Cutting acrylic

[Rich Kruyer]

When cutting acrylic is it better to set the freq.(pulses) on the laser at a higher rate or lower rate? I am cutting a lot of 1/8" acrylic and want to get the best edge possible.

Thanks,

[brian saban]

Not sure your machine but usually higher, epilog suggests 5000 I believe. which is the highest

[Dan Hintz]

Higher is better for a smoother edge.

[Larry Bratton]

Epilog manual does state that. However, it was told to me by Epilog that you also have less power to vector at higher frequency..I asked why,,said they didn't know. I had always just used 5000 without question until I ran into an issue and they recommended dropping the frequency. I now routinely cut 1/8" acrylic at 12s/100p/1500f and have cut it as low as 1000 without any glaring results on edge quality.

Not sure your machine but usually higher, epilog suggests 5000 I believe. which is the highest

[Kev Williams]

According to (the much maligned on this forum) Full Spectrum lasers, their laser doesn't pulse in vector mode, specifically to cut a cleaner edge. Sounds logical... My LS900 is factory-set I guess, because changing the dpi/ppi settings do zilch in vector mode. I have no idea the pulse rate...

[Dave Sheldrake]

their laser doesn't pulse in vector mode,

Yup, it also strikes up the beam while the gantry is moving to prevent penetration of the initial strike pulse. Must say I was very impressed when I looked at the numbers for that, the acceleration is somewhere around 10^10,234 G, I was a little surprised that they didn't opt for using a method that requires less energy such as reversing the rate of the Earths rotation.

cheers

Dave

[David Somers]

I was a little surprised that they didn't opt for using a method that requires less energy such as reversing the rate of the Earths rotation.

Dave,

As we have learned from Superman movies, doing that would reverse time and undo all that carefully done acrylic cutting. It is counterproductive. Not to mention all the annoying ocean sloshing that occurs if you don't ease into it just right.

<grin> Dave

[Michael Hunter]

However, it was told to me by Epilog that you also have less power to vector at higher frequency..I asked why,,said they didn't know.

I see this very clearly on my machine - some things just won't cut at higher frequencies.

I assume that lower frequency = more recovery time for the tube = fewer but higher powered pulses.
However, I think that the *average* power remains pretty much the same across the frequency range.

I have never found any advantage in lowering the frequency for acrylic though, and lower frequencies definitely lead to poorer edges.


PS DON'T mess with the rotation - all sailors will hate you.

[Ernie Balch]

You are right about the recovery time needed between pulses. The diode pumped YAG lasers I have used have an optimum pulse rate for highest average power. They need 1 millisec between pulses to achieve maximum pulse power. This caused the first pulse after a move to be huge unless it was suppressed with a galvo shutter. The maximum average power as I recall occurred at about 5 kHz. Pulse rates up to 70 kHz were possible but the average power measured by thermopile dropped off quite a bit.

[Dave Sheldrake]

The technical cause for lower power at very high frequency is a product of both Photon Saturation / Gas Cooling time and the amount of molecules in the base state being too few to provide a stable beam.

In a sealed tube you have a finite amount of gas molecules in the unpumped state <000>, when excitation takes place they reach a fully pumped state <010> and liberate a Photon, the excited molecules hitting the side of the resonator cavity cause the <010> state to drop back quickly to the <000> state ready to be pumped again. In a DC tube this can take a comparatively long time to achieve so reducing the number of Molecules available for pumping.(the rise time of a DC tube is considerably longer than an RF pumped tube). In a DC tube Helium is used to speed up the reduction in pump state time to base as well as catalysing the inside of the resonator with Gold but even with all the latest modifications there is a finite limit on how much energy can be directed via the coupler based on the amount of molecules available and their heat state.

In essence at a calculable maximum frequency there comes a point of extra cycles being counter productive (and in some cases detrimental to the resonator life)

cheers

Dave

[Larry Bratton]

Hummm..take a bow Dave.:)

The technical cause for lower power at very high frequency is a product of both Photon Saturation / Gas Cooling time and the amount of molecules in the base state being too few to provide a stable beam.

In a sealed tube you have a finite amount of gas molecules in the unpumped state <000>, when excitation takes place they reach a fully pumped state <010> and liberate a Photon, the excited molecules hitting the side of the resonator cavity cause the <010> state to drop back quickly to the <000> state ready to be pumped again. In a DC tube this can take a comparatively long time to achieve so reducing the number of Molecules available for pumping.(the rise time of a DC tube is considerably longer than an RF pumped tube). In a DC tube Helium is used to speed up the reduction in pump state time to base as well as catalysing the inside of the resonator with Gold but even with all the latest modifications there is a finite limit on how much energy can be directed via the coupler based on the amount of molecules available and their heat state.

In essence at a calculable maximum frequency there comes a point of extra cycles being counter productive (and in some cases detrimental to the resonator life)

cheers

Dave

[Dave Sheldrake]

It's something I've had to look at lately Larry :) almost to the nth degree to get some figures for a client.
At first glance it looks quite complicated but the end results are in reality very simple :)

The worst part for us here are the differences in the way tubes run, RF (Epilog / Trotech / ULS etc) are so much more efficient than DC (RECI / EFR / YongLi etc) and that's before looking at different types like diode pumped etc I've noticed of late the wide difference in resources on the web, going to people like Dr Sam Goldwasser, Professor Shaol Ezikiel and there equals gives great information so long as you have a background in Particle Physics, at the other end there is the "This is a laser tube that makes a laser beam" without a great deal of in between information for anybody that wants to understand past the "this is a tube" but doesn't need a lesson in advanced Physics.

The net result has been nights like tonight where I'm still awake at 03:09am with a blinding headache trying to create the middle ground :)


I assume that lower frequency = more recovery time for the tube = fewer but higher powered pulses.
However, I think that the *average* power remains pretty much the same across the frequency range.

Pretty much spot on :)

cheers

Dave