question on cutting acrylic

[Craig Hogarth]

I'm cutting out several .093 inch acrylic rectangles with rounded corners. I started out at 100p, 10s, 500ppi and 4 image density. It didn't go through. I kept lowering speed and it started cutting at 3 speed. However, it only cut through on the x axis. I can see smoke fill the honeycomb when it goes through, and there's no smoke on the y axis. :confused: Why is this?

In order to cut all the way around, I'm at 2.5 speed. I thought acrylic was much easier to cut through.

This is Optix by Plaskolite purchased at HD if it makes a difference.

[Joe Pelonio]

With my 45 watt I'd cut acrylic that thin at speed 30, 100% power, frequency 5000. It cuts like butter. Sounds like you have something wrong going on. I can cut 3/8" acrylic at speed 3.

Try cutting it using an image that's been known to work before, in case it's your file. Maybe your lines are in colors and you have color mapping changing the settings as it runs. If a customer provided the art and created it with a cad program there could be any number of problems with it.

Double check that you are focused properly. Can you still cut wood at the same speed as usual? Lack of power due to bad tube, mirror or lense can reduce power to where it barely cuts.

[Larry Bratton]

Craig,
The frequency is the thing. Set that laser to 5000. I can't even cut thin engraving plastic clean at 500.

[Craig Hogarth]

I don't know how frequency translates to universal, but I upped ppi to 1000 (max) and image density to 6 (maxed out also).

I did get it to cut all the way at 4 speed. I guess I'll call tech support for more info tomorrow.

[Dave Jones]

If you have air assist, make sure it's turned on.

[Larry Bratton]

Sorry, I was thinking Epilog.

[Nancy Laird]

Craig, we are cutting 1/4" acrylic at 100% power, 0.5 speed, and 1000 ppi, 6 density, on a 40W machine with air assist, 1.5" lens, and no problems. Are you using air and a 1.5" lens?

Nancy

[Lee DeRaud]

I don't know how frequency translates to universal, but I upped ppi to 1000 (max) and image density to 6 (maxed out also).

I did get it to cut all the way at 4 speed. I guess I'll call tech support for more info tomorrow.I'm not sure you have a problem: the settings document from ULS calls for 54P, 0.5S, 1000PPI for a 35W machine cutting 0.2" acrylic. Assuming the power/speed/thickness relationship is close to linear, that works out to roughly the same as 100P and 2S for 0.093". So you're within a factor of 2. I've found some of the settings in that document to be a bit aggressive, so speed in the 3-4 range isn't unreasonable.

But I have no idea why it would have any directional dependency unless the speed is way off on one axis for some reason.

(I also have no idea why acrylic takes that much power to cut, unless the stuff is semitransparent to that particular wavelength.)

[Lee DeRaud]

This is Optix by Plaskolite purchased at HD if it makes a difference.One other possibility: are you sure that's acrylic and not polycarbonate? I also get my clear acrylic at HD and that brandname doesn't sound familiar.

[Dave Jones]

According to the Plaskolite webste, Optix is a high impact extruded acrylic.

[Mike Mackenzie]

Craig,

Are the settings you send from the computer the same as what is on the system?

If not check to be sure that your color management is set to off.

Next be sure your focus is correct.

Try cutting in a different area of the table (try all four corners)

Did you check the alignment?

is the driver function set to normal?

Are you using one of the standard RGB colors?

[Richard Rumancik]

Craig, I doubt that the difference in cutting between the x and y axes is a "defect" in the laser system. There are a couple of possibilities I can think of that could cause differences in cutting between x and y axes.

The polarization of the beam is one possible factor. I don't want to get in a technical discussion of polarization, but to simplify, polarization has to do with the plane in which the laser beam is oscillating as it hits the material.

Polarization direction of the laser beam is a big issue for cutting metals. For high power lasers the beam is circularly polarized so it will cut equally in any direction. Although I have read that for polymers the polarization should not have much effect on cutting in any direction, I am not entirely convinced. Most smaller lasers (50 watts and less) are likely linearly polarized. Lasers with two tubes will probably be circularly polarized or simulate circular polarization.

In any event, polarization can result in cutting differences in some materials. I can't say for sure if it is an issue for acrylic. However, if you see differences in kerf width and energy requirements between axes it might be a polarization issue.

