Settings: Synthetics

@jeanneleigh, in the spirit of this being a “Settings:” posting, I will post finished projects elsewhere and keep the discussion here focused on techniques. As I proceed with the project I expect there will be more postings, as I’m still trying to figure out how to keep multiple layers of synthetic fabric in close contact while cutting/stitching over a large span…

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Wherever your finished projects end up being posted I’m looking forward to seeing them! :grinning:

@caribis2, I too did wonder where the beam goes after hitting the metal surface.

Despite how reflective the copper (or aluminum) tape looks, the surface is a sufficiently diffuse reflector to cause the beam to diverge as it reflects away from the metal surface. The energy/area drops with the square of the beam diameter, so it doesn’t take much divergence to really drop the power.

In another posting ( ) I found the beam is already diverging on its own about a factor of two over the span of 0.4" - so the beam out of the gantry is quartering it’s power density roughly every half inch. Combine that with setting the beam power to minimum and bouncing off a diffusing surface, leaves me hoping there’s little to no damage to the GF’s innards.

Nonetheless, this posting is in “Beyond the Manual” for reasons like this.


Silk is unique in the realm of fabric - like OP noted, silk melts, cotton and other fabrics don’t, so, stacking fabric other than silk can be hazardous. (an old, established trick for people who buy oriental rugs is to test to see if it’s really silk or something being passed off as silk: take a thread from the loose fring and burn it - only silk melts as opposed to burning).

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OK - that’s twice I’ve heard mention that stacking up layers of cotton is a fire hazard, so I had to check. The picture below is an 8-layer stack-up of cotton fabric I just cut:


Settings were: power=50, speed=500, passes=10

There were only a few puffs of smoke for the first half of the passes. I tried the same test with a second cotton fabric and got the same results. No hint that it was going to catch fire. Of course, I know better than to walk away from a laser cutter while it’s running, so I’m not going to get complacent about this.

My observation so far is: problem, what problem? Is this worth starting a “Settings: Cotton” topic?


Stacking paper/cardboard can be bad. I haven’t particularly heard of any problems with fabric.

I discovered some shoddy wiring in my house a couple of weeks ago. It didn’t catch fire. But, that doesn’t mean that it was good to have. And I left a candle burning once at home. It didn’t burn the house down. But, both are large causative factors in household fires.

Everyone has different levels of risk tolerance. Some will never take their machines beyond PG-material. Some will push the envelope. Some, unfortunately, will have incidents.

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Hmm… 8 layers of cotton requiring 10 passes? Given the GF recommendation against stacking materials, I’d cut one layer at a time to stay safe. YMMV, of course.

I would think that the point of cutting a stack is that you can be assured of the registration, even if it does take about the same number of passes as cutting the sheets individually.
Happy to see someone test it and post the settings, and appreciate the cautions as well.


I’m betting I could get even Proofgrade material to ignite with the wrong settings - I have absolutely no interest in going there however. Rather, I’ve been trying to explore settings and techniques that enable new materials and/or higher quality without turning my GF into an expensive, high-tech wood stove.

The general principle I’ve been trying to follow when experimenting with settings, is to use the lowest energy possible when cutting, either by keeping the beam moving as fast as possible or the beam power as low as possible. I then use multiple passes to “saw” the material with much gentler settings than are required in a single pass. Multiple passes has been my new best friend.

One other technique I used for cutting the cotton, was to clamp down the multiple layers with strong magnets, which compresses out the air gaps that could promote combustion:

This cuts with 1/10th the sturm und drang of cutting Proofgrade draftboard with standard settings. That was just a test cut pictured - for the final pattern I cut up the cardboard my Proofgrade shipments come in (yes, really) to match the outline of the cut lines to keep the fabric from getting blown away from all the airflow in the chamber.

Oh, and this hangs on my wall just behind my GF, as a safety reminder:


This is so incredibly helpful!!! Thank you for posting.

