Adding steps/mm to a Chinese laser

[Ian Johnson]

When rastering, the background always has a pattern of vertical lines, which is always in the same position regardless of speed or power. Someone did a lot of testing, and found that the pitch of the lines corresponds with the distance the X axis moves in each full step. There are additional artifacts visible in cuts that correspond to microsteps, but microsteps are prone to error so the motor movement can still be more biased to the full step - https://www.youtube.com/watch?v=aOi8Mxg85vQ.

I'm thinking that increasing the resolution of the X axis could significantly improve the quality of engraving. Upgrading the driver in some way to increase the microsteps may not help much, however improving the ability to execute microsteps might. On drivers used in 3D printing, there is a pot that adjusts the current to the motor. Tweaking this can affect how smoothly the motor runs, and get it to microstep more reliably. Do the drivers on a laser cutter have a similar adjustment?

The easiest drop-in solution would seem to be changing to .9 degree steppers, doubling the steps/mm. Unfortunately the Y stepper has a double shaft, and it doesn't seem possible to find a .9 degree NEMA 17 stepper that also has a double shaft. Is it possible to set different steps/mm for X and Y? It would be preferable to increase the resolution of both axes, but even just upgrading the X should be a big improvement.

The next option is gearing the output of the steppers. That would require making new mounts for the motors and pulleys which I can do, but is much more complicated.

Has anyone tried any of these options?

Improved motor control to eliminate emphasis on full steps
Higher resolution stepper motors
Geared output with belts and pulleys

My particular Chinese laser is a Gweike 60W.

[Bert Kemp]

would in creasing the scan gap help at all?

[Ian Johnson]

The scan gap affects horizontal lines, which combined with the vertical stepping artifacts creates a kind of canvas texture. Here you can see some horizontal scan gap lines which are a different pitch from the vertical stepper pulses-

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[Kev Williams]

I'm not sure I'm understanding "vertical" banding lines having anything to do with Y-axis travel. Any glitch in Y travel should show up as horizontal lines. Vertical lines are caused (by my machines anyway) by the beam overlapping in the X path.

Back when we were having our lasered photo contest, I laser engraved this pic below of our boats in our harbor. It turned out extremely well IMO, but I didn't enter it in the contest because, check the sky above the mountains, it's riddled with horizontal bands :( - This is likely the result of Y-axis microstepping issues --which is good to know because I've never known what to blame them on!
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As for vertical bands, these are test runs at 50 lines per inch (except the top of pic 2 which is either 400 or 500 LPI) I did with my LS900 before it was a year old. The left pic shows how the beam wobbles. The first 3 lines are rasters at different speeds. While the wobble changes a bit, it's still there. The bottom line is vectored at 100% speed (which is about 25% of full raster speed), but notice there's zero wobble, lines are pretty much dead-straight. What this tells me is that the wobble is not caused by a mechanical issue, and service reps weren't kidding when they told me the wobble is "by design", supposed to help with photo engraving. The 2nd pic shows what happens when the beam paths overlap more in some places and less in others, the bright areas will just keep going as far down as the engraving goes. This is really annoying and apparent on black anodized aluminum, and REALLY bad on plex and glass.
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Anyway... :)

>edit< You got your post in before I was done with this one ... ;)

[Bill George]

I have used a Chinese laser, a GWeike Storm 500 and never saw those lines?

[Clark Pace]

Never had that either on my limited useof gweike. Or on my Redsail. Although on my ups I got banding if my bearings were dirty