Hey Laser Peeps…I have read several posts about the focal height and material height and I am confused…I cut cotton fabric backed with a lightweight fusible backed with paper…thickness about 3/16th of an inch at the very most. I have had issues with cutting through some things, have power etc. correct but does not always cut through and I am not sure how to set these two together…anyone have a SIMPLE explanation?
How do you know the power is “correct”?
If it’s not cutting through, then I would argue the power is not correct, and you need more. You might need to make more than one pass…
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Because its the same setting for power I have been using effectively for a long time now (also increased in increments of 5 to see if it would change)…Not good to do multiple passes on fabric…
When was the last time you cleaned your machines optics?
last week actually also did the camera refocus…I am actually asking about the focal height and material height though, I know it can have an impact on cutting…can you help with that?
Your material height is the thickness of your material measured from the top of the crumb tray. The medium proofgrade materials are nominally .125 inches thick (although not unusual to be anywhere from .119 to .123 for some materials).
The focal height (focus height in the image below) is where you set the laser to “aim” at. It is nominally equal to the material height but you can set it higher or lower, de-focus your laser, to achieve different affects.
Hope that helps.
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I just tested cutting 2, then 4 layers of fabric, which was my ultimate goal…I can’t get a speed setting that high! Mine only goes to 500? Is it supposed to go higher or is that for PG?
Anyway, was able to cut 2 layers on high power, speed of 500 and I can cleanly cut through. Cotton fabric is really thin even backed with paper backed fusible…the 3rd layer almost cut all the way through but it was not as clean. Tiny threads still attached. Layer 4 had some laser marks in a few spots but did not cut at all.
My goal is to have it cut through those 4 layers which measure less than 1/4 of an inch. If it will cut through that thickness of wood I should be able to cut through 4 layers of fabric…
Is the focal height affecting my cut? I made it the same as the thickness…I have read they need to be the same but its not working for me…any ideas?
Oh and thanks for trying to help 
He posted an engraving setting. You are cutting and that is 500.
Thanks, wasn’t sure I just cut have not done any engraving…
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Maybe. Maybe not. Things like acrylic and to some degree wood rely heavily on what’s called Total Internal Reflection. With the right angle of incidence, those materials can reflect the beam back and forth, cutting deeper. The beam itself is only in focus for about a tenth of an inch.
As for your question, material height is basically used for camera dewarping. Focal height is the height above the crumbtray surface you want the beam to be focused at.
Unless you are purposely overriding the autofocus (by specifying a different focal height than material height), it will scan the material before the job and use the autofocus calculation.
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I appreciate you answering but I still don’t get it (asked for simple explanation) Sorry just still new at this and have read SO MUCH my head is spinning…I’m just trying to cut 4 layers of fabric that has an actual height of just a smidge over 1 /16th of an inch…how do I set this so the laser cuts through that? What settings determine how DEEP the laser will cut? I still don’t understand the correlation between the focus height and material thickness and how they work together…"material height is basically used for camera dewarping”…not sure what dwarping is…"Focal height is the height above the crumbtray surface you want the beam to be focused at.”…what I want is the beam to cut 4 layers of fabric…lol…Trying to understand, maybe I am not asking my question right?
The settings don’t “tell the laser how deep to cut”, they state where the focus is. The problem you may be having cutting fabric, is that cutting layers of fabric is actually not recommended. No matter how flat you hold the layers, the cutting process can allow air in between the layers and that can cause a flare up. The laser’s impact on the first layer of fabric is never going to be the same as it is on the fourth layer of fabric.
I suggest you read the tips regarding manual settings and search the forum for tips regarding cutting fabric. Here is a start: https://glowforge.com/support/topic/first-three-prints/working-with-manual-mode
Material thickness tells the machine where to focus the beam, which is necessary to cut cleanly. The AutoFocus feature allows the machine to check and adjust that setting.
There is no “camera refocus” procedure but I assume you mean calibration - that just allows the UI to more accurately represent the cutting bed. The actual focus process uses a laser and sensor in the head of the machine, not the camera on the lid.
