On Fri, 19 Aug 2005 02:18:06 -0400, Michael Horowitz
wrote:

I'm reading about welding. Here's an article about how to cut a
'fishmouth' joint (and I visualize clamping the tube in a vice, in the
meanwhile making small marks in the metal), then the pre-cleaning
(using an abrasive, another thing my A&P told me not to use when
cleaning tubing) then the actually welding.

On the other hand, sometime ago someone mentioned the harm that might
occur if one were to mark on the metal with a pencil.

In one case you're handling the material and putting in a nominal
number of nicks and scratches; on the other hand I'm told not to mark
with a pencil?

What am I missing? - MIke

fishmouth joints help to get the weld penetration even. with properly
prepared setups you can adjust your welding speed to get structurally
reliable joints.

the chemistry of the pencil will be what your man is concerned about.
some materials introduced as contaminants in welds can substantially
reduce the weld strength.

you'd never see this in aircraft but braze through a lump of solder
and you will have a stuffed brazing.

Stealth Pilot