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Filing Basics for Machinists

Guide · Updated October 28, 2026

A file still finishes edges, fits parts and blends radii that machines leave behind. Pick the right cut, push with pressure on the forward stroke only, and keep the file clean.

Measure after filing

Filing removes thousandths quickly. Check with a mic proved on gage blocks. The free Gage Block Calculator builds the stack.

Step by step

  1. Choose the file: Bastard for stock removal, second cut for general, smooth for finish; Swiss pattern for fine work.
  2. Fit a handle: Never use a file without a handle.
  3. Hold the work: Clamp it low in a vise with soft jaws.
  4. Stroke: Push with pressure, lift on the return.
  5. Draw file: Hold the file across the work and draw it along for a flat fine finish.
  6. On the lathe: Left hand on the handle, slow speed, long strokes, sleeves clear.
  7. Clean the file: Use a file card to remove pins.

Worked example

A 12 in second cut file removes roughly 0.0005–0.001 in per few strokes on mild steel. To take a part from 1.0030 to 1.0000 in, measure every 10 strokes. If 20 strokes took 0.0012 in, the remaining 0.0018 in needs about 30 more; slow down near size and finish with a smooth file.

Swiss vs American pattern

American pattern files are coarser (bastard, second, smooth). Swiss pattern files run from cut 00 (coarse) to cut 6 (very fine) for precise work.

Common problems

Pins scratch the work; chalk the file and card it. Rounded surfaces come from rocking; keep the file level. Dull files skate.

Tips

Worked example: draw filing a flat

To clean a 1 in × 4 in flat, draw file with a mill bastard file, both hands, at 90° to the length. Remove 0.002–0.005 in per pass. Check with a straightedge and feeler gage; a 0.001 in feeler that passes means more work.

Common problems: pinning (chips stuck in teeth) scratches; clean the file with a file card and chalk.

Quick shop check

Common problems: filing on a running lathe without a handle is dangerous; always use a handle and file left-handed with the left hand on the handle so your arm stays clear of the chuck. Keep file strokes long and slow, and use light pressure on the return stroke.

FAQ

What is draw filing?

Pulling the file sideways along the work for a flat fine finish.

Which cut?

Bastard for removal, second cut general, smooth for finish.

Why does my file scratch?

Pins; clean with a file card and chalk.

Is lathe filing safe?

Yes with a handle, left-hand grip, slow speed and sleeves clear.

What are Swiss pattern files?

Precision files graded by cut number.

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General shop information only — follow your machine and tooling manufacturer's instructions and your shop's safety rules.