Alignment Error Map - What is acceptable?


To check accuracy start with images on the paper and try to align an engraving over the top. You can make the original marks with a 2D printer or use the GF.



As Erin pointed out the post and pre images do not align. Do a search using the terms “post image alignment” and you will find multiple people who have pointed this out. Palmercr’s suggestion is the way to avoid any pre/post image discrepancy.

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Oh, that’s really cleverly simple. I was coming up with all kinds of ridiculous processes that involved, like, a key for scale and alignment marks and overlaying photos and all kinds of nonsense. I’m just going to try your way instead.



I printed out my alignment targets on paper and taped the paper to the crumb tray.

The vectors in the GFUI do not consistently align with the picture captured by the lid camera. An interesting item of note. The vectors in the GFUI that are misaligned are always to the left of the targets captured by the lid camera. Considering the lid camera picture is a distortion corrected fish-eye photo, I would suspect the misalignment to be biased left, right, up, or down depending on the targets location relative to the center perfectly aligned target.

Here is the GFUI after running the program.

Two items of note:
1.) The misalignment between the vector elements and the picture captured by the lid camera remain the same. If you stack the two images in PS or GIMP and do a difference between layers, the only significant changes you see are the cuts in the paper.

2.) The cuts in the paper are all uniformly misaligned. Relative to the printed target, every cut is roughly .120" to the right and 20 degrees above horizontal. This can be seen more clearly in a cellphone photo I took of the paper taped to the bed.

In conclusion, it appears the algorithm being used to flatten out the fish eye photo taken by the lid camera is not creating an accurate representation of the material within the GFUI. This error is then compounded by the actual cuts being shifted right and up. The .006" difference between the paper’s actual surface and the minimum height of .010" may account for some of the errors, but I highly doubt it accounts for a significant portion of the errors, especially considering my experience attempting to cut on proof grade remanents.



That’s what I expected, too! It’s so interesting that you’ve got those centered ones perfectly aligned, but all the misaligned ones are off in the same direction. Maybe that’s the effect of the lens correction they’re trying out as the moment?

But this is what’s weirdest to me. I wonder how much rounding up the height and/or focus height are contributing to that. It seems odd because those centered ones looked perfectly aligned, so I wonder what it’s using to determine placement. Maybe ungrouping all the targets after they aligned but before they print would give a different result? And I wonder if you can correct for the uniform offset manually (at least until algorithms or whatever get tweaked - I believe this is an ongoing thing). Like, if your machine always prints slightly down and to the left, could you line up your design in the gfui, get it exactly where you want, and then nudge it, like, 3 times right and one down, or whatever.

I don’t mean to imply you should have to test anything further, I’m just always full of theories :blush: If I get around to doing any of that myself, I’ll be sure to post it. For science.



This sounds like this…created by @cynd11 ;

A way to improve object placement

I set this up and use it quite often.



Fellow Glowforge’ians

I did something like this 3 weeks ago and sent my results to the GF team on Jan 1st and to be honest was a little disappointed in the reply.

After I reported they asked me to perform one more test on the Owners Ruler and send those results. The reply I got was:
Thanks for taking the time to perform the troubleshooting and provide the details. The test with the Gift of Good Measure shows that your Glowforge is performing within the range of accuracy that we expect right now. Most importantly, that means that as we make improvements to the software, I expect you to see much better alignment.

If you look at my target results they are similar to what others are seeing, and as you get closer to the edges of the bed they get even worse.

My Results.:

The second image is the final test they had me do with the object directly under the center of the lens and even that was off . I was using the PG Draft Board for my test.

Hopefully GF can get some serious updates flowing here to correct this error, as like many of you I have burned through a lot of materials with the cut not aligning up to the material placement.

Hope this helps,

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One can see the alignment will be out when the outline of the board is not shown square.

Did anybody notice an improvement in accuracy in Dec? Examples like this seem just as bad as they ever were. The announcement implies there should be a big improvement if they have started using machine specific calibration data. Perhaps the machines shift in transit or need to be on a perfectly flat surface for the calibration data to be valid.

It would be interesting to see how it varies with a small shim under a corner.



I did not have my machine until Mid Dec so could not really tell you how much it improved. I can tell you that my machine is on a piece of solid Bamboo table that is both 100% level and flatter than I have the ability to measure. Those results I shared are with that taken into account.



