MIL-HDBK-660 Fabrication Of Rigid Waveguide Assemblies Sweep Bends And TwistsThis handbook is intended for the electronic installations technician to be used as a guide for fabricating rectangular waveguide bends and twists used in the microwave region of the electronic spectrum.

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MIL-HDBK-660B

FIGURE 18.  Detail of forms for sideways bend.

4.4.3  Hydraulic push press and portable hydraulic bender method.  One disadvantage encountered in using this method is that the waveguide must be filled before bending.  This disadvantage can be overcome if one of the flexible mandrels previously described is used; the polytetrafluoroethylene mandrel is especially suited for these types of benders.  This is the preferred method for making bends of sharper radii and where no two bends are alike.  It is also the most convenient to use at a forward area or advanced base.  Another distinct disadvantage to this method (using a filler) is that puckers or wrinkles that usually form as a result of the bending operation must be removed.  This is done by using a rolling machine or by hammering.  A typical hydraulic bender and a simple hydraulic press is shown

in figures 19 through 21.  The procedure for using this method is as follows:

a.    Anneal and fill the waveguide.

b.    Insert the waveguide between two bending pins or dies (with suitable protection slabs in place).  A bending form, curved to suit the desired radius of the waveguide, contacts the waveguide as the hydraulic hammer moves forward.  For a desired 18-inch (45.72 cm) radius bend in the waveguide, the radius of the curve of the bending form should be 17.5 inches (44.45 cm).  This compensates for the springback of the waveguide.  A complete bend is formed by bending the waveguide in short sections along the radius distance.  The bend will not be smooth but will have "puckers" or hills and valleys in the surface; these will have to be hammered out.  Shift the points of the pressure of the ram.  Force ram surface against the "puckers".

c.        A complete 18-inch (45.72 mm) radius, 90-degree bend can be made in the waveguide sideways (E plane as the throat and back) with one rosin filling; however, if the waveguide is bend edgewise (H plane as the back and throat), two rosin fillings are necessary.

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