Laser Rubber/Rubber stamps troubles

[Orestes Pouliasis]

Hello,

I need some help with engraving laser rubber. Namely, with the following 2 problems:

#1:

The engraved surface of the rubber isn't smooth! Apart from being aesthetically displeasing, it may also cause problems with the stamp (depending on its design). I also sometimes get a "ridge and valley" effect (see pic #1.1) that I have no idea as to what is causing it.

What I've tried so far:

• Different material (the green is cheaper variant that I use for testing - normally I do my engraving on trotec/trodat laser engraving rubber, basically the best you can get - same thing).
• Different power settings: Well, I haven't really fiddled max power (I have set it at 52%, as high as my tube will go), I've mainly experimented with min power, ended up leaving it at around 10-12% (my tube starts firing at 7/8%) since most people recommend setting it a tad higher than your tube's firing threshold for engraving.
• Turning the "ramp effect" setting on/off. Nothing notable happened as far as the engraved surface goes.
• Different DPI settings: I engrave these stamps at 800 dpi. I export a B&W (non dithered) .bmp from CDR X6 at 800 dpi and load it in LB and use the passthrough option. I sometimes go up to 1000 dpi for some stamps with some really fine detail, but for the most part 800 dpi does the job. They both look the same as far as the engraved surface is concerned.
• Speed: Mostly changes the depth, I use 150 mm/s for the most part.
• Happens both with uni and omnilateral X axis engraving.

#2:

My X axis doesn't move in a straight line. I don't know if you can see it from the picture, but the engraving lines at the bottom (machine was engraving from the test pattern from the bottom up) are wavy instead of straight. Same thing goes for almost all the rest, but much less noticeable. My X axis belt is reasonably tight, my lens is securely held in place by its securing ring, my gantry doesn't wobble and frankly I am all out of ideas.

Reducing the engraving acc setting on the controller helped a lot (initial setting from the factory was at 8000mm/s^2, turned it down to the lowest value that the controller will accept, 1000 mm/s^2) but the problem is still there. Are there any other settings that I need to change in the controller?

My machine is a 50W chinese blue/black with a orange tint acrylic window, I use LB and a CVD 38.1mm FL lens.

Any suggestions are welcome.

[sebastien laforet]

i really don't understand why you use 800DPI or more.

you should aim for 0.1mm interval, since you can not PHYSICALLY have a better resolution. at 800DPI, the interval is 0,03mm, which is way under the precision of the machine.

so instead of having a line each 0.03mm, you probably have lines that are on the same spot, then a "jump".

suppose you have to divide a line by third of cm, but with only one decimal number for precision... your values would be

0 - 0,3 - 0,7 - 1 - 1.3 - 1.7 .... --> obviously the interval between each step is not regular, so you have the curtains.

you should probably try 256 DPI which is the resolution closest to the "natural" size of dot of the machine (0.1mm/dot == 256 dots per inch), and run with more power. it may not give a better result but at least it will process waaaaayyyy quicker and you will not even loose on details.

[Orestes Pouliasis]

I know that the max. "real" resolution of the laser with a 38.1 mm lens sits at around 300 dpi. However, when engraving rubber for use in rubber stamps, the same rules don't apply with regards to the engraving resolution.

If you tried engraving a stamp with any amount of fine detail (say 10 pt text) it will come out very very rough, basically unusable. It is absolutely necessary to engrave at such high resolutions (>600 dpi).

Trotec also recommends the same thing (https://www.troteclaser.com/en-us/knowl ... engraving/) and my finding support this. Any stamp with text on it can't be produced at 300 dpi.

[sebastien laforet]

what you are doing is probably the same as using 256DPI and 3 passes at low power.

[Orestes Pouliasis]

I don't have any photos from before, but trust me, after watching Russ' video on DPI, I set my machine to engrave rubber at 300 dpi and couldn't get any decent results. Once I increased it to ~500 dpi, I could then get a decent rubber die. This isn't 2D engraving but 3D. I honestly can't explain why but after having looked tens of failed tries under my loupe, higher DPI resulted always in higher quality.

My biggest problem right now is the wavy lines issue. At 250 mm/s, the issue becomes very noticeable, even without the loupe. What is causing this?!

I am also attaching my controller settings. Do they seem OK to you?

TIA.

[Leo Lidwell]

Wavy cuts possibly a loose lens or head assy? Could also be the rails collecting some stuff.

[Orestes Pouliasis]

Like I mentioned, I tried moving the head with my hands to see if it would budge but it stayed securely in its place. The lens is also securely held in place by the silver ring that screws on top of it. I cannot find anything that's loose!

I also cleaned the rails and applied a tiny amount of thin oil over them. Nothing still.

[Gene Uselman]

Orestes- I am having problems understanding your issue. For one thing we all use Ruida controllers so none of our settings will correlate to your controller/software. I have looked at your picts but most of them look good to me- I don't think you are going to get a nice flat engraved area on your stamps- that is most often the texture of the material you are engraving. You could try raising your focus to smooth out the individual burn lines- that sometimes works on acrylics. Your pictures of what must be an eye-loupe don't help much because we don't know how much magnification you are using. Gene

[Orestes Pouliasis]

I will try my best and provide you with any information that you may need.

Orestes- I am having problems understanding your issue. For one thing we all use Ruida controllers so none of our settings will correlate to your controller/software.

Apart from speed factor (which from what I can tell acts as something of a multiplier, probably not exactly like a multiplier but close enough), aren't all if not most of those settings on that screen common for all machines/controllers? Things like engraving acceleration (min, max), etc?

I don't think you are going to get a nice flat engraved area on your stamps- that is most often the texture of the material you are engraving. You could try raising your focus to smooth out the individual burn lines- that sometimes works on acrylics.

I was given a sample stamp from my supplier that he made using his RF CO2 laser. It isn't a big brand laser like a Trotec speedy or anything like that, just a RF tube Chinese laser from what I can tell. He rans his machine at 1000 dpi and his resulting stamp is smooth as silk. I do not aim for that, I just want some level of uniformity on the engraved surface and most of all, to eliminate highs and lows in the engrave surface (namely when you have e.g. a row with text, the area to the right and to the left of the text is raised, and then the gap between the rows of text sits lower than the rest of them).

And then what beats me is, that every now and then, I get a perfect stamp - nice big flat surfaces on the areas that are to be inked and a flat, uniform engraved surface. It's crazy.

Finally, wouldn't running them out of focus produce less detail overall?

Your pictures of what must be an eye-loupe don't help much because we don't know how much magnification you are using. Gene

I am using a printer's loupe. This loupe must be over 30 years old and I have no idea what magnification it has, but most printer loupes on the market have either a x5 or a x8 magnification.

That photo is used to highlight the wavy lines issue, which I also can't find the solution to.

Please ask me for any other information that you may need and I have omitted to mention!

Thanks.

[Gene Uselman]

All controllers do the same thing and mostly have the same functions in them but they are called by different names and even if they are the same name, may do different things... so be aware.

RF lasers are quite different from CO2 lasers- again they do the same thing but differently. They can fire much faster-
Russ has explored some of the differences on his video channel.

By de-focusing the beam it will lose definition- a larger spot engraved. First you engrave in focus to get nice sharp edges and then de-focus and run the same file over it again to level the background field.

The eye-loupe must be quite powerful [over here our loupes are usually 1 inch square- I assume your is metric?] and the lines are quite far apart compared to the kerf or burnt lines. The kerf on my machine is about .5mm and your spacing appears to be 1.5 times the kerf- what is your scan interval?