An easy brake?

[Hank Jarrett]

Re: An easy brake?

NEAT Bill! Your rule of thumb method looks a LOT easer than the complex way they showed us. It doesn't account for spring-back but all you need to do is use the brake to "bump" the angle to the final setting (takes all of a few seconds!). You DO still need to know what the minimum bend radius is for your material (or it will crack in the bend, and sometimes the minimum is DIFFERENT with the grain than across it). Also, some materials should be bent in one pass, not in steps or they will work harden.
Now we know at least one of the methods used by "Ole Crusty"!
Hank

[M Jones]

Re: bending metal

Got the brake built and am practicing on scrap sheet metal.

I've set the clamping bar about 1/8" back from the fold, and I set the intended location of the bend (the line I drew on the work) over the fold. When I bend the metal, the line ends up about 1/16" up the other side!, so I'm trying to figure out the allowance. I'm trying the build a piece of channel (see attached) with a floor of 1".

CAn anyone suggest how to set my allowances? The sheetmetal is .035 - Mike

Mike,

Bill's rule of thumb sounds like a good idea and will work for you I'm sure. I would suggest you pick up, if you don't already have one, a used "Machinery's Handbook". You won't be sorry to have it anyway. There's enough reading, charts, formulae, etc. to keep anyone happy on the longest and coldest winter evenings... In a previous life, I designed sheet metal enclosures for a large Electrical Mfg. company (starts with a G, and ends with E), and this was on my drafting board all the time. (Yes, drafting board. I’m crusty also.)

On page #1930 on the old 21st Edition I have, the formula for 1/32" (T) soft steel and aluminum sheet, using a 1/4" radius (R) bend says add 0.216" per 90 degree bend. You're using .035 T, so it's close.

L = (0.64 x T) + (1.57 x R) is the formula for half-hard copper and brass, soft steel, & aluminum

[mhorowit]

Re: An easy brake?

Networking.

but tackling the landing gear looks outside my current abilities; however, if some authority says I could simply overlay all the pitted areas with new metal ..... needs research - Mike

[M Jones]

Re: bending metal

On page #1930 on the old 21st Edition I have, the formula for 1/32" (T) soft steel and aluminum sheet, using a 1/4" radius (R) bend says add 0.216" per 90 degree bend. You're using .035 T, so it's close.

L = (0.64 x T) + (1.57 x R) is the formula for half-hard copper and brass, soft steel, & aluminum

Oops... The formula and result are right, but I stated 1/4" R. I believe you said 1/4 rod, which would be 1/8" R. The .0216" bend allowance is correct for 1/8 R. Sorry, I just messed up the reply.

Mike

[VictorBravo]

Re: An easy brake?

My R+T comment was from the sheet metal instructor at A&P school. I think it is even the "official" way to do it under SOME circumstances.

I was assuming you are talking about a 90 degree bend, and having enough of a radius not to crack the metal.

Spring back, more or less than 90 degrees, and exotic tempers or metals will require the full textbook approach of course.

I'm in the middle of doing an amateur sheet metal job right now, making up new cooling baffles for the A-65. What a pain in the ass! The stamped parts are of course cracked and twisted and nibbled to death.

Knowing how important it is to have those baffles tight and keeping all the air in the fins, but trying to do it out of straight sheet metal bends, is a chore! I finally gave up on the T-3 and had to resort to O condition aluminum. This is going to be a lot of work, but probably worth it in cooling. It's been 100-110 degrees in Los Angeles for over a week!

[mhorowit]

Re: An easy brake?*%#$^

I can't bend the 3/8" end of the rib.
There is apparently some minimum piece of sheetmetal on the leaf side.
When I tried to do the bend, the gap between bed and leaf opens too much. (sigh)

Is there any reason I can't weld the bottom to two sides to build the rib?

[VictorBravo]

Re: An easy brake?

Mike, get a pair of sheet metal folding or seam forming pliers. They look like a pair of Vise-Grip locking pliers, but the jaws are 6 inches wide, thick sheet iron. Air conditioning system installers use them for doing exactly what you need to do... grabbing a thin 3/8" strip of metal and bending it. I just used my set several times recently and they work well for certain emergencies when you can't put the whole thing in the brake. Most big box home improvement stores should have them, if not then call an air conditioning contractor and ask them where to get a pair. My hangar neighbor "Air Conditioning Bob" Cappiello let me use his pliers, and they were a lot nicer than my cheape set, but they did the same job. I think I got mine at Harbor Freight, and they were genuine Taiwanese s**t, but with a short trip to the grinding wheel they had a straight and smooth bending edge. If you are clever, you can file or grind one side of the jaws to a 1/8" radius and the other side to a 1/16" radius for different options.

Also, you can make up a tool from two pieces of angle iron. Sandwich your 3/8" flange between these pieces of angle iron and put it in a vise. Then pound the non-clamped part of the metal over using a piece of thick plywood as a buffer between your sledgehammer and the metal. The plywood spreads the impact over a wider area so you get a smoother bend.

I saved the best for last... another emergency measure (to get your job done today without delay) is to put a wider piece of thin scrap aluminum or steel underneath the piece you are trying to bend on the brake. The leaf will grab the wider piece and bend it, and your work piece will follow along for the ride.

NEVER forget that the world's greatest aerospace engineers were Rube Goldberg and his English cousin Heath Robinson!

[mhorowit]

Re: An easy brake?

Problem solved.
Took a brisk nap,followed by some heavy washers between the work and the leaf.
Variation on VB's last suggestion, although the pliers sound like a good thing to have around.

I'll practice this again on more scrap then get out the good stuff - Mike

[mhorowit]

Re: An easy brake?

Mike, get a pair of sheet metal folding or seam forming pliers. They look like a pair of Vise-Grip locking pliers, but the jaws are 6 inches wide, thick sheet iron.

Or...
"Throw out that welding rod and come out with your hands up!"

[mhorowit]

Rolling the edges of this practice rib

1. do you roll the edges after welding this rib in place or before? After welding would make it easier to handle, but I'm concerned about bending the frame.

2. What's the prefered method for rolling the edges? I built a tool by hacksawing a groove in a bar of metal; also tried clamping a piece of metal on the inside of the rib and hammering the edge over. Both methods look ratty. Suggestions?