What's safer - 2 passes or slower speed?

Hello all! Newbie user here, cutting on some 1/4 in birch plywood from Lowe’s. I know others have discussed challenges they’ve had with this product - but, for better or worse, this is what I’m stuck with cutting for the moment.

I’m making a bunch of memorial ornaments for my aunt’s funeral this weekend. They have largely come out surprisingly great! However (like others have reported), sometimes my cut doesn’t go all the way through. Unfortunately, I don’t figure it out until I have moved the surface, so I can’t easily re-cut without some jittering of the line. So - I’m trying to decide whether it’s better to have it cut with two passes, or whether I should just slow down the cut speed to reduce this issue. I previously had it cut twice (by accident) and it seemed pretty… High energy, with a lot of charring on the bottom suggesting the laser was bouncing around or heating up the crumb tray. So - I’m worried about fire, either way. What do you think is the safest choice?

My current cut settings (basic): full power, speed 140, focus height 0.25 and 1 pass. (this is plenty sufficient for virtually all of the cuts - just a couple areas have been problematic, but that damaged the product.) Thanks friends!

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Yep, all completely normal when cutting on plywood from home improvement stores. There are usually voids and dense glue plugs inside that will cause those flare-ups, char everything, and fail to cut through.

About all you can do is check the material and try to lay your cuts around the bad spots…grab a high power light source (flashlight, light table) and move it around behind the material…you can spot the bad places and circle them with a pencil so you place your design cuts where they don’t hit them. :neutral_face:

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When buying that sort of plywood if you hit one of the Bondo spots, you are better off just trying again as sometimes you cant blast the Bondo enough without making an ash of everything else,

This was similar Birch from Home Depot…

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If you have a Dremel or similar, what I have found for the Home Improvement store wood. https://www.amazon.com/Dremel-543-Cutting-Shaping-Wheel/dp/B000HI5WUS/ref=pd_sbs_469_img_0/

or

https://www.google.com/search?q=dremel+543+cutting%2Fshaping+wheel&bcutc=sp-006

Thanks! That looks like a much better tool than the exacto knife I had to use.

I have used 170, full power, and 2 passes pretty successfully on birch from Lowe’s. But, you also have to make sure you use something to pin the board down because they are sometimes pretty warpy.

To get back to your original question, all things being equal, 2 higher-speed passes are safer than 1 slow pass, at least in terms of your material catching fire.

It’s a question without a real firm answer, but in general the faster the laser is traversing your material the less likely it will be to ignite.

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Thank you!!! This is exactly the info i was looking for =)

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This is absolutely true, however it is also the case that many woods are hardened by heating, and charcoal can insulate the wood below from being cut. So many times one cut does a better job than many.

In addition some of the more flammable woods like Zebrawood are more likely to ignite if the passage is over charred wood than (the same engrave especially) over fresh wood. So less than a firm answer it can be really squishy and dependent on the particulars.

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Masking or a sheet of cardstock can help with the flashback.

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Thanks! I don’t so much care about the appearance, just the significance. Or, are you saying that masking the bottom would reduce the availability of extra burning surface?

Yes, if I understand, the bottom where the laser reflects off the bed grid and singes the bottom.

@PrintToLaser when you say a sheet of cardstock …do you mean just any ole piece of plain Jane cardstock laid on top of the plywood?

Underneath. I use aluminum foil when I need to prevent flashback – less chance of fire. :slight_smile:

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Sorry I wasn’t clear. II was referring to the laser hitting the crumb tray and reflecting back onto the material and marking it. The masking on the back prevents that, unless your power is really too high.

I had to do thousands of tokens, and pulling the mask off before running the file saved like a week of weeding, so I used plain light cardstock to protect the back.
I used household ammonia to wipe the tokens on both sides to clean off the smoke stain.

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Thankyou!!!

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