The other possibility is that the extruded acrylic you are using has a "directionality" to it. It is analogous to wood having a grain such that it will saw differently in each axis. I have not experimented with this possibility myself, but one test that you could do to check for it is to cut a square in a small sheet at S3 (or what ever speed/power combination exhibits the "problem"). Then rotate the sheet 90 degrees and cut another square. If it cuts poorly in the "x" axis both times, it is not a material direction issue. But if "y" becomes the problem axis, then it shows there is a preferential cutting direction in the material. (Also, what happens with the material at 45 degrees on the bed? What happens with 1/8" MDF? I expect MDF would be non-directional.) Stretched plastics have an "axis" to them, extruded plastics can also show directionality. For example, if you anneal extruded acrylic, it will shrink differently in each axis. Cast acrylic probably would not show any directionality.

When setting up a laser job, it is time consuming to find the "optimum" cutting parameters, so lots of people will cut with 10-50% more "energy" (speed/power combination) than actually needed to cut through. This isn't always the best method for high production, but for quick-and-dirty jobs it is adequate. When you try to find the optimum by reducing speed till it cuts, like you did, you may find some odd things about the material and/or your optics at the "threshold" of cutting that you wouldn't otherwise notice. But it doesn't necessarily mean something is wrong with the laser itself.

[Craig Hogarth]

I'm not sure you have a problem: the settings document from ULS calls for 54P, 0.5S, 1000PPI for a 35W machine cutting 0.2" acrylic. Assuming the power/speed/thickness relationship is close to linear, that works out to roughly the same as 100P and 2S for 0.093". So you're within a factor of 2. I've found some of the settings in that document to be a bit aggressive, so speed in the 3-4 range isn't unreasonable.

But I have no idea why it would have any directional dependency unless the speed is way off on one axis for some reason.

(I also have no idea why acrylic takes that much power to cut, unless the stuff is semitransparent to that particular wavelength.)

Thanks Lee and others for their response.

I've sorta made it a habit to not look at the manual as it's always been easier for me to learn with trial by error. I've just read several posts here, including this thread, where some people have been able to cut it at much higher speeds.

[Craig Hogarth]

The other possibility is that the extruded acrylic you are using has a "directionality" to it.



That makes sense. I have a few jobs lined up at the moment, but as soon as I can, I'll test your theory.

[Richard Rumancik]

I am having some trouble rationalizing all the data points in this thread. There are different wattages of laser, different material thicknesses, and of course speeds of all lasers are not the same so 3% speed on a ULS may not be the same on an Epilog or LaserPro or whatever. But just the same, I've been playing with the numbers like Lee to get crude comparisons.

I think Lee's analysis for the ULS is a reasonable approach to try to "normalize" the data so it can be compared. I just looked up the Mercury parameter table and it says S2% P100% for 2mm (.080) acrylic on a 25 watt system. This is in the same "ballpark" compared to what Craig is seeing.

For example, using the linearity assumption, Nancy should be able to cut .093" acrylic at about S1.5% P100%. This is with 40 watts.

What sticks out in my mind is the numbers Joe quoted. Joe, I want your laser. . . I realize you have 45 watt, but how is it that you can cut acrylic 10 times faster than some of the other 25/30/35 watt system? I am puzzled by this. Did I understand correctly?

Other than Joe's data point, I would say Craig's system is probably operating "normally". But I'd like an explanation for Joe's better performance.

[Lee DeRaud]

I've just read several posts here, including this thread, where some people have been able to cut it at much higher speeds.For some indeterminate value of "higher speeds".

A speed setting of X% on machine A isn't necessarily the same speed as the same setting on machine B of a different model/manufacturer. Until you can describe "speed" in terms of inches-per-second of laser movement or (equivalently) minutes to cut a given job, you don't really know if anyone is actually cutting acrylic "much faster" than you are.

Note: what I just said doesn't mean they aren't cutting acrylic faster than you are. Joe (for example) is talking about a 45W machine and yours is a 35W. That's a pretty big difference, even if you assume that both machines are running exactly at their rated power...and it's highly unlikely that either of them are.

[Joe Pelonio]

What sticks out in my mind is the numbers Joe quoted. Joe, I want your laser. . . I realize you have 45 watt, but how is it that you can cut acrylic 10 times faster than some of the other 25/30/35 watt system? I am puzzled by this. Did I understand correctly?

