Fiber Laser Not Cutting? Work Passes, Not Power
If your fiber laser isn't cutting through metal, don't just crank up the power. This guide from our workshop explains why focus, wobble, and the right number of passes are your real levers for success, especially with tricky sterling silver.
If your fiber laser isn't cutting through metal, you've probably already tried adding more power. We've been there. The immediate, frustrating symptom of a laser not cutting through is one we know well from our daily work with sterling silver. The good news is that for most cases, the problem isn't a weak laser or bad material. It's usually one of a few critical settings, and the solution rarely involves maxing out your power. Instead, you need to work the passes.
Here’s our troubleshooting checklist, from the easiest and most common fixes to the more subtle issues we've learned the hard way in our jewelry workshop.
1. Focus Height: The Number That Kills More Cuts Than Any Other
The single biggest reason a fiber laser doesn't cut through sterling silver, even with perfect parameters, is incorrect focus. The beam from a galvo fiber laser is incredibly precise, but that precision depends on hitting a tiny sweet spot. Even a small error here will cause your laser not to cut through.
On our machines, the factory-calibrated focus lives in EzCad3's Motors.ini as m_dFocusPos. For our setup, this value is -59.6 mm, representing the head position where the platform surface is in perfect focus. When you're cutting sheet metal that rests on the platform, the top surface of your material sits above the platform by its own thickness. This means your focus height calculation should always be: Z = focus + material thickness.
For example, if we are cutting 1 mm thick silver sheet, our Z-axis setting needs to be -59.6 mm + 1 mm = -58.6 mm. The consequences of getting this wrong are dramatic. We verified this the hard way: -58.5 mm cuts, but -56.5 mm does not cut at all. That's only 2 mm of defocus. A mere ±0.5 mm error can be barely noticeable, but 2 mm kills the cut completely.
For months, our own software seemed to need far more passes than EzCad3 for the same job. The reason wasn't power, protocol, or the source; our Z reference was about 2.1 mm too high, causing every cut to run out of focus. Fixing that reference immediately dropped our required pass count. If your cuts suddenly got worse, or your laser appears weaker, check your focus height before you touch anything else. A bent jig, a thicker batch of material, or even a platform that has shifted can all present as "the laser got weaker."
For a complete rundown, see our article: It Cut Fine Yesterday: Your Laser Focus Checklist.
2. Wobble: The Cutting Setting Nobody Explains
After focus, the next most common and frustrating reason for a laser not cutting through is an incorrect wobble setting. Cutting metal with a fiber laser relies on a technique called wobble, where the beam oscillates sideways as it follows the cut line. This creates a kerf (the width of the cut) that is wider than the beam itself. A wider kerf is crucial because it allows the molten metal to be ejected from the cut line instead of re-welding behind the beam as it passes.
Our working recipe for sterling silver uses a wobble with a diameter of 0.15 mm. This is a critical setting. We once had the wobble diameter set to 0.015 mm instead of 0.15 mm – a factor of ten error, just one decimal place off. The machine marked perfectly, drawing a thin line, but it would never open the cut. Everything else in the recipe was correct: power, speed, frequency, and passes were all set properly, yet the machine simply would not cut through.
A wobble that is too small (or effectively off) does not cut at all. So, if a recipe that used to cut suddenly only engraves a line, check the wobble diameter before you touch any other setting. It’s one of the most misleading failures on the machine, because the job looks like it’s running exactly as it should, just not going all the way through.
You can find more details about how to handle tiny parts and wobble in our related article: Cutting Tiny Jewelry Parts: Hold Them in Place and Get Them Right.
3. Work the Passes, Not the Power
Once your focus is spot on and your wobble is correctly configured, the primary lever for getting a fiber laser to cut through metal is the number of passes, not the power. Turning up the power on a job that won't cut usually just widens the kerf and heats the piece, leading to distortion and a messy cut, without actually getting you through the material any faster.
Our Sterling Silver Cutting Recipe
On our machine, with our 100 W MOPA source, we use the following common recipe for cutting sterling silver sheet on the platform:
- Power: 95 %
- Speed: 190 mm/s
- Frequency: 60 kHz
- Wobble: Enabled (with diameter 0.15 mm, end diameter 0.05 mm, distance 0.07 mm)
With these settings, here are the pass counts we actually use for sterling silver:
| Silver Thickness | Passes (Our Machine) |
|---|---|
| 0.8 mm | 17 |
| 0.9 mm | 21 |
| 1.0 mm | 28-29 |
These numbers are from our machine and our material; treat them as a starting point, not a universal rule. Fitting these three real points gives a curve of roughly passes ≈ 27.5 × thickness^2.23 (thickness in mm). This equation predicts thinner recipes well (e.g., 0.3 mm might need ~2 passes, 0.5 mm around ~6), but every derived recipe must be proven on scrap before it goes near a real piece.
Frequency for Cutting vs. Engraving
It's important to note that frequency behaves the opposite way in cutting and in engraving. For cutting through metal, higher frequency wins. We tried dropping the cut frequency to 20 kHz (which creates fat pulses, ideal for deep engraving) on 0.3 mm silver, and it cut worse—16 passes and it still didn't go through. Back at 60 kHz, it cut in a handful of passes. For actual cutting, you want the high frequency. For surface ablation depth and deep engraving, lower frequency and fatter pulses are more effective.
