So here’s the thing about laser cutters. Before I bought one, I always assumed that with infinite patience, you could cut any thickness. Just keep making passes, and it will eventually cut through.
I was wrong.
Instead, the best way to cut thick pieces of wood with a laser cutter is by cutting halfway through on one side, then flipping the material and cutting the same pattern on the other side of the wood. Alignment circles help ensure that the pattern is placed correctly.
This can get a bit confusing, so I’ll break down all of my tests, reasoning, and process below.
Laser Cutter Background Information
I have the xTool M1 as well as the Glowforge Aura. Both are small diode craft lasers, 10 Watt and 6 Watt respectively.
All my tests were performed on the xTool M1 because I like it better (read all about that over here.)
However, the theory probably applies to all diode lasers, although the maximum thickness they can cut will differ depending on the strength of the laser.
I don’t know quite enough laser theory to speak about if this applies to CO2 lasers, although my guess would be yes.
Why 100 Passes Won’t Cut Through Thick Wood
As I mentioned above, I really thought that if I just kept running the laser cutter, it would eventually cut through thick pieces.
The problem, though, is that the laser is focused at the set height you input, which is usually the top of your piece.
As you run more passes and cut deeper into the wood, the laser gets less focused, resulting in diminishing returns for each pass. I ran something like 15 passes on this triangle, and never managed to cut all the way through.
So then, you’re probably thinking, change the focus of the laser. Yes, that was what I tried next!
But then the laser is super powerful when is runs by the top of the wood on the way into the center groove. It burns the top of the wood, charring it more than can be saved.
I experimented with a couple of different things, changing the speed and power to try and save the top of the plywood. I never hit on anything that worked well. See my many attempts:
And, despite refocusing at multiple thicknesses, I still haven’t managed to cut all the way through the plywood consistently.
I did, however, manage to consistently cut through sporadically:
That was enough for me to work with.
How to Cut Through Thick Wood With a Laser Cutter
If you have a piece of thick wood that your laser cutter can cut halfway through, then you can get all the way through by flipping the piece over and cutting from the other side.
The biggest barrier to this, though, is making sure the pattern is perfectly aligned. This is where alignment circles come in.
By creating alignment circles outside of your pattern, you can burn/char the wood as much as you need to get the alignment circles to appear on the other side.
Then, when you flip the piece over, you can align your pattern to the alignment circles, ensuring that your cut lines up almost perfectly.
Alternatively, you can you create the alignment circles, then drill through them with a drill bit. I haven’t tried this method and I think it would be less precise, but maybe a little safer since there’s no risk of fire.
(There is not that much risk of fire, and definitely a low risk of a wild crazy fire. But I am using the laser in a way that wasn’t intended, so I keep a close eye on it when I’m doing this.)
I used this method on my jewelry organizer, and I’m thrilled with the way it turned out.
I started by cutting my pattern and alignment circles with strong settings. On the xTool M1, cutting 1/2″ Sandeply Plywood, that was with the following settings:
Then I had the laser cutter ignore the main pattern, and just cut the alignment circles with the following settings:
Note how I bumped down the thickness and power. I refocused the laser, but made it less powerful in hopes of charring the top of the piece a little bit less.
This is what I found worked best with my laser cutter on this plywood. If you’re doing something similar, I would absolutely play around with some scraps on your machine to figure out what works best for your material.
Finally, I ran it through one more time, bumping the thickness down further, just to make sure that I got all the way through.
Note that once you move your material, you can no longer place it back exactly where it was. So it’s impossible to check to see if you’ve gotten all the way through then do more passes.
So I’ve found it’s better to error on the side of too many passes than not enough.
Either way, at this point I had enough of a circle on the other side to use it for alignment:
Then I flip my material over. I also simultaneously flip my pattern over in the software the same way I flipped my material.
That bit is important. If you forget to flip your pattern, it won’t line up perfectly unless your pattern was perfectly symmetrical.
Then I set the laser cutter to score the alignment circles, and adjust the positioning of the material and pattern until the alignment circles line up perfectly.
This is a little easier to do if you took care at the beginning to make sure your material wasn’t crooked in the machine, but not impossible to do if you didn’t.
Once I’m as close as I think I’m going to get, I cut my pattern.
I was worried that being even a little bit off meant that my project would look sloppy and bad. That was not the case.
I certainly settled for “good enough” when doing the alignment circles, and it still looked pretty good, so I don’t think perfection is needed.
That said, if you’re doing one of those finger joint projects where you’re stressing about the width of the kerf and other technicalities, than this method probably isn’t great.
My jewelry organizer was a finger joint project, but I didn’t need perfection, and everything glued up just fine.