Originally Posted by TASEsq
This is a “vibrating pencil” for want of a better description. Not a pencil and not lead.
I’ve tried marking after etching (I’m using Stewart systems clean, etch then prime) - but the sharpie marks really don’t bleed through hardly at all. Haven’t had much success with the other methods listed below.
Is a couple of dots here and there really the doom and gloom you predict? I figured a little scratch with the vibrating pencil to mark orientation would not be that bad - I’ve made much worse by accident with the male dimple die! (Albeit scotchbrited them out before priming).
As an example, the doubler plates for the rudder spar had to go on with one face to the spar. Would one dot on each face make a difference?
Don’t get me wrong, I don’t know either way!! I just thought I had found a good solution in Turner’s idea...
That's an excellent question! The short answer to the "doom and gloom" query is of course, it depends. The longer answer is, well, longer.
Just like a fire requires three components (heat, fuel, oxygen) to burn, a crack requires three components. First you need some kind of initial flaw. This could be a tool mark, an imperfection in the material, poorly formed grains, etc. Secondly, there must be repeated loading on the part. The final component is sufficient stress in the area of the flaw to cause it to grow on a microscopic level. If any of these things are missing a crack will not form.
A scratch not only serves as your initial flaw, but it also bumps up the far field stress at the flaw by the stress concentration factor.
I'm not suggesting that you can't have small blemishes here and there still be safe. I know I've got a few on my build, but nothing that gives me concern. Just like in real estate, it's all about location, location, location. In high load areas like spar flanges I'll make sure to remove any and all defects. For control rods like those mentioned in Turner's blog I don't have a problem with dots especially if they're not near fastener holes.
Regarding the marking issue, I was suggesting you mark the parts after the primer is cured. You just have to take steps to remember which part is L/R/front/rear while there's no identifier. I use little notes and lay the parts on opposite sides of the table to keep track of them. As soon as they're cured I mark them.
I looked at the link for the tool and it's labeled as an engraving tool. I would avoid using that and find another alternative. I remember before I started my build I read a great many builder's logs online and found one builder who stumbled on what he thought was a great idea. He started engraving the part number on all his parts with an engraving tool. I shuddered when I saw that.