Why does my toolpath preview show an uncut block, or not update after I change a toolpath?

Why it happens

The preview is a simulated block of material that only changes when you tell it to cut. It is not a live picture of your toolpaths. Editing or deleting a toolpath does not un-cut what was already simulated, and a new toolpath is not shown until it is previewed. Most "blank" or "wrong" previews come from that, not from a fault. (A black or garbled 3D view is a graphics problem with its own entry.)

Usual causes, most likely first:

1. The block still holds cuts from an earlier version of the toolpath.
2. You used Preview Visible Toolpaths while the toolpath you care about was unticked in the list.
3. The cut is there but hard to see: with Material Color selected, machined areas take the same look as the block.
4. The toolpath calculated with no moves, so there is nothing to simulate.
5. A display hiccup after a long session.

How to fix it

1. Open Preview Toolpaths and click Reset Preview. That returns the block to solid material.
2. Tick the toolpaths you want in the toolpath list, then click Preview All Toolpaths, or select one and click Preview Toolpath.
3. Under the machined area color options choose Global Fill Color or Toolpath Color so cut areas stand out. A toolpath set to No Fill shows in the material color.
4. If nothing cuts, select the toolpath and read its summary. An empty or failed calculation needs fixing at the toolpath (see the entries on empty toolpaths and toolpaths that fail to calculate).
5. If the view itself still looks stale, save the job, then close and reopen the program. Users on the public forum report this clears it.
6. Check the animation speed slider. At full speed the preview can finish so fast it looks as if nothing happened.

Preview All Sides is only for two-sided jobs. In a single-sided job it is grayed out by design.

How to confirm it is fixed

After Reset Preview and a fresh preview run, the block shows only the current toolpaths, in the fill color you picked.

Pro tips

• Make Reset Preview a habit before every final check, so you never approve a cut based on leftovers.
• Turn on Animate Preview and Draw Tool to watch the order of cuts and catch a toolpath running in the wrong place.
• The preview trusts your tool and material settings. If the real cut differs, see the entry on telling whether the software or the machine is at fault.