Ideal focus point

[Joe Peacock]

Since the laser beam is hour glass shaped would the ideal focus point be one half way through the material thickness for vector cutting?

[Rodne Gold]

Yes and no , the problem with focussing 1/2 way in is that when the beam hits the material its cross section is bigger and the energy density is low , this might be too little to actually thermally shock the material into a vaporisation state and the laser might actually cut worse than focussing on the surface.

[Rob Bosworth]

Joe, I have found 1/3 of the way down into the material seems to give better cutting ability on many materials.

[Tim Bateson]

Agreeing with the prior posts. Depending on the thickness & type of material matters as well.
For wood, you'll get a wider vector with more charring. Leaving you with a cut that may not be as clean, not as precise as you may need and requiring more clean-up.
In addition for thinner material, you may get more bounce-back from your vector table.

[Zsolt Paul]

I go slightly into the material (1/3rd sounds about right) and I also mirror the image and cut it upside down. This way, if you hit it with just the right speed and power, by the time the beam comes out at the other end the spot size has reduced due to the loss of energy, giving you a very clean edge. For inlay work / marquetry this is great b/c the bevel is greater at the top (which becomes the bottom of the piece after you flip it over) and produces a tighter fit on top with the neighboring pieces.

[Zsolt Paul]

I go slightly into the material (1/3rd sounds about right) and I also mirror the image and cut it upside down. This way, if you hit it with just the right speed and power, by the time the beam comes out at the other end the spot size has reduced due to the loss of energy, giving you a very clean edge. For inlay work / marquetry this is great b/c the bevel is greater at the top (which becomes the bottom of the piece after you flip it over) and produces a tighter fit on top with the neighboring pieces.

ps: of course if you go to slow and/or with too much power, the flare back can give you a worse surface, so its important that you test for the correct power / speed combo. Generally I always go for 100% power and then find the greatest speed that just makes it through.