# Laser missing details while engraving

It’s not clear. There’s a switch to enable / disable the adjustment, so why not use that?

This is not as difficult as you are making it.

• Turn off the `Scanning Offset Adjustment` switch
• Use the rectangle you’ve already set up
• Make five copies of the rectangle, line them up in a neat vertical stack for easy comparison
• Put each rectangle on a separate `Fill` layer, with a `Line Interval` of 0.5 mm
• Set the layers for 100, 200, 300, 400, and 500 mm/s (assuming you have changed the X axis speed)
• Set the layers for an appropriate power; maybe all around 15% will do
• Run the job on something cheap
• Take a high resolution photo of the result and upload it

Then we can measure the actual results and reach some valid conclusions.

A simple test pattern that should get you started:

These pix were downsampled to be 1500 pixels tall, because the forum chokes on the original camera files. The key is to keep enough dots in the images so you can actually see the details.

Without the offset adjustment:

With the offset adjustment:

You can get close by eyeballing the offsets in relation to the line spacing, but, hey, you know you want a magnifier anyway.

Thanks for this.

Here are the results after doing what you suggested (I have also cleaned the mirrors and double-checked mirror alignment).

Hopefully, this is high enough quality.

Well, that shows part of the problem.

Print it as full-page picture, apply a ruler, and find the lines are 1.89 mm apart, so multiply by 0.265 = 0.5 / 1.89 to get the actual 0.5 mm spacing. That distance will be different when you print it, but that’s how to get the scale factor.

Then measure the offsets between adjacent line starts / stops:

• 100 = 3 mm → 0.79 mm
• 200 = 5 mm → 1.32 mm
• 300 = 6 mm → 1.59 mm
• 400 = 6 mm → 1.59 mm
• 500 = 7 mm → 1.85 mm

The 300 & 400 mm/s distances are the same here, although some averaging & pondering would likely show small differences.

On my machine and, I think, yours, the first line in each pattern is on the bottom. This may be due to the LightBurn `Cut in direction order` optimization, with `From bottom` selected. That line is processed from left-to-right, so its starting point is delayed from the nominal starting point.

Divide those numbers in half:

• 100 = 0.40 mm
• 200 = 0.66 mm
• 300 = 0.80 mm
• 400 = 0.80 mm
• 500 = 0.93 mm

Pop those values into the `Scanning Offset Adjustment` table, enable the adjustment, run the same patterns again, and let’s see what happens to the edges.

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I have added the appropriate numbers and have ran tests.

This is the result of the first test:

The lines are further off than they originally were.

Just for fun I ran the test with negative numbers as well:

I apologize for it being slightly blurry.

Y’know, we techies do have an … odd … idea of “fun”.

I’m willing to change my mind based on evidence: negative offsets are the right answer for your machine. There’s obviously some fine tuning possible for some of those speeds, but that’s what measuring magnifiers are for.

At this point (I think) you have:

• Increased the axis speed limits to 500 mm/s
• Tweaked the mirror angles for uniform results across the platform
• Set up a good-enough scanning offset table

One more quick test for beam shape is in order:

• Set the manual pulse parameters (using the machine console, per section 8.3.4 of the 6442 manual) for 10 ms
• Set the power to 20%
• Put a paper target at the entrance to Mirror 1
• Pulse the laser using the console `Pulse` button
• The result should be a light scorch darkening toward the center

Something like the one on the left from this set:

Twiddle the power or time to get a toasty, not overdone, scorch.

If the spot looks like that (which is what I expect) then the tube is working just fine.

Then set up your original wood coin pattern, dial in the speeds & powers (having changed the configuration affecting those values) to get the darkness you expect, and let’s see what it looks like now.

I don’t actually have any of those paper targets. I’ll have to buy/cut some soon.

In the meantime, I did the only natural step and skipped right ahead.

The results are…much worse. The left one shown here is from the bottom left corner of the machine (bottom as in closest to the operator), and the right one is on the bottom far right side of the machine. In the photo they look as if they are rotated slightly…that is only the photo. They engraved pointed up as they should.

They are not only skewed quite a bit more but also fuzzy and they lack even more detail.
And unfortunately, the weaker lasering still exists on the right side.

I’m stumped!

It’s worse than that.

Rotate the image so they’re aligned to the scanning direction:

Notice the little fragments of the pattern scattered around where they shouldn’t be, with some looking inside-out.

Try this. Without changing anything else, make all the values in the `Scanning Offset Adjustment` table positive and run that pattern again. Yes, I know. Just do it. Then flip them back again.

The file you uploaded above comes from V 1.6.03, but uses the old-style `*lbrn` file format. Is there a reason for not saving as a compressed `*lbrn2` file?

That’s why I want to see the beam shape. That won’t affect the scattered geometry problem, but if the tube is not behaving properly, it may be impossible to focus the beam.

Also, the beam may be grazing the inside of the nozzle opening and generating a reflection off to one side. Stick a piece of masking tape over the nozzle, fire one pulse through it, and verify that the hole is in the middle of the aperture.

I use a little target with wings, but masking tape is fine:

I know you want to be done with alignment, but the results suggest you’re not.

