Metal Bending Layout Help Needed

[twistedpiston]

Hi everyone, I have been lurking for some time and gleaning tons of great info, I however find myself needing some help with something for which I just can't seem to find the answer. I'm sure someone here will have no problem figuring it out...

I need some help figuring the flat dimension for a 2 bend piece of aluminum. The final piece will be a simple “U” channel with 2 side legs measuring (outside dimensions) .56”, 90 degree bends with .171 radius and the middle part 1.92” The material is 2024 T3 .064

My calculations:

Setback = .235
Bend allowance = .369

.56 - .235 = .325
.56 - .235 = .325
1.92 – (2 x .235) = 1.45
.369 x 2 = .738

.325 + .325 + 1.45 + .738 = 2.838

My sight line is the BTL + 1 Radius

Can someone please verify / correct my calculations? When I bend the part, the .56 legs are long and the center flat is narrow. The sum of the differences in the short legs is close to the shortage in the center.

Thanks in advance. -Keith

 

[ilovevocs]

Not a direct answer to your question, but IMHO unless your intention is to use this math for a more complex project, your making allot of extra work for yourself.

How are you bending this piece? I bend allot of material this thickness and rarely use complicated math to do it. Once I bend the first piece I would forget the math and make adjustments based on my first bend test. You don't have to bend a full length when you get started, make a few drops that have the same stretch out as the full length piece you intend to bend. Bend, measure, adjust, repeat as required. Keep track of the bend locations ect and when you get it dialed in you will be all set. If your constantly bending on the same machine you will quickly get a feel for what it takes to produce any part within a few test bends.


I always start by drafting the piece, producing a bend sheet in excel, then its out to the shop. I use a calculator in the shop to adjust the measurements but its just simple addition and subtraction.

 

[Snaps1992]

Looks mostly right, but I get a bend allowance of 0.319, using a k factor of 0.5 (as the bend radius is larger than twice the thickness)

(90\360)*2*pi*(0.171+0.5*0.064)

That gives an original width of 2.738

 

[twistedpiston]

Looks mostly right, but I get a bend allowance of 0.319, using a k factor of 0.5 (as the bend radius is larger than twice the thickness)

(90\360)*2*pi*(0.171+0.5*0.064)

That gives an original width of 2.738

...That might be my mistake, I used a k factor of 1.

I would forget the math and make adjustments based on my first bend test.

...That's what I ended up doing, but I make many different parts and although time is not a factor, I should be able to do the math and make the part once.

Thanks guys for the input!

 

[A_Pmech]

How are you planning to hit that radius? The calculations are all academic if you can't hit the bend radius. A standard leaf brake will only produce that bend radius if a suitable nose bar is used.

 

[twistedpiston]

How are you planning to hit that radius? The calculations are all academic if you can't hit the bend radius. A standard leaf brake will only produce that bend radius if a suitable nose bar is used.

Yep, using a nose bar. The radius was verified with a piece of scrap .064

 

[Sureshot]

If possible make the bends then cut off the excess.

 

[NUTTSGT]

If possible make the bends then cut off the excess.

That is what I would do.

 

[stomperxj]

I use software to figure that stuff out...

 

[Kevin54]

Twisted.....Figure your length using the middle of the stock. To figure your radius length, IIRC it is length = radius x angle x 3.1416 / 180 So in your case add .032 to your radius which would give you .203. So it will be .203 x 90 x 3.1416 / 180 = .319 bend length. Multiply that x 2 for both bends and you have .638 length. Now add your straight legs to it and it should get you very close.

.638 (rad. length) + .325 (wall length) + .325 (wall length) + 1.450 (bottom length) = 2.738 blank length.

The difference between your figure and my figure, and also with Stompers figures is that you are using a bend allowance chart. In doing this work for 30+ years, I have collected a vast number of bend allowance charts and no two were ever the same. Some weren't even close to being the same, so I started figuring sheetmetal down the middle, and 95% of the time it comes out almost on the money. If you notice Stompers answer, his and mine are the same (other that two place versus three place decimal) and his was done using the computer program, and mine was done on a piece of paper.

Write down the formula somewhere and hang on to it
Length = Radius x angle of radius x Pi / 180
That is the formula for figuring the length of your radius. Then just add your straights in and your good.

