[Cathode]

Check out the beam expander/reducer I picked up on Ebay for $50 bucks. It includes the expander/reducer, a stepper motor, lead screw, feedback pot, connectors, and slide assembly. It was advertised as being from a medical CO2 laser. I want to use it on my 60 watt CNC laser cutter.

Does anyone know how I can determine its focal length? I tried shinning a laser pointer through it, and you can see the beam narrow, but can't tell where the focus is. Any suggestions? I'm hoping this will work, but I'm afraid the focal length by be too long.

Thanks
Rick

[Laser.Tech]

ricswika, nice looking piece of optical hardware. Using the laser pointer was a nice idea, but the beam diameter is too small to help. Instead, you need a large diameter beam. The surest way is to use an actual CO2 beam. But since you don't have one yet you can use a 'point source' to come close. This can be a bright light placed as far away as possible (across room). Or, use the sun. Just don't fry any ants....

Brent

[Ortin]

Check out the beam expander/reducer I picked up on Ebay for $50 bucks. It includes the expander/reducer, a stepper motor, lead screw, feedback pot, connectors, and slide assembly. It was advertised as being from a medical CO2 laser. I want to use it on my 60 watt CNC laser cutter.

Does anyone know how I can determine its focal length? I tried shinning a laser pointer through it, and you can see the beam narrow, but can't tell where the focus is. Any suggestions? I'm hoping this will work, but I'm afraid the focal length by be too long.

Beam expanders/reducers DO NOT focus beam when properly adjusted. They just make it's diameter bigger/smaller. If they are not properly adjusted, then beam divergence or "focus" somewhere.
As I understand, you want to use this piece of hardware as an adjustable (with moving Z) focusing head. In this case you probably should take out all lenses exept one, which is installed in moving part. Or, if lens is not suitable for focusing, replace it with a new focusing lens. Of cource, this device will be renamed from "Beam Expander" to "Focusing Head".

[Ortin]

Check out the beam expander/reducer I picked up on Ebay for $50 bucks. It includes the expander/reducer, a stepper motor, lead screw, feedback pot, connectors, and slide assembly. It was advertised as being from a medical CO2 laser. I want to use it on my 60 watt CNC laser cutter.

Does anyone know how I can determine its focal length? I tried shinning a laser pointer through it, and you can see the beam narrow, but can't tell where the focus is. Any suggestions? I'm hoping this will work, but I'm afraid the focal length by be too long.

Beam expanders/reducers DO NOT focus beam when properly adjusted. They just make it's diameter bigger/smaller. If they are not properly adjusted, then beam divergence or "focus" somewhere.
As I understand, you want to use this piece of hardware as an adjustable (with moving Z) focusing head. In this case you probably should take out all lenses exept one, which is installed in moving part. Or, if lens is not suitable for focusing, replace it with a new focusing lens. Of cource, this device will be renamed from "Beam Expander" to "Focusing Head".

[Cathode]

I was looking for a way to narrow the beam and columinate it, thereby increasing the depth of field and sqaureness of the kerf. I got the idea from posts here and lenes ads on ebay that suggest this is possible. I've been getting conflicting information and am a little confused about exactly how this works. If you know more, please share.

For the machine I'm building, this would probably be overkill anyway, since I'm only planning to cut fairly thin materials, less than 1/4 inch. However, I could see how a wider depth of field would be useful for etching something of non-uniform depth.

[mexico.redsail]

collimating the beam produces a bigger spot than focusing it so this actually reduces the power density, you will need many times the power to "cut" with a collimated beam than with a focused beam, your "kerf" also will be larger but then your depth of field WILL be gratly enhanced