Pure laser machine, mpcnc vs lr3 vs ...?

Mostly Printed CNC - MPCNC Advice
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I’ve been thinking about building a second machine to laser some big parts, like custom boxes and maybe sewing patterns and things like that.
Not super powerful per se, but preferably quite big.
I would be using a diode laser as they’ve been dropping in price and getting stronger in the past years.

What do you guys think is a good motion system for this idea?
I could build a big mpcnc without a z axis. It doesn’t really touch anything it’s cutting, so I guess I could get away with it not being super rigid.
Could also build a version of the LR, but that feels like a way bigger machine and I’ve had some trouble with my LR2 and repeatability (my own mistakes, but something I worry about regardless).
I’ve seen videos of people building fold away tables for the mpcnc which sounds like a nice feature for a big machine. I don’t think a LR would be as easy to fold away.

I’d love to hear your opinions on this or any other systems I should be aware of!

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I built a dedicated diode laser machine.

I also have a laser mount for the LR3, which I use for a “40W” (10W optical power) diode laser, but for the 5W laser, I built a smaller CoreXY maxhine for it specifically.

The smaller machine can move faster, which has advantages, and change directions faster. This makes handling outlines and complex shapes more consistent and even. Also, there is little need for Z axis control with a laser, so the machine can be much simpler. I also just wanted to play with my own design :rofl:.

It would need tweaking for a larger heat sink but this is my thread for the CoreXY Laser Engraver

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I keep looking at all the cheap desktop machines and they seem to be selling at less than the cost of the parts, even if I factored in a new laser and control board?

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I run a 10W laser module on my Primo. I love it, but larger projects can take lots of time, and there are issues with larger projects. For example, I made a tray (open top box) for our cupboard for storing Tupperware. It was roughly 22" x 28" x 4" and was made with 5.4mm plywood. The base took 50 minutes of cutting, and the whole project took 150 minutes. When I start adding nice design cutouts on things, cutting times go way up.

With my Primo, engraving takes lots of time. A full engraving on a 4" x 4" tile takes around 75 minutes. If I increased the tile size to 6" x 6" it would take around 165 minutes. If I try to increase the speed or acceleration, unacceptable artifacts creep in. So, for engraving, the larger size of a Primo or LR3 does not provide benefits.

With larger projects, I also have the issue of warped stock. I buy most of my wood from the big box hardware stores, and it is not perfectly flat…especially across a 24" x 24" piece. My laser has a larger working distance, so I can work around minor warping, but most diode laser modules on the market have very little working distance. The laser will end up catching on edge of a cut in the stock and ruining the cut. Even with my larger working distance, I’ve had this happen to me.

I would be using a diode laser as they’ve been dropping in price and getting stronger in the past years.

My perception is that, over the last three years, the price per watt of diode laser modules has gradually gone up (a bit faster than inflation). But more importantly the power of lasers has gone up dramatically in that time. While not a perfect match, you can expect to pay around $250 for 10W module, $500 for a 20W module, $750 for a 30W module. Machines with 40W modules are appearing, but I’m not seeing sales of just the modules (yet?).

I could build a big mpcnc without a z axis.

For laser cutting, there are benefits to having an active Z axis. Often cutting is done in multiple passes, and an active Z allows the laser head to drop a bit on each pass. This drop changes the focus point in the wood.

I’ve been eyeing buying a laser engraver. Price and performance have me eyeing the Longer 30W and 40W (preorder) machines. With a working area of just under 18" x 18", it would handle 95% of the projects I’ve done over the last couple of years. I’m only hesitating because it is still a lot of money when I have a working solution.

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And that’s my point too - a 30W module is $750 W - is it worth adapting my LR3 or even making a new machine when for an extra $250 I can get a whole machine? I might have to sleep on that!

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I don’t really know if there’s a better alternative for big work area than the LR3.
I think the LR3 is quite unique in the way it can be easily and cheaply extended in Y direction, and by the fact it can be easily removed from the workbench and/or parked on one side without taking up the rest of the surface (see my side mounted Y mod)

Most lasers I have seen are either cantilevered (but that’s pretty bad for long reach), or Core XY with aluminium extrusion, which get pretty costly …
Maybe some adaptation of the ZNXY?

Anyway, concerning the laser, if your primary goal is to cut material, I wouldn’t recommand diode laser…
Even powerful ones (I got a 10w optical diode laser), you need something like 1mm/s to 3mm/s for it to cut 5-6mm thick material
Plus it will leave significant charring for anything above 10mm thick :confused:
It may be preferable to get a CO2 laser if cutting is your primary goal

Going this route may also mean you need to be sure you really need a working area that big, because most CO2 lasers will come with an enclosure, and getting the whole thing right migh be hard to DIY

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There is a middle ground, which is what intrigues me. That is buying a 30W/40W laser engraver (whole machine), but re-engineering the mounts so that the laser module can be swapped to my Primo when I want to cut something big. My concern, based on pictures, is that moving the laser to a new control board might not be as easy as current module-only purchases.

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What size would you really build it? Would you really never do anything that has a load (like a router?)

If it was really big, the LR still has an advantage because you can use the table. It uses less material to get bigger. And the gantry of the MPCNC can still flex with its own weight at very large sizes.

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But it does make it more difficult to properly cover the laser and to extract fumes. Of course I am considering that anyway so perhaps this is a bit of a moot point for me at least.

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Definitely a factor… I had almost all of the parts on hand already, except for the designed 3D printed pieces. I did buy a laser module, but the 5W module I bought was a lot cheaper than the machine it would have sold with, and even then it was meant as an alternate tool for a 3018 machine which would have had a much smaller working area.

Also, I wanted to try my hand at my own designs, I started with thinking H-bot and ended up with CoreXY.

Still, I know that within its capabilities, the CoreXY laser is faster than the LR based one just because the greater acceleration is possible. The LR is capable of high speeds, but not the same acceleration because of the much heavier gantry. Even with a more powerful laser, it can’t match the lighter machine.

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Why do you say that? Seeing as the laser’s mass at the end of the cantilevered arm is so much less than the mass of a router and there are zero side loads imposed on the head during operation and that the necessity for absolute perfection in the z axis isn’t there when lasing any potential ‘droop’ at the end of the cantilever is, in my experience, irrelevant.

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I actually bought a TwoTrees TTS 5.5w (used) from their site for $79 just for parts. EVERYTHING worked, but I didn’t care for the control board so I gutted it to feed like 6 projects.

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I’d expect the arm to vibrate and lag behind a little when reaching the end, but yeah, probably this is insignificant
I don’t know what size we’re talking about, but a 1 meter long cantilevered arm doesn’t seem right :confused:

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While I would happily admit it may not be the best method to check for it I didn’t see any artifacts when laser cutting fuselage sides out of a 36" length of balsa. The cantilever axis was not that long anyway Perhaps at 1 meter there might be some…it depends on how it is built!

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One could build a fixed Z LR3…
Keep the rail in the back, two small side plates with the rollers on and two tubes for the X, and build a small carriage that rolls on those tubes and support the laser

You’d only need to design clamps for the tubes on the plate and an X carriage
Maybe if you want to cut some cost even more, you could have a single Y motor with belts and pulletys

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I think this scales pretty easily

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The triangle strut/gantry is a good design. I would first just try to incorporate the two plates to still use the gantry, core, and struts without the linear rails or Z motors.

But that may be overkill for a laser. The LR2 plate with your modified design would probably work fine. I’m not sure how to quantify the differences in cost and performance without building both.