Why don't many lasers have a movable z axis

[chrisash]

Looking around at hobby lasers and nearly all do not have a movable z axis driven by a stepper motor, you just focus on the surface and that's it

With 3D printers and cad machines, they all have a stepper driven z axis and the price of steppers is peanuts

If the lasers had a z stepper, then as you get further into the depth you could lower the focal point as you go to get deeper cutting depths, so maybe cut the first 3 or 4 passes at surface fixed focus then automatically adjust z axis up a small amount to keep focus at the new depth

Just curious 

[Matt S]

Some of them do, either a third linear axis or a controllable focus. The cost of another stepper motor may be small, but there's also the cost of the leadscrew, rails/linear bearing, a third motor controller, a home/position sensor, extra power requirements, the extra space required... it all adds up, especially in a market saturated with bargain-basement penny-shaving designs sold at razor thin margins. The better designs have a height adjustable bed, which must really cost.

[Bert03241]

MOST DESK TOP LASERS  wont have a z axis but some have a removable bottom so you can block it up for some larger objects. You'll find the most lasers over 60 watts and up will have a z axis. Look at Rabbit, Boss , Thunder to name a few.