All American Products Co.

INSTALLATION DATA: To maintain accuracy in the production operation, extra care must be taken in mounting hole preparations. Factors to consider are diametral interference fits, alignment, chip clearance and proximity of bushing to work piece.

          Mounting holes - An important point to consider is the roundness of the mounting hole. Because bushings tend to assume the shape of the hole into which they are pressed it is recommended that all mounting holes be jig bored or sized with a reamer to assure roundness. An ordinary twist drill will seldom produce a hole that is accurately sized and truly round.

          Interference fits - In any press fit installation, metal is displaced. Usually, a combination of bushing closure and jig plate distortion results; therefore the best practice is to use the minimum interference necessary to retain the bushing in the jig plate. In most installations diametral interference of 0.0005 to 0.0008 inch is adequate for installation of headless press fit bushings or liners.

Bushing installation - Before installing a press fit bushing always lubricate the inside diameter of the mounting hole and the outside diameter of the bushing. Bushings installed without lubricant may pick up metal and score the mounting hole during installation. Lubricated bushings are more easily removed for replacement with less chance of damaging the jig plate. Use a hand arbor to press the bushing or liner into the jig plate whenever possible. If not, use some other means such as drawing the bushing into the jig plate with two steel plates and a nut and bolt. A hammer should be used only if no other methods are possible and then never strike the bushing directly; use a block to take the hammer blows. Whichever method is used, care should be taken to maintain centerline perpendicularity, otherwise inaccuracies may result in the production operation.

          Diamond and/or serrata groove bushings which are locked in the mold prior to the molding operation need special attention regarding centerline perpendicularity. Also beware of molding materials in the bushing I.D., inside diameter.

          Serrata groove and/or serrata press bushings can be used in drilled holes in imbedment or soft materials. Pilot hole size will vary according to ductility or hardness of the materials which bushings will be installed into. Due to the variations in the materials used specific pilot hole size recommendations cannot be made.

*Points to consider regarding pilot hole preparation:

          1. Sufficient interference is necessary to assure a firm hold of the bushing. However, excessive interference may crack or distort the jig or fixture because of the displaced material.
          2. Heating plastic materials during bushing installation expands the hole which allows easy insertion. Due to shrinkage of the plastic during cooling, the material flows around the serrations providing a shrink fit.