CO2 Tube power

[tonywish]

In doing research on my laser build I found that a 80w laser is not powerful enough to cut through three quarter inch acrylic. My question is can you cut at a slower speed or do multiple passes to achieve the same result as say a 100w laser.
Tony Wish
In-Tech Systems

[Techgraphix]

Both, lower speed and multipass (with z-lift after each pass) will work, but what is the focal length of your lens??

For 3/4 inch (19mm) there is one problem: your depth of field is smaller if your laserbeam is wider, as this is the case with higher power tubes (CO2)
With a 3mm bundel (like 25-40W) and a 100mm (4") the DOF is ~ 29mm and a spotsize of ~0,45mm but with a bundle of 7mm ( like your 80W tube) and the same lens the DOF is only ~5.5mm and the spotsize ~ 0.2mm

Kees

[tonywish]

Thank you for the info. I plan on having two lenses, a 50mm and 75mm. When engraving I will use the 50mm and when cutting I will use the 75mm. I still have a question in when I exchange lens do I have to somehow change the distance to the material and the laser head? Also you mentioned when cutting 3/4 inch acrylic in multiple passes to raise the "Z" after each pass. I don't understand the reason. Please explain. I have a large cnc router with plasma attached and am retrofitting a laser to add versatility. Still learning basics on how to properly set up so any help is appreciated.

[Techgraphix]

Lifting the Z is a trick I use in combination with some electronics. I use the U-axis to lift my table after each job. I doubt that a "normal" machine has these capabilities, you have to create that..
The reason for lifting the table is to set the focuspoint deeper in the material after each pass.

Kees

[tonywish]

Kees,
Great idea. I suppose I can put this in the g-code somewhere to automatically do this. What is your suggestion as to how much more you would raise the head?

Tony

[Techgraphix]

If your machine works with G-code, it could be that it works that way.. But that depends on your controller..
Many here, have a LightObject controller like the AWC608 or LO-X7 or maybe even an older DF212..
This controllers have a BLOW-signal which can be used for various purposes. This blow-signal is active while a job is running, from the moment you press Start til the job is finished (extending this time is also possible in the software, to let blowers run a number of seconds to retract the last fume)
When you want to use the U-axis to lift the table a given distance. you have to divert the PUL and DIR pulses from the U-axis to the Z-stepperdriver while the BLOW-signal is active. The Z-PUL and DIR from the controller are disconnected at that time..
In the software you can enter how many times you will do the same job, together with the travel-distance for U..

Kees

[tonywish]

Kees,

I just realized my mistake in interpreting your reply. Your table moves to change the Z height. My gantry moves to change Z. So in moving to change focal length you bring the laser point closer to the material after the first cut in 3/4 inch acrylic. Correct?

Tony

[Techgraphix]

Yes, after each pass I move the table a little upwards.
Kees