Double or ghosting engraving

[Allan Stephens]

Hello Guys, I really hope someone can help out, i have been using a laser for about a year and a half now but i have never been very happy with the engraving side of things. It is OK but it should be Great and its not, for some reason it seems to engrave double or ghost the image or text (see picture) I have reed some stuff on here about it and have tried the like bearings, Laser alignment, belts etc, but they seem fine i have just thought while writing this I will see if it does it when i type in laser-cut program instead of corel and will be in-touch but any ideas to fix this would be fantastic because as i said its OK but could be great.

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Lasercut engrave the same, i am now trying to slow machine down as slow as i can to see if that makes a difference or not.


Speed has seem to do the job i have gone from 600s/35p to 150s/15p. means it will take a lot long to do job but are happier with out come.

if any still has ideas what else i can do or how i can speed it up please lets us know.

i hope this will help others with same problem....

[Russ D Wood]

I've got a cheapo laser and when my machine does that it is usually out of focus. It doesn't take much. It also shows up if the material is the least bit reflective as the laser light seems to want to wander a little. Russ

[Kev Williams]

Does your machine's driver have an alignment function, so you can align the left-to-right lens sweep with the right-to left sweep? (not exactly sure what that's called?)

My LS900 driver has a test, where it runs a dozen rows of small vertical lines. From line 1 the vertical lines will be doubled, much like your engraving, then for each progressive row the lines get closer together, to a point somewhere from rows 4 to 6 where they line up perfectly, then from about row 6 on the lines start spacing themselves out again- My job is to close look at each row and decide which one has the best aligned lines, and enter that row's number into the driver.

My old 25w ULS laser, to the best of my knowledge doesn't have such a test, but I wish it did!

[Dan Hintz]

Those edges are crisp (relatively speaking), which leads me to believe it's a mechanical issue, not tube or driver based. Check for a loose lens mount, loose grub screw (this would be my first check), etc. It just looks like the belt is slipping a specific distance on each pass.

[Rodne Gold]

If the problem disappears if you use unidirectional and not bidirectional mode (ie only engraves when the head goes one way) , it needs you to set backlash compensation..chinese use odd names for this function .. dunno what yours will be called

[George M. Perzel]

Check to make sure head is aligned perpendicular to table and lens is not loose.
Best Regards,
George
Laserarts

[Dave Sheldrake]

Bean scatter Allan, looking at the pics the beam is hitting the edge of the cone on the way out of the head. It causes a secondary line to appear and reduces effective power, George is right, it may be loose lens, loose mirror or bad cone alignment.

Easy check is the head temperature, if it's getting quite warm then some of the emitted radiation is hitting it causing it to heat up.

cheers

Dave

[David Somers]

Bean scatter Allan, looking at the pics the beam is hitting the edge of the cone on the way out of the head. It causes a secondary line to appear and reduces effective power, George is right, it may be loose lens, loose mirror or bad cone alignment.

Easy check is the head temperature, if it's getting quite warm then some of the emitted radiation is hitting it causing it to heat up.

cheers

Dave

Dave, as I have been digging into lasers prior to purchasing I noticed in the manuals for the Rabbit units that they recommend drilling out the cone on their lens mount if you move to a longer focal length lens from the supplied 55mm. Apparently there is not enough clearance at the working end of the cone to accommodate the width of a beam of a 100mm/4 inch lens and it will strike the edges of the cone and scatter, as you describe. I don't see anything in Allan's posts saying what focal length lens he is using? Just wondering if he has put a longer lens in and may be encountering the problem you are describing but from another cause?

Says the person who doesn't yet own a laser! (grin...caveat lector)

Dave

[Frank barry]

Hi yes I had a look at the rabbit site and I must say it is a very good read for anyone like me who is starting out with a laser and I did read with interest the bit about drilling out cone Frank

[David Somers]

Frank, A bit off topic for the thread, but have you purchased something already? Just curious what you got and what you think of it? I am still in the digging phase. (as everyone here has heard ad nauseum <grin>) You are welcome to send me a PM if you want so we don't clutter up the post with a side conversation. Or if you had an interesting experience perhaps start another post on it to share?

Dave

[Kev Williams]

Why do they have these cones in the first place? My lasers have no cones, and if they did they'd come off because a great deal of the parts I engrave have stepped areas or whatever, which requires the full 2" focus space so the lens doesn't hit the parts--

[David Somers]

Kev,

Keep in mind I am basing this on simply reading their manuals, but I get the impression the cone is there to direct airflow to keep stuff off the lens and to clear smoke and particles from the beam as it cuts to keep efficiency up. It looks like the nipple for the air compressor goes right into the cone. It might also be there to keep a bit of distance between the delicate lens and the surface you are cutting. One thing to bang the cone into your piece by mistake, another to scrape the lens surface across it.