Stick tape over the mirror apertures and show us the spots at each end of the axes. All three should be on center and have pleasant beam shapes.

I will try what you suggest. Although quick note. The faded arrows on the image are actually the top and bottom. The “6” in the image is actually at the top of the coin.

So the image corrected would look like this:

Also, with regards to the file type. Jack requested a .lbrn file. So I switched it from a .lbrn2 to a .lbrn. In hindsight he probably didn’t mean for that and he definitely has more experience on here and with lightburn so I would guess people have dropped the “2” since .lbrn2 is the new standard it seems. I however, did not know that. So I switched the file type🙂

Here are the results.

I switched the numbers back to positive and then ran it again. Not sure if you wanted to see the results or not. But here they are.
Far-left (the bottom one), not the one marked with 1.

And the far right one.

Again, I wish I could provide the beam shape, but I do not have those paper targets at the moment. Perhaps this will have to wait until I get those.

Here are the beam tests I can do.

Here is it coming directly out of the laser head:

Here is it coming into the laser head module:

Here is it coming off of mirror 2 (the one on the X/Y gantry):

And here is it coming off of mirror 1 (right next to the laser tube):

And yes, I can see these are not aligned very well. I should clear something up. This laser is at a small shop and I was told as long as the laser comes out of the laser head module on the X/Y gantry is not super far off and is not hitting the sides, then all is good. And that since the other mirrors were aligned a while ago, it should be OK. I took this as the truth but, perhaps it isn’t.

Update: I have now aligned all the mirrors. They aren’t perfect but are much better than before.

They’re not “aligned” in any meaningful sense of the word.

The grossly off-center spot on the entry to M3 says the beam is splashing off the inside of the nozzle and reflecting everywhere.

Until the beam is centered in all the mirrors and you get a single dot at both ends of the axis travel for both M2 and M3 and the beam is centered in the exit nozzle, then there is no point in doing anything else with that machine.

Note that I will insist on proof the machine is properly aligned, as in “photos of those spots on the targets or it didn’t happen”.

Also, take the lens out and make sure it’s nice & clean.

Heck, no need to get all fancy. Use tan or blue masking tape (not clear packing tape) like everybody else and get the job done. When the machine is up & running, lay out & cut your own targets from a manila folder to perfectly fit the apertures.

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I’ll be honest, this made me laugh out loud.

I’m away from the machine for a little while. Once I get back though, I know what I have to do!

I did try using masking tape once, and it caught on fire. Not “burn anything catastrophically” fire, but there was a flame.

You are using way too much power/time for your alignment checks… You will get much better results if it’s lightly marked.

You should only discolor the target, not punch through it or make it black.

That’s why setting the controller for a timed pulse improves the outcome: you get the same pulse energy every time you poke the `Pulse` button and can tune for best scorch.

That said, I don’t like the look of the pulse at Mirror 1. If I’m seeing it right, there’s a little hole off-center in a ring, which is not the energy distribution of a good tube:

Sacrifice a manila file folder, slash it into little squares with a razor knife, tape 'em to the entrance apertures, find a pulse energy that gives a nice scorch, and let’s test that suspicion.

Also: beam alignment is an iterative process. First you twiddle the grub screws to get the beam parallel to the axes. Then you slide the mirror mounts back-and-forth to center the beam on the mirrors, which wrecks the angular adjustments. So you re-parallelize the beams & tweak the mounts again. Worst case, the machine has an immovable laser head, so you must shim the tube up-or-down to center the beam on M3.

What I went through the last time around turned into a series of posts:

After a while, it becomes meditative …

This would make sense. I was aiming for a hole through the tape, not just a burn mark. I will try lowering the pulse time.

This is clearly what I need to do. I am not entirely sure if I can slide the mirror mounts, but I will check.

And thanks for those blog posts, I will probably be referencing them.

Okay. After fiddling a little with the alignment, I have ended with this:
(BTW I labeled the mirror on the laser head as “M3”, the one in between “M2”, and the one next to the tube “M1”. I realized you spoke of them in the reverse order after I had labeled them all …sorry).
M1

It is definitely a little low. I hope this will suffice but I can shim up the tube as you mentioned.

M2

M3

And here are the scorch marks (they won’t be centered on the targets, since I already checked that with the tape).

M1

M2

Not a great shape on M2…I even cleaned M1 just to make sure that wasn’t it.

M3

Do either of the m1 or m2 spots look round?

Does the power distribution across the spot look like there is more power at the exact center and less as it goes outward?

No…the shapes are more of an oval.

For M1 I would say yes. But not for M2. I am honestly not sure what is happening with M2. The beam is a…crescent?

Does this first image really look round with an even decrease in power from the center?

I can see what you are saying when looking at that photo. However, I only used the blue tape to get the laser centered.

I shot the laser at that same mirror with a piece of manilla folder on there and got this as shown previously:

To me, this looks like an oval. Now the power distribution looks okay to me. But then I realize I don’t know half as much about this stuff as you guys do. So, I will defer to you.

What would be the next steps to counter act the oval and lopsided shot? Replace the laser tube?