I just came across this post and I am not sure what fabric actually was cut here, but i am sorry to say I don’t see how it could possibly be 100% silk. Silk burns, it does not melt. As a natural protein fiber it burns, as does wool or hair. It does “bead”, but when you touch that bead it crushes into dust, it does not stay together. Manufactured fibers such as polyester, which many lower cost silk fabrics include without necessarily disclosing that information (illegal, but sadly it happens), do melt and look exactly like what is shown above. My best guess is that the fabric is a blend of some sort but not 100% silk as it was apparently sold to the poster. I really hate to contradict someone on the forum, but I really do not think people should expect to get this same result with pure silk fabric.

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@eciv, thanks for the heads-up. I got the fabric from an expert, but I suppose even they could have been fooled. How can I verify myself, and figure out exactly what it is? I can edit the post once I know how to describe the fabric.

I really hated to post that and felt badly, but didn’t want people to be excited and then confused when their silk didn’t do the same thing. I suspect the merchant you bought it from also was told it was silk. Many “silk” fabrics sold in Asia are silk/poly blends. I have been offered fabrics in Vietnam, Thailand, South Korea, China, Cambodia, India, And Indonesia that were being sold as 100% silk and ended up being blends - some I bought without testing and found out later. Very beautiful and still perfect for what I was using them for, but not 100% silk. Of course I have bought beautiful 109% silks as well. Many times the weavers don’t even know they bought blended threads to begin with. In Bhutan, they tell you something is made with Bhutanese cotton or Indian cotton. It took me a few days to figure out that what they were referring to was not the country of origin, but the purity of the cotton. Bhutanese Cotton was their name for pure cotton and Indian cotton was the name for poly cotton blends,

back to your question. It is nearly impossible to know from home tests exactly what a fabric is composed of but there are clues.
The burn test is a good clue. Take a match or lighter, light it and slowly move a piece of fabric into the flame. Remove the fabric from the flame and quickly watch what happens. Does it go out fairly quickly? Or keep burning? Extinguish it if it keeps burning. Smell it. What does it smell like? Look at the edge. What does it look like? Wait some seconds for it to cool down - then touch it with the forefinger and thumb and squeeze. What does it feel like? Some common answers are listed below (from the sewing directory in the UK, but there are many sources). There are other tests as well such as letting fabrics sit in nail polish remover, but this is far easier and more differentiating, I think.

SILK: Burns slowly and will self-extinguish if flame is removed. Smells like burning hair.
Leaves crushable black beads of ash.

POLYESTER: Burns slowly and melts, with black smoke. Will self-extinguish if flame is removed.
Smells sweet or fruity. Leaves hard black and brown beads.

NYLON: Burns slowly and melts. Will self-extinguish if flame is removed. Smells like
celery. Leaves hard, grey beads.

COTTON: Burns quickly and steadily with a yellow flame. Continues to burn if flame is
removed. Smells like burning leaves or paper. Leaves soft, grey ash.

WOOL: Burns slowly and will self-extinguish if flame is removed. Smells like burning hair or
feathers. Leaves brittle, black ash.

LINEN: Burns quickly and steadily with a yellow flame, but takes longer to ignite than cotton.
Continues to burn if flame is removed. Smells like burning paper or rope. Leaves soft, grey ash.

ACETATE: Burns slowly and melts. Continues to burn if flame is removed. Smells like vinegar.
Leaves hard, black beads.

ACRYLIC: Burns, melts and sputters. Continues to burn if flame is removed. Smells acidic.
Leaves hard, black crust.

Hope this helps.

Edgar Chambers IV, Ph.D.
University Distinguished Professor
Sensory Analysis and Consumer Behavior


@eciv, it’s all about adapting to new information, and I appreciate your effort to help that along. I’m in the process of investigating the background of the fabric so I can update the language in the posting. If I can’t definitively identify it, I could go with something broad, like ‘synthetic’.

I’ll add a section on testing fabric for suitability, which in turn may extend the utility of this method to a broader range of materials.

The salient property of the fabric is that it melts under the lowest power settings of the GF, which enables self-sealing cut edges and concurrent cutting/stitching. The idea is to turn the GF into a CNC hot-wire cutter. I hope to save the post on that merit, for the appropriate fabrics - whatever they’re called.

Great idea