Other than Joe's data point, I would say Craig's system is probably operating "normally". But I'd like an explanation for Joe's better performance.
Lee makes good points on comparing lasers. If I may add, if I'm cutting 1/8" acrylic at 15% speed, it's 15% of the maximum speed on my machine with my power of 45 watts +-. In order to compare apples to apples we would all have to use the same image, say a 3" circle, and cut the same material with a stopwatch on to see which is actually faster. One would expect a higher power machine to be able to cut faster. When I bough mine I went for 45 watts knowing that I would be cutting 1/4" acrylic frequently. While some lower wattage machines can also, speed is an important factor when you're doing a tall pile of material.

[Richard Rumancik]

Joe, I'm not trying to nitpick . . . okay, maybe I am a little bit. . .

I brought this thread back as it still bothered me about what I saw as an anomaly in your 45 watt performance, compared to other lasers and using the "linearity assumption".

I think your idea of a test circle and a stopwatch to compare laser performance is a great one. That ensures that the same distance is being covered, and it is in "real time" (seconds), as opposed to percentages of max speed and max power. It still leaves the power with some uncertainty, because most of us don't have power meters to check what our lasers are putting out (and this degrades with time) but at least it gets rid of a great deal of uncertainty.

Having said that, and since we can't use your method in this crude comparison, you said earlier that on your 45 watt you could cut .094" at S30 and .375" at S3. These speeds seemed faster than anybody else was achieving. But today I think you said in a different thread that you cut .375" at S1. That is closer to what I would have expected, as using the "linearity assumption" then you would be cutting .094 at about S4 or so. Maybe you could actually do a bit better - S6 or S7 would not surprise me with thinner material. But there is a big difference between S4 and S30. So either the linearity assumption is not useful, or there is a data error. Or I misunderstood something.

Just for the record, do you mind checking your notes and verifying your cut speeds of say .062/.094/.250/.375 acrylic?

[James Stokes]

Just for grins with my 100 watt laser at 3 speed 100 power I can cut about 1.33 to 1.5 inches deep in a 2 inch thick piece of acrylic

[Frank Corker]

Wow, that's some power, I'd kill for that. Do you know anyone you want killing?

[James Stokes]

Not at the moment Frank but I will keep your name handy just in case.

[James Stokes]

With the 100 watt, I can cut 3/4 red oak at speed 5 100 power.

[Frank Corker]

Wow..... I'm free on Wednesdays and Thursdays and late afternoons on Monday.

[Joe Pelonio]

Joe, I'm not trying to nitpick . . . okay, maybe I am a little bit. . .

I brought this thread back as it still bothered me about what I saw as an anomaly in your 45 watt performance, compared to other lasers and using the "linearity assumption".


Just for the record, do you mind checking your notes and verifying your cut speeds of say .062/.094/.250/.375 acrylic?

I did make an error and picked up the .062 speed for .094!

These are the speeds I use for acrylic, all are at 100% power, Frequency 5000, air assist on:

.062 Speed 30
.094 Speed 24
.125 Speed 18
.250 Speed 8
.375 Speed 3

[Dave Jones]

I love seeing real figures. And I figured it got non-linear as it got slower:

[Marc Myer]

Graphs! Numbers! AAAIIIEEEEEEE!
My right brain is writhing in agony!

[Richard Rumancik]

Thanks Joe for looking this up and thanks Dave for plotting it. Marc, don't read this!

Dave, did you mean that you expected that for thicker materials the linearity assumption would fail? If so, I would agree, as my own experience suggests that as I try to cut thicker acrylic that "last little bit" seems to take a disproportionate amount of extra energy to cut through. And if using 100% power already, the only way to get more energy is reduce the speed.

But the linearity assumption can be useful as an estimate when comparing materials that are closer in thickness to each other. In other words it would be risky to use .062" data to estimate cutting .375" material.

But if you compare .062 to .125 then you have 1:2 ratio approximately. Half of 30 is 15; the actual speed used was 18. Pretty good correlation. Between .125 and .250 is 1:2. Half of 18 is 9. Joe used 8. Pretty good correlation.

A few considerations. I forgot that a lot of the material is actually metric but often referred to and sold as the nearest "fractional" (imperial) equivalent. At least in Canada it is. There are a few fractional sizes available but often I see metric sizes. eg .060,(1.5mm) .080,(2mm), .098, .118, .177, .220, .236, .354, .375. etc. Depends on the series too. Second thing - for thin materials focus point is not all that critical (surface, 1/3 way in, half way in etc.) But for thicker materials it will matter quite a lot. Third thing . . . when setting up a job I usually do a few test cuts - but I want to have a bit of margin as well. I don't set my laser to "just cut through" as I might end up with a lot of scrap if the parts cut 98% through. I assume lots of people work this way. If the volume is high enough, it may pay to cut the margin a bit tighter, but for a few parts it isn't worth a lot of effort. So if someone says they cut .xxx acrylic with S20 P100 that is not to say that S18 P100 would not work.

