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In fact, this is mainly from the pencil production process to consider. If the end is not cored or hollow at the end of the pencil, it is necessary to control the length of grooves in each board (the end is not open), and add one more part to allow the grooving tool to move up and down to leave a blank. This undoubtedly increases the cost of machine manufacturing, operation and maintenance, and correspondingly increases the rate of defective products. Compared with that pencil lead, it is not cost-effective.
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