Aluminum Grain

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Postby russell » Thu Jan 04, 2007 1:11 pm

I have a piece of 7075-T6 x .080 aluminum and I need to know if there is anyway to tell the direction of the grain other than test bending it. It's been rubbed with ScotchBrite so it's smooth and shiney. Dale Kramer said that it bends better across the grain, but will snap parallel to the grain if bent tight. The bend I want will be slight. If it bends without showing signs of fracturing would it still hold it's integrity?
Anyone have any suggestons?

Russell
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Postby lazairiii » Thu Jan 04, 2007 3:05 pm

Are you making a factory replacement part? If so, which one?

Dale is right. You do not want to bend with the grain. Always bend cross grain...if you can tell which direction that is. There is a rule of thumb too as I recall that says something like this. You should always make your radious 8x the thickness of the material being bent. Now I could be off here, but it was something like 8x which keeps the radious from being too tight on hard materials like 7075. Otherwise it will crack and you loose all integrity.

Just an opinion...
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Postby russell » Thu Jan 04, 2007 4:11 pm

It's the fitting that attaches the lower end of the wing strut to the frame. Yeah, Dale said he thought it is 6 times for 7075. He didn't elaborate on the bending direction, he just said it would bend easier across the grain. I didn't talk to him directly, just read this off a post he made to this forum. I have noticed that the bracket on the later series has a double directional bend in order to form around the down tube of the frame, so at least one of these is going to be with the grain I would think. That's what confused me. 'Course it doesn't take much to do that. What ya think?
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Postby uscgairdale » Thu Jan 04, 2007 6:16 pm

I always bend perpendicular to the grain too as it really does make a diffence. Anyone whos tried to bend parallel to it gets an unwelcome suprise when they are half way through the bend.

My previous ul project was a plans built Hummel CA-2 so I've spent some time bending aluminum. I don't claim to be an expert, but I've experienced a fair bit of manipulating metal. Generally, the thicker the material, the larger the radius required. You can "get away" with less of a radius with thinner material. 6061 T6 bends real well, 2024 T3 is harder to bend, and 7075 T6 is harder to bend still.

Identifing the grain is harder on certain alloys. If you can't see it, there are other ways to tell. If the piece is large enough, you can look for the manufacterer/alloy/material thickness stamp. It's always put on the sheet parallel to the grain.

.080" is really thick stuff. Maybe two .040" thick plates stacked on top of each other would be acceptable and easier to fabricate?.......
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Postby russell » Fri Jan 05, 2007 8:13 am

The angle of deflection is approx. 9 deg. , which is a radius of 16" and which is 200 times the thickness of the metal. The piece has been polished so the markings are gone. .080 is an overkill for sure, but if I had designed the plane it would have weighed in at around a 1000 pounds!
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Postby russell » Fri Jan 05, 2007 8:26 am

George, you had fabricated and posted some photos of the fittings on the later series that attach the struts to the axle which have to circumvent a vertical frame tube that it crosses. These fittings have two bends in them which are at about 90 deg. to one another so one of these had to be perpendicular to the grain, right?
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Postby lazairiii » Fri Jan 05, 2007 7:08 pm

Yes I did, but I made these out of Titanium...and the bends actually only go in one direction. So that's why it wasn't any big deal that the factory originals could be made out of aluminum.

Your series II brackets should be a snap to make as the bend is in fact slight. Still, have the grain running parallel to the ground...if you can determine the grain direction that is, as the bend in that part is vertical when installed. That will put the grain opposite the bend.
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Postby lazairiii » Fri Jan 05, 2007 7:30 pm

Another look at these brackets from the bottom side and you can see they only have a bend in one direction...
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Postby bdiedenhofen » Sat Jan 06, 2007 12:41 pm

I recall a note somewhere on this site from Dale Cramer. He suggested that for those fittings, they could be left straight and don't necessarily have to be shaped to fit around the tubes.

I can't remember where exaclty it was posted, but I'm pretty sure that's what it said.

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Postby ola » Sat Jan 06, 2007 2:58 pm

it looks sooooo nice GEORGE.

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