Using CoreFile2 to Calibrate Your Galvo Lens

[@peterchan217]

Hi, thank you very much for your video. It was very nice and clear. At 10:02, it shows that the corfile actually override the field size you type in (174mm x 174mm). Actually i think the field size should not affect anything but it would be problem if i have to amend the corfile. The field not being stable will also screw up the calibration.

[@aliaswave]

Lightburn needs an easier way to setup lenses, adding to the software this should of been one of the features at release.

[@lightburnsoftware7189]

Most fiber lasers come with presets provided by the manufacturer of the machine, so it was not seen as a high priority by any of the users we asked.

[@aliaswave]

@@lightburnsoftware7189 I have 3 Fiber lasers and only 1 machine came with presets for all lenses included.

[@edsai2041]

Completely agree. This is way more cumbersome than it should be.

[@ians9390]

100% agree, makes me not want to pay after the trial. What a pain

[@ians9390]

@@lightburnsoftware7189 Yeah well it looks like no everyone is of this opinion

[@zaprodk]

I believe there is a typo in the video title. It's /cor/file, not "corefile" :)

[@SteveN-bh3wv]

Measurement has been a BIG question of mine. It is stated that you should measure from point to centerlines. But you decided to measure point to point. With substantial bulge, this can be a substantial difference in measurement point to point vs point to centerline. Why are you measuring point to point and not point to centerline? And what are we SUPPOSED to be measuring? What distances is Corefile2 actually looking for? I can't find a definitive answer to this. Also, do you know how it determines field size?

[@imajeenyus42]

I spent a lot of time looking at how exactly Corfile2 behaves, and eventually gave up. Its way of measuring from each point to the centreline makes no sense. For one thing, it is impossible to correct for skew distortions, because you are assuming that points 2,4,6,8 lie on their respective axes and have a distance of zero. As for how it works out field size, here we go 😊 Corfile2 takes the test box size (in bits) and divides it by the SMALLEST distance entered in the distance boxes. This gives a “scaling” factor in bits per millimeter, and this is stored in the COR file itself. When the COR file is imported by Ezcad or Lightburn, it divides 65535 bits (the maximum range of the galvos) by the scaling factor to produce the field size in mm. Corfile2 offers absolutely no benefit over using the normal galvo corrections.

[@SteveN-bh3wv]

Thanks a ton for the info. Field size. Before I knew about Corfile2, I: 1. Determined focus. 2. Got the red dot to be on top of the primary beam. 3. Used the red dot to adjust all bulge, trap, skew, scale. 4. Verify with actual beam and tweak slightly if necessary. 5. Drew a max field square and hit paper with the beam until I didn't have corner fade (Not sure if I should care about corner fade or not since I never draw in the corners and would rather have largest field size possible...thoughts?) 6. Profit Now a persistent problem I see, that nobody seems to address, is that scale is not uniform over the field. If I calibrate a 2x2 near the center, the 5x5 will be slightly out. Likewise if I calibrate the 5x5, then the 2x2 is off slightly. There needs to be a parameter for at least one derivative of scale as a function of distance from field center. Or am I missing something?

[@imajeenyus42]

Regarding field size, I would stick with what is specified by the manufacturer. I agree that sometimes it doesn't entirely make sense, because it may be possible to achieve a larger field size. However, my understanding is that the field size is the area for which the lens will operate "normally", i.e. without significant distortions or clipping. It also handles differences between different galvos having different maximum deflection angles. For example, my 112x112mm lens on a Ouya M103 galvo gives about 140mm square at max deflection, while on a Sino SG2206 it's only 125mm square. So if you're using EzCad's correction stuff (scale/skew/bulge etc), enter the provided field size. You are correct that the distortions are nonuniform. As a result, the scale/skew/bulge/trapezoid can only correct so much. I actually ran into exactly this problem recently when trying to do a double-sided PCB - when I came to drill the holes, I found that they didn't quite line up with the tracks on each side. This led me down a whole rabbit hole of first Corfile2, then deciphering the COR file structure itself. For most purposes (i.e. decorative), I would calibrate the lens using a square the same size as the field size, rather than anything smaller. It's not perfect over the whole area, but it's as good as you're going to get. As mentioned above, the 9-point correction provided by Corfile2 doesn't offer any benefits. There is another version of Corfile going around that appears to offer a 25-point (5x5 grid) correction, but I haven't tried it. Besides, if the 9-point is anything to go by, it would likely be even more confusing to use. The COR file itself contains three important things (there's more, but this'll suffice for now). A "scaling" value in bits per mm, which tells the controller _approximately_ how many bits of galvo signal correspond to 1mm of movement at the focal plane. An "orientation" flag (8 possibilities) which specifies which galvo is assigned to which axis, and whether they're inverted. And, most importantly, the correction table. This is a 65x65 table of displacements for both galvos, covering the entire range of galvo movement. The controller uses this table to see how much it needs to adjust a particular galvo position in order to achieve an exact result at the focal plane. I eventually wrote my own script which will generate a COR file based on the measured offsets for points on a 5x5 grid - however, my brain was full up at that point and I took a break from it ;-) I need to get back to testing it to see if it all behaves correctly - I have a larger PCB to do, which will need a bigger lens, so that'll be a good test for it.@@SteveN-bh3wv

