Depron foam - Deep materials

[Nicolas Juskoff]

Hi everyone,

Last week I was asked to make some signs in depron foam (or Polyfoam/Polyboard) for a company I work part-time:





All in all, I (and the customer too) am pleased with the results.

However, the cut was not all good I expected it to be:



All the letters I made had the same problem. At around 8 mm the cut was straight and clean; after that, the was a deviation with a jar-like shape as you can see at the picture above.

Looking around, checking on other people's work in the street, I saw that 20 mm clean cuts are the common denominator. Even I had the chance to check on a small sign of a cafeteria with two layers of 20 mm (sticked together, of course) perfectly cut.

What I have made to tackle this issue:

1. I had already flipped the lens over, so the flat side of it faces the work.
2. Using the focus ramp, with above setup, I got approximately 6-8 mm of good focus, which matches the final result. (I will upload a picture of this)
3. I had to practically stick the nozzle to the material (less than 1 mm away) and I am still not getting a deep clean cut.

Full specs of my machine (TS6090 - W4 Reci tube) are available here: http://www.transoncnc.com/ts-cabinet-mo ... chine.html

Here's a picture of my nozzle:



I used the following config:

Min power: 10%
Max power: 65%
Speed: 42 mm/s

Although I am afraid I already know the answer to my question (my lens/nozzle just won't do), I still have to ask: is there any way to get a deep clean cut with this machine?

Thanks in advance for the help!

[Pete Cyr]

Min power: 10%
Max power: 65%
These are setting that would be used for a 3D engraving job not a cuting job

Not an optimum setting for cutting - set min and max to the same value of 65% and 10-15 mm/s
Do a test and see if that improved the cut

[Jeffrey Aley]

Am I the only one who is unable to see the photos?

Thx,
-Jeff

[Gene Uselman]

What is the FL of the lens you are using- the nozzle looks very long to me.

[Nicolas Juskoff]

Min power: 10%
Max power: 65%
These are setting that would be used for a 3D engraving job not a cuting job

Not an optimum setting for cutting - set min and max to the same value of 65% and 10-15 mm/s
Do a test and see if that improved the cut

Will check and let you know! Thanks!

Am I the only one who is unable to see the photos?

Thx,
-Jeff

Sorry for that. You can check them over here:

What is the FL of the lens you are using- the nozzle looks very long to me.

I am not sure. I've been told to measure the distance from the beak of the nozzle to the lens with a cocktail straw to find that out. Is that right? Otherwise, how can I know?

Thanks for your assistance!

[Pete Cyr]

Am I the only one who is unable to see the photos?

Thx,
-Jeff

I am unsure of everyone else but I can see the photos:)

[Gene Uselman]

Remove the lens from the tube and use this procedure -
https://www.ophiropt.com/co2-lasers-opt ... ns-youtube

The focal length of the lens is different from the FL from the nozzle to the material to be cut. You should have a spare lens on hand- you need to know the focal length and the diameter of the lens.

[Tim Mellor]

Things to consider you are actually Melting the foam more than Cutting it. You are dealing with a product with a density of 20-30kg/m3 (9-13lb/cu yd) and a very low melting point. I have cut a fair bit of 1.5-2mm depron (R/C indoor planes) so the edge shape isn't much of an issue. but very low power and fast got the best results on the thin sheet.

In commercial signage foam is still cut with a hot wire be it over patterns or CNC as you can accurately vary the temperature of the wire to minimise kerf and speed to minimize dragging the wire. CNC Routing is also used but depron would likely tear out of the face when cutting.

Apart from adjusting the focal length toward the center of the foam not a lot more you can do with a Laser other than stack multiple cut sheets then hand finish them when glued.

[sebastien laforet]

Although I am afraid I already know the answer to my question (my lens/nozzle just won't do), I still have to ask: is there any way to get a deep clean cut with this machine?

the laser beam is a cone, and the height of the cone is the focal length.

obviously, if you use a shorter focal, the focus zone is pretty small, and diverges quickly when you get out of focus.

what you see is that the top of the material is correctly burnt by a thin laser beam, but after that the cone enlarges and the power is dissipated on a too large zone, thus the melting (while on the "focused" zone, the depron is vaporized, not melted)

you can either try a longer focal (4" is the most you can get on common machines), or you can try to reduce power to just cut halfway, the flip out the job and cut from the other side (the hard part is setting the material in place exactly) so that the 2nd cut finishes the job.

[Nicolas Juskoff]

Well, I could do some experimentation yesterday.

My findings:

-Reducing the speed somewhat turned out better, but still not good.
-Using the cocktail straw technique resulted in 1.6" approximately (which I presume is then 1.5"). On the other hand, for what I read in recent posts on this thread here and trying to recall my optics lessons at the university, the FL is given by the curvature of the faces of the lens. So,

Remove the lens from the tube and use this procedure -
https://www.ophiropt.com/co2-lasers-opt ... ns-youtube

The focal length of the lens is different from the FL from the nozzle to the material to be cut. You should have a spare lens on hand- you need to know the focal length and the diameter of the lens.

I will give this a try to be sure.

Also,

the laser beam is a cone, and the height of the cone is the focal length.

obviously, if you use a shorter focal, the focus zone is pretty small, and diverges quickly when you get out of focus.

what you see is that the top of the material is correctly burnt by a thin laser beam, but after that the cone enlarges and the power is dissipated on a too large zone, thus the melting (while on the "focused" zone, the depron is vaporized, not melted)

Yes, I guessed this too. My first impression was that the laser started to diverge after these 8 mm.

you can either try a longer focal (4" is the most you can get on common machines), or you can try to reduce power to just cut halfway, the flip out the job and cut from the other side (the hard part is setting the material in place exactly) so that the 2nd cut finishes the job.

I will try to get a 4" lens to see what happens. Otherwise, my last guessing was the same as Tim's statement:

Apart from adjusting the focal length toward the center of the foam not a lot more you can do with a Laser other than stack multiple cut sheets then hand finish them when glued.

Which, for now, considering that I have just purchased my machine and not pursuing only one goal with it, I believe this will be the best choice.

Thanks everyone for clarification!