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Session 8: Pockets, Step-Over & Step-Down

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Session 8

Pockets, Step-Over & Step-Down

Last Time

Profile cuts follow a line. A pocket clears out an entire area.

That's a different problem — the bit can't just trace an outline once.

Clearing an Area Takes Many Passes

The bit sweeps back and forth, slightly overlapping each time, until the whole area is clear.

Step-Over

Diagram comparing an even step-over, where overlapping passes clear the entire pocket area, against a step-over set too wide, which leaves ridges of uncut material between passes

Too Wide a Step-Over

Leaves thin ridges of material standing between passes — the pocket looks clear from above but isn't.

A Different Problem: Depth

Cutting a thick panel to full depth in one plunge stresses the bit hard.

Step-Down

Cross-section diagram of material being cut in three progressively deeper passes before reaching final depth, with an arrow labeling the step-down distance between passes

Why Shallow Passes Instead of One

  • Less heat and stress on the bit — lower breakage risk
  • Cleaner chip clearing at each depth
  • A broken bit mid-cut is worse than a slower job

One More Thing: Tabs

When a Profile cut fully separates a part from the stock, what's holding it in place at that final moment?

Tabs

Small, deliberately uncut bridges that hold the part to the stock until you remove them by hand after the job finishes.

No Tabs, No Warning

A fully-cut part can shift or come loose mid-job — right next to a spinning bit.

Two Things to Remember

Step-over and step-down solve different problems.

In Fusion you will find them under an operation's Passes tab — step-over as Stepover (or Optimal Load on an Adaptive operation), and step-down as Maximum Roughing Stepdown, which only appears once you tick Multiple Depths.

Step-over is about area (side to side). Step-down is about depth (top to bottom). Don't confuse which one fixes which issue.

Two Things to Remember

Tabs are a safety feature as much as a practical one.

In Fusion, tabs live on a 2D Contour operation's Geometry tab — tick Tabs, then set their width, height, and spacing.

A part that's still attached can't become a projectile mid-cut.

Next Time

Session 9: Apply CAM to a Practice Piece

Everything from these two sessions, programmed for real in OnShape.

'F' → Fullscreen

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Build

Step 1: Diagnose a Bad Pocket

A pocket cut with too-wide a step-over comes out with visible ridges still standing. Explain, in your own words, why this happens even though the toolpath ran the whole area.

Step 2: Step-Over or Step-Down?

For each problem below, name which one (step-over or step-down) is the actual fix:

  1. A pocket comes out with thin uncut ridges between passes
  2. A bit snaps partway through cutting a thick panel to full depth
  3. A pocket's bottom is rough and uneven, even though the sides look fine

Step 3: Why Tabs?

Explain what would actually happen, step by step, if a Profile cut fully separated a part from stock with no tabs, while the job was still running.

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Checkpoint

Before you move on, confirm you can explain, out loud, the actual difference between what step-over fixes and what step-down fixes.

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Reflection

Answer these on your own. Reflections are individual, even when the rest of the session was team work.

  1. A pocket toolpath is really many overlapping profile-like passes. How does that change how you'd set one up, compared to Session 7's single profile cut?
  2. Session 9 has you apply all of this for real. What's the one thing from these two sessions you're least confident about actually setting correctly?
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Submit

Submit your pocket diagnosis, your step-over/step-down answers, your tabs explanation, and your reflection.

Activity Complete