4. Reflectivity: Why Silver is Hard and Gold is Easy
Understanding material properties is key when your fiber laser not cutting through. A fiber laser operates at 1064 nm, and its effectiveness depends entirely on how much of that beam is absorbed by the material. The more a metal reflects the laser, the more power simply bounces off instead of doing work.
Sterling silver is the most challenging of the common precious metals for this. It is the most reflective metal there is, and an excellent heat conductor. This means it both rejects a significant portion of the beam and quickly carries away any heat that does get into the material. This is precisely why it needs so many passes to cut through, as shown in our table above.
Gold, by contrast, reflects less of the 1064 nm beam, and the difference on the bench is obvious. The laser works very well on gold: it cuts and engraves more easily than silver, using the same machine and the same operator. If you have only ever cut silver, cutting gold will feel like your machine suddenly got a significant upgrade.
Cutting Gold: Starting Points
The good news is that the core cutting recipe doesn't change from silver to gold: 95 % power, 190 mm/s, 60 kHz, with wobble enabled. Only the number of passes changes. Gold absorbs more of the beam, so it needs fewer passes. In practice, our derived gold table works out at roughly half the passes we use on silver for the same thickness. Remember, these are derived figures and starting points for a typical yellow gold, not measured in metal. Always prove them on scrap first:
| Gold Thickness | Gold Passes (Starting Point) |
|---|---|
| 0.25 - 0.4 mm | 2 |
| 0.5 mm | 3 |
| 0.6 mm | 4 |
| 0.7 mm | 6 |
| 0.8 mm | 9 |
| 0.9 mm | 11 |
| 1.0 mm | 14 |
For comparison, our measured silver at the same settings requires 17 passes for 0.8 mm, 21 for 0.9 mm, and 28-29 for 1.0 mm. Always start low and work up. A cut that doesn't go through just needs one more pass; a cut with far too many passes widens the kerf, heats the piece, and can distort thin sections. Gold is expensive to learn on.
Karat and alloy change everything. 18k yellow is not 14k, and white gold behaves differently due to its alloying metals. Never judge a machine, a recipe, or your own skill on silver alone; it is the hardest common case.
5. The Board's Buffer: When Big Jobs Drop Passes Silently
This is a more subtle failure mode that can make it seem like your laser is weak or your settings are suddenly off, especially on larger or more complex jobs. Your PC sends the job to the laser controller board (like a JCZ DLC2) as a stream of lists. The board buffers these commands and then drives the galvos and laser source in real time. This buffer is finite – on our board, it's typically a few hundred lists, in the order of a couple of megabytes.
On a big cut with many passes over extensive geometry, it's possible for the PC to send commands faster than the board can actually mark them. Once the board's buffer is full, further lists of commands can be silently dropped. You might have programmed for 39 passes, but the metal only received 25. The symptom checklist includes: big jobs cutting worse per pass than smaller ones, the machine going quiet long before the software says the job is done, and adding passes helping less than it should. Our operators' reaction to this was always to add more passes, which simply hid the underlying bug and wasted time and consumables. If you suspect this, check your machine's behavior on a small, simple cut versus a large, complex one with many passes.
6. Calibrating a Metal You've Never Cut Before
The key to success with any new metal or thickness is a methodical calibration process. Never calibrate on a real piece; always use scrap of the same alloy and thickness. Change only one variable at a time. A grid of speed against power, with each square marked with its own settings, will tell you more in ten minutes than an afternoon of guessing.
- For cutting, find the pass count that just barely goes through, then add a small margin (one or two passes). Going far beyond that widens the kerf, heats the piece, and can distort thin sections.
- Write down your winning recipe immediately: material, thickness, power, speed, frequency, passes, and focus height. A recipe missing any of these details is not reproducible.
- Recalibrate whenever anything in the chain changes: a new material supplier, a different alloy, a new jig height, or even after cleaning your optics. "It worked last month" is not a setting.
- Recipes are not transferable between metals. Our silver curve does not predict gold, and gold needs its own two or three calibration points before you trust any of it.
For a detailed guide on this process, refer to our article: Calibrating a Metal You've Never Cut Before.
Safety First: A Quick Reminder
A fiber marking laser is a Class 4 device. The 1064 nm beam is invisible and can cause permanent eye damage instantly and silently, even from reflections. Laser safety glasses rated for 1064 nm (with an OD suitable for your source power) must be worn by everyone in the room, always. Metal is a mirror, and reflections go everywhere. Never leave a running job unattended. Metal marking produces metal fume and fine particulate, so extraction with a proper filter is health equipment, not an accessory.
Practical Takeaways: What to Check First
When your fiber laser not cutting through, resist the urge to just increase power. Follow this order:
- Check Focus: This is almost always the culprit. Verify your Z-axis height using Z = focus + material thickness. A small error here makes a huge difference.
- Check Wobble: Ensure the wobble diameter is set correctly (e.g., 0.15 mm for silver cutting). A tiny wobble acts like a thin line and won't cut through.
- Add Passes: Once focus and wobble are correct, systematically add passes. This is the most effective way to cut through metal cleanly, especially reflective metals like silver.
- Consider Your Material: Understand that highly reflective and conductive metals like silver are inherently harder to cut. Adjust your expectations and pass counts accordingly.
- Calibrate Methodically: For new materials, always calibrate on scrap, changing one variable at a time, and meticulously record your settings.
By following these steps, you’ll likely solve your "laser not cutting through" problem and achieve reliable cuts, saving both time and precious material.