Max wood cutting thickness?

[Jeshua Lacock]

Greetings,

Can anyone tell me what is the thickest wood I could expect to cut with a 130W CO2 laser?


Thanks,

Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated
<http://3DTOPO.com>
Phone: 208.462.4171

[Stefan Hechenberger]

About 1/2" with a 75mm lens is reasonable to assume. Although the
performance depends a lot on the kind of wood density. Birch plywood
works well for example and you should get fairly nice cutting speeds.

As a reminder, when cutting thick materials it's important to adjust the
focus to the middle (or slightly above the middle) of the material. This
way you have enough energy density towards the bottom of the sheet.
Acrylic is an exception to this and can be focused at the top as it
creates its own wave channel for the laser beam.

Stefan Hechenberger, Nortd Labs
http://labs.nortd.com | http://blog.nortd.com

[Jeshua Lacock]

On Jun 21, 2012, at 2:52 AM, Stefan Hechenberger wrote:

> About 1/2" with a 75mm lens is reasonable to assume. Although the performance depends a lot on the kind of wood density. Birch plywood works well for example and you should get fairly nice cutting speeds.
>
> As a reminder, when cutting thick materials it's important to adjust the focus to the middle (or slightly above the middle) of the material. This way you have enough energy density towards the bottom of the sheet. Acrylic is an exception to this and can be focused at the top as it creates its own wave channel for the laser beam.

Thanks Stefan, good to know.

Is it possible to do another pass with an adjusted focal point to say cut 3/4"? If I could cut 3/4" I could do everything I plan to with a laser cutter.

Or would I need more power, like 150W?


Thanks again,

[Stefan Hechenberger]

Multiple passes are an option but it's hard to tell how well this works
without trying. The beam waist is like an hour glass meaning the entry
of the cut will widen when moving the focus further down. So naturally
you will get a bit more charring.

With the focal length of the lens you are basically trading off depth of
focus for a bigger focal point.

Here is some more data on this:
http://labs.nortd.com/lasersaur/manual/optics

If you go with a 150W laser you might very well try a 100mm lens to get
more depth of focus.

tl;dr; I haven't tried anything thicker than 1/2".

Stefan Hechenberger, Nortd Labs
http://labs.nortd.com | http://blog.nortd.com

[Andy Dingley]

On 21 June, 09:39, Jeshua Lacock <jes...@3DTOPO.com> wrote:
> Can anyone tell me what is the thickest wood I could expect to cut with a 130W CO2 laser?

Wood cut thickness isn't about tube power, it's about species,
construction and wood flammability.

To cut wood, you dump energy into it. Enough to burn it locally and
make some disappear as fumes, not enough to heat the surrounding bulk
up to make the whole thing catch fire. With an adequately large laser
you can of course cut this wood, however you presumably want a fairly
neat cut, not just a firelighter.

In most cases, a laser machine will find a maximum single-pass wood
cutting thickness and this will depend on the wood type, the air
assist, the travel speed and power settings, and the wood type.
Balancing power vs cut speed, pulsing too, can improve this single
pass depth, but simply turning the power up to 11 won't - that will
just char it and probably ignite it. So anything "thick" is multi-pass
work. Fortunately that's just a trivial setting to change. As lasers
aren't mills, the mechanical repeatability is good enough that this
just isn't a problem.

You can also choose your timber carefully. "Laser plywood" is chosen
so that it's well-behaved for cutting. Some materials are just a pig.

IMHE, servomotors (compared to steppers) cut thick, flammable, wood
faster than huge tube power does. Go round repeatedly, but do it fast.
Power allows you to cut the same depth faster (your limit is energy /
length, i.e. heat dumped into the bulk wood) so powerful tubes can
start to help their, but you also need a real cutbeast to work it.

You also have a cut depth and focus issue. This is (IMHE) where
Epilogs are good, as their beam expander optics give a deeper depth of
useful focus. Progressive auto-focussing between passes can help too.

There's also a weird effect (mostly in narrow drilling, not cutting)
where smoke density diffraction causes beam steering, defocussing and
corkscrew holes! (try thick rubber). Air assist solves this, if
there's enough slot kerf to get deep airflow.

3/4" can be done, but it's a trial for a machine builder and operator
to set it up right. Cut speed in birch ply is at least twice what it
is in MDF.