Best distance from laser diode assembly to object? - 445nm engraver/cutter.

[Probedude]

Got the itch to build a laser engraver/cutter after seeing that laser diodes are reasonably inexpensive and also remembering that I had a PCB router in the attic.

Dug out the router, updated it with GRBL, been successfully driving the unit around with the cutter and now I'm ready to strap a laser to it.

Bought DTR's Nichia 3W'ish 445nm laser which should be here soon.

Question- what is the optimum distance for the laser from the object being burned/cut?

Reason I ask is that for now I'm playing with a 400mW red laser and noticed:
- When close to the object I can focus a small spot but the lens is also unscrewed quite a bit - wouldn't this reduce the output due to coupling less of the laser through the lens?
- When close, variations in height changes the beam spot quite a bit, so probably not ideal for cutting foam core due to the beam spread.

- Farther away - can the spot be focused as small?
- Farther away - better to keep the fumes from clouding the lens.
- farther away - beam spread less with z height changes?

Has anyone determined the 'optimum' distance for this type laser diode/lens relative to the object being engraved or cut?

Thanks!
Dave

[swamidog]

Got the itch to build a laser engraver/cutter after seeing that laser diodes are reasonably inexpensive and also remembering that I had a PCB router in the attic.

Dug out the router, updated it with GRBL, been successfully driving the unit around with the cutter and now I'm ready to strap a laser to it.

Bought DTR's Nichia 3W'ish 445nm laser which should be here soon.

Question- what is the optimum distance for the laser from the object being burned/cut?

Reason I ask is that for now I'm playing with a 400mW red laser and noticed:
- When close to the object I can focus a small spot but the lens is also unscrewed quite a bit - wouldn't this reduce the output due to coupling less of the laser through the lens?
- When close, variations in height changes the beam spot quite a bit, so probably not ideal for cutting foam core due to the beam spread.

- Farther away - can the spot be focused as small?
- Farther away - better to keep the fumes from clouding the lens.
- farther away - beam spread less with z height changes?

Has anyone determined the 'optimum' distance for this type laser diode/lens relative to the object being engraved or cut?

Thanks!
Dave

you will have a smaller point size with a shorter focal length lens. this will also give you a shallower beam waist. welcome to physics

angle a jet of air to be as colinear to the to the laser beam as is possible. that is important for projecting the lens and blowing smoke out of the way of the laser beam.

[planters]

angle a jet of air to be as colinear to the to the laser beam as is possible. that is important for projecting the lens and blowing smoke out of the way of the laser beam.

Would it be hard to do this like on the big machines with a nozzle, side fed by an air supply tube and through which the air flows around an axial laser beam \ l / ?

[swamidog]

Would it be hard to do this like on the big machines with a nozzle, side fed by an air supply tube and through which the air flows around an axial laser beam \ l / ?

that is exactly what i would do.

[lasermaster1977]

In case you might be interested here some good sites for info, sharing and collaborating all things CNC including DIY laser cnc machines.

http://www.buildyourtools.com/forums/

and for CAM http://www.cambam.co.uk/forum/index.php#1

[VDX]

... here are some older infos - http://www.reprap.org/wiki/Laser_Cutter

I'm adjusting focal distances between 15 and 40mm for engraving with smallest spot diameters - ye shorter, the smaller ... best spot diameters are around 40 microns with the standard collimator optics.

For cutting foam with around 5mm thickness, I've set it to 60mm, but then you'll start to see the bad beam-quality of the diode - it will give more a small square (around 400x100 microns) than a round spot ...

Viktor