PATTERN ALLOWANCES
Five types of allowances were taken into consideration for various reasons. There are described as follows:
1. Shrinkage allowance
2. Draft allowance
3 .Finish allowance
4. Shake allowance
5. Distortion allowance
SHRIINKAGE ALLOWANCE:
Solid shrinkage is the reduction in volume caused when metal loses temperature in solid state. The shrinkage allowance was provided to take care of this reduction. For Aluminum permissible shrinkage allowance is 0.013 mm, but 0.01 mm shrinkage allowance was provided in the pattern.
DRAFT ALLOWANCE:
At the time of withdrawing the pattern from the sand mold, the vertical faces of the pattern are in continual contact with the sand, which may damage the mold cavity. To reduce the chances of this happening the vertical faces of the pattern are always tapered from the parting line. This provision is called draft allowance. Suggested draft values for wood pattern are outer 0.25 to 3.0 degree. The above values were provided for provided for wood pattern.

FINISH ALLOWANCE:
Extra material is to be provided which is to be subsequently removed by machining or cleaning process. Suggested machining allowance or pattern for non ferrous metal up to 3 mm but 2mm allowance was provided on pattern.
SHAKE ALLOWANCE:
Before withdrawal from the sand mold, the pattern is rapped all around the vertical faces to enlarge the mold cavity slightly which facilitates its removal. Since it enlarges the final casting made, it is desirable that the original pattern dimensions should be reduced to account for this increase.
DISTORTION ALLOWANCE:
A metal when it has just solidified is very weak and therefore is likely to be distortion prone. This is particularly so far weaker sections such as long flat portions, V section or in a complicated casting which may have thin and long sections.

CASTING PROCEDURE:,
First a bottom board was placed on the floor. The drag molding flask was kept upside down on the bottom board along with the pattern at the center of the flask on the board. Dry facing sand was sprinkled over the board and pattern to provide a non sticky layer. Freshly prepared molding sand was then poured into the drag and on the pattern to a thickness of 30-50 mm. Rest of the drag flask was completely filled with the sand and uniformly rammed to compact the sand.
After the ramming was over, the excess sand in the flask was completely scraped using a flat bar to the level of the flask edges. Then with a vent wire vent holes were made in the drag to the full depth of the flask, as well as to the pattern to facilitate the removal of gasses during solidification. That completed the preparation of the drag. The finished drag flask was of the rolled over to the bottom hoard exposing the pattern. Using a slick, the edges of the sand around the pattern was repaired. The cope aligning again the drag was located aligning again with the help of the fins. The dry parting sand was sprinkled all over the drag and on the pattern. Runner and riser pin was capped at an appropriate place and freshly prepared molding sand similar to that of the drag along with the backing sand was sprinkled. The sand was thoroughly rammed, excess sand scrapped and vent holes were made all over the cope as in the drag.
The runner pin and riser pin were carefully withdrawn from the flask, later the pouring basin was cut near the top of the runner. The cope was separated from the drag and any loose sand on the cope and drag interface of the drag was blown off bellows. The pattern was withdrawn by using the draw spikes and rapping the pattern all around to slightly enlarge the mold cavity so that the mold was not spoiled by the withdrawing pattern. The runners and gates were cut in the mold carefully. Any excess or loose sand found in the runner and mold cavity was blown away using the bellows. After then the facing sand in the form of paste was applied all over the mold cavity and the runners which mold gives the finished casting a good surface finish.

MACHINING OPERATION:
After casting the job machined into shaper machine and grinding machine to obtain the desired shape and dimensions. About 3mm thickness was chipped to get the satisfactory level. After shaping, the rough surface was ground by grinding machine for smooth finishing.