If your machine was cutting fine, and now doesn’t, then either the power is reduced (dirty optics can cause that), the beam could be defocused (could be caused by putting the lens back in upside down, or specifying the wrong material thickness), or the material itself has changed slightly.
THIS has been very helpful and has given me a better understanding of what I am trying to do and what I can actually do…(We do not leave the laser unattended when working with it ever.)…I also use magnets to hold the fabric down so cut pieces do not fly in the path…I am going to try it slowing down my speed some and see if that helps…at this stage I am just testing what I can do. I can cut smaller runs of things but I am trying to sell some of my laser cut appliqués wholesale and need to consider my time…I have back up plan if I get busy but would rather not send it out when I have my own laser…Thank you SO MUCH!
Unfortunately, sometimes things are complex and there isn’t a simple explanation. There is a lot to learn about laser use, you’re trying to compress literally years of techniques and theory that we’ve collectively developed into a single post. You’re just going to have to invest in the learning process, cutting multiple layers of a material brings a number of challenges, there’s no magic bullet.
The learning curve is sometimes steep but can be really rewarding, never hesitate to ask stuff but don’t be surprised if it’s not as simple as it seems on the surface.
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I understand that totally…I was interested in “how” the settings worked, height, focus all that and was having a hard time understanding the posts I read with a ton of technical aspects…I was actually able (because of the link that dklgood posted) able to understand it better and changed my speed and adjusted my power and was able to successfully cut all 4 layers with no flare ups etc. Even if I am just planning on cutting 1 layer, slowing down the speed will make things better as well. This is still a major learning curve for me and while there is a TON of info in the forum for cutting all sorts of things, there is very little on fabric that pertained to what I am doing. It may also be HOW I am asking, still learning all the laser lingo…lol I do appreciate EVERYONES input, I am working it out
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I’ll try and talk about this as I understand it. I am not an engineer. This is a simplification, but it may help.
Focus can refer to how the lid camera focuses on the surface of the material to accurately dewarp the image so you can get excellent design placement. That is what the calibration routine is for and why the initial material thickness is important to get right. The Set Focus command helps in this.
But then there is the focus for the lens in the head for the laser beam. Set focus also is part of this now. The set focus now uses the head camera to focus so the lid camera’s image is more accurate.
Then there is focusing for the beam focal point. The most intense power of the laser is at the center of the focus cone. In thin material it isn’t much of a deal, but once you start getting material thicker than the beam width, you can sometimes adjust focus manually to get a better cut, especially in very thick material with multiple passes. The Glowforge manages all this with autofocus and you shouldn’t have to worry about it.
But introduce something like a layered stack of material, you are now changing the apparent density of the material. The fabric may be stacked tight, but it is still not going to be a consistent density through the cut. So like cardboard, there are issues with how you apply power and speed. It isn’t always best to apply full power with cardboard because the inner corrugations allow for air to feed flames that can’t be accessed by the air assist. Hence easy burns.
In general when cutting, you apply full power and then adjust speed to prevent overburn.
But when you have less dense material, I have often found that full power needs to be backed off.
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I backed off my power to 95 and my speed to 250, this cut cleanly through all layers with a bit of scorch on the paper backing of the fusible…I have found however, then by laying some freezer paper (it kind of clings onto the crumb tray) that it mitigates the scorch on my paper backing. I am still going to play a bit more with the speed and see if that makes more of the scorch go away…but I got good cuts. The laser cuts quickly but cutting one layer at a time is labor intensive. Trying to avoid outsources larger jobs and this may help…
Thank you for your explanation, it makes a TON more sense to me now…It really does take a village sometimes! lol xx
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Magnets, particularly strong ones, can cause components in the laser head to malfunction. I think understand what you’re trying to do but I suspect Glowforge is not the right machine for the kind of production work you’re aiming for even tho it’s fantastic for prototyping with fabric.
Have you considered having steel rule dies made of your appliques and then using a clicker press or small arbor press? (depending on your design size/complexity) It’s not terribly expensive to have the dies made. Clicker presses aren’t cheap but small arbor presses are and there are also many services you can take/send your dies and fabric to who can click them for you.
This issue was resolved. Magnets simply slowed a fan, which the software detected as a problem. They changed the software to not abort a print due to this.