"Do not file weld"

I know that if I scratch 4130 I set up a stress riser. I also know
that I can polish out the scratch.

Reading about welding, I see the warning not to file a weld, but under
at least one circumstance, I don't see the problem.

For example, I fill in a hole I'd previously drilled in a tube. The
filler material sticks up above the tube surface. Why can't I file the
material down, followed by polishing out any scratches? - Mike

Here's my answer. The idea is not so much as not to file a weld, but as not
to destroy the integrity of a weld. When you weld, you're really just
"casting in place." This sets up a certain kind of grain flow in itself
which follows along with the exterior of the weld surface. If you file the
weld surface, you mess with the "grain" of the weldment, which if happens to
be at a shallow point in a joint, or in a particularly high stress area, it
can cause the same as a stress riser to occur.

I file a bump off here and there, but not very often as I really don't see
the need (my welds are pretty good, *blush*). In my Skybolt fuselage, or
instance, I did it maybe 4 or 5 times, but that is with careful
consideration on where I was filing and how it might affect the joint
integrity. For instance, it you want to file an intersection flat in order
to weld on a fitting of it, the fitting itself is a reinforcement that will
take the load so it's no problem. In the right spot, it's not a problem.
In the wrong spot, it's not good. It's easier to simply tell folks, never
file a weld.

In your case, depending on how big the hole is, how stress flows through the
part, and how much surrounding material there is. For instance, it you're
talking about a 1/16" hole in a 7/8" .049 wall tube, I'd file and polish
away. If it were a 1/4" hole, I'd leave it alone. Also, if it was right
next to a joint (where you can sometimes blow a hole when welding on fitting
or not paying attention to what you're doing) I'd leave it alone regardless
of the size.

Polishing does absolute wonders for fatigue resistance, but if stress flows
through the part in a manner where the polished area isn't taking the load,
it doesn't help. If a tube is in pure tension or compression, this can be
the case.

Take a good hard look at it, "be the tube" and try to see how stress flows
through the area, and make the call. Stress concentration factor tables
might help too...

Scott

"Michael Horowitz" wrote in message
...


I know that if I scratch 4130 I set up a stress riser. I also know
that I can polish out the scratch.

Reading about welding, I see the warning not to file a weld, but under
at least one circumstance, I don't see the problem.

For example, I fill in a hole I'd previously drilled in a tube. The
filler material sticks up above the tube surface. Why can't I file the
material down, followed by polishing out any scratches? - Mike