SteelMike

SteelMike

Well Known Member
Hey guys, quick question here:

Last night I'm cutting stiffeners. I'm still getting used to all of my new power tools, so I decid to trim the stiffeners with snips instead of cutting them on my band saw. This was stupider-than-stupid, because the band saw turned out to be easier-than-easy. Anyway, I make one single cut with the snips, and the dumb thing "crushes" the stiffener I'm working on, putting a little "tear" in it (see below). Here's what I'm thinking: can I throw this baby on my drill press and drill that little tear out into a half-circle, the scotchbright/grind all the corners smooth? My stiffener would have a little notch in it, but something tells me that's probably okay.

tear%20004.jpg


tear%20003.jpg


tear%20004.jpg
 
Sure that's ok. If its small just blend it a bit or just start a new one if you have enough material. What ever makes you sleep better. Did it to a wing skin corner.
 
Does that tear extend nearly all the way down the web or is that just the photo? If it does and you blend it completely out, you might be close on edge distance on that hole.
 
Oh, I see what you're saying about edge distance. If memory serves, it's actually not that close but I'll check when I get home. I take it that's the only real concern? Assuming it's not too close to that hole, drilling out the tear is an acceptable solution?
 
Don't give up on the snips

Mike,
Your saw may have done these particular parts better, but don't totally give up on the snips. They are handy and will be useful further into your build. I assume you have some of the aviation style from Wiss or similar, rather than the tinnermans style that look like giant scissors. If you have not figured it out already, don't close the snips all the way during a cut, that is what usually causes a crack. Close about 1/2 way, open and move forward, kinda' keeping the snip cutting edges engaged in the metal, for the next cut. If you "disengage", you can get a wavy or stepped edge or sharp "stickers" that will bite you.

Keep at it! :D
 
SteelMike said:
Oh, I see what you're saying about edge distance. If memory serves, it's actually not that close but I'll check when I get home. I take it that's the only real concern? Assuming it's not too close to that hole, drilling out the tear is an acceptable solution?
Click to expand...

There are 2 issues:

(1) Not having a discontinuity that could cause a crack to initiate in service. Can address that by blending out the crack with a generous radius as you suggest.

(2) Keeping the function of the upstanding flange of the stiffener. From the photo, it appears that if you repair as suggested, the flange would essentially structurally "cut in two" at the repair point. Again, that's based on the photo which APPEARS to show the tear about 2/3 of the flange's height. In other words its ability to "stiffen" the skin against bending ("up and down" in the photo) aft of the hole would be gone or greatly reduced.

I'm not an aircraft structures guy so I have no idea if (2) would make any difference. My gut reaction would be that it would probably make the skin/stiffener a little more likely to flex and crack at the location of the repair.

Also on the aviation ships, the different types (left/right/center) do deflect the material a little differently; choosing the correct ones can help avoid this as well.
 
I love using the snips, but I always give myself about 1/16" to 1/8" inch extra material on the part I'm cutting, and then use a scotchbrite wheel to dress it down to exact fit. The snips are not really meant for precision, but they are useful for bulk material removal.
 
Yeah, I admit it, the tear was caused by user error - letting the snips close all the way. I didn't know that was a problem at the time... I seem to be learning most of these things the hard way. For instance, even though you might be lis-dex-sic, #21 and #12 are not, in fact, interchangeable! Ask me how I know!

haha! oh well... onwards, upwards, right?
 
I use right/left snips a lot, but then I'm a sheetmetal person by trade. I leave the 1/16" to 1/8" as suggested elsewhere in this thread, and then trimmed it to size with a 1" wide bench sander. Edges are then smoothed and rounded with the six inch scotchbright wheel.

The 1" wide bench sander (Delta) was one of my most used tools. So much so, that I have two, for different belts.

L.Admason -- RV6A
 
It should be fine in that application, but because of the webbing concerns raise, note that in a more critical application it might have not been ok to do what you are planning.
 
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