Marking sheetmetal with a scribe? No, No??

[mhorowit]

I think I've made a mistake.

When laying out this rudder rib I'm working on, I first layed on Magic Marker, then scribed/scratched a line where I wanted to bend.

I'm reading a book on sheetmetalworking and it says NEVER scribe a line because it weakens the metal. This statement is familiar from previous discussions we've had on scratches.

So I guess I need to re-do the rib. Anyone care to jump up and say "Nah, you don't have to worry about it"?

I know it doesn't make a difference if I'm scribing a cut line, but what do you use to mark a bend line? Pencil on metal doesn't show; Magic Markers aren't thin enough. - Mike

[Dick Huish]

Re: Marking sheetmetal with a scribe? No, No??

Mike, use a ball point pen. Dick

[mhorowit]

Re: Marking sheetmetal with a scribe? No, No??

Mike, use a ball point pen. Dick

OK, I'll give her a try.
Today I'm going to read up on hammerforming; can't get into too much trouble unless I hit my thumb - Mike

[jgerard]

Re: Marking sheetmetal with a scribe? No, No??

I use a scribe to mark cut lines in steel all the time. I even use a scribe to cut holes in aluminum. Sharpie makes a few different type of fine line markers. They even make them in silver(my favorite for marking 4130)

[crispy critter]

Re: Marking sheetmetal with a scribe? No, No??

If you look at the dollar store,wal-mart,etc they have the sharpies with the fine tip on one end(like a felt tip ink pen...very fine line) and a normal sharp tip on the other end. They are the best to use.

[mhorowit]

Re: Marking sheetmetal with a scribe? No, No??

I use a scribe to mark cut lines in steel all the time.

Cut-line yes, bend-line no.

Sharpie makes a few different type of fine line markers. They even make them in silver(my favorite for marking 4130)

Sounds like a field trip to Staples/Office Depot is in order - Mike

Just got back from Home Depot Aerospace with my first chunk of MDF. It's too early to start up the saw so I'll wait another hour to cut a hammer-form.

[Acroeric]

Re: Marking sheetmetal with a scribe? No, No??

Mike- Don't feel bad about the use of the scribe on your stuff- at least it was only one plane and you caught it in time. . . . .recently a large repair station used hard plastic paint scrapers during a strip and paint job on a 737. Actually they used this process on many airliners-

Some time after the new paint job was applied we started finding cracked skins where they used the scrapers. This led to an AD and millions of dollars in rework. Luckilly nothing broke in the air but it was a serious issue.

[Len Petterson]

Re: Marking sheetmetal with a scribe? No, No??

Sharpies are nice to work with.
They gives a "thick" (thin) line if you consider the margin of error is the twice the width of the line.
Mark the accurat spot with a DARK pensil. Using a straigth edge, draw the Sharpie line so the edge of the line is on the mark. Clamp down the straight edge so it remaines in place.
You have to deside if the Sharpie line is Left, Right, Above and Bellow the true mark.
For example. If you are working on the wing, all lines are outboard of the true line.
YOU pick a system what work for you and the part you working on. And stick with it!
Or you will get mixed up! And wright it down in your worklog, You have one a pressume.
Now it don't madder if the line is 1/4" wide. You are followning the edge of the line.

The work log will keep track of when, how, who, how many $, phone numbers, critical measumnets USED, all for later verification. The brain
(mine for shure ) will go into over load trying to ACCURATLY remember it all.
Have fun Mike.
Len

I have been told a ballpoint pen leaves a premanent line in the metal as well.
for what reason I have never used one.

[mhorowit]

Re: Marking sheetmetal with a scribe? No, No??

Len - I think you hit the nail on the head; I need to standardize on the _edge_ of the line rather than trying to measure to the center. Thanks - Mike

[VictorBravo]

Re: Marking sheetmetal with a scribe? No, No??

Yes, you have to adopt a policy of "the inside edge of the iine is where I cut", or something like that. It's up to you, whatever is easier to remember. This starts to come in handy when you are tracing the outline of an old part onto new metal, where to match the size of the old part you have to cut the new one out so that none of the marked line is showing, etc.

[Mark Julicher]

Re: Marking sheetmetal with a scribe? No, No??

Some observations FWIW

Sharpie works well and does not cause corrosion when used on aluminum which is the biggest reason to use it IMHO. There is also a Pilot brand marker that works the same as Sharpie, but it has more ink and lasts longer.

Pencil graphite may be fine on steel, but it corrodes aluminum.

Using the -edge- of the line is a brilliant idea. If you simply must have an incredibly fine line go to a shop selling machine tools and purchase Layout Fluid. You brush it on a part and then scribe lines into the colored residue. Works great on steel, but still a high potential to make a scratch on softer metals.

[high time cub]

Re: Marking sheetmetal with a scribe? No, No??

As a kid, I had a summer job working on C5A leading edges. They used cases of Dykem Fluid....I think one can should be enough for a T-Craft!

http://www.globaltoolsupply.com/cgi-local/SoftCart.exe/online-store/scstore/p-GTS-P1-3234.html?E+scstore

Or by the case....

http://ami.thomasnet.com/viewitems/dykem-layout-staining-fluid/dykem-layout-staining-fluid?&forward=1

Jim