IV. Mounting

4.2 Declination Bearing Housing

Before the fork could be fabricated we had to decide if the declination bearing housing would be fabricated or cast. A fabrication would require four very thick pieces of plate, 1.500" to 2.000" or so, to be welded at the end of the fork tine for the Declination bearings. A piece of the 0.250" plate would need to be bent through a pretty tight radius to form strange conical shape to mate with the trapezoid cross section of the rest of the fork. A casting would require a pattern, a core, a mold, and finally casting the part from aluminum. The declination housing shape would be easier to form when making a wooden mold. We decided the shape of the top of the fork would be easier to control with a casting.

The first task for making a casting was to make a pattern for the outside of the declination housing. The pattern was fabricated from 1/8" plywood. The casting would need to be a hollow with a wall thickness of 0.250" with two 1.500" thick bearing plates for the inner and outer declination bearing bores. A sand core would be needed in order to cast a hollow declination housing. The core would need a core box so that the core sand could be molded in the proper shape. Bill built a  core box with steel. The core box was made in four pieces so that the core could be removed. I made three sand cores so that three castings could be made. Figure 4.2.1 shows the wood pattern, left, the sand core, middle, and the core box, right.

Figure 4.2.1 Three components had to be fabricated before the declination casting could be made. From left to right are the wood pattern, the sand core, and the core box.

 The Castings were made at the CSU, Chico foundry. Each of the casting required approximately 30 lbs. of aluminum. The pattern and core were used to form a mold for the sand casting. The drag was filled with sand and leveled off. The declination housing pattern was placed on the drag and the cope was assembled onto the drag and filled with sand. The cope was pulled from the drag and the pattern was removed. The resulting cavity is shown in Figure 4.2.2a. The sand core was placed on the drag after the gates, sprue well, and runners were cut into the drag by hand, Figure 4.2.2b. a  b

Figure 4.2.2. The cope of the flask is shown with the cavity exposed, 4.2.2a. The pattern was used to make 3 casting for the declination portion of the fork. The drag of the casting mold with the sand core in place is shown in 4.2.2b. The gates, sprue well, and runners also be seen in 4.2.2b.

 The Aluminum for the castings was salvaged from scrap parts. The primary component used for the casting was scrap aluminum automobile wheels from the local wrecking yard. Wrecked aluminum wheels can be picked up cheaply. The wheels were sawed into pieces and placed in the furnace for melting. Figure 4.2.3a and b shows of the furnace and the author waiting for the aluminum to melt in the natural gas fired furnace. a  b

Figure 4.3.3. The furnace and crucible, Figure 4.3.3a. Waiting for the aluminum to melt, Figure 4.3.3b. Each pour required 30 pounds of aluminum.

 The flask for the declination casting was not thick enough to allow for a sufficient large riser. A small casting flask was added to the top of the cope so that a sufficiently large riser could be formed.

Figure 4.3.4. The cope, drag, and extended cope are stacked on each other to form a casting flask. The aluminum is poured into the sprue. The photograph is of the flask after the aluminum was poured.

 The riser is needed to allow for shrinkage of the aluminum as the casting cools. If the riser is not large enough the thickest part of the casting will shrink and be ruined. In this case the outer declination bearing plate would be ruined. The completed casting flask is shown in Figure 4.3.4 after the aluminum was poured.

A completed casting is shown in Figure 4.3.5. The sprue, runners, gates and riser can clearly be seen. The sprue is the funnel where the aluminum is pored. The runners are where the aluminum is distributed around the casting and the gates are where the aluminum is feed to the casting. The riser is the thick aluminum cylinder on the thickest part of the casting. As was stated earlier the riser is used to control to control shrinkage.

a  b

Figure 4.3.5. Figure a and b show the declination casting after being removed form the sand mold before clean up. The important features of a sand casting are shown in figure 4.3.5a and b, including the thick areas for the bearings.

 Casting clean up is removing the runners, gates, riser and sprue, Figure 4.3.6. The remaining aluminum was removed by grinding and filing to produce a smooth surface.

Figure 4.3.6. The casting after clean up. The gates, risers, sprue, and riser have been removed with a band saw. The final cleaning of the casting to smooth the casting for machining and welding was done with by filing, grinding, and sanding.

 The casting provides the final shape for the end of the fork tine. Three castings were made. One of the castings was ruined when the core floated during the pour. The result was a thin casting on the outer declination bearing plate. Each casting took about 4 hours to make and required 30 pounds of aluminum. The three castings were made over a period of 4 days.

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