Common-line (joint) cutting

Common-line cutting — also called joint or shared cutting — lets neighbouring parts share a cut where matching straight edges meet. Done well, it shortens cut length and can reduce pierces. Done blindly, it can add a sheet or worsen idle travel. This guide covers the idea and the live Shared cut control in AllTerra Calculator.

What common-line cutting is

In a normal nest, each part keeps its own outline. Two rectangles side by side are cut as two full perimeters, with a gap between them for kerf and heat. Common-line cutting places matching edges so one cut separates both parts along that shared edge.

The benefit is less torch-on distance and often fewer pierces along those shared edges. The risk is packing that needs an extra sheet, or a head path with more rapid moves so machine time does not fall even when cut length does.

Not every shape pair qualifies. Shared cuts need matching straight edges and enough copies of the same part to form a block. Free-form contours without common straight edges do not magically merge.

When it helps

Shops look at shared cutting when:

• The order has many identical parts with long straight sides (rectangles, trapezoids with matching edges).
• Material is expensive enough that cut metres and pierces matter, and sheet count stays stable.
• The controller and process allow common-line strategies your CAM would also accept.

Always compare sheet count, cut length, pierces, and price with the option off and on. A shorter cut that adds a sheet is usually not a win.

Limits and failure modes

Common limits in practice:

• No matching straight edges among copies — nothing to join.
• Quantity too low — blocks typically need at least two copies of the same part.
• Extra sheet — shared blocks pack worse overall; an added sheet costs more than the cut saved.
• Idle travel grows — cut shortens but rapid moves rise, so machine time can worsen.

Grain locks, fixed rotation, or process rules that forbid certain mirrors can also shrink candidate edges. Treat shared cutting as an option to measure, not a default for every DXF.

In AllTerra Calculator

On the live order form at calc.1cterra.ru, Shared cut is a user-facing checkbox (Russian/English/German UI). A field hint explains that copies of the same part with matching straight edges are grouped into a block before nesting and cut on a shared line, so cut length and pierce count drop by the shared edges.

Company defaults can remember default_joint_cut with other order defaults. The flag is sent with the calculation request as joint_cut.

Results can report shared-cut joints and metres of cut saved. If the strategy is not applied, the UI can explain why: no matching edges, extra sheet versus baseline, or not profitable because idle travel / machine time grew. Partial application is possible: blocks kept for some part types and skipped for others when a full block set would add sheets.

Nest preview paths may warn that shared cutting is not supported in some preview modes — that warning is about preview capability, not about removing the order checkbox. Production calculation still follows the joint-cut pipeline when enabled.

Verified on the live product code path: OrderPage Shared cut checkbox + hint.jointCut; result strings for joints, partial apply, no edges, extra sheet, and not profitable.

How to evaluate it on a real order

Run the order once with Shared cut off and once on. Compare sheets, utilisation, cut length, pierces, and final price. Keep the better commercial result, not the prettier buzzword.

If the UI says shared cut was not applied, read the reason. Fixing geometry (more identical copies, straighter matching edges) may help more than forcing the flag.

Shared cutting interacts with spacing and kerf: common lines change how edges meet, but your gap and process rules still apply elsewhere on the sheet.

For packing context see the nesting engine and DXF nesting pages. For money impact see the cost calculator. Return to the guides index for related articles.

Operators care about slag and heat on shared edges. Even when the calculator shows a shorter cut, confirm your process allows common-line strategies on that thickness and gas. Software savings that the floor will refuse are not quote savings.

Identical parts with grain lock (direction of brush or film) may lose candidate rotations that would have created matching edges. If Shared cut stops finding blocks after you lock grain, that is expected geometry, not a random failure.

Partial application messages matter: some part types may nest as blocks while others stay separate. Read the kept-versus-total note before you tell a customer that “shared cut was on for the whole order.”

Pair shared-cut trials with the time-estimation guide: cut metres saved are only half the story if idle travel and machine time move the other way. Price follows the full machine-time core in AllTerra, not cut length alone.

Keep a short internal note on which part families benefit from Shared cut in your shop — for example rectangular flanges in batches of ten or more. New estimators can start from that list instead of enabling the checkbox on every mixed artistic nest.

If preview warns that shared cutting is unsupported in a preview path, still trust the calculation result strings after a full order run. Preview limitations and production joint-cut evaluation are separate stages in the live product.