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Lens combination for a DIY SLS 3D printer

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Waka

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Hello,

I'm starting a project to build a DIY SLS 3D printer and I have some ideas about how to achieve what I'm looking for, but I'd like some help when it comes to lenses.

The design involves shining a 405nm/445nm laser onto some mirrors attached to an X-Y gantry in the same way laser cutters do.

From what I understand I need a lens that doesn't focus the beam attached to the laser module itself and then the final mirror directs the beam through a focusing lens at the correct focal distance from the powder.

Here are the products I'm looking at:

Laser:
2W Copper 445nm M140 Blue Laser Module W/X-Drive & 405-G-2 Glass Lens | eBay

- Replace the g-2 lens with a non-focusing one and use the g-2 lens after the last mirror.

Mirrors:

3XReflection Reflective Film/Lens/Mirror 405nm-445nm-532nm-635nm-650nm RGB Laser

Do these look suitable for my purpose?

Can someone give me an example of a non focusing lens that will screw to the module, please?

Also does anyone know of a focusing lens that has a longer focal length?

A 20-30mm focal length would be great, but most seem to be 8.3mm (Which is still workable in the design if necessary).


Also a side question:
I'm looking for a glass that I can shine the laser through without reflecting and damaging the laser and also without reducing too much of the laser output.

I've seen BK7 optical glass, but this is quite expensive, is anyone aware of an alternative?

50mm Diameter x 1.2mm N-BK7 Plano Optical Window (AR WIN 50-1.2) | eBay

Thanks for your help in advance, :yh:
Waka
 
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There is no such thing as a non-focusing lens. You will still need the G2 on the laser module - that is required to actually form a beam, otherwise you just get a big fat, rapidly diverging blob of light - much light a flashlight. You need a second lens to focus the beam to a point. You'll want a larger diameter second lens so that you can fit the beam, someone else may be able to recommend a source for those, I'd just check eBay for focusing lenses. Those mirrors look like they should do the job, although the description isn't great - basically you're looking for "first surface" mirrors.

What powder are you planning on using? I'm going to assume it's some sort of plastic?

You can use regular glass for the window, at a slight angle to prevent back reflections, but you'll lose at least 5% through that. You want an optical window AR coated for ~445nm, Thorlabs has those, but you should also be able to get them on eBay. Won't be as cheap as plain glass though.
 
diachi said:
There is no such thing as a non-focusing lens. You will still need the G2 on the laser module - that is required to actually form a beam, otherwise you just get a big fat, rapidly diverging blob of light - much light a flashlight. You need a second lens to focus the beam to a point. You'll want a larger diameter second lens so that you can fit the beam, someone else may be able to recommend a source for those, I'd just check eBay for focusing lenses. Those mirrors look like they should do the job, although the description isn't great - basically you're looking for "first surface" mirrors.

What powder are you planning on using? I'm going to assume it's some sort of plastic?

You can use regular glass for the window, at a slight angle to prevent back reflections, but you'll lose at least 5% through that. You want an optical window AR coated for ~445nm, Thorlabs has those, but you should also be able to get them on eBay. Won't be as cheap as plain glass though.
Click to expand...

Thanks for the info. So are the g-2 lenses variable focus? Or is it a case of screw it fully in and forget about the focus just bounce the beam on the mirrors and aim it through the second lens?

The powder I'm looking at at the moment is nylon SLS powder used in commercial SLS printers. The idea is to heat the powder to about 5 degrees lower than melting point and then the laser brings the area it hits up to melting point. It doesn't have to be a powerful laser, I think it was calculated to require at least 130mW with black nylon powder to bring it up to temperature.

I may reduce my laser to a 500mW 405nm instead as it can have a smaller dot I've read.
 
Waka said:
Thanks for the info. So are the g-2 lenses variable focus? Or is it a case of screw it fully in and forget about the focus just bounce the beam on the mirrors and aim it through the second lens?

The powder I'm looking at at the moment is nylon SLS powder used in commercial SLS printers. The idea is to heat the powder to about 5 degrees lower than melting point and then the laser brings the area it hits up to melting point. It doesn't have to be a powerful laser, I think it was calculated to require at least 130mW with black nylon powder to bring it up to temperature.

I may reduce my laser to a 500mW 405nm instead as it can have a smaller dot I've read.
Click to expand...


G-2 can be adjusted, yes, you screw it in or our of the module to adjust focus. You can focus to infinity and forget about it though.

Was just checking on the powder - several people have come here wanting to do SLS with metal using similar lasers to the one you're using, had to point out that it's not really possible. Nylon is definitely possible though. Please post updates with your progress, that'd be good to see!

Yes, shorter wavelengths will have a smaller spot. Not only that, the 405nm lasers we have access to have a better beam profile than the high power 445s, that also improves things if you're going for as small a spot as possible.
 
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