Opposite sides of pipe

[Thrashsmith]

I fully expect I thought up a needlessly long winded method & there's a much simpler way that sensible people with half a brain use...what is it?
What's the usual method for finding the opposite side on a piece of round pipe? I fabri-bodged up a jig from scrap bits of 25mm box I had knocking around. It collared snugly all the way around the pipe. I traced lines down the sides of the 25mm box that ran the length & then found the middle of that.
I expect the Romans had a far quicker & simpler method that involved a piece of string & a maths calculation I probably learned for my GCSEs...but have since forgot.

 

[Paul.]

Clamp it to the bench and run a scribe block down it at the radius height

 

[Thrashsmith]

I did wonder about that but didn't think I'd be able to keep the block from rotating, or be confident that when I rotate the pipe over I've got the exact opposite side.

 

[knighty]

when you clamp it to the bench and run a block of wood down the side with a pencil on top... you do one side then the other right away without moving the pipe :-)

 

[Paul.]

you dont need to rotate it, just run it down both sides

 

[8ob]

Center finder in here, then mark it http://www.mig-welding.co.uk/forum/threads/big-pipe-cutting-tips-tricks.77763/#post-1131723

Bob

 

[Parm]

Clamp it to the bench and run a scribe block down it at the radius height

It’s what I do when marking up cylinders for BBQs

 

[Bill Edwards]

Clamp it to the bench and run a scribe block down it at the radius height

This is probably the easiest, most simple and most accurate method. Not hard to do, provided you have a big bench that isn't covered in clutter!

 

[Turbo]

Pull a piece of string tight around the pipe & cut it where it overlaps. Fold the string in half & then use it to mark the pipe.

 

[wookie]

provided you have a big bench that isn't covered in clutter!

And how many of us on here have that ? I certainly have a decent size bench but I definitely fail on the 2nd requirement

 

[keithski122]

How about marking a straight line along an odd shaped tube such as a roll cage?

 

[Agrismith]

And how many of us on here have that ? I certainly have a decent size bench but I definitely fail on the 2nd requirement

Then surely you are left with only one option you would just have to buy a lathe capable of holding the pipe and a dividing head and put a scribe on the toolpost
The answer is always in buying more tools

 

[wookie]

The answer is always in buying more tools

Normally I'd agree with you but I can't get into my garage to use the tools I have, mind you it doesn't stop me looking....