Inconsistent Vector Cutting

[William Noyer]

Hey guys, I have a 50W Epilog Helix and I am having an issue with cutting 1/8" craft plywood. I was doing some vector cut Christmas trees for our youth group at church. I cut a 24x12" sheet of 1/8" ply with about 8 sets of components for the trees and most of it came out fine set for 1/4", but barely touched it set for 1/8". I have tried using the recommended settings for cutting 1/8" plywood and barely cuts half way through it. When I use the settings for the 1/4" it will generally cut all the way through, but I have this inconsistent cutting going on. About 98% of the cut is just fine, but then there will be these areas that only cut about 80% of the way through. It is frustrating to have this high tech machine to cut and then you have to finish some of the parts off with an Exacto knife.

Here are the recommended settings I downloaded from the Epilog site for my machine:
For 1/8": S: 30%, P: 60%, F: 500 Hz
For 1/4": S: 20%, P: 100%, F: 500 Hz

I have cleaned my optics per the manual, though I do not think that has much if anything to do with it since the majority of the cutting is working. As well after cleaning, I saw no appreciable difference.Christmas Tree.ai.zip

[Ronald Erickson]

I've only been lasering for about 6 weeks, but in my short time I've found that each material needs to have the settings fine tuned to cut well and the "recommended settings" won't necessarily apply. They are a good starting point, but you have to adjust them based on the results you're obtaining.

Material plays a BIG factor as not all materials are made the same. The type of glue the plywood is constructed with plays a factor as well as the wood used in the inner core. I have an 80 watt Speedy 300 and one of the first pieces of 1/4" baltic birch plywood (picked up from Mendards) I tried to cut resulted in failure at any setting. At appropriate settings, it would cut two-thirds of the way through, but never all the way through. Upping the power and slowing the speed just resulted in a firey mess; a three inch fire column trailing behind the cut means it isn't going well. Burying the focus in the material also didn't help and it would stop cutting at about the same spot, suggesting an issue with the plywood. (Edit: Of course this was before I realized that my laser was out of alignment; I'll have to give that material a go again now that I have more experience and the laser is aligned.)

Switching to another type of 5 layer 1/4 inch plywood resulted in a butter cut all the way through, one pass, with a golden honey cut edge.

How does the cut look in the 1/8 material using the 1/4 inch settings? Is it turning to crispy burnt carbon, or is it still clean of excess charring? If you slow it down just a bit more (say 18% or 15% speed) does it make fire and produce an overly charred edge?

[Michael Hunter]

It is frustrating to have this high tech machine to cut and then you have to finish some of the parts off with an Exacto knife.

Don't blame the laser - it is the plywood that is inconsistent!

Ronald is right about the different glues* used, but there is no "fine tuning" for ply.
There are voids (often filled with glue) and knots in the inner layers and these prevent the laser cutting well all the time, even in stock that is generally laser-friendly.
Find a setting which works most of the time, and then approximately double the power going into the cut - that way you won't need the Exacto too often.
Keep the frequency low though - a higher frequency usually means more charring.

*
In general, waterproof glues are often laser-proof too, producing lots of black smoke and mess.
Interior grade ply *usually* has laser-friendly glue, but since no-one at the supplier end knows what the manufacturers actually used, you still need to experiment with different brands/suppliers.

[David Fairfield]

Plywood is a problem material. As Michael does, for production runs I usually give it much more power than needed. Dave

[William Noyer]

I truly appreciate everybodies answers. It may not solve all my problems, but at least ya'll have assuaged some of my fears that it is not a machine issue. I kind of thought it might be the plywood due to the fact that there was no consistency in where it cut and where it didn't. As well, when I would try to run the area a second time, it would sometimes still not cut all the way through. Luckily I do have a scroll saw in my repertoire of tools.

[Dee Gallo]

Bill, I share the same opinions already stated, but wanted to add you might start a notebook to chart all these things so when you need to buy something in the future, you know what did what. I write down settings, thickness, source store, etc. to help my dwindling memory keep track of things. I also write on scraps of stuff, and/or keep test burns to see how things will engrave or cut at different settings. After a few years, you'll know more what to expect, but by then you'll have done so much you'll forget which settings work with what substrates. You can also gauge whether your laser is losing power or focus over time by comparing results. Predictability is very helpful when you are in this biz.

cheers, dee

[Ross Moshinsky]

Plywood is just one of those materials you have to blast with power due to the inconsistencies of the product. You can also focus into the material a bit which will help on 1/4". When you say the material won't cut through even on a second pass, that is typically a sign of the focus being a bit off.

[david a graham]

Dee, that is great advice, keeping a notebook. Simple yet effective.

[Rich Harman]

Also make sure that the piece is held flat and that your table is level. A small change in focal distance will make a big difference in the way it cuts.

[William Noyer]

There was a slight bow in the piece when I put it in. Any suggestions for hold down short of just cutting my piece down to a smaller size?

[Rich Harman]

I use a combination of magnets, weights (1/2" thick plates of metal, shampoo bottle full of lead shot, etc...) and small "tees" cut from acrylic that are pressed into the honeycomb.