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Trimming Long Edges of Skin- How?

D

David Paule

Well Known Member
Sometimes on my RV-3B, I've got a long straight edge of the skin that I need to trim. Right now I'm about to do the tailcone sides and the bottom edges need a bit of trimming.

What's a good way to do that and get a straight edge without any built-in waviness?

Thanks,
Dave
 
Dbro172 said:
Good set of aviation snips and then a knarly vixen file will clean it up nicely. Like this https://www.aircraft-tool.com/shop/detail.aspx?id=20547N. Took me awhile to get the hang of it but man those things work good. Need a pair of leather gloves handling that thing too. I use it to knock the tabs off the factory sheared edges.
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The vixen file is easier to use if broken into a shorter section and a wooden tab glued (RTV is usually OK) onto one side.

Hold the tab in your fingers and run the blade parallel to the edge just like a wood plane.

Here is a commercial version -

http://www.yardstore.com/files/hand-files-vixen/vixen-file-on-palm-block.html

A bit longer than 3 inches would be better for the edges you mention.
 
Make 2 or more cuts. If the final cut only takes about 1/8" the waste will curl up without imparting the waviness. Then finish off with a vixen file and/or belt sander.
 
I use blue masking tape as a guide to trim to. If more than 1/16" I use my band saw then my 1" belt sander to get close to the tape edge and file to finish.

When sawing thin sheet metal, I saw curf into piece of aluminum and tape it to the saw table so there is support right up close to the blade which prevents the saw blade from deforming the sheet being cut.
 
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Score with a olfa knife

Anytime I need a clean straight cut I clamp the metal under a straight edge and score with an Olfa knife. Score it mulitple times and deep then snap it off like glass.
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Vixen file

scsmith said:
I'd love to know how they drilled and countersunk that piece of file to screw the wood block on. The only way I can imagine would be to EDM it. A file is probably Rc=68-70 or so.
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I think the teeth are cut and the holes/countersinks are made before heat treating.
 
Trimming long edges

Hi Dave: I clamped a straight edge to my long sheets and used a router with a straight cut carbide bit installed. Try it on some scrap first, you won't do it any other way after.

Terry
 
I cut as straight as I could with snips then clamped a straight edge and used a file to take down the high spots similar to Terry but without the power tool, routers scare me...
 
scsmith said:
I'd love to know how they drilled and countersunk that piece of file to screw the wood block on. The only way I can imagine would be to EDM it. A file is probably Rc=68-70 or so.
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Exactly, that's why I recommended RTV for bonding. :D

Mine has stood up for over a decade using Shoe Goop, and unlike using a raw vixen file, no gloves are needed.

The file is hard, but also brittle, so grinding a slot across it and snapping seems to work to get a custom length and to remove the tang.
 
Thanks, everyone, for your suggestions.

A few comments -

1. The Vixen file is a great tool. For long straight trims, like this, longer is definitely better than short.

2. The router is a very good idea and ought to work pretty well. However, I don't have a 9' straight edge and am far enough along on the fuselage that creating that many chips would be a significant shop project. Could probably be done in sections manageably enough, though.

3. The part's too wide and the metal's too thin to use my 14" band saw.

So what I'm going to do is use my nibbler to get close, and then my Vixen file for clean up. The nibbler produces a long spiraled chip about 0.2" wide. It's main issue is that it's rather hard to keep straight. It leaves a reasonably clean cut.

Thanks again, everyone!
Dave
 
I used a length of steel angle (2" x 2") on the edge of my workbench. The aluminium sheet is clamped to the bench with the angle underneath and lined up with the trim line. Assuming you have already cut the sheet close to the trim line it is an east task to finish with a file right down to the edge of the steel angle. Easily forms a nice straight line. If your sheet is 9' long, use a 10' or so length of angle. Should be able to pick up a length from your local hardware or steel supply shop.

Clive Whittfield
Auckland
New Zealand
 
snips do a nice job if you set up the last cut to be only 1/8" or so and you don't close the snips entirely. This should avoid stretching the metal which creates the waviness. I use English Gilbow snips rather than aviation snips as they don't have serrated edges. I have also used the Olfa scriber along with an 8ft piece of aluminum angle I have. It works very well if you have a guide. It guarantees that you won't have any waviness but it does leave a nasty burr that has to be filed out, since you score, then break the material. And don't try to fold it over to break it until you have enough of it scored or you will bend the material if it is not real hard like 2024T3
 
Another mthod

I typically scribe a line into the sheet with a steel scribe
Then trim as close as possible using your preferred method.
At that point i take a heavy grit two foot long perma grit sanding block and sand it down to the line. I have also used a board with stick on sand paper, which works well too. (For me this works better than a vixen file.)
Then finish it up with either some scotch brite or deburring tool.
Works for me.
 
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