Why the lead-in matters more than most shops admit
A plasma cut does not start cleanly by accident. The torch has to pierce the plate, stabilise the arc and get moving before the cut edge settles into a consistent line. If the lead-in is too short, too sharp or placed in the wrong spot, that unstable start can leave a hard mark, extra dross, or a blown edge that needs grinding.
In a busy Gauteng job shop, that one bad start can turn into six or eight bad starts on the same sheet if the nesting is tight. On mild steel, stainless or aluminium, the problem is the same: the first few millimetres are where heat, slag and arc flare do the most damage.
The aim is simple. Get the torch into the material cleanly, keep the lead-in outside the finished profile, and give the cut enough distance to settle before it reaches the final edge.
Choose the lead-in shape for the job, not by habit
There is no single lead-in that suits every plate thickness or every machine. Straight lead-ins are quick and easy, but they can leave a visible mark on fine work. Arc or tangential lead-ins are often better for profiles that need a cleaner entry, especially on parts with a visible outer edge. For holes, a spiral or ramped entry may help reduce blow-back and keep the round more accurate.
- Use a straight lead-in for general cutting where speed matters more than appearance.
- Use an arc lead-in for better edge appearance on visible parts.
- Use a ramp or spiral entry for holes and internal features that need better roundness.
- Keep lead-ins away from corners, tabs and thin bridges where heat can build up.
On thicker plate, the lead-in also needs enough room for the arc to pierce fully before the profile starts. Too little distance and the entry gets rough. Too much distance and you waste cycle time. It is a balance, not a rule of thumb, and the right setting changes with amperage, plate thickness and gas setup.
Protect edge quality by placing the entry where the finish can take it
If a part has one hidden edge and three visible ones, put the lead-in on the hidden side. That sounds obvious, yet plenty of scrap starts come from parts being nested without thinking about the final inspection point. The lead-in should land on a section that can tolerate a small witness mark, not on a face that a client will see straight after cutting.
For cabinet work, signage, machine guards and brackets, the visible face is often the first thing customers inspect. A careless entry can mean extra filing, delayed powder coating and an unhappy customer. In coastal areas like Durban and Cape Town, humidity can make that rework worse because fresh cut edges start to oxidise faster if they sit too long before finishing.
- Place lead-ins on scrap side areas whenever possible.
- Avoid starting on sharp corners or narrow necks.
- Leave enough material around the entry point so heat does not distort the part.
- For thin sheet, keep the lead-in short enough to avoid unnecessary burn-back.
Match the lead-in to material thickness and machine condition
A 1.6 mm sheet does not behave like a 12 mm plate, and the same entry settings will not suit both. Thin sheet needs less heat build-up, so the lead-in should be short and controlled. Thicker plate needs a more patient start so the arc can pierce properly before the motion begins. If you rush the entry on heavy plate, the edge can break down near the start point and leave a wider heat-affected zone.
Machine condition matters too. Worn consumables, poor torch height control, slack mechanics and dirty earth connections all change how the lead-in behaves. A shop in Vereeniging that runs mixed material all week may find the same lead-in works on Monday and fails on Friday simply because the torch parts are tired. That is not a software issue alone, it is a setup issue.
A practical setting sheet should record the entry style, pierce height, cut height, pierce delay and feed rate together. If one is changed, the others should be checked too. Otherwise operators end up chasing faults one by one and blaming the wrong setting.
Signs your lead-in is costing you money
Bad lead-ins usually show up in the same few ways. The first is obvious dross right at the start of the cut. The second is a rough notch that needs grinding before the part can move to bending or welding. The third is a series of small defects that are easy to ignore on one sheet but expensive over a month.
- Start marks are deeper than the rest of the cut edge.
- Small holes are oval instead of round.
- Parts need extra hand finishing before assembly.
- Operators keep adjusting pierce settings to compensate for a poor entry path.
If these are showing up often, do not just slow the machine down and hope for the best. Check whether the lead-in is too short, too close to the final edge, or aimed at a section that simply cannot handle the heat. Many shops overcorrect with feed rate when the real fault is the entry geometry.
A Pretoria example from a mixed-workload plasma shop
A Pretoria shop cutting brackets, small signs and repair parts was losing time on cleanup because every small hole needed a second pass with a grinder. The main problem was not the torch or the plate it was the lead-in. Their internal profiles were starting too close to the finished edge, and the holes were using the same entry style as the outer cuts.
After changing the setup so the small holes used a more controlled entry and the visible outer faces used lead-ins on the least noticeable side, scrap starts dropped and the finishing bench cleared faster. The team also started saving successful settings by material and thickness, which made it easier for different operators to get the same result. On a busy week, that kind of consistency matters alot.
For shops working across Pretoria, Johannesburg and the East Rand, the lesson is simple. A few extra seconds in programming can save hours in cleanup later.
A simple lead-in checklist for day to day use
Before a job runs, ask the operator or programmer to check the entry points with the same discipline every time. That keeps surprises down and makes troubleshooting much faster when something does go wrong.
- Is the lead-in placed on a non-visible edge?
- Does the entry shape suit the feature size?
- Is there enough clearance for the torch path?
- Are pierce height and delay set for the material thickness?
- Are consumables in good condition before the job starts?
- Has the setting been tested on a small sample before full production?
In South African shops, this is especially useful when load-shedding or interrupted shifts break the rhythm of the day. A checked setup is easier to restart after a power cut than a job that was already marginal. Good lead-ins do not just improve cut quality. They protect time, labour and material, and that is where the real saving sits.