The point is that the data is always a bit rough, so we can't expect to get precise predictions. But I think material comparisons in 1:2 ratio seem to work well enough to be useful, maybe even up to 1:3 ratio.

Joe, your speed of 30% for .062" and 3% for .375" still looks impressive to me. But I am still pondering your suggestion of stopwatch/standard shape as a much better way to compare laser performance.

[Larry Bratton]

Richard:
Would you please fill in your profile so I can see what university you teach at?:D Is it Laser U?

[Rob Bosworth]

Something else that has to be thrown into the formula is the quality of cut. If you are trying to cut acrylic and get a flame polished edge, you will have to run slower than if your are just "hacking" it out. Different jobs require different quality.

Also, you can greatly enhance your cutting speeds and quality by using O2 as an air assist rather than compressed air. The oxygen will enhance the "burn", letting the motion system to run faster with a flame polished edge.

[Dave Jones]

Richard, what I meant is that it seems that when you start reaching slow speeds with the Epilog that I believe they are no longer linear reductions in speed. For example, if the first 3 points on the left make a straight line, and you follow that line until it crosses the .250" material, it would suggest that a spedd of maybe 2 or 3 was required. And that the 3/8" material would be impossible to cut.

But based on the way those thicker ones are able to be cut with a speed that's not as slow as the proportion of the speeds used on the thinner material I would guess that a speed of 3 is not actually 10 times slower than a speed of 30, but maybe 20 times slower or more. I suspect that when you go below some threshold (maybe 10 or 15?) that the steps in speed get larger than the actual number representing them, allowing a much wider range of slow speeds.

[Mike Burroughs]

My laser did a similar thing.. I can cut square edge items just fine, but when i applied 'rounded corners' for some reason this seemed to confuse the laser. I have not seemed to fix the problem...yet. If i come up with any results i will be sure to post.

Mike

[Gary Hair]

and of course speeds of all lasers are not the same so 3% speed on a ULS may not be the same on an Epilog or LaserPro or whatever.

This is one of my pet peeves... If we would get used to talking about speed and watts ACUALLY used it would be a lot easier to convert, and compare, from machine to machine.

For example: I have a 30W, 80IPS (raster) 40IPS (vector), Pinnacle ZX. If I use 10% S and 100% P for a vector cut then I should tell you I am using 4IPS and 30 watts. If I use 40%S and 80%P for raster then I should tell you I am using 32IPS and 24 watts. These numbers can be equated very easily to another machine. If you have a 45 watt, 42 ips machine then all you have to do is figure out what % of P and S give you the numbers I post - SIMPLE!

I realize that the power numbers are rarely, if ever, what they are "supposed" to be but at least this gives you a smaller target to hit.

If everyone put their speed/power settings in their signature then this would be a bit easier, but it would be easiest if you would just post the P and S actually used.

Gary

[Dave Jones]

It goes deeper than that and just calculating a speed based on what your machine's theoretical speed is, times the percentage, won't translate either to another brand. For example on mine 50% speed on vector is nowhere near 1/2 the physical speed of the 100% setting. They are very close to the same thing. At least when drawing a circle.

[sunil jain]

Today i got jobwork to cut letters on 10mm milky acrylic. I work on spirit 25 watt. I used same p/s setting that i used to cut cast acrylic ie speed .5 and power 100. The problem was that the lower side of letters stucked. but this never happened on cutting letters on cast acrylic.
Firstly i thought it was an alignment problem i checked for it, and it was ok. then again i tried on cast acrylic, again cutting was ok. I adjusted ppi and other parameter to solve the problem.
The problem was only on white milky acrylic. laterly i excercised to find the optimum speed/power setting, it worked out to be .9/95. but the problem of stucking was still there.
Any one help me to cut white milky acrylic letters cleanly.

[Frank Corker]

Sunil, try lifting the workpiece off the cutting bed using a couple of coins, then try setting the focus point midway through the thickness of the workpiece. You should be pleasantly suprised, your laser will cut through the first couple of millimetres like butter even though it's below focus and the underneath will be MUCH smoother.