content_image/612111.jpg content_image/612112.jpg
There are a number of different methods of forming joggles. For example, if the joggle is to be made on a straight flange or flat piece of metal, it can be formed on a cornice brake. To form the joggle, use the following procedure: 

1. Lay out the boundary lines of the joggle where the bends are to occur on the sheet. 

2. Insert the sheet in the brake and bend the metal up approximately 20° to 30°. 

3. Release the brake and remove the part. 

4. Turn the part over and clamp it in the brake at the second bend line. 

5. Bend the part up until the correct height of the joggle is attained. 

6. Remove the part from the brake and check the joggle for correct dimensions and clearance. 

When a joggle is necessary on a curved part or a curved flange, forming blocks or dies made of hardwood, steel, or aluminum alloy may be used. The forming procedure consists of placing the part to be joggled between the two joggle blocks and squeezing them in a vice or some other suitable clamping device. After the joggle is formed, the joggle blocks are turned over in the vice and the bulge on the opposite flange is flattened with a wooden or rawhide mallet. [Figure 4-163] 

Since hardwood is easily worked, dies made of hardwood are satisfactory when the die is to be used only a few times. If a number of similar joggles are to be produced, use steel or aluminum alloy dies. Dies of aluminum alloy are preferred since they are easier to fabricate than those of steel and wear about as long. These dies are sufficiently soft and resilient to permit forming aluminum alloy parts on them without marring, and nicks and scratches are easily removed from their surfaces. 

When using joggling dies for the first time, test them for accuracy on a piece of waste stock to avoid the possibility of ruining already fabricated parts. [Figure 4-164]  Always keep the surfaces of the blocks free from dirt, filings, and the like, so that the work is not marred. 

## Lightning Holes 

Lightning holes are cut in rib sections, fuselage frames, and other structural parts to decrease weight. To avoid weakening the member by removal of the material, flanges are often pressed around the holes to strengthen the area from which the material was removed. 

<img src='content_image/612111.jpg'>

<img src='content_image/612112.jpg'>

