Troubleshooting Cut Quality: Solving Dross and Taper Issues on Your CNC Plasma Table

Nothing's more frustrating than watching your plasma cutter complete a job, only to find excessive slag clinging to your parts or beveled edges that don't meet spec. Cut quality issues like dross and taper can turn profitable jobs into costly rework nightmares. The good news? Most cut quality problems have straightforward solutions once you understand what's causing them.

Whether you're running a StarLab CNC plasma table in a professional fabrication shop or your home garage, this guide will help you diagnose and fix the most common cut quality issues: dross buildup and edge taper.

Understanding Dross: The Enemy of Clean Cuts

Dross (also called slag or spatter) is re-solidified molten metal that doesn't blow clear during the cutting process. Instead, it adheres to your workpiece—usually along the bottom edge, but sometimes on top—creating rough edges that require grinding, chipping, or sanding before parts can move to the next phase of production.

While some minimal dross is inevitable with air plasma systems, excessive buildup indicates something in your cutting process needs adjustment.

Types of Dross You'll Encounter

Low-Speed Dross
Appears as a thick, bubbly accumulation resembling a weld bead along the bottom edge. This dross forms when your torch moves too slowly, causing the plasma arc to expand and widen. The gas velocity can no longer effectively blow away all the molten metal, resulting in heavy slag buildup.

Characteristics: Solid bead-like formation, easily removed with a hand scraping tool
Primary cause: Cutting speed too slow for the amperage and material thickness

High-Speed Dross
Shows up as hard, dotted globs of uncut metal on the bottom of the plate. When cutting too fast, the plasma arc lags behind the torch, and the high-pressure gas at the nozzle orifice can't keep up with material removal.

Characteristics: Dotted or beaded appearance, difficult to remove (requires grinding)
Primary cause: Cutting speed too fast for the amperage being used

Top Spatter Dross
An accumulation of re-solidified metal along the top edge of the cut. The swirling plasma jet flings molten material forward instead of down through the kerf.

Characteristics: Light accumulation on top surface, usually easy to remove
Primary causes: Worn consumables, excessive cutting speed, or torch height too high

Corner Dross
Appears at direction changes and tight corners where the machine slows down or dwells. This is a normal occurrence when cutting intricate patterns with many corners.

Characteristics: Minimal accumulation at corners only
Primary cause: Machine slowdown during direction changes

Troubleshooting Dross: Your Action Plan

Step 1: Check Your Consumables First

Before adjusting any parameters, inspect your consumables. Worn cutting tips, electrodes, and nozzles are the number one cause of dross problems.

What to look for:

• Nozzle orifice showing signs of wear, gouging, or elliptical shape
• Electrode with excessive cratering or pitting
• Shield damage or deformation
• Any consumable past its recommended life span

Solution: Replace worn components. Fresh consumables often solve dross issues immediately.

Step 2: Adjust Cutting Speed

Finding the "dross-free window"—that sweet spot between too fast and too slow—is key to clean cuts.

For Low-Speed Dross:

• Increase cutting speed in 5 IPM increments
• Monitor results after each adjustment
• Stop when dross is minimized
• Check cut charts to ensure you're within recommended speed ranges

For High-Speed Dross:

• Decrease cutting speed in 5 IPM increments
• Verify you're not exceeding material capacity
• Look for vertical lag lines instead of slanted S-shaped lines
• Use manufacturer's cut charts as a baseline

Pro Tip: Watch the arc during cutting (through appropriate welding lens). For air plasma, the arc should exit vertically from the bottom of the workpiece. If the arc lags at an angle, you're cutting too fast.

Step 3: Optimize Torch Height

Your StarLab CNC's Torch Height Control (THC) system maintains optimal standoff automatically, but you still need to set the correct target voltage for your material.

For Low-Speed Dross:

• Raise arc voltage setting in 2-volt increments
• This increases torch height slightly
• Monitor for improvement

For High-Speed Dross:

• Lower arc voltage setting in 2-volt increments
• Reduce torch standoff distance
• Test cuts between adjustments

For Top Spatter:

• Lower arc voltage (reduce torch height)
• Decrease cutting speed
• Verify consumables aren't worn

Step 4: Fine-Tune Amperage

Using the correct amperage for your material thickness is crucial for dross-free cutting.

General Guidelines:

• Use the lowest amperage consumables that will cut your material
• Don't exceed 95% of the nozzle orifice rating
• Refer to your plasma cutter's cut charts for recommended amperage
• For thin materials (16 gauge and lighter), use fine-cut consumables at lower amperage

Step 5: Verify Air Quality and Pressure

Poor air quality or insufficient pressure causes numerous cut quality problems.

