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Woodworking Math

Thickness planer guide

What snipe is and what planer makers say reduces it, what cuts per inch means for the finish, straight knives and helical heads, and the safety rules. A thickness planer makes a board's second face parallel to the first and brings it to an even thickness.

Planer snipe: causes and fixes

  • Snipe is a deeper cut at the ends of a board, made when an unsupported end drops and tips the other end up into the cutterhead.

    One source: DeWALT, the maker of that planer , sources [1]

  • Support long boards level with the planer bed going in and coming out, with extension tables or rollers.

    3 sources agree , sources [1, 2, 3]

  • Set the outfeed (and infeed) extension tables level with the main table; one that slopes down causes snipe.

    Two sources: Grizzly and DeWALT , sources [2, 1]

  • Some snipe is unavoidable on any planer: it can be made small, not removed.

    Two sources: Grizzly and JET , sources [2, 3]

Sources

  1. DeWALT, DW735 13" two-speed thickness planer instruction manual (specifications; feed speeds; snipe), read 2026-11-07
  2. Grizzly, G0477 planer/moulder manual, troubleshooting: snipe, read 2026-11-07
  3. JET, JPJ-12B jointer/planer manual, performance troubleshooting: planer, read 2026-11-07

Cuts per inch and the finish

A straight-knife planer leaves tiny scallops, one per knife cut. Cuts per inch says how close together they are: RPM × knives ÷ (feed in ft/min × 12). More cuts per inch means a smoother surface, so a slower feed setting gives a better finish on the last passes. The cuts per inch calculator works it out for your machine and checks the figure its maker states.

Straight knives or a helical head

A straight-knife cutterhead carries full-width knives: three or four on the planers in the calculator. A helical (spiral) head carries many small inserts set in rows that wrap around it. The cuts per inch formula fits straight knives only, so this guide gives no cuts per inch figure for helical heads.

  • DeWALT’s DW735 uses three straight knives at 10,000 RPM, with two feed speeds giving 179 or 96 cuts per inch; it recommends the slower one for hard or figured wood.

    One source: DeWALT, the maker of that planer , sources [1]

  • JET’s JJ-6HHBT jointer’s helical head carries 14 inserts in 2 spiral rows, and RIKON’s 20-600H 12 two-sided HSS inserts.

    Two sources: JET and RIKON , sources [2, 3]

Sources

  1. DeWALT, DW735 13" two-speed thickness planer instruction manual (specifications; feed speeds; snipe), read 2026-11-07
  2. JET, JJ-6HHBT 6" helical benchtop jointer manual (specifications; operating safety), read 2026-11-07
  3. RIKON, 20-600H 6" helical benchtop jointer operator’s manual (specifications), read 2026-11-07

Safety

  • OSHA requires metal guards over a planer’s cutting heads and a hood or guard over its feed rolls (1910.213(n)(1), (n)(3)).

    One source: OSHA, the federal standard , sources [1]

  • DeWALT: change the DW735’s feed speed only while the planer is running, never in the middle of a cut; changing speed while planing can cause kickback.

    One source: DeWALT, the maker of that planer , sources [2]

Sources

  1. OSHA, 29 CFR 1910.213, Woodworking machinery requirements, read 2026-11-07
  2. DeWALT, DW735 13" two-speed thickness planer instruction manual (specifications; feed speeds; snipe), read 2026-11-07

To flatten a cupped or twisted face before planing, see the jointer guide.