Laser isn't Cutting Square to Material Surface

I’m still confused. It sounds like you’ve got it figured out, so support may be able to help you. A tilted beam angle would generally mean something wrong with the machine.

The thing that’s hard for me to understand though is how a slant from the beam hourglass is easier to account for in the design than that of a tilted beam. It seems like if you need right angles, either way it isn’t going to work.

It’s ok though, no need for me to understand of course. But I am curious, so I’m interested to see what support decides or needs to see.

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I know what the problem is, but not if it is normal - i.e., within expected tolerances.

When the beam is parallel normal to the surface, the resulting cuts are consistent and the slot sides, while not flat, are average parallel. This means the tab going into the slot will be square to the part that the slot is in. I can account for the lack of flatness in adjusting for kerf and the tiny amount of space caused by the hourglass is just about enough for the glue to wick in. I can clamp the parts square if I am worried about precision and they will cure square.

When the beam is tilted, I now have to account for both the hourglass, which if the focal point is at the top surface is actually a V, and the fact that the average wall on the slot is angled to the surface, meaning when I adjust the slot to allow the parts to be square I have a much larger gap between two faces. The gap is larger than the glue will fill, leaving an unslightly and weak joint.

I will see if I can get some pictures to turn out. The ones so far haven’t shown the issue.

@rita Is there any way someone from GF support can take a look at this issue for me? The pictures show as well as I am able the problem I am seeing. The part is cut from Proofgrade clear thick acrylic and I have checked the sheet for flatness.
My GF is level within 0.2 degrees per my smartphone app, from taking measurements in all four corners.

DSC04402

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Where are you setting the focus height?
If you are too high (or too low) then all you will see is the slanted part of the cut rather then an hourglass shape. Can you try making a straight cut in a piece of the same material and show it to us from the edge looking into it?

In other words if the beam axis is Z, the head moves in X, and the gantry moves in Y, place the edge of the material parallel to Y, make a single cut into it along x and then take a picture parallel to X.

That way we can see the cut kerf in context instead of just one side of it.

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Have you checked that the head is firmly seated on the carriage? Perhaps remove it and check to be certain the surface where the magnets are is clear of any debris? Check that the carriage does not have any vertical play?

Any of those could tilt the head unit. Were those cuts (in the XY plane) parallel to the X or the Y? That could inform you of what might be most important to look at. For example, if the carriage is loose, that would imply that horizontal cuts would have the beam angled slightly toward the rear of the machine. Whereas debris under the head could cause any possible direction of error.

@jkopel This piece is made up of four straight cuts. If it were just the kerf, the slope angle on all sides of the part would be about the same but in opposite directions, with the narrow part of the removed area at the top of the material and the widest part of the cut at the bottom, making the resulting cross-section of the part a trapezoid.
The actual resulting part cross-section is closer to a parallelogram, with opposite sides sloped in the same direction, though a slightly different amount, as expected, since the kerf will change the slope of opposing sides.

@johnse Per my original post; I have reseated the head several times to be certain there are no debris under the print head. I have wiped the holder arm down, I have removed and inspected the print head for foreign objects, and carefully reseated the head to ensure that it is firmly and properly seated.

I was having the same problem. Had to return my original unit,

I have assembled a diagram of what I am seeing with my parts, why I assume the laser is not normal to the material surface. I have seen this with thick Proofgrade acrylic and medium Proofgrade Maple for sure. I have not looked for it with other materials yet. It seems to be only in one direction, but I have not yet been able to determine which direction as I have not done any structured tests.

@Rita @dan I realize you are busy. If you or one of the support technicians can take a look at this, I would like to know if this is within tolerances for the machine or if there is a problem. If there is a problem, I would like to know if it is something that I can repair myself or if I will need to return the Glowforge. Other than this alignment issue I am happy with the laser cutter as it does everything I ask, so I do not want to return it unless I have to.

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I liked your post, not because I like what is happening (obviously), but because that drawing is a very clear description of what you’re seeing and that the unit is not behaving properly.

Unfortunately because the expected behavior is to get a cut that is not normal to the surface it’s hard (for me, and I suspect support also) to figure out whether people are describing the expected or an unexpected outcome.

Another one of those cases where taking the time to draw the picture is worth a lot since more words may actually increase confusion.

I suspect you’ll need a replacement laser cutter. Edit to add: But maybe it’s just the mirror in the replaceable head?

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I’m so sorry for my late response.

I’m looking into what’s happening here and will update the thread when I know more.

Thank you for letting me know. I am happy to provide any additional information upon request.

Right now it looks like most of the misalignment is in the Y axis, as if the support bracket for the print head isn’t perfectly level.

I have checked the crumb tray and the gantry and print head as best I am able with my phone, using a level app, and they all seem to have about the same tilt.

Thanks for your patience.

Would you mind trying something for me:

  1. Create a design of a 1" circle.
  2. Print the circle on a scrap of Thick Clear Acrylic.
  3. When the print is finished, keeping both pieces in the bed, rotate the circle clockwise in the hole. Are you able to rotate it all the way around?

Please let me know how it goes and send me photos of the pieces (both the circle in the hole and the edges of the circle)!

Thanks for your help. I will conduct the experiment and let you know what I find.

@jaz I have conducted your requested experiment. I adjusted the design slightly to give you as much information as I could think of. What I observed is that the circle would not turn until I broke it free of the mating part. It did not cut completely through.

Then I turned the circle and while it turned inside its hole, it did not stay centered. You can see the change in the photos below. Each picture is at about 45 degrees from the last.









The next test was to see if I could isolate the error to a single axis. The slots in the base are cut to be a tight fit, with very little wobble. I estimate the wobble at about 0.2 degrees.
X-Axis:


I see a variance of about 0.5 degrees in the X axis alignment, from perfectly square to 0.5 degrees. This gives an approximate X axis error of 0.25 degrees. The tilt is top to the right of the laser.

Y-Axis:



At the base of the insert I measured a gap of 0.075 inches. The tab is 2.09 inches tall at its inside face, measured vertically. A little trigonometry gives an error of 2.055 degrees. With the estimated wobble, I will just call it 2.0 degrees.
I did not see anything on the head or the head support that would lead to the top of the head being tilted toward the back of the laser by 2 degrees.

Please let me know if there is any additional information you require.
Thank you for your time and attention.
:edit: Adjusted error value on X-Axis

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I forgot the pictures of the edges! Sorry!

Looking down the X negative axis:

Looking down the Y negative axis:

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If it will help, I will also send you the parts. Just give me an address.

I had some down time tonight so I looked at the X-Carriage as much as I could without disassembling anything. I found that when I pull up gently on the air assist fan shroud, the entire X-Carriage rocks. It seems to be spring-loaded and drops right back into place, but this action also lifts the back rollers out of alignment with the gantry. I don’t know if this is something that may be causing it.

If GF is willing to provide the information and permission, I think that I could potentially put a set of spacers on the front X-Carriage wheel posts that would shim the X-Carriage to the right dimension. I would just need to have the geometry to calculate the thickness of the spacers. This would save a return.

Thanks so much for doing that!

I’ll keep looking into this and update the thread when I have more information.

Thanks for your patience.

Once again I apologize for our delay. There may be an issue here, but unfortunately, it’s difficult to tell from the photos. I’d like to send you a part and have you send one back so that we can examine it to deepen our understanding. I’ll email in a moment to make arrangements.