Requirements:

• Maintain at least 90-100 PSI at the plasma cutter inlet (not just at the compressor)
• Use quality filters and moisture separators
• Change filters regularly
• Ensure proper CFM delivery for your plasma system
• Check for air leaks in lines and fittings

Understanding Taper and Bevel

Taper (also called bevel or angularity) refers to the angle of the cut edge relative to the material surface. A cut with zero degrees bevel is perfectly perpendicular to the plate—though achieving this with air plasma systems is nearly impossible due to the physics of the cutting process.

What's Normal vs. What's a Problem

Normal Taper:

• Air plasma systems: 1-8 degrees typical
• "Good side" (right side with torch moving away): 1-3 degrees
• "Bad side" (left side): 3-8 degrees
• Slight taper is inherent to the plasma process

Problem Taper:

• Consistent bevel greater than 8-10 degrees
• Unequal bevel (positive on some sides, negative on others)
• Parallelogram-shaped parts instead of square
• Taper varying significantly around the same part

Positive vs. Negative Bevel

Positive Bevel (Top Wider Than Bottom):
The kerf is wider at the top of the cut than the bottom, creating an outward taper.

Primary causes:

• Torch height too high
• Cutting speed too fast
• Amperage too low
• Worn nozzle

Negative Bevel (Bottom Wider Than Top):
The kerf is wider at the bottom, creating an undercut.

Primary causes:

• Torch height too low
• Cutting speed too slow
• Amperage too high

Unequal Bevel (Mixed Positive and Negative):
Different sides of the same part show different bevel angles.

Primary causes:

• Torch not perpendicular to the table
• Damaged or misaligned consumables
• Electrode and nozzle centers not aligned
• Inconsistent torch height control in different axis directions

Troubleshooting Taper: Your Solution Guide

Check Torch Perpendicularity

The torch must be perfectly square to the cutting surface.

How to verify:

• Use a machinist's square against the torch body
• Check from multiple angles (front, side)
• Measure with the torch at cut height
• Even 3-5 degrees off can cause severe beveling

Solution: Adjust torch mounting until perfectly perpendicular in all directions.

Optimize Torch Height for Material Thickness

Torch height has the greatest effect on bevel angle.

General principle:

• Higher torch = more positive bevel (top wider)
• Lower torch = more negative bevel (bottom wider)
• Find the middle ground for minimal taper

Your StarLab CNC's THC advantage: The automatic torch height control helps maintain consistent standoff, but you need to set appropriate target voltage for your specific material and thickness.

Recommended approach:

• Start with manufacturer's recommended voltage for your material/thickness
• Make test cuts and measure bevel with a protractor or bevel gauge
• Adjust voltage in 2-volt increments
• Document successful settings for future reference

Match Speed to Amperage and Material

Incorrect cutting speed is a major contributor to excessive taper.

Guidelines:

• Follow cut chart recommendations as a starting point
• Slower speeds generally reduce taper but increase dross risk
• For holes, reduce speed to approximately 60% of straight-line speed
• Maintain consistent speed (avoid acceleration/deceleration during cuts)

Use Appropriate Consumables

Using the correct amperage-rated consumables for your material thickness dramatically improves cut angularity.

Best practices:

• Use the lowest amperage consumables that will cut your material
• Fine-cut or precision consumables produce better angularity on thin materials
• Replace consumables showing any wear or damage
• Verify proper consumable assembly per manufacturer specs

Special Considerations for Holes

Holes are inherently more challenging due to the continuous directional changes.

Hole quality tips:

• Rule of thumb: Hole diameter should be at least equal to material thickness for best results
• Smaller holes will have more taper
• Use longer lead-ins (at least 0.25" for most applications)
• Cut holes at 60% of straight-line speed
• Some low-speed dross is acceptable to minimize taper in holes
• Consider using radial or curved lead-ins for better acceleration

The Role of THC in Cut Quality

Your StarLab CNC plasma table's integrated Torch Height Control system is your first line of defense against cut quality issues. Here's how THC helps:

Consistent Standoff: Automatically maintains target arc voltage throughout the cut, compensating for warped material and uneven surfaces.

Reduced Taper Variation: Keeps torch-to-work distance constant, minimizing inconsistent bevel angles.

Better Dross Control: Proper standoff helps maintain optimal cutting conditions in the dross-free window.

Adaptation to Material Conditions: Responds to plate warpage, temperature changes, and surface irregularities in real-time.

While THC is essential, remember it maintains the height you tell it to maintain. You still need to set the correct target voltage for your specific application.

