Help with Burnt Edges

[David Sabot]

Hi there.

I have a 40 watt GCC Spirit CO2 laser engraver and I am trying to cut through 1'4 plywood.

The problem I am having are the burnt edges of the cuts, they get all over your hands and are a mess.

I am using 100% power and a speed of around 1. I can cut through in 1 pass, but like I say, the edges are charred.

Any advice on how to eliminate the edge burns? I really didn't want to do multiple passes if I didn't have to.

[Ross Moshinsky]

You're cutting with heat. It's always going to cause some charring. You can decrease the charring by lowering the PPI/HZ and adjusting air assist. I'm not sure how much flexibility you have with your machine as far as changing the speed to 1 vs 1.1 but minor tweaks might also help a bit. You also might find changing the type of plywood will result in improved edge quality.

Those are the only suggestions I know other than a more powerful machine or multiple passes.

[David Sabot]

You're cutting with heat. It's always going to cause some charring. You can decrease the charring by lowering the PPI/HZ and adjusting air assist. I'm not sure how much flexibility you have with your machine as far as changing the speed to 1 vs 1.1 but minor tweaks might also help a bit. You also might find changing the type of plywood will result in improved edge quality.

Those are the only suggestions I know other than a more powerful machine or multiple passes.

Thank you. For 1/4" material that is around 24x18" in width, do you suggest anything other than plywood? What would provide the least char?

[Chris DeGerolamo]

Bass should cut with little charring, though it's relatively soft...not nearly as strong as 1/4" ply. Cherry cuts nicely too from my experience.

[Andrew Holloway]

You can also try MDF.

[Matt Turner (physics)]

What type of plywood are you using? Baltic birch may char less than something from the hardware store.

[Mike Lassiter]

I cut 3/8" exterior siding for a customer with 135 watts @ 2.1% speed 100% power and it chars too. Don't like to cut it, but you sort of have to do what the paying customer wants. Glue pockets, voids in the plys, knots in the inner plys all create issues. I can cut some areas faster, but then you have places that will not fully cut through. So to ensure a 100% (or close to it) cut thru I have to run a slower speed. I also have reduced the PPI to 250 I think and that helps some with the charred edges.
Baltic Birch cuts fine with a light brown edge. Plywood like you get a the big box store is going to have voids in the plys and glue pockets from glue filling some of those voids up. They all create cutting issues as opposed to a good solid wood or good quality Baltic birch plywood.
I would suggest looking at Baltic Birch if you need a good edge quality.

[Rich Harman]

Different materials char less than others. Last year I cut a bunch of 1/4 sandeply from Home Depot. It is a product from Ecuador if I remember correctly. It made very little, if any charring, cut easily and was cheap. The 3mm MDF also from Home Depot cut with no charring at all, but the 1/4" MDF makes a fair bit of charring.

At Home Depot there is a also a 1/4" underlayment that I used quite a bit. Fairly strong but the edges charred a bunch and needed cleaning. Haven't used it at all since discovering the sandeply.

[Henri Sallinen]

Most of the charring is because of the wrong kind of glue used in the plywood (black glued exterior quality). You can find white glued interior-grade plywoods that leave less charring. Wood itself should leave no charring dust at all at the cut edges.

[Rich Harman]

Wood itself should leave no charring dust at all at the cut edges.

I'm not convinced of that. I've cut a fair amount of wood - not ply - and it all chars to some extent. Very light and dry wood should char the least, maybe not at all. I would expect that woods that have a higher resin content would char more.

[Bert Kemp]

I cut 1/8 cherry and have virtually no charring, the edges are a tan color and if you rub your hand across the edges theres no rub off . I think it would be real hard to cut 1/4 or more with out a charred edge tho.

[Scott Shepherd]

Rich, are you talking about thick wood chars or all wood you cut? We don't get charring on 1/8" thick woods, it's like Bert described. That's plywood, alder, maple, etc.

[Rich Harman]

Rich, are you talking about thick wood chars or all wood you cut? We don't get charring on 1/8" thick woods, it's like Bert described. That's plywood, alder, maple, etc.

I don't cut very much 1/8" wood. 1/8" alder and the new 3mm MDF from HD (recently discontinued) cut clean. The older 1/8" MDF from HD charred a fair amount. I mostly cut 1/4" ply. The sandeply cuts almost clean. I can't think of anything that I have cut over 1/4" that cut without some charring.

By "charring" I mean a darkened edge. When I tried to cut marine ply, it charred too - the edge turned to charcoal.

[Matt McCoy]

Hi David,

Your speed seems very slow to me. I would check the condition and alignment of the mirrors as well as making sure the lens is clean.

Multiple passes that are dialed-in will reduce charring and should leave a nice light brown patina on most woods.

[Jay Selway]

I usually wear gloves, and the first thing I do is wipe the edges with a rag soaked with a bit of denatured alcohol. Takes care of it right away.

[Henri Sallinen]

When I said charring, I meant that it leaves a black residue that comes off the cut edge. Tanning/darkening does happen every time I cut wood.