Question

Draft or tapper allowances are provided in patterns on all the 0.4pt of the pattern.

• A. horizontal surfaces
• B. sides and round surfaces
• C. vertical surfaces
• D. corners

Hint:

Think of trying to pull a perfectly cylindrical peg out of damp sand vs. a slightly conical (tapered) peg. The tapered peg comes out much more easily without messing up the hole. That taper is the draft allowance.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Pattern allowances are dimensional modifications made to a pattern to account for various phenomena that occur during the casting process. Draft is a specific allowance made to facilitate the removal of the pattern from the sand mold.

Step 2: Detailed Explanation:

• A pattern is used to create a cavity in a sand mold. After the sand is compacted around the pattern, the pattern must be withdrawn to leave the cavity behind.

• If the pattern has surfaces that are perfectly perpendicular to the parting line (i.e., vertical surfaces), withdrawing it would create a vacuum and the friction between the pattern and the sand would likely damage the edges and walls of the mold cavity.

• To prevent this, a slight angle or taper, called

draft, is applied to all

vertical surfaces of the pattern—that is, the surfaces that are parallel to the direction of pattern withdrawal.

• This slight angle allows the pattern to be lifted out cleanly without disturbing the sand mold. Horizontal surfaces (perpendicular to the withdrawal direction) do not need draft.
The term was missing in the OCR for option (C), but based on the context of the question and the standard answer, it is "vertical surfaces".

Step 3: Final Answer:
Draft allowance is a taper provided on all the vertical surfaces of a pattern to allow for its easy and clean withdrawal from the sand mold.