Centre line both sides of a cylinder

OK chaps this query actually comes from the plastic modelling side of my hobby but I'm sure you blokes are the ones to solve my problem as usual.

OK I have a cylinder about 4" in diameter and 18" long. Imagine a piece of plastic drainpipe with a hemispherical cap on each end.

I need to draw or (lightly) scribe a centre line onto this cylinder such that it goes along its length, around the end, back along the underside (so to speak) parallel with the one on the top then back around the other end to join up where it started.

How do I do this?

Hi Wolfie,

I'd use a height gauge or one of those magnetic block stands with a scriber or even a pencil attached to it. Set the height of the scriber to the radius of your cylinder, clamp your work piece to a flat surface and scribe your line around. It's the way I've done boot topping on model ships.

Hope this helps, all the best,
Ed.

Edited By Ed Duffner on 20/06/2014 20:19:06

Ed pretty much has it covered but if you can use a couple of Vee blocks or even a couple of strips of wood fixed to a bit of Mdf it will stabilise the cylinder: they doo have a habit of rolling.

If you have a milling machine, rest the cylinder in the bed tennon and fix some sort of scriber in a drill chuck or collet and simply move the table along marking the outside as you go.

A quick way, put the cylinder on a flat surface, mark a broad line down each side, take a square, hold cylinder , move the square down each side leaving a mark in the line that you marked. Ian S C

I say TOP marks to Ian, No measuring , no complicated set ups, Job done , Simple ! Brilliant