Confused on this DPI thing/I Need another vocabulary lesson

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#1

Ok laser experts out there. Time for me to beg for help with my lack of knowledge.

I’m not really understanding this DPI thing. I always understood it to mean the number of dots you could place in a line one inch long.

But the kerf of the laser is .008 inches which to me seems like 125 DPI. I see the motion precision to .001 inches which would be 1000 DPI And I can see where .008 inches motion would mean any thing that wasn’t cut with laser on during motion would be more perforated than cut. So I guess my question is how does this all work and does it relate to monitors and PPI or printers and DPI?


#2

Interesting point about the cut kerf, but the answer may be more complicated than it seems and all I got is more questions!

There has been discussion about the kerf from a laser cut being hourglass shaped, since the actual point of focus is a little bit below the surface being cut. Maybe the stated .008 number is the widest part of the hourglass?

But if you are engraving away the entire surface (as opposed to trying to cut clear though) then perhaps you want the point of focus ON the surface and so the dot might be smaller? If that is the case then a .001" move and then pulse might in fact produce a 1000dpi image on the surface.

Another factor to consider is that you are burning/melting things rather than cutting them with a sharp tool.
So if your piece of wood decides to keep burning for a little while it may not matter how precise the motion is, .001" is pretty small!


#3

I noticed something similar. In one of their videos they mentioned how much space one dot took up which equalled 1250dpi. I wouldnt be opposed to the increase in DPI, but im ok with 1000 as well considering a lot of competitors are running around half that.


#4

Well too high a dpi and it will take forever just make worthwhile discernible marks for a bitmap. Maybe that will be @dan / Glowforge’s next disruption a dual focusable laser so it can do one fast pass to get the big stuff with a large kerf then back to small for the detail work


How much data is transferred while lasercutting?
#5

Lasers usually advertise the positioning resolution, which for us is 1k dpi. It would also be reasonable to advertise (spot size) / space, which would be a smaller number. But spot size varies with material and gets really complex given the distribution of the beam, and you can put multiple big-spots in different positions, so we went with the standard. It’s not unfair for you to poke at that standard for being incomplete and optimistic, though.