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Question

Difficulty: MediumChisels, Files, and Planes

A technician is filing the flat edge of a mild steel plate clamped in a bench vise. After several strokes, the file begins to slip across the steel without biting, leaving deep, irregular scratches on the workpiece surface. What is the cause of this problem, and what corrective action should be taken?

  1. A
    The file teeth have lost their hardness; reheat the tool with a torch and quench it in oil to restore the temper.
  2. B
    The file is being pushed too slowly; apply heavy downward pressure on both the forward push and backward return strokes.
  3. Metal particles have packed tightly between the teeth (pinning); dislodge the debris by brushing across the face with a file card.Answer
  4. D
    The workpiece surface is too dry; coat the file teeth thoroughly with motor oil before continuing the filing operation.

Answer

Metal particles have packed tightly between the teeth (pinning); dislodge the debris by brushing across the face with a file card.
When metal filings become wedged between the cutting teeth of a file, the condition is known as 'pinning.' Pinned chips prevent the file from cutting cleanly and leave deep gouges on the workpiece. The correct shop remedy is to clear the teeth using a file card with wire bristles pulled in the direction of the tooth angle.

Step-by-Step Solution

1
Diagnose the cause of the file slipping and scratching the workpiece.
Identify that metal particles have become wedged into the gullets between the file teeth, a condition known as pinning.
When chips accumulate in the tooth spaces, the cutting edges cannot penetrate the metal, causing the tool to skate over the workpiece while the trapped pins gouge the surface.
2
Select the proper tool and technique for clearing the clogged file teeth.
Use a specialized file card and draw its wire bristles across the file face parallel to the rows of teeth.
Brushing in line with the tooth grooves extracts the compacted metal pins without damaging the cutting edges.

Key Concept

File maintenance, pinning identification, and file card application
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Topics

Chisels, Files, and Planes

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