The snowflake challenge

[Guy Hilliard]

Keith;

On the Speedy 400 (and the Universal X660 I had before that) I spent a good day or more getting the focus as close to perfect as I could (and resetting the focus tool) and reseting the alignment from "factory / install" good enough to as close to perfect as I can manage. Proper adjustment of the air assist is important in cutting things this fine. Not enough air and the part overheats, melts, re-welds or warps and is destroyed. Too much air and the cut looks rippled as the molten acrylic is being pushed out of smooth and frozen. And of course the power, speed, and PPI settings need to be properly adjusted to limit the amount of heat in the piece and to ensure a clean cut. Basically everything.

And it only took me 10 years to get here - with a bit of help from SMC and other sources.

[Bert Kemp]

So basically me and my 6 month old rabbit are sc you know we just don't have the time or experience.

[Guy Hilliard]

Bert;

I'm sure that your machine can achieve results very similar to what I am doing but you will need to spend some time and effort and burn lots of material experimenting to get there. A good place to start practicing would be the projects on the Trotec and Epilog sites. As you learn start doing larger and smaller, thicker and thinner parts. Try every material you can get your hands on (except PVC and a few other non-laser friendly materials). Where you learn the most is at the extremes. If something isn't working keep changing things (one at a time and keep notes) until it does. And read the archives here at SMC. There is a lot of information here that will put you years ahead of learning it from scratch by yourself. Additional information can be found on other laser forums, laser machine and tube manufacturing sites, and in blogs of other people that run lasers. It will not be quick or especially easy but very few things worth doing are.

[Kev Williams]

Couldn't open the other snowflake so I made my own--

Forgot to remove the masking- I was a little hot I think too, probably could've done it with about
3% less power---
snowflake5.jpgsnowflake2.jpgsnowflake3.jpgsnowflake4.jpg

[Keith Colson]

Hi Guy

I had a quick look at my focus tonight, I cut a 25mm cross-hair into some 3mm acrylic. I slid my feeler gauges into the cut and it measures 0.152mm +-0.01 basically a 6 thou feeler fits the slot with minimal friction. What does your measure?

Great job Kev, that looks tiny. I was wondering if you could measure a cut on yours too.

Cheers
Keith

[Guy Hilliard]

Keith

I don't have a set of feeler gauges but I did cut a 1" square and the difference between the piece and the hole is 0.010" so the kerf is 0.005".

How are you measuring in Microns and 1/1000's of a mm? Optical comparator?

[Keith Colson]

Hi Guy

Thanks, it sounds like my focus is pretty good if mine is 6 thou and yours is 5 thou. The difference is probably measurement error.

Keith

How are you measuring in Microns and 1/1000's of a mm? Optical comparator?

I have a Japanese Olympus stereo zoom microscope. It is calibrated. The graticule reasolution is 40 microns so I can get 20 micron resolution with a plus or minus 10 microns of sighting error. It is very handy to have in the "clean" workshop. I use it for soldering tiny pcb's etc.

Cheers
Keith

[Guy Hilliard]

Keith;

I don't want to be alarmist or anything but if my spot size is 0.005" and yours is 0.006" then if we had the same power then your power density would be 44% less than mine, i.e. the area of your focused spot is 44% larger than mine. That is a significant difference.

[Dave Sheldrake]

It would if the beam profile was flat at the end like a cylinder Guy

[Guy Hilliard]

Dave;

Regardless of the beam shape, if you have the power focused on a spot 0.006" in diameter it's power density (W/cm^2) is 44% lower than the same amount of power focused on a spot 0.005" in diameter. Yes, there are areas in the spot that will have higher (and lower) power densities than other areas in the spot (because of the Gaussian distribution of power across the width of the beam and artifacts created by the optics) but over the entire focal spot my statement is valid - and I believe both Keith and I are using the entire focal spot to cut the material, at least I know that I am.

My bad - mixing units like that, I should have said J/cm^2 or W/in^2. Sorry if I offended anyone.