Safe speed for engraving

[Dominik Kop]

Hi
What is the safe engraving speed?
I mean Chinese machines with ordinary stepper motors
I know that the slower the more accurately
But isn't the speed of 800 mm / s too high?
Is 400-500 mm / s safe speed for stepper motor and belts?

[Gene Uselman]

I normally use 300, maybe 400. Our non-RF CO2 lasers cannot fire as fast as RF lasers and that would limit the speed? Have any of the [young] smart kids thought this through?

[Doug Fisher]

Like Gene, I rarely go over 300. You can do your own tests at each speed and see if there is quality degradation at speeds above 400. Most Chinese lasers can't go the blinding fast speeds of a Trotec... but they don't cost nearly as much either. Tradeoffs!

[Tim Mellor]

I have been running my short (300mm) axis Laser at 400mm/s which has been fine. As you get longer in the Axis and start using heavier lens assemblies you will get into inertia issues with accelerating and decelerating the head along with belt or drivetrain flex/slap.

So unless you are carefully controlling the acceleration like the 3D printers do on direction change the bigger/heavier you go the slower you will likely need to go.

[Dominik Kop]

Thanks for the answers
I have been using 400 mm / s for several years and it is fine. I also have a Chinese machine with glass tube 80W
I just wonder if higher speeds of 800-1000 mm / s
demand:
- RF tube
- servo motor
- better power supplies?
- lighter laser head ?

I am wondering about the configuration
- 60w co2 tube for engraving
- servo motor
- light laser head
- good power supply
Will then speeds of 800 mm / s be available?

[Pete Cyr]

Higher speed will not hurt the machine - it just creates a bad engraving if it is too fast. You will have to experiment to see how fast you can go without a degrade. My manufacturer recommended 400mm/sec as the top speed for consistent and good engraving.

[sebastien laforet]

CO2 laser have a response time of about 1ms. so, the interval between two "pixels" when engraving depends on the speed and this response time.

at 1000mm/s, a "pixel" can NOT be shorter than 1mm wide. obviously, you can not achieve any real detail with this horizontal resolution. this is where you need a RF laser which is quicker to modulate the laser power.

with a speed of 400mm/s, you can have pixel that are "only" 0.4mm wide, this is mostly ok on most job. but you have to be careful with the backlash correction. i believe this is a real maximum to obtain a valid result.

our machines can handle high speeds for the mechanical parts (especially with backlash correction in the software), but the laser is the weak point.

[Dominik Kop]

that is, the tube is the weakest link
thanks for the answers

[Dominik Kop]

And what speed do you use for cutting?
I mean thin materials that don't need much power

[sebastien laforet]

And what speed do you use for cutting?
I mean thin materials that don't need much power

depends on the material. on anything that needs "enough" power, it's fine to go full power and then up the speed until the cut is clean and non-charred.

for thin/fragile materials like paper, same idea but you start with a much lower power.

it also depends on your machine and the design : for detailed design with a lot of direction changes, setting a higher speed will result in bad results (vibrations, backlash). also, the machine will NOT sustain the max speed when changing direction so it will keep accelerating/decelerating. even if you set your speed very high (like 300mm/s) there is almost no change that you can obtain this speed unless in the middle of linear segments. (and, at the end, you have a mean speed that is not so high as expected)

another problem is the power modulation. obviously, the "output power per mm of line" depends on the speed (for a fixed power setting), so you have to adjust min/max power. the problem is that our tubes are non-linear in power output, so this is all try-and-guess.

if you have a design with a lot of small details and some long flat curves, with min/max power too close, you will burn the small details or not have enough cutting power for the long lines.. so you have to set the max power to cut everywhere at max speed, and then adjust the min power to reduce the output when the laser slows.

rinse and repeat for each material