Glossary and FAQ

Glossary: Kerf width

Kerf width is the width of the cut made by the plasma torch. When defining a plasma tool in SheetCam you set the kerf width to match the actual cut width produced by your torch. The software uses the kerf value to offset the toolpath so that the finished part dimensions are correct.

Glossary: Feed rate

The feed rate is the speed at which the plasma torch moves along the programmed path. In SheetCam you specify a feed rate for each tool; the controller uses this value to determine how fast to cut. A slower feed produces more dross and wider kerf, while too fast a feed causes lagging and bevelled edges.

Glossary: Pierce delay

Pierce delay is the time allowed for the plasma arc to punch through the material before the cut begins. A pierce delay that is too short will cause the torch to start moving before the hole is complete, resulting in misfires or a damaged edge. A longer delay may waste time but ensures a clean pierce.

Glossary: Pierce height

Pierce height is the distance between the torch and the workpiece when firing the plasma arc. For piercing you raise the torch higher than the cut height to prevent molten metal from splashing into the nozzle. The SheetCam manual notes that you should pierce "as high as possible but still low enough to allow the arc to transfer".

Glossary: Plunge rate

The plunge rate (sometimes called the plunge feed) controls how fast the torch moves from rapid clearance height down to cut height. Setting an appropriate plunge rate prevents the torch from crashing into the material and helps maintain a consistent start to the cut.

Glossary: Pause at end of cut

Some plasma cutters delay turning off the arc at the end of a cut. A “pause at end of cut” setting adds a brief wait after finishing a contour so the kerf is completely through the material, preventing gouging when the torch lifts.

Glossary: Lead‑in / Lead‑out

A lead‑in is a small path added before the start of a cut so the pierce occurs away from the final contour. A lead‑out is a short move at the end of a cut to finish the kerf cleanly. SheetCam offers arc, perpendicular and ramp lead‑ins; choosing the right type and length avoids dimple marks or undercuts on the part.

Glossary: Start point

The start point is the location on the drawing where the plasma torch begins cutting a contour. In SheetCam you can place and adjust start points manually. The start point marker appears as an orange “S,” and you can override default lead‑in and lead‑out lengths when space is limited.

Glossary: Nesting

Nesting refers to arranging parts on a sheet of material to maximize material usage and minimize waste. After creating operations in SheetCam you can drag parts or enter coordinates in the Pos X and Pos Y fields to position them before running the post processor.

Glossary: Torch height control (THC)

Torch height control (THC) is an automatic system that maintains the correct torch‑to‑work distance during cutting by monitoring arc voltage. When the arc voltage increases, the distance between the electrode and the plate has grown; when it decreases, the torch is too close. The THC samples the voltage and adjusts the torch up or down to keep the voltage at the set target. Consistent height improves cut quality and consumable life.

Glossary: Initial height sensing (IHS)

Initial height sensing (also called retract distance) is the process of finding the surface of the plate and retracting to the proper pierce height before firing the torch. IHS can be accomplished using motor stall detection, proximity sensors or electrical circuits that sense contact between the nozzle and the plate. Accurate initial height sensing ensures that the pierce occurs at the correct height and protects the consumables.

Glossary: Standoff (torch‑to‑work distance)

Standoff is the distance between the plasma torch and the material during cutting. The torch height control maintains the standoff by measuring arc voltage: as the distance increases, voltage rises; as it decreases, voltage falls. Maintaining the correct standoff is critical for cut quality and consumable life.

FAQ: Why won’t my torch fire?

[Inference] If the torch does not fire, first ensure that the plasma power source is on and that all safety interlocks (e.g., air pressure sensors, torch‑cap switch) are satisfied. Check that the machine has performed its initial height sensing cycle and is at the correct pierce height. Inspect consumables for wear and verify that the control software’s output pins are mapped correctly to the plasma start signal. A mis‑set pierce delay or cut height can also cause the arc to fail to transfer.

FAQ: How do I set the kerf width in SheetCam?

Open the Tool dialog (Create a new jet cutting tool). Choose the plasma tool type and enter a tool number and name. In the settings area enter the Kerf width to match the actual width of the cut produced by your torch. Using the correct kerf width ensures that offsets are accurate and that parts cut to size.

FAQ: What is the proper pierce delay for my material?

Always consult the cut charts provided by your plasma system manufacturer for recommended pierce delays based on material thickness. In general the pierce delay should be long enough for the arc to penetrate the material, but not so long that molten metal builds up. For thicker material you need a longer pierce delay; for thin sheet metal you can reduce it.

FAQ: How do I adjust the torch height control (THC)?

Set the target arc voltage according to the cut charts for your plasma cutter. After initial height sensing and pierce, the THC samples arc voltage and moves the torch up or down to match the target. If cuts are showing positive bevel (top wider than bottom), the torch is too high; decrease the arc voltage. If cuts show negative bevel (bottom wider), increase the arc voltage. Always verify that the height control is enabled in your controller and that the voltage divider card is connected.

FAQ: Why do I need lead‑ins and lead‑outs?

Lead‑ins and lead‑outs allow the plasma torch to start and end the cut away from the final contour, preventing blowback and dross at the part edge. SheetCam lets you choose arc, perpendicular or ramp lead‑ins. Adjust their length so that the pierce takes place outside the finished geometry.

FAQ: How can I improve cut quality and reduce dross?

Proper machine setup and maintenance greatly affect cut quality. Make sure your gas flow and pressure are set correctly; too low produces a weak arc, while too high makes the arc unstable. Confirm that pierce height, cut height and arc voltage are correct: a pierce height that is too low splashes molten metal into the torch; too high causes the arc not to transferf. Match the cut speed to the material – moving too slow causes bubbly dross and a wide kerf, while moving too fast leaves a narrow kerf and a hard bead of dross. Finally, inspect and replace consumables regularly and choose the right consumables and amperage for the material thickness.

FAQ: How do I restart a cut after an interruption?

[Inference] To restart a cut, note the approximate line number where the program stopped or the last completed contour. In CommandCNC load the G‑code file, then use the “Run from line” or “Set next line” feature to move the program pointer to the appropriate line. Jog the machine back to the point where the cut should resume, ensure the torch is at the correct height, and restart the program. It is often best to add a small lead‑in segment or start slightly ahead of the interruption to ensure a smooth restart.