"Do not file weld"

[mhorowit]

We 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

[Robert Lees]

Re: "Do not file weld"

You could do, but why file it down, Mike? The additional weight is not of great concern, is it?

Filing can leave great gouges, which is the concern....but minor scratches (as referred to in other posts) might not be of such stressful significance.

Rob

[mhorowit]

Re: "Do not file weld"

You could do, but why file it down, Mike? The additional weight is not of great concern, is it?

Filing can leave great gouges, which is the concern....but minor scratches (as referred to in other posts) might not be of such stressful significance.

Rob

Hello Rob - someone mentioned relocating holes in tubing in the tailfeathers by filling by welding, then drilling holes at 90^. I think they were discussing the bolts that hold the horizontal stab. to the fuse. It seemed reasonable to dress down any excess material (so it doesn't poke thru the fabric), but that conflicted with EAA's instructions not to file a weld. Was wondering what was the rationale for EAA's statement. Of course if any filing was done, no scratches would be left. - Mike

[Robert Lees]

Re: "Do not file weld"

Well I don't know, Mike, but I do know that I have filed welds 2000 flying hours ago, and the plane is still there, and so am I, but I did use some fine files.

I have recently repaired my elongated holes where you describe by welding, and I dressed the exces weld by fine filing...I am not worried.

Perchance you are thinking too much into these things? If a few filing marks are of such structural significance, then CGT would not have been such a great designer, eh?

[Guest]

Re: "Do not file weld"

We 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

Frankly I don't believe the stress riser theory you mention. Perhaps in some high stress high vibration environment I might buy it.

But I suspect that the reasons for not filing are
1) so one does not disturb the weld appearance which is key to determining the quality of the weld
2) FAA wants the welds "throat" to be about 25% larger than the base metal thickness so don't file the extra 25% off


Ironically the Battelle Memorial Institute published a documant for the Navy (US) in 1966 "Fatigue of Aircraft Structures" NAVAIR 01-1A-13, page 184 stats that grinding off the weld bead increases the weld fatigue strength and gives references to the British Welding Journal, vol. 7, 1960

Also AC43-13-1B specifically forbids welding up (filling) holes and redrilling. I forgot the paragraph number. The way to fix an elongated hole in stab support is to internal sleeve, weld around the outer end edge, drill undersize, ream to light drive fit.

Like Rob says, only responsible for non-free advice!