Best Practices for Consistent Cut Quality

Document Your Success

When you find settings that work well for a specific material and thickness, write them down:

• Material type and thickness
• Amperage setting
• Target arc voltage
• Cutting speed (IPM)
• Pierce height and delay
• Any special notes

Establish a Pre-Cut Checklist

Before starting production runs:

• Inspect consumables for wear
• Verify air pressure at cutter inlet (90+ PSI)
• Check that work clamp is secure
• Confirm THC is functioning properly
• Run a test cut to verify settings

Perform Regular Maintenance

Daily:

• Clean slag from cutting area
• Check consumables for visible wear
• Drain moisture from air filters

Weekly:

• Deep clean torch and consumables
• Inspect air system for leaks
• Check THC sensor operation

Monthly:

• Replace air filters
• Inspect electrical connections
• Calibrate THC if needed
• Review and update cut parameters database

Material Matters

Remember that material quality affects cut quality:

• Lower-grade steel often has more impurities leading to increased dross
• Painted, galvanized, or rusty material requires different parameters
• Material temperature affects dross adhesion (hot material = more sticking)
• Sheet flatness impacts THC performance

Advanced Troubleshooting Scenarios

Scenario: Good Cuts Then Suddenly Dross Appears

Most likely causes:

1. Consumables just reached end of life
2. Air pressure dropped (compressor issue or demand elsewhere)
3. Material changed (different thickness or quality)
4. Arc voltage drifted from optimal setting

Action: Replace consumables first, then verify air pressure.

Scenario: Cuts Fine on Simple Parts, Dross on Intricate Designs

Cause: Machine slowdown at corners and direction changes builds heat and creates low-speed conditions.

Solutions:

• Accept that some corner dross is normal on intricate cuts
• Use lead-outs on corners to allow arc to stabilize
• Slightly increase cutting speed on straight sections
• Plan for light dross removal as part of the process
• Consider using plasma-specific design practices (corner loops, larger radii)

Scenario: Bevel Changes Depending on Cut Direction

Cause: Torch not perpendicular to table, or mechanical issues with one axis.

Actions:

• Re-square the torch
• Check for mechanical binding or backlash in gantry
• Verify cut height is consistent in all directions
• Test with consumables from different batch

Scenario: Perfect Settings Yesterday, Problems Today

Common causes:

• Different material batch (thickness variation or quality)
• Ambient temperature changes affecting air system
• Consumables nearing end of life
• Air compressor losing performance

Action: Start with fresh consumables and verify air supply before changing other parameters.

When to Accept "Good Enough"

Here's the truth: With air plasma systems, achieving absolutely perfect, zero-dross, zero-bevel cuts on every piece—especially intricate designs with tight corners—is unrealistic. Professional fabricators know when to optimize for production speed versus when to chase perfection.

Factors to consider:

• Will the part be visible in final assembly?
• How tight are dimensional tolerances?
• Is light dross removal acceptable in your workflow?
• What's the cost of additional setup time versus quick cleanup?

Many successful shops run "95% dross-free" as their target, accepting that some minimal cleanup is faster than endlessly tweaking settings.

Quick Reference Guide

Dross Solutions at a Glance

Taper Solutions at a Glance

Frequently Asked Questions

Q: Why do I get more dross when cutting thinner materials?
A: Thin materials heat up quickly and have less thermal mass to absorb the plasma energy. The narrow kerf means less room for molten metal to escape. Use lower amperage fine-cut consumables and higher speeds for thinner materials.

Q: Can I eliminate bevel completely with my StarLab CNC table?
A: Some bevel is inherent to air plasma cutting due to the physics of the plasma arc. You can minimize it to 1-3 degrees on the good side with proper settings, but zero bevel throughout requires high-definition plasma systems. Focus on achieving consistent, acceptable bevel rather than perfection.

Q: How often should I replace consumables?
A: It depends on usage, but watch for: enlarged or elliptical nozzle orifice, electrode cratering, arc wandering, increased dross, or declining cut quality. Don't wait for catastrophic failure—replace at first signs of wear.

Q: My THC is working but I still have cut quality issues. What gives?
A: THC maintains the height you set, but can't compensate for incorrect target voltage, worn consumables, poor air quality, or wrong cutting speed. THC prevents problems caused by warped material and surface variations, but you still need correct base parameters.

Q: Should I use different settings for mild steel vs. stainless vs. aluminum?
A: Absolutely! Each material has different melting points, thermal conductivity, and cutting characteristics. Always reference your plasma cutter's cut charts for material-specific settings. Generally: mild steel is easiest, stainless requires slower speeds, aluminum needs special attention to prevent dross.

Q: What's the single most important factor for cut quality?
A: Fresh, quality consumables. More cut quality problems are solved by simply replacing worn consumables than any other single change. Don't try to squeeze every last arc out of a worn nozzle—it's false economy.

The Bottom Line

Achieving excellent cut quality on your StarLab CNC plasma table isn't magic—it's methodical troubleshooting, proper maintenance, and understanding the relationship between cutting variables. Your integrated THC system handles one of the most challenging aspects (maintaining consistent height), giving you a head start on quality cuts.

Start with quality consumables, follow manufacturer recommendations, make incremental adjustments, and document what works. Before long, you'll develop an intuition for reading your cuts and making corrections quickly.

Remember: the goal isn't perfection on every single cut. The goal is consistent, predictable results that meet your application requirements while maintaining productive cutting speeds. Sometimes that means accepting minimal dross that's quickly removed rather than spending hours finding the absolute perfect settings for every scenario.