Print and Cut alignment accuracy - red dot or beam combiner


" I have a CO2 and a diode laser, both with a simple red dot pointer mounted on the head vertically, so parallel to the laser beam."

Thanks Dave, that is great to know about the offset accuracy.

I have spent the past few days designing a laser mount (inspired by similar designs on the internet) that will run a parallel crosshair to the beam. I will add the offset in Lightburn too. I tried a red dot off the side of the laser head and found it moved out of alignment every time I moved the laser head across the bed or lowered the z axis. Most frustrating!

Should my crosshair design not work, I’ll try a red dot mounted vertically like yours - I have seen a few diode lasers with this system on YouTube.

When making my mount, I found I couldn’t get the laser lines fine enough in the crosshair even though the laser’s focus is supposedly adjustable. I came up with the idea of printing some half caps for the ends of the lasers and can rotate them perpendicuar to the laser line. This seems to work well and I now have a super fine crosshair guide.

I did the same for the red dot laser, making a fine holed cap for the end which gives it a very fine dot that is more precise. I have added some pics of my 3d printing so others may use the same idea :slight_smile:

xhair 1

Moving out of alignment for Z-axis makes sense but not for moving across the bed. You may want to check your bed for level. It’s likely not at equal distance to laser head across the bed. Do you get different quality of cut depending on placement of material on bed? If so, that would be another indication of bed level problems.

Hi Angie, the red dot laser i used looks the same as yours though mine was a single dot version. It is suposed to run on 12v but at the close range we are using it, the dot is too bright making quite a large dot even when focused ok. The solution was to add a small adjustable dc-dc converter and reduce the voltage to around 2.5v which although dimmer is perfectly visible and a tiny dot.

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good tip :innocent:

I just made new laser beam alignment targets using Print-and-Cut and measured the results to see how closely the cuts worked out.

They’re printed on a Letter size sheet cut from an old manila folder:

I used the upper-right and lower-left crosshairs for the P-n-C alignment:

I burned pinholes after jogging the laser to the targets to mark those locations. The inner circle is 2 mm diameter, so the upper-right target is dead on and the lower-left is off by less than half a millimeter.

The inkjet printer maintained good accuracy left-to-right and was off by 1.3 mm vertically; the manila paper is at the outer limit of what it can handle. The corner P-n-C crosshairs should be 150 mm × 240 mm and came out 150 mm × 241.3 mm. I used the Scaled version of P-n-C to adjust the cuts to match the printed dimensions.

All of the P-n-C targets have a 2 mm circle burned in Dot Mode to show the difference between the adjusted position and the actual position. The maximum error looks to be about 1 mm vertically along the left and right sides, with maybe half a millimeter of horizontal error.

The perimeter cuts should lie along the red outlines. Their actual locations matches the errors in the adjacent P-n-C crosshairs:

So I think you can expect about 1 mm of positioning error if you hit the P-n-C targets dead on, at least for Letter sized layouts. I’d budget maybe 2 mm around printed patterns to prevent clipping the edges.

The inkjet printer error seemed to be linear along the vertical direction, so a simple scaling could correct it. Before figuring out P-n-C, I tried directly laser-cutting a laser-printed pattern, but found the paper deformed unevenly in all directions. If that’s the case for your UV-printed images, P-n-C will have trouble compensating for the errors.

More details on my blog: