of a round tube so that it is actually strait and 180 degrees to your other center line or even at 90 degree intervals? It would seem to me that having the tubing marked would help determine a base line for when you make bends and cuts.

Thanks

Brian,

Try putting two same diameter pieces of tubing side by side then scrape a straight edge along them. This will make a mark along the centerline of both pieces of tubing.

John Scott

And after scribing the line, wrap a piece of Post-It paper around the tube putting one edge on the scribe line and making a mark on the paper where it comes around and overlaps the edge on the scribe line. Then remove the paper and mark it with half and or quarter ticks. Wrap the paper again around the tube and transfer the tick marks onto the tube with a Sharpie ultra fine point permanent marker or scribe the tick marks.
Darrel

You can do what John says to get the first line, then on my web site I have a template to find the 180 or 90. I call it a tube center line finder. What I do is lay the tube next to a metal bar that is straight but not as fat as the tube. Then draw a line on the tube using the bar as a straight edge. Then use my template for the other locations.

This is one of those tips from EAA that makes things very easy. If you have a table saw in the shop, simply place the tube in the miter guide slot and using a silver Sharpe marker, run the sharpie along the table saw surface with the point stuck firmly into the area between the tube and the table and draw the line. Perfectly straight every time. You only need one line to keep everything in proper alignment.
Marty

www.xanga.com/martyfeehan

Thanks for the tips guys! I'm very green when it comes to working with metal tubing and welding. I've gotten a little bit of experience with machining by taking a few courses at the local votech - just enough to make me anal about accuracy and tolerances.

Quartering Pipe

Sorta along the same lines as the post it note.

Get a roll of adding machine tape. Wrap a piece around your pipe and cut it straight across so you have a piece that is the circumference of the pipe. Fold it in half to mark 180 degrees. Fold it twice to mark quarters and so on.

You can use a piece of angle or a speed square to draw a straight line on the pipe. You can also use a center finder to mark the pipe at certain angles.

http://www.pipefitter.com/existing_php/fwsmcent.php