Re: [CAD_CAM_EDM_DRO] Re: Stainless tubing/gun drill

Many years ago as an apprentice armourer I was taught to check the
straightness of rifle barrels. The way I was taught to check the
straightness of a rifle barrel (or any tube come to that) is to look down
the barrel at a bright light with a straight edge across it (say a window
frame) from a few yards. If the barrel is moved up and down it will be seen
that the straight edge will cast a tapered shadow in the barrel. The sides
if the tapered shadow will be straight if the barrel is straight. If the
sides are convex or concave, or bending to right or left, the barrel is not
straight. Rotating a bent barrel will alter the shape of the shadow. The
shape of the shadow indicates which way the barrel is bent. Some years ago
in the Royal Small Arm Factory at Enfield Lock it was the job of a man with
a lead hammer and block to check each barrel for straightness and if bent
give it a good thump in the right place to straighten it.

> <Snip>If you look through a tube at a bright light you can see concentric

circles

> down the "barrel".