Dave

[Dave Sheldrake]

Air Kev, the air assist isn't just there to keep muck away from the lens, on a bigger machine correct air assistance is a requirement for a number of reasons. The Chinese implementation of an air cone isn't great (more a feature than a tool) and mainly just cools the lens. If the cone is correctly modified (to get as close as possible to a laminar flow) then the gasses and carbons generated when cutting can be kept away increasing both efficiency and depth of cut.

The Western implementation of lens layout is a work around to get clearance, what can become a problem with higher powered lasers is aberration caused by heating of the lens (optical head) making both the beam mode and focal position change.

When it's done right you end up with material cutting like the picture below (no staining)

275486

The MDF in the picture hasn't been cleaned up or modified in any way and when removed from the machine it's not possible to say which side it has been cut from.

In general, small hobby machines / mid size machines use a feature that true industrial machines have been using for years in an effort to get better results (but rarely as shipped achieve it). For small business use 200 watts is considered massive but for industrial use 2kW is considered entry level.

cheers

Dave

[David Somers]

Dave,

I am curious....how would you modify a Chinese air cone to improve it? I ask this selfishly since I will likely end up with a Rabbit once I make the leap and would like it to work as well as I can make it.

Hoping all is well with you back in the UK!! <grin>

Dave

[Dave Sheldrake]

I'll PM you my email and send you the pics Dave :)

The simplest mod costs about a buck and fits rabbit machines perfectly :)

cheers

dave

[Kev Williams]

Curious about "cooling the lens"... my lens- and I just checked it after a good run- doesn't even get warm.

No cone cover, my air assist (I put the tube down just to take this pic, usually it's up out of the way), and half my auto-focus is removed so it doesn't hit the steel bar holding down the acrylic on the far left...

http://www.engraver1.com/erase2/laserlens.jpg

[Rodne Gold]

My Mods...remove air assist off the cone and direct it... that whole head assembly , all the gold bits are a princely $12 ex china if you order a spare.....

[Vicki Rivrud]

Hi Allan,
Not sure if you are aware of the quirk in the way Lasercut handles overlapping text, it creates a void when trying to engrave the connecting tails, which you can see at the m a s connecting points. If you create the word Christmas in Lasercut you will have the voids.


In Corel, Convert your text to curves and shape:weld. Export your vector artwork as a dxf to import into Lasercut. This way your text will flow nicely together without the little blank spots in your engraving.

Just a suggestion to improve the look of your engraving.

From my experience your beam is either hitting the inside of the cone or you need to tighten the screw-nut that holds the lens in place.
Vicki

[George M. Perzel]

Another variation on Rodne's theme using tubing L connector and piece of 1/8" copper tubing.
This provides air on bottom of lens and at material surface.
Best Regards,
George
Laserarts275583

[Kev Williams]

Seriously, how could you possibly etch something like this on both levels with that lens cone in the way?

http://www.engraver1.com/erase2/2step.jpg

[George M. Perzel]

Kev;
Use longer focus lens-4" will work fine
Best Regards,
George
Laserarts

[Dan Hintz]

Seriously, how could you possibly etch something like this on both levels with that lens cone in the way?

Well, it wouldn't be as efficient, but I'd orient the piece vertically rather than horizontally...

:D

[Rodne Gold]

That example is a little problematic without long lenses or a naked beam

For less extreme stuff on these machines you can tell the laser where to start and end the engraving , any of these positions

* * *
* * *
* * *
For eg the centre of a bowl , I would start and end here

* * *
* X *
* * *

Or you can cut the cone off...my air doesn't come thru it and I dont rely on the cone orifice for anything

[Scott Shepherd]

That's an easy one for a Universal or Trotec. With a programmable Z-Axis, I'd engrave that without the nose cone (no need for it), and I'd just have the top surface one color, the bottom shelf another color, have it engrave the top surface and then when it's done, it would move the z-axis automatically and engrave the next color. 1 setup, 1 run, all levels complete.

[Dave Sheldrake]

Put the job through one of my Galvo's :)

cheers

Dave

[axs karaci]

hello
i recently change my tube and psu . i have a 50w tube and a 60 w psu.
cutting works perfect ...engraving....not so well ( see pics)

i have checked the belts, motors, mirrors, lens, cables ....still nothing

on x swing the "effect" is in both sides, on y swing , the same only vertical, unilateral left/right , the same left or right
this happens only at speed higher than 60mm/s

i have read about voltage tickle ......a jumper on my laser control board or something like that....that is the only thing that i haven`t tried
thank you348072348073