1.5" Lens Engraved Vertical lines breaking up

[David Fairfield]

Been doing all my miniature work with the 2" lens and no problems at all, but the 1.5" lens hasn't been very cooperative. I realize its more sensitive to focus, but even when properly focused, I have intermittent problems engraving vertical lines. Sometimes they are too thin, weak and broken up. Due to the extremely small size of my work, its clearer to illustrate the problem with a diagram.

Strangely, not all the vertical lines are effected, just some, and sometimes a good solid line only 1mm or so right next to a broken one, same problem occurs same spot, when job is run more than once. I'm pretty sure the lens is properly focused. It is definitely clean. I am working on cardstock, around 20 to 50 speed speed 10 to 50 power. Material is lying flat, 1200 dpi. No problems with vectors.

All works fine with the 2" lens. So far, the 1.5" lens has not given me the results I was hoping for. Can anyone help?

Thanks!
Dave

[Tony Lenkic]

David - are you sure the line thickness is only 0.002? It looks thicker.

What I would do is duplicate the image on top of original and flip it over vertically. It will engrave both at same time so there is no time loss.

[Rodne Gold]

Only 3 things will change with a 1.5" lens compared to a 2" and that is focal point , degree of divergence from the focal point and the spot size.
One would have to work out how these would affect just vertical lines?
The one factor might be that the power density at the spot is much higher than a 2" lens and thus one gets a very clean vaporisation rather than a clear mark -leading to verticals looking sketchy?
raster ever increasingly wide verticals and see if there is a difference from the edges to the centre in terms of the mark contrast.

[Andy Joe]

have you tired changing the speed ramp at start and stop? Im not sure if you can adjust on your machine but when i had this problem it worked for me. And before i learned how to do it i just made a box around image i was engrave and out side of the area the material would be and then the ramp start and slow down would happen out there instead of on the thin line i was engraving. I always use a 1.5" lens unless im engraving cermark on chrome or cutting thicker material and that was how i fixed the problem when i had it

[Brian Jacobs]

David,

You didn't mention this, but are you are rastering or vectoring these outlines. If raster, have you tried vector-etching this frame? Also, have you tested different power/speed ratios?

[Dan Hintz]

As a test, up your power by 20% and see if all lines cut cleanly, do the vertical ones still skip, and is there now any overburn of the horizontal lines.

Cut/copy the problem lines and paste them multiple times into a test document. Laser it and see if the problem is consistent in the same spots on the lines over various places on the table.

[Peck Sidara]

Dave,

A few thoughts & comments:

Look at the sample under magnification, is there a laser mark or is it simply not there at all. If it's there but just faint, see below points:

How are you checking focus? I recommend having a separate focus gauge for the two different lenses. Each lens, even if the same focal lengths will have different focal points. The best method to check true focus is to raster engrave a black filled box onto anodized aluminum using the recommended settings. While engraving, press focus and adjust the table up and down until you get the brightest burning beam. Pause the job and set your focus gauge to this depth.

If you're raster engraving very thin lines, your laser match could probably use some fine tuning. Laser match is covered in the manual and when adjusting, keep all other variables off the table, change in increments/decrements of 1, save the settings & resend the job for the new settings to take place.

Not sure what to think if the raster line is intermittently not raster engraving sections of the vertical lines.

What does tech support think?

HTH,

[Richard Rumancik]

. . . I have intermittent problems engraving vertical lines. Sometimes they are too thin, weak and broken up. Due to the extremely small size of my work, its clearer to illustrate the problem with a diagram.

Strangely, not all the vertical lines are effected, just some, and sometimes a good solid line only 1mm or so right next to a broken one, same problem occurs same spot, when job is run more than once.

David, if I understand correctly, you have drawn vector lines .002" wide and are rastering them at 1200 dpi. I assume this means that you are letting the laser do the vector-to-bitmap conversion on-the-fly.

Okay, 1200 dots/inch x .002inches = 2.4 dots. Hmmm. The laser can only lay down 2 or 3 "dots", not 2.4 dots. So it has to think and decide whether to lay down 2 or 3. Depending on how the driver does its automatic conversion and roundoff, things will end up differently. That is, does the driver algorithm use straight conversion, or add dithering? or anti-aliasing? Which settings it uses will affect the result. (Try for yourself - draw a box .50 x .50" with line width .002". Then do a forced "convert to bitmap" using various settings.)

When you said some lines were "broken up" it just made me think it was not mapping the vector very well when it converted it. Also, since it is repeatable, that tells me the laser is converting to bitmap the same way each time. (It should.)

If I was drawing lines that were to be rastered, I would probably draw them with a line width was a multiple of 1/1200". But I don't think that will solve the whole problem as I believe the laser is mapping a pattern of shapes to a .00083333" grid. (1/1200") So over the whole image you are going to get some "hits" and some "misses". That is, some vector lines won't be exactly on the grid. So the left side of the shape might map to 2 pixels and the right side to 3 pixels. You might find that moving a shape .0002" (say) to the right causes the "good" line to become bad and vice versa.

One approach might be to manually make a bitmap of the shape you need, then insert it at the appropriate places. (Create in CorelDraw, edit in Paint, and insert.) If you can figure out an easy was to keep all the shapes on the page entirely "on grid" then maybe you will be able to solve it.

Could you use 1000 dpi instead of 1200? Using a grid of .001" is a lot less painful to work with than a .000833" grid.

Somehow I think the solution is to make the bitmap conversion yourself, with lines a know number of pixels (dots) wide, rather than letting the laser do it. But I think I'll stop here with this train of thought in case you spot a flaw in my logic . . .

(BTW I really don't think the problem is with the lens at all.)

[Rodne Gold]

Just an aside , if I do inside borders of a plate , I let the laser do em as vectors and not raster (it takes much less time then letting the laser scan side to side engraving the verticals)
If I need a thick line , I use the contour tool and contour the vectors inward and outward to give me the line thickness I want and with a small enough pitch between vectors to make the one vector partially overlap the other

[David Fairfield]

Just a quick reply to say many thanks for all the ideas. Lots of things to try that I hadn't thought of, and I think there must be a solution among them. I'll report back!

Dave