What Determines Whether a Laser-Cut Part Needs Tabs Left in Place During Cutting to Keep It From Dropping Into the Scrap Bin?

Tabs come down to part size relative to the slat gap it's sitting on, and how much of the perimeter the laser has already cut before reaching the last connecting point. Small parts, parts with a lot of internal cutout relative to their outer footprint, and parts cut near the end of a nest where surrounding scrap has already fallen away all need a deliberate tab or they drop through the table before the head finishes the last pass.

Why gravity wins sooner than you'd expect

Gravity doesn't wait for the last cut.

A laser-cut sheet sits on a slatted or grid support table so the beam has somewhere to go once it's through the material. As cuts progress, finished parts and scrap webs lose their connection to the rest of the sheet piece by piece. A part that's mostly perimeter, like a simple bracket outline, tends to stay put because there's a lot of surrounding material still holding it in plane right up until the final cut closes the loop.

A part that's small, or has large internal cutouts finished early, can lose its support well before its own outline is fully cut. Once it's resting on friction and a sliver of uncut material, table vibration or the assist gas jet is enough to tip it through a slat gap. When that happens mid-cut, consequences range from a lost part to a head crash if the laser's follow sensor suddenly reads a gap where it expected flat material. Neither is acceptable on a production nest.

How the fix actually works

A tab solves it with almost nothing.

A tab is a short, deliberately uncut segment, sometimes called a micro-joint, left in the cutting path to keep the part physically attached to the surrounding scrap or sheet frame until it gets removed. It goes on an edge that won't matter cosmetically or functionally, sized just large enough to hold the part's weight through the rest of the cutting cycle without requiring real force to snap free afterward.

Placement matters almost as much as whether the tab exists at all. A tab near a tight internal feature can leave a nub that interferes with an adjacent bend or a mating part. A tab on a long straight edge is usually invisible once broken away and deburred. For sheet metal headed to a forming step, tabs stay clear of bend lines entirely. A nub right where material needs to fold cleanly is its own problem.

Who decides, and when

This is usually a call the shop's nesting software and operator make, not something a customer needs to specify on a drawing. The software flags parts below a size or geometry threshold and proposes tab locations automatically, and the operator moves them if a proposed spot lands somewhere that matters. If you're designing a part with an unusually delicate internal feature near what would be a natural tab location, a note on the drawing calling out non-critical edges saves a round of questions.

DigiForge's sheet metal line runs laser cutting, press-brake forming, and PEM insertion, holding a cut tolerance of ±0.13 mm with a standard lead time of two weeks. Tab placement is ordinary production setup on our end and doesn't change either number.