DIY CO2 laser cutter thin form factor

[Nicolas Raynaud]

Hi all, I am starting a new project, that would be a CO2 laser cutter but thin enough to be used as table/desk when not running. I just checked a secretary, I think I can get away with 15/20cm thickness while still being able to use the thing as a sitting table.

I am thinking of going for a 1250 x 80mm Reci tube and the associated power supply. For the control I'm thinking of using a grbl-LPC board, because I like to be able to read the code source and the communication protocols of my gear (unless I get convinced otherwise).I am envisioning a 1220 x 650mm envelope, which is a little bit bigger than a standard sheet good size in my neck of the woods (120x60 cm), but I think with all the space around the cutting area we reach a comfortable bench table size of 150x80cm. For access when stuff is on top, I'm thinking of having a flapping door in the apron as well as the usual top door access.

I think the highest thing inside the machine has to be the laser beam (to pass over the rails) which would make the tube axis quite high, I could either just leave it there and have a table with a bump at the back, or lower it and add a mirror wrt. the usual configuration and have a vertical beam at the second segment. I think the second "thick" thing is the focal length, which brings me to a question: why are lenses so far from the mirror in the Z axis in a lot of designs? I feel like it's lost space.

I have not yet thought out the Z axis, I want a motorized system that would have to be moved up to make space for my knees when used as a table.

The budget might be a bit spicy, but I am at peace with that. I enclose a first draft of the kinematics and optical design.

What do you think of all those points? have you seen designs on the internet that go for flat that I should look for inspiration?

[Rodney Edington]

For the control I'm thinking of using a grbl-LPC board, because I like to be able to read the code source and the communication protocols of my gear (unless I get convinced otherwise).

You will need a control that has "backlash compensation" to get any precision out of the machine.
I don't know that much about grbl (I looked at when I built my CNC router a few years ago and it didn't have it then).

why are lenses so far from the mirror in the Z axis in a lot of designs?

I think the main reason is that the beam needs to withstand the forces of a tight belt. I used 2040 extruded aluminum for my X and I have over .025" deflection in the center.

[Nicolas Raynaud]

Thank you, I had not though about that, I will be sure to address those points.

[Nicolas Raynaud]

this belt tension thing is on my mind, I intend to use a rectangular section beam, I guess I should try to put the compression plane inside the beam to limit the arcing.
something like that:


it's not perfectly aligning the compression and the axis of symmetry, but at least all the walls of the beam would be in compression.

[Rodney Edington]

That looks like it will work. I'm sure you'll be going through some trial and error as you build. The only way to find out is build it and see unless you have the software and know how it to figure deflection .

[Nicolas Raynaud]

I have a question regarding camera and optics, I see a lot of products with cameras onboards, but the inside of the machine gets coated with tar over time, how does that play with the optics?

Do people use shutters or do they simply clean them up a lot?

[Rodney Edington]

but the inside of the machine gets coated with tar over time

If you have good ventilation to the rear, all the tar and other gunk should stay away from the camera (if it's mounted up front).

[Nicolas Raynaud]

thanks. I need to read on the topic of ventilation as I'd like to mitigate the noise.

[Nicolas Raynaud]

does anyone have an opinion on gantry mounted laser tubes?

I just realized that mounting the tube on the gantry allows to put it a bit lower. Basically the plane of the beam doesn't have to be horizontal anymore because the first and second mirrors are at a fixed position relative to each other. That could be an interesting tradeoff in my quest for a thin table-like device. I guess I would be trading acceleration along one axis, but maybe the weight of the gantry could help stabilizing the machine when accelerating strongly in the lighter axis.

(I know my thread is old, I just bought a home that I'm renovating, so I shouldn't be working on the laser, of course my brain is only thinking of lasers)

[Charles Jones]

I have a large format laser with a gantry mounted tube. I would say that the effect on engraving is negligible, but in cutting, there are noticable effects from the added mass. For example, when cutting a circle through thin material at high speed (such as card stock) I don't see significant variations, because as the servos change speed to cut the circle, the changes are fairly gradual. However, when I am cutting a sharp corner, there are notable oscillations when the Y axis stops moving abruptly (and oscillates for a short time) and the X axis starts moving, resulting in a decaying sinusoid pattern. This all boils down to how sharp the corner is, and how quickly I'm cutting. For thicker materials even at full amperage rating on the tube, the cut is slow enough to have no notable effects. Ways to mitigate this limitation involve designing rounded corners into your cuts (not always feasible) and slowing down the cut speed. If you've watched Russ's videos on cutting, he usually uses the highest power and then adjusts the speed to achieve the right cut quality. Because you would hypothetically have a maximum speed that works for eliminating oscillations, you might have to adjust cutting power as well to achieve the cuts you want. In summary, having a heavy gantry introduces additional limitations, but doesn't prevent your machine from being usable. A side benefit is that your laser path length will be shorter and you'll have less beam divergence. My large format is 10'x5' and has less maximum beam divergence than my 4'x3' because the tube is mounted on the gantry.