[@markthrasher5847]

Great video! I know it has been posted for a while. Followed it to the letter... but, my dimension in Lightburn are not what is coming out when I engrave. Is there a way to scale the output? Example: If I make a 2" box in Lightburn I am getting a 2.375 box when I engrave. Have redone the Correction file several times. Not sure what I am doing wrong?

[@lightburnsoftware7189]

Currently there is no way to adjust scale after the CoreFile but we are working on adding this ability to LightBurn. It will make it much easier to correct for scale discrepancies between design size and machine output.

[@WeeIrishLaddie1]

Thanks for all the videos. Will you do a video on calibrating the timings?

[@lightburnsoftware7189]

Its not currently one we're planning on doing but that doesn't mean that won't change.

[@WeeIrishLaddie1]

@@lightburnsoftware7189 thanks. I think calibrating the timings is critical to being able to get good quality engravings at the extreme speeds some of these galvos advertise

[@zaprodk]

I can recommend this video and the downloadable files. watch?v=NdFr70yoRyA

[@lightburnsoftware7189]

@@WeeIrishLaddie1 - true, but there are many existing videos that cover timings, and the software used wouldn’t matter for this.

[@I-LOVE-EARTH]

You guys are awesome!

[@TheDopalgangr]

i have a 30w Raycus and when running this with the same exact parameters as you it burned right through the paper and cut out all the shapes??

[@raminzare7073]

I add cor file that I make with corfile2.exe in ezcad 2.14 to ezcad 2.9 and not engraved calibrated? Why this happen? And How should I calibrate with ezcad 2.9.9?

[@GrangerFabCo]

hi, I am trying to make an accurate ruler so I went through thius procedure for my 60w 174mm lense. when I run the corrected lense test, the most outer squares are good( around 150mm) but the smaller squares (around 70mm) are too big by .5mm. Is there a way to correct this?

[@lightburnsoftware7189]

You would need to run the CorFile tool that creates more squares to correct for the additional distortion. Instead of the 9 point version, there is one that will do 25 points that produces a better correction, but it takes significantly longer.

[@peterchan217]

@@lightburnsoftware7189 So you mean Lightburn can recognize 25 point cor file?

[@lightburnsoftware7189]

@@peterchan217 - a cor file is a standard format. It doesn’t really matter if it’s a 25 point or a 9 point.

[@peterchan217]

@@lightburnsoftware7189 Thanks for your reply. I will try with my laser. By the way, would you know the difference between corFile.exe and CorFile2.exe? i used to use CorFile.exe but i saw many people is using CorFile 2.exe instead.

[@hurzmcwurz750]

I just made this core file last week. And you have the same problem as I have. After you import your core file (10:00 at video) your workspace is 204.5 x 204.5 mm. Not 174mm 🤔

[@lightburnsoftware7189]

I would go based on what Corfile generates. Of course if you notice that you are getting distortion towards the outside you will want to adjust. Usually the difference is not quite so high from what the lens manufacturer shows and what Corfile gives you.

[@hurzmcwurz750]

​@@lightburnsoftware7189 In my case I have a 180mm Lens and after Corfile generation I had a workspace with about 183,xmm. The most time I engrave round parts, so I need to center all my text. No big thing at ezcad, 0 is the center. With lightburn and 180mm workspace I set X=90 & Y=90 and I have center of marking area. But with 183,x mm it is horror.

[@Naushad322]

Can I use any lense with any machine Galvano head. Is there any size issue?

[@hateca1]

Hint, don’t use this. Do the Galvo lens correction. Even that is a bigger PITA then it should be.

[@lightburnsoftware7189]

I believe you are referring to the 9 point correction that is built in to LightBurn. This did not exist when this video was created. The plan is to do an updated video using that method.