A program I have at home for drawings and such is DeltaCad. It's something like $40, you can get it online, plus they have a 30 day trial period for free www.deltacad.com It's very user friendly, it does most everything more expensive 2d drawing packages do. Download their trial version and give it a go. It also will figure radius lengths with the click of the mouse button. Myself, even though I use it all the time, I still like to figure stuff like that in my head just to stay a little sharp.

 

[twistedpiston]

Thanks for all of the responses, I knew this was the place to turn!

stomperxj - That software looks cool. What program is that?

Kevin54 - Thanks! I was using charts in an old military book, the title escapes me... then my wife found a "bend calculator" application for my "smart" phone (the phone is smarter than me) an I have been using that. I prefer to work out the math on paper. I am being dragged kicking and screaming towards technology.

Here's an example of the type of stuff I'm making.

 

[Kevin54]

Twisted.....what plane is that? I've worked for Grimes (now Honeywell) for 30+ years as a Toolmaker and Tool Designer. Our product is aircraft lighting. Inside, outside, commercial, and military. So any lights you see on the older planes, chances are they were ours. Any more pics of the huge project?

 

[twistedpiston]

Kevin... It's a B17. I'll have to take more pics these are a few months old. The port cheek window is in, we've got the chin turret section shot in and the astro dome and surrounding skins shot in. It doesn't look so much like a porcupine now. I hope I live long enough to see her fly.

The Memphis Belle (tribute, used in the movie) is here for the winter.

 

[stomperxj]

stomperxj - That software looks cool. What program is that?

Autodesk Inventor Pro 2014. It has some really cool sheet metal tools in it...

 

[Kevin54]

Kevin... It's a B17. I'll have to take more pics these are a few months old. The port cheek window is in, we've got the chin turret section shot in and the astro dome and surrounding skins shot in. It doesn't look so much like a porcupine now. I hope I live long enough to see her fly.

The Memphis Belle (tribute, used in the movie) is here for the winter.

Sweet!!!! We recently had a museum built in our little Podunk town, And I think it is a B-17 that they are redoing in there along with having a B-25. Next door to it is the original hangar for the locals, but the hangar was separated, pulled apart and there is a plane in there (Beechcraft) called "The Flying Lab". Warren G. Grimes who basically invented lights for aircraft, they acquired the Beech and that used to be the test bed for the aircraft lighting. Here is a small article on it http://www.generalaviationnews.com/blog/2009/11/04/the-grimes-flying-lab/ People that saw it at night, called in numerous times that there was a UFO over their area. It's got a buttload of lights and strobes on it. When Grimes Aerospace was taken over and eventually was bought by Allied Signal, they got rid of the plane. The employees wanted to buy it, but it was a no go. So the plane was sold and was going to be used for crop dusting. It ended up sitting on a field. A person that worked at grimes ran across it years later. It was eventually bought back by Honeywell and donated to a group to rebuild it and maintain the aircraft. It made it's debut on the Fourth of July a few years back, all repainted in it colors with all of the lights again working. It's a real site to see, and it does travel around to different airshows. There is a lot of history with Grimes Manufacturing. So when you start getting to the light portion of the B-17, look and see if they don't say Grimes Aerospace.

 

[theknurl]

How are you planning to hit that radius? The calculations are all academic if you can't hit the bend radius. A standard leaf brake will only produce that bend radius if a suitable nose bar is used.

want to do it without a nose bar?

bend a piece of scrap leave it in the brake, bend another ...repeat until you get the required radius......yes, you have to set the clamp back too,

no you can't do big radii

Psst; listen to Kevin54

my Father started at Lockheed in '29, making seats and tanks....

when you can make the entire wing root fillet out of one piece of metal without grinding sanding or filing let me know

here's my Father's work;
http://www.google.com/url?sa=i&rct=...RWbE62uP3IL-enF_6OPK46VQ&ust=1384827998440325

yes, in the Smithsonian

I have pictures of my Father and Jack Northrup working on it, it doesn't have fuel tanks in it (Dad built the originals) or its ID tag......I have a blank one

because TWA was too cheap to fly my Father back to work on the plane.....its not complete

jackasses!

 

[twistedpiston]

my Father started at Lockheed in '29, making seats and tanks....

That's awesome. Such a dying art.

It is a shame that this and other skills will be gone soon. The younger generation doesn't seem to care about working with their hands (unless it's holding a game controller) or learning a trade (I know, not all but most). Hell, you would be hard-pressed to find a 20-something that can read a rule, technical drawing, a micrometer or even a road map for that matter... if it doesn't plug in or run on batteries it's an antiquated and useless “thing”.

