<p>There are few possible scenarios that come to my mind:</p>
<p><strong>Fire hazard</strong></p>
<p>If the risk of incinerating the material is too high, because the laser needs to move slowly to cut all the way through, it's better to cut in several passes instead.</p>
<p><strong>Melting material</strong></p>
<p>If the material has the tendency to melt at the cut edges (instead of evaporating cleanly) but you need high power to cut all the way through, you can end up with unclean cuts that are wider at the top than the bottom. This is due to the top receiving more laser light and therefore more heat, which causes more melting. It might be beneficial to cut only partway through and letting the area cool down before the next pass cuts further through the material.</p>
<p><strong>Refocusing for thick material</strong></p>
<p>When cutting thick material like plywood, it may be beneficial to change the focus distance of the laser between cutting the upper and lower layers. However, you must be extremely cautious not to move the material around or the next pass will cut in a different location and ruin everything.</p>
<hr />
<p>In my hobby-level experience with laser cutters it was always safest to cut all the way through in one pass. Every pass increases the risk of <em>something</em> going wrong, simply because there is more time and movement involved that can go wrong.</p>
<p>You won't reduce the charring of the edges, because the laser has to burn all the way through anyways. You might reduce the amount of soot that forms a shadow at the cutting edges, but only if you have any air extraction at all and that extraction is too weak to remove the soot in a single pass.</p>

CC BY-SA 4.0
2023-08-29T20:37:07.360Z
The sooting up can be materially reduced by placing an adhesive-backed layer over the material.
Pekka
CC BY-SA 4.0
2023-09-09T19:52:32.777Z
@AaarghZombies I added a new paragraph after an *extremely frustrating* experience with a horrible material that started melting at the top before the laser could get all the way through. Full power left a charred and uncleanly melted edge behind, while 3 passes with half power were much cleaner because the material had time to cool between passes. Needless to say the cutting failed twice because there were 3 times more chances of *something going wrong*.
Elmy
CC BY-SA 4.0
2023-10-03T18:19:19.227Z
Using an adjustable hole cutter would allow sufficient clearance to cut even a large hole on a spherical surface due to the longer arms of the tool. Carbon steel thicker than typical sheet could be near the limit of what is a good idea. With the correct tool, a large diameter boring head for a milling machine could provide the power and rigidity to perform the cut reliably and safely.
Pekka
CC BY-SA 4.0
2023-07-10T07:27:35.093Z
2023-09-09T19:45:16.930Z
2023-09-09T19:45:16.930Z
Elmy
<p>Under what circumstances would it be preferable to choose to cut or engrave using multiple lower powered passes rather than a single higher powered pass with a diode laser?</p>
<p>Please presume a material that burns rather than melts (for example, cutting wood or leather, rather than ABS).</p>

<cutting><tool-usage>
When would multiple low power passes of a laser be preferential to a single higher powered pass?
Aaargh Zombies
# When would multiple low power passes of a laser be preferential to a single higher powered pass?

(Asked by: username_0 on 2023-07-09)

Under what circumstances would it be preferable to choose to cut or engrave using multiple lower powered passes rather than a single higher powered pass with a diode laser?

Please presume a material that burns rather than melts (for example, cutting wood or leather, rather than ABS).

**Tags:** cutting, tool-usage


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## 1 answers

### Answer by username_1 on 2023-07-10. Score: 2

There are few possible scenarios that come to my mind:

**Fire hazard**

If the risk of incinerating the material is too high, because the laser needs to move slowly to cut all the way through, it's better to cut in several passes instead.

**Melting material**

If the material has the tendency to melt at the cut edges (instead of evaporating cleanly) but you need high power to cut all the way through, you can end up with unclean cuts that are wider at the top than the bottom. This is due to the top receiving more laser light and therefore more heat, which causes more melting. It might be beneficial to cut only partway through and letting the area cool down before the next pass cuts further through the material.

**Refocusing for thick material**

When cutting thick material like plywood, it may be beneficial to change the focus distance of the laser between cutting the upper and lower layers. However, you must be extremely cautious not to move the material around or the next pass will cut in a different location and ruin everything.

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In my hobby-level experience with laser cutters it was always safest to cut all the way through in one pass. Every pass increases the risk of *something* going wrong, simply because there is more time and movement involved that can go wrong.

You won't reduce the charring of the edges, because the laser has to burn all the way through anyways. You might reduce the amount of soot that forms a shadow at the cutting edges, but only if you have any air extraction at all and that extraction is too weak to remove the soot in a single pass.

> **Comments:**
> **username_2**: The sooting up can be materially reduced by placing an adhesive-backed layer over the material.  
> **username_1**: @AaarghZombies I added a new paragraph after an *extremely frustrating* experience with a horrible material that started melting at the top before the laser could get all the way through. Full power left a charred and uncleanly melted edge behind, while 3 passes with half power were much cleaner because the material had time to cool between passes. Needless to say the cutting failed twice because there were 3 times more chances of *something going wrong*.  
> **username_2**: Using an adjustable hole cutter would allow sufficient clearance to cut even a large hole on a spherical surface due to the longer arms of the tool. Carbon steel thicker than typical sheet could be near the limit of what is a good idea. With the correct tool, a large diameter boring head for a milling machine could provide the power and rigidity to perform the cut reliably and safely.  

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