confused -laser heads- which one?

[injunear]

I have a 90 watt cutting machine I built myself in 2014. I purchased a lot of stuff from this site, including the laser head. It's a "K40-ish" type head with a 20mm mirror (fixed at 45^) and a screw on body that houses an 18mm lens. The head has no sliding tube, The lens assembly screws on the upper body and the nozzle is held on with a grub screw. The distance between the bottom of the lens and the bottom of the nozzle is about 28mm. The nozzle opening appears to be about 4.75mm.

So, finally the questions:
I want to use these lenses: 38.1mmFL, 50.8mmFL; 63.5mmFL; 101.6FL (currently using 50.8mm, exclusively)

>>Am I ok with the K40-ish head or should it be replaced? If so, what's the recommendation?

>>Also, I see heads with a sliding tube that has scribed markations for different FL's, eg. 50.8 , 63.5, 101.6....I cannot make any sense of this
other than one would align and focus the lens at 50.8mm (tube retracted) and set the workpiece at a distance that corresponds to that FL
using a supplied fixed depth gauge(?).
Then if one changes the lens to 101.6, one would slide the tube down to the mark for 101.6FL and lock it down, then use the same gauge
to set the FL to the workpiece? That's the only sense I can make of this setup.
Am I correct?


>>Finally, I'm also confused with what's shown as LR in the product descriptions. Is that Left to Right? If so, is that the direction of the
beam from the tube?
Mine is what I would consider a RL machine, from the tube the beam travels (RL) in a CCW direction from mirror 1 to mirror 2
on to the laser head mirror 3 on the Y gantry.

Thanks,
Bob T.

[Tech_Marco]

The distance between the nozzle and the lens is fixed.

lens.gif (3.68 KiB) Viewed 5367 times

Some people make the nozzle hole bigger so it does not block the beam. But for 100mm focal length, you need high pressure air to make good cut. The original nozzle is not for high pressure air anyway.

LR means the last mirror open to the left.