# Lines per inch test

Is there such a test. I was thinking of drawing horizontal lines that get closer together each line and seeing when they start to overlap. Kind of like the focus test with changing Y instead of Z. The only way I can think of doing it is a script to write the gcode. Any suggestions? I’m interested if I can increase lines per inch by adjusting Z for better focus.

Multiple lines converging to a single point is how I’ve seen it done. Where the lines start to merge is your limit.

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Hmmm, that sounds interesting, do you have an example of this somewhere that I can see?

Thanks.

I don’t have an example handy, but it’s easy to explain.

What you do is engrave a number of lines that are equidistantly spaced at one end and converge to a single point on the other end. The size of your beam will determine where those lines converge with respect to the length of the line (assuming you aren’t over exposing the substrate you’re engraving).

So, to take a random example, let’s say you want to check the resolution of a K40 laser. Now, theoretically, that’s a pretty small beam, but, for the sake of argument, let’s say it’s about 0.03 mm.
If you start 5 lines, spaced 1mm apart vertically at one end of the X axis and have them all converge 300mm at the opposite end of the workspace, pick an exposure that is low (15%) and a speed that will leave a mark, but not burn the material (3000mm/min), then, after you expose the pattern you will see a fairly distinct area, some distance from the convergence point where the lines are still separate.
Be sure to blow off the soot and don’t brush it or touch it in any way to get the best results.

Now, measure from the starting points (the end point may be obliterated) to where the distinct convergence area is. Let’s just say it’s about 288mm from the start. In this case, the beam size is:
BS=1mm x (300-288)/300 = 0.04mm.

With as fine a beam as this, you’ll get more information if you use more lines, all radiating out from a single point, but you want as long a line as possible so you get better accuracy on the result. As it is, this gives you a pretty good figure of merit without a lot of effort.

Obviously a diode laser is easier since it’s a bigger beam.

Paul, Show what you came up with. Show us some picts too. I am interested in this. Everybody says .110 “line interval” is what you want, but would be nice to see a real world example. Thanks!

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