View Full Version : Cutting Foam for the first time and ran into questions...

Brian Lamb
05-26-2016, 10:07 PM
I needed some foam cut to cradle a part we make, essentially a custom fit foam box liner. I tried cutting 1" thick EPS, the white stuff I buy in sheets and use my hotwire cutter on. I also had some "cushy" grey foam that is not rigid like the EPS. I have a few questions.... first, everything was a guess on power and speed, so I ended up at 100% power (50 watt machine), speed was about 10% and 250PPI. Does pretty well on the grey foam, but on the EPS it cuts pretty close to on the line at the top surface, but tends to get a lot of melted kerf and sideways blow out by the time it gets through the 1" EPS.

I played with focusing a little higher, or lower, didn't seem to have any better results. Would I have better luck at less power and dramatically slower speeds, say maybe I drop to 50%-60% but speeds down closer to 1% or less?

Also, I had issues with consistent depth cutting. At a power level and speed that would get all the way through in the curves, the straight bottom cut and slightly tapered top cut, where the carriage moves much faster, were not cutting all the way through, like maybe 75%. I assumed when you set a speed the controller would make it move that speed along the full path, not dramatically faster on straight lines and a lot slower on any curves. I suppose I can change colors on the two straight lines and hit them with less speed/more power, but it just seemed odd that it would be that different.


Michael Hunter
05-27-2016, 7:51 AM
I used to cut a lot of 30mm (1.25") grey foam and found that I got the best results by focusing about 1/3 the way into the material.

It sounds as though your machine is over-compensating for corners - perhaps worth talking to ULS to see if there is an adjustment for that.

Brian Lamb
05-27-2016, 9:54 AM
OK, I'll try focusing deeper and see if that helps, also will contact ULS about the speed issue, I've noticed it a few times before cutting thin plywood and thought maybe it was just inconsistencies in the wood that were causing me to be completely through in some areas and not quite in others. Probably not as dramatic when I'm specifying 2 to 4% for speed on wood and trying to run 10%-20% on the foam.

So, 30mm in one pass? Any suggestions on less power, less speed vs. full power and set the speed to what cuts thru?

Brian Leavitt
05-27-2016, 10:28 AM
Both my X2-600 and X-660 do that on corners. They always get more power to the curves than the straight lines. It's speed up on curves if you turn on "enhance" in the print driver. If you're running at 10% speed with enhance on, it should move pretty much as fast on curves as it does on straight lines. whether or not enhance is on, though, you will still get a deeper cut on curves than straight lines, from my experience.

Mike Null
05-27-2016, 10:47 AM

Mayo Pardo
05-31-2016, 3:56 PM
I have cut 1/2 inch thick virgin EPS foam that is 2lb density, on my 30 W machine.
Most home center store white EPS foam is only 0.80 lb. density and it's got recycled foam content as well - this makes for uneven texture/density.

It took me over 30 tests to find a setting that gave me acceptable results but I finally dialed it in where it was OK.
The speed and power was the main issue, then focus depth - however I also found that varying the PPI (pulse per inch) had a noticeable effect on the edge creep. I don't know how you would alter that on a Universal - I'm using a Trotec Speedy 300 and the software (Job Control) allows for this adjustment.

Slowing down for curves I believe is a function of ramping or slow corner speed in the software - similar to CNC machines.
When a laser slows for curves it can be because the curve may have more "nodes" than a straight line or it can be because the machine is set to ramp into the curve so it maintains smooth motion. I don't believe the power will lower itself when the machine slows for a curve, and that may be why it seems to cut deeper or hotter in the curves. I don't know if this is a user adjustable setting on your (or my) machine.
It would be worth looking into for long jobs with multiple copies.

Brian Lamb
05-31-2016, 7:25 PM
I did have enhance on in my tests, but the cutting speed change on straight vs. curved is very noticeable.


Thanks for the info, I'm doing close to what I would call acceptable cuts on the gray 1/2" foam, the 1" EPS I have was not what I could pass along to a customer. I have been using a hotwire cutter I built for my own packaging, which does a pretty nice job on all the foam cutting, but it requires an opening to get into the cut, I was hoping to be able to sped up and produce a nicer packaging with the laser.

As for changing the PPI, that's a setting on the print driver for the ULS, so it's a matter of telling it whatever you want. I've tried down to 250, I guess I could go as low as you want, never tried it and I'm assuming you want lower rather than higher? Regarding the speed, on my CNC mill, it will stay at the commanded speed within reason, if I commanded 100 ipm and am trying to move 1000 lbs of table in short moves with lots of directional changes it's not going to accelerate and reach the top speed.... and I could possibly see that with the laser if I was at 75% speed or more, but at 10% I would have expected it to maintain an even speed throughout the cut, after all, there is almost no mass in any of the laser mirrors and such involved in these gantry machines.

I have contacted the service guy at ULS, but he's off until next week sometime, so it might be a while before I get an answer from them.

Kev Williams
05-31-2016, 7:34 PM
what lens you using? For that deep I might try a 4" (100mm) or even a 5" (125mm) lens. Fatter beam but a 5" lens will remain in a much tighter focus cutting an inch of foam... Not sure where to get a 5"er but 4"ers are all over ebay for $20 shipped...

Norm Zurawski
05-31-2016, 8:06 PM
Cutting 1/2" Harbor freight foam (floor mat stuff)
60% power, 20% speed, Freq 1000
Cuts really clean.

Brian Lamb
05-31-2016, 9:46 PM
I'm using the standard 2" lens with my machine. 4" lenses on ebay? Just the piece of glass or a lens assembly I can actually use on my ULS?

I will check out that foam at Harbor Fright... is it interlocking floor foam?

Brian Lamb
06-01-2016, 12:02 PM
I heard back from ULS, according to them, the software is more "plotter" style than CNC mill, so speeds vary based on curves vs. linear moves. So my options are to change colors on straight lines and vary speed and/or power to get proper penetration on the cuts.

Kev Williams
06-01-2016, 10:02 PM
Might sound counter productive but maybe not-- since you're dealing with the different speeds (and ULS's best guess on the power change) on curves thing, what I've found that works is to slow the speed down (and the power) to the point where the straight and curves cut at or near the same speed-- once that happens, the power will remain the same during all cuts.

The tradeoff is you'll be cutting slowwww. But-- a slow cut done once may just well take less time than fixing a fast cut that didn't work the first 3 times... ;)

Brian Lamb
06-01-2016, 11:09 PM
Good points Kev, will give it a go and see what happens.

Mayo Pardo
06-02-2016, 1:16 AM
Brian regarding the PPI, I found when I had it too low, (on the 1/2 inch EPS) the cut was more like a dashed line at the bottom although the top was nice. So I had to increase it enough to eliminate the dashed line effect but not so much that the top of the cut was too melted.
I focused about 1/3 into the material rather than at the surface. And this was using my 1 1/2 inch lens. There was a slight angle to the cut but not to the point of it being unacceptable for the intended use. (Temporary decoration)