I am 80% up and running with my 5.5w 450nm laser using the Rambo 1.4. I went the pin 45 route.
So now that I can send Gcode and draw things with Light burn - I’m having issues with the laser. When I turn on the laser it turns on 100%, so to combat this I added a 10k ohm resistor between GND and the PWM pin on the lasers controller board. This works, but I think its screwing with the lasers strength.
For instance, it takes 10 passes at 100% intensity, with a 7.5-8mm/s travel speed to cut through 3mm birch plywood. The “documentation” if you can call it that, alludes to the laser being able to cut through 3mm plywood in three passes at 20mm/s.
Is there something i can add to the firmware to send an initial pwm signal to the laser on boot to turn the thing off, so I can get rid of the resistor? Can someone share their laser firmware settings?
10kOhm is pretty big and a good choice for a pull down resistor. I doubt it’s messing up the signal. Are you sure it works any better without it? I would more question either the instructions, or something with the lens, or focus, or needing an air assist.
Seems when it just turns on (no resistor) it burns right through the wood in a couple seconds. When I have the resistor and power it on to 100% (255) it takes much longer and mostly chars the wood
Do you have any bigger resistors? Or could you confirm that with the same cut test, trying to cut through the 3mm birch without the resistor?
I am not familiar with any settings to do this. But you could assign the pin to output, with a low signal somewhere. It is pretty hacky though. @jamiek, do you know of any settings like that?
Hmm I am not aware of an easy way to add stuff that runs “on boot”. I’m curious about the resistor idea but I will have to do more research separately because I’m unfamiliar with laser drivers. It sounds a bit odd to use a resistor on a PWM pin but thats why I need to learn more.
I don’t think you are losing power. “Larger” diode lasers have much larger spots and can sometimes be less powerful than “smaller” diode lasers because of it. Focus, and smoke on the lens can also kill efficiency. I am really doubting a 5.5 diode getting through 3mm ply (has glue) in 3 passes at 20mm/s. if so that is a very perfect setup.
I assume the reason is that it starts in a floating state, and the laser turns on. Using a pull down resistor will make it stay off until the arduino turns it on.
Yeah that resistor makes complete sense to me sometimes, other times it just does not seem right. Wish I had more practical electronics classes under my belt. Path of least resistance …
Keep the resistor like it is. You won’t lose power because of it. Instead turn your attention to these things.
The marketing material is giving you your best case. Meaning 3mm solid SOFT wood. With perfect focus and a clean lens.
Meaning no glue, no hard wood, and no guessing the perfect focus.
I have been using my laser on several woods recently and I have learned a lot. In order to cut through wood you can try some of these tips.
Find the the sweet spot for your laser lens. Mine says it can work from 30mm to 120 mm. But I recently found that the optimal distance is 65mm. Find that sweet spot for yours that allows you to get that dot size as small as possible.
Keep a fan blowing to clear the smoke. This will prevent your lens from getting dirty and also make the air clear for the beam to hit the wood at full strength.
Use air assist to blow into your cuts so it clears out some of the debris for multiple passes. I have heard aquarium pumps and compressed air work best. I occasionally use compressed air manually right now.
Test different wood types. Soft wood is better. Avoid wood with glue in it. My laser cut almost 1/2 inch through solid pine and yet couldn’t cut through 1/4 inch ply wood because of the glue.
Cut multiple parallel lines. I use estlcam not light burn. In estlcam you can engrave right on the line and also inside the line and outside the line. This way you can get three passes next to each other so it cuts a wider channel through the wood. Helps to allow debris to be blown out of the way.
Consider replacement lenses. Here is a post of mine about endurance laser lenses like the G2, G7, G8. Laser lens information, specs and 4 pack (Endurance Lasers)
It has some good info about different lens types for different situations. It also talks about how much power can get through each lens type. Then consider buying from another source. I am sure Jtech sells their own lenses.
Last tip and I can’t be sure this works or not. Keep the wood you are cutting warm. On a warm day last week my 5.6 watt laser easily cut through 1/8 inch plywood with glue in 2 passes. The next day was colder and it couldn’t cut through the exact same wood in 18 passes. I have ordered some ceramic heat lamp emitters to test this theory better.
I have a JTech 7 watt+ Laser 445nm and it will cut 3mm baltic Birch plywood (3 ply, all layers are baltic birch) in 2 passes at 100mm/m. I am using the JTech High resolution lens so the focal spot is pretty small. 20mm/s seems like a pretty high feed rate, do you know what diode is being used? Have you tried slowing things down? and like others have said, make sure your laser is focused properly, that makes a huge difference in the efficiency of the beam. you could also try a G7 or G8 lens. they both are single element lenses and have a high transmission rate but the spot is larger. A G2 3 element lens will give you a smaller spot but slightly less transmission thought the lens. sounds like you are on the right track just need some dialing in … Good luck!
What is the “laser goal” - do you want to cut quickly with a handful of passes or slowly with few passes - all else being equal the time being the same or is the real goal to minimize charring?
Also Im having a hard time with rastering images - any insight there?
I think that you want to go slow but not so slow that you burn the edges. It gives the beam time to heat and cut.
Raster images. Not sure. But with the MPCNC it takes time to speed up and slow down so I try to burn faster images at a slower speed as well. But I have to go fast enough to make sure it doesn’t burn too dark.
Maybe I’m the odd man here, but I’d just put a switch on the power wire going to the laser. Turn the MPCNC on and prepare your cut. Then turn the switch on just before starting the cut.
I’m trying a bunch of things to raster images. I first tried LightBurn, then image2Gcode now i just tried LaserEtch.
the problem is the laser doesnt raster. it makes a point, fires the laser, moves a fraction of a mm and makes another point, no matter what i set the feed rate at it moves very slow.
I am suspecting an issue with the way you are firing the laser. are you using TTL or PWM to control your laser? and with lightburn can you engrave some text with both line and fill selected? in the photo attached I used light burn at 1400 mm/min @ 85%