The days of an apprenticeship are gone, college grads living in their parent's basement are looking for that six figure, entry level CEO position for which they feel they are “entitled”. It's sad to see all of these “old timer” machinists, fabricators and craftsman fading away with no one to pass their years of knowledge to. These fields are being taken over by automated machines and computer programers.

Technology has no doubt made some facets of our lives easier but maybe that's the problem... everyone wants things to be provided to them with the push of a button and the least amount of effort possible.

We should seek out these “old timers” and pick their brains for as much information as they are willing to give.

...stepping off the soapbox now

 

[hunter1151]

If you are doing this stuff for an airplane, there are charts for minimum bend radius, and standard bend radius. There are also minimum flange lengths for bending up material. There are also standard bend radii for T material. I don't have a chart in front of me, so I will have to check and get back with you. I build parts out of sheetmetal for the aircraft industries, Boeing, Lockheed, Cessna, Beech, Learjet, and the federal government. You should be able to find setback charts online, they are the easiest to use. They will list the standard size material thicknesses, and then they will list the setback based on the degree of bend. How are you making these bends, with a press brake or on a box and pan with radius bars, or using a form block?

 

[theknurl]

That's awesome. Such a dying art.

twistedpiston;
the sad thing is when I asked my Father to show me to 'bump' a motorcycle tank out.....he borrowed a shot bag and roughed out the 2 halves in 15 minutes....

then he put the wood hammer down and said "this is going backwards.......you figure it out"
and walked out of the shop WTF????

I guess I should have expected it, at 7 or 8......
"this is an A/O torch, this is an oxidizing flame, this is a neutral flame, this is a carburizing flame, thats what you want, here's a coat hanger, weld the 2 tin cans together, call me when you can do it and don't burn yourself"

by 10 I could weld circles around my Father, I figured that out, but for one of the grand masters of tin bending not to teach his own kid.....that's screwed up

because with tin bending there are lots of tricks......if you don't know them you are screwed......

just try doing the reverse compound bend in a aircraft wing root fillet IN ONE PIECE from the trailing edge around the front edge and back to the trailing edge

1st you're not starting with a 4'x8' sheet or 3'x10' sheet try 2 1/2'x 35'

stick that in a English wheel

 

[PugetDude]

You'll need to figure the length of the neutral axis (a centerline dimension through the center of the material thickness ) rather than the outside or inside dimensions and bend radii. . Assuming you don't coin or stretch the material while bending, this should get you a spot-on dimension. Bend one piece, measure it up, and then adjust to compensate for any stretch in the forming processes.

Post results!

 

[A_Pmech]

want to do it without a nose bar?

bend a piece of scrap leave it in the brake, bend another ...repeat until you get the required radius......yes, you have to set the clamp back too,

no you can't do big radii

That's an interesting approach.

Being a machinist, I just make a nose bar.

It is a shame that this and other skills will be gone soon. The younger generation doesn't seem to care about working with their hands (unless it's holding a game controller) or learning a trade (I know, not all but most). Hell, you would be hard-pressed to find a 20-something that can read a rule, technical drawing, a micrometer or even a road map for that matter... if it doesn't plug in or run on batteries it's an antiquated and useless “thing”.

Not all. You'll find there's a greater than average number of us here than most forums. I can think of at least three of us who probably don't know which end of a game controller to point at the TV.

You're doing great work from what I can see, BTW. Is this a scratch build or are you rebuilding an existing airplane? From the work I see going on I can only assume this is from the ground up...

 

[hunter1151]

Ok here goes in case you are still interested.

Standard bend radius for .064 2024-T3 is .25 set back for a 90 deg bend is .1909
Minimum bend radius for .064 2024-T3 is .22 set back for a 90 deg bend is .1774
Standard bend radius for .064 2024-0 is .16 set back for a 90 deg bend is .1504
Minimum bend radius for .064 2024-0 is.12 set back is .1370

To figure the flat pattern for your channel you add the 2 flange lengths .56+.56 + the 1.92 minus 2 set backs from the four above to get your flat pattern.

For the channel dimensions you have given you would need to make this out of 2024-0 material, bend it in a brake, or form it over a form block( the spring back on 2024-0 would be 2-3 degrees, I think) and then it would have to be heat treated to T4. If you try to brake this with the radius you called out you will stress crack or break the material. This is standard aircraft practice..............