Hi there,
I am trying to use the work-origin method (start laser job on the machine without laptop). This worked fine, but I would like to know about the safety of the 10W laser. I have trouble setting the work origin with the goggles on, as I barely see the blue dot, nor do I see my manual markings on the stock to align them.
Am I supposed to take the goggles off when adjusting the work origin, is that blue dot safe to see? I guess it’s a percentage of the actual laser power.
Thanks!
If you have a source of replacement retinas for your eyes, feel free to ignore laser safety practice.
If you don’t, however, you can burn a calibration image onto a preprinted, calibrated test card. One pass to measure and a second pass to verify should be sufficient.
This is not about calibration, but about exact placement of the work piece (“work origin method”).
It’s the same answer. Put a calibration card on top of the work piece.
I’m sorry, but this is not my question. I need to mark a precise position on the work piece that I can align with the ‘work origin’ blue dot. The question is if the work origin blue dot should only be seen via goggles or not, because with the goggles that dot is very faint for me, and I would need to use a particularly strong contrast on the work piece to actually find the alignment point. Putting a card on the work piece doesn’t help, it’s not about Z spacing.
Nothing I’ve said is about Z spacing.
Then how does putting a calibration card on top of my work piece help me determine the work origin?
Something you can try that has helped me in the past. Use the camera on your phone to view the piece under the laser. Sometimes it magnifies the image and amplifies the light enough for me to see what I need while wearing the goggles.
You can also use your camera to take a picture and then view it without goggles when you are safely away from the laser.
TL;DR: To be on the safe side, wear goggles.
Full story:
According to this post the laser power when the door of the enclosure is open is set to 0.5%. On first glance, that would be 50mW for the 10W laser and safe to look at. BUT. In order to assess the risk, you need to understand how laser power is controlled. It is not that the laser is really set to 50mW, but the method used is pulse width modulation (PWM). This means that the laser is switched on and off in rapid succession, depending on implementation a few ten to several thousand times per second. It is “switch on laser for time x, switch it off for time y, repeat.” The ratio between x/y determines the average power the laser emits. E.g. is the laser is switched on for 0.25 ms and switched off for 0.75 ms each cycle, the average power emitted would be 25%, i.e. 2.5 W. However, during the 0.25 ms switched on, the laser emits the full 10 W, in the 0.75 ms 0 W. If 0.25 ms of 10 W laser directly hitting your eye would be enough to create damage, then you should always wear goggles.
With Snapmaker 2.0, when I looked in the source code two years ago or so, the PWM frequency they used was ~100 Hz (pretty low). So 100 on/off cycles per second. One cycle would be 10 ms, with 0.5% duty cycle that would mean a 10 W laser pulse of 50 µs every 10 ms. Is this enough to damage your eye on a direct hit? Honestly, I don’t know, I guess with a bit of research you could find out.
Last thing that goes into the equation: Reflection. If the laser hits material that reflects the light diffusely, like e.g. white paper or wood, the 10W laser power are widely distributed and become harmless very quickly with distance. The danger comes in if you get a beam reflection, like e.g. from a mirror or a piece of metal (like the screws that hold down your laser platform). A direct beam hit to your eye is what is most dangerous, and my cause irrepairable damage within fractions of a second.
I personally can feel your pain handling work origin with goggles on. Also, the color scheme of the touchscreen is a bad choice with amber goggles, it is difficult to handle it with goggles on. So I personally do work origin without goggles IF I can be pretty sure that I’ll have no direct reflection, i.e. the material is not shiny/reflective like a mirror anywhere near the work origin AND there is basically no risk of accidentily moving off the material and hitting something metallic by a mistake press on the touch screen. But this is me taking the risk, I do NOT encourage you to follow my example. And: I am not an expert, just a lay man like you.
So again: long story short - wear goggles all the time the laser is on.
The alternative is to follow the posts on using Lightburn, ok the licene is £52 but you get 2 of them so you could share if thats permitted. This way you know where your 0,0 is all the time. It takes a bit of setting up but if I can do it anyone can the image shows how I place my work every time.
The strips are printed with flexible filament and are very secure. The design is based on this https://www.thingiverse.com/thing:4601778.
Always put safety first where eyesight is concerned.
Hope this helps
Graeme
Thanks, the PWM explanation seems a reasonable warning not to drop the goggles, and the camera solution or adding a defined border ruler seem good approaches, I will try these.
Your question triggered me reading a bit around, verifying that my statement above is still true. It certainly was with the 1.6 W laser, because the PWM pulses resolved into individual dots a higher laser movement speeds - see here. But I just learned that there are more sophisticated circuits which do “true” laser power control by finely controlling the current through the laser diodes and using optical feedback to ensure stable operation - if they use this in the 10 W laser, 0.5% may really mean 50 mW constant output power, and then it would be safe to look on that dot. I guess when I’ve a bit more time at my hands, I may look a bit deeper.
We know for a fact that the Snapmaker uses PWM from both the code and the circuit design. The Snapmaker does not use a constant current design.
Did anyone reverse engineer the 10W module? It seems that there exist circuits that receive PWM as control signal, but convert it to constant current. Are we sure that this is not inside the module? Not that I really expect this, but I’d be curious.
I have the same problem, especially when engraving on a dark material such as slate coasters. Here’s what you do: Make sure you clearly mark your origin. Get a good little flashlight and with the door open, shine the flashlight where the blue dot is. You see it fine even with the safety glasses.
If you are engraving on a dark surface, use a light color to mark the origin.
My curiosity sparked, I grabbed a phototransistor and my oscilloscope and sent the laser beam into the phototransistor to see if the laser is PWM or current controlled. Result: Both are PWM controlled at ~250 Hz. So, @CNC-Maker was right after all.
Here’s the 1.6W laser (Enclosure door open):
PWM frequency ~250 Hz.
For the 10W the phototransistor went quickly into saturation and I had to measure in the weaker side reflections of the beam, so the pulses look broader than they are, but the situation is clearly PWM:
The Counter got confused by the bad signal, saying 715 Hz, but if you look at the timebase it is clearly the same ~250 Hz.
I re-ran the grayscale-square from this post, and again the PWM pulses resolved into individual dots. A bit disappointing…
Still, firmware has improved since past then: Inline power control is clearly now in the firmware, and also the laser does not stop at power changes. That at least is a huge step forward!