I don’t remember what post it was in but I recall a conversation about the stickiness of the feet on the glowforge and the flex in the machine. At least one user said despite a flat and level surface, when they placed their glowforge the one foot stuck and caused some flex that they didn’t really notice until later but after picking that side up and carefully placing it back down so the flex was relieved, their camera alignment improved. Going from your post I’m sure you’ve already made sure of all these things but thought I’d throw it out there anyway just in case.



Just my 2d (UK) worth.
How many people check the flatness of the top surface of the crumb tray ?
When I was considering an early version of my vacuum bed insert for the tray, I realised that the design wouls only work if thre was no distortion cused to the honeycomb.
So a quick experiment - pressed down on it, and yes, it can be flexed.



Thanks @josephtpage you had me second guessing myself… just ran in and checked both of the foot pads are perfectly flat… was hoping I missed something and had an easy fix… no such luck. :frowning:



Bummer that wasn’t the easy fix.



Interesting because the crumb tray is boxed separately so it is unlikely the machine is calibrated with the crumb tray that it comes with.



When I first set up my new Pro unit I mapped it out and needed to do a 2 ticks right & 1 tick up move of my design vs where I wanted to align it on the material. Two weeks later I went to verify something for Support and repeated the alignment check but started with my 2R/1U adjustment and found I was off :slightly_smiling_face: It’s now dead on - for my purposes…about 1/64" in horizontal which I can’t correct with an arrow key tick unless I zoom all the way in. Generally I don’t care about 64ths so I don’t bother.

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why isn’t there a user calibration option?
it’s seems to be such a simple implementation, compared to the rest of the software developed so far. there are so many variables that would make a factory calibration inadequate, such as transport, bed level, temperature, trays manufacturing tolerances, degradation and many, many more: and any calibration, in any machine with moving parts will tend to drift over time. my inkjet printer can run a calibration or an autoalignment, why can’t my laser cutter?

there are so many ways this can be achieved, including the map above (which we can print on our own), a separate alignment jig, a test cut on draftboard… the engineers at GF don’t need my 2 cents on how to achieve this, but they do need to trust us, the users, the owners, with at least the option to calibrate our own machine.
The ease of dropping the design over a picture of my material is at the core of GF’s innovations, but if it is unreliable and doesn’t work the way we expect it to, it will cause more frustration than anything else!



Thanks everyone for your thoughts and contributions to this discussion.

@erin, the nudging solution is problematic. First the amount of nudge changes with the level of zoom, and second the error isn’t uniform. You’d need a nudge map just to know how much to nudge a design at any given location or zoom level.

@alexmcclure, it’s interesting your error map shows the error radiating from the center, while my error radiates from the center but is biased to the right (or left depending on what you use as the point of reference).

@josephtpage, thanks for the reminder about the table/feet situation. I will have try moving my GF to a more rigid table to see if that helps any. I suspect it won’t make too much of a difference considering the degree of the distortion, but I’ll take any improvement I can get until there is a more robust solution. Unfortunately, twisting of the frame doesn’t explain my center points being consistently shifted to the left about an 1/8th of an inch.

@leahgee2, I agree an at-home re-calibration procedure would be helpful. I wonder if the calibration is stored in firmware or if it is in the cloud and keyed to each unit by serial number. I would like to think Glowforge could ship a calibration map with the crumb tray. The user would just have take a picture of the map with the lid camera and then connect the center of the calibration map targets with a target overlay thus creating a vector map for properly de-fish-eyeing the camera. The calibration map could be photographed at multiple heights by stacking proof grade material under it.

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Is that just in the centre or over the entire workspace?

I seem to remember @Jules has a very accurate machine as well but most people seem to have gross errors in the corners and rectangular sheets don’t look rectangular in the screen view.



oops - didn’t see who the reply was too - please disregard



My screen view changed quite a bit after the last update, and then it’s slowly been improving again, but it’s still off by about a quarter inch at the outside edges.

They’re obviously doing stuff behind the scenes that affect the placement alignment all the time. If everyone can just expect this kind of thing while they are working out the kinks, it won’t be quite so frightening. It’s not going to be like this forever, but it might be for a while. (Possibly months folks…they’re not going to get it fixed on our schedule.) Easiest to just work around it for the time being.