New member, which laser head.

[Greolt]

New member here. Been doing a lot of reading of the forum and elsewhere.

Thinking of building a engraver/cutter. Looked at it in the past but, this time I am starting to get enthusiastic.

Not new to CNC and Mach3. Built a few routers and retrofitted a mill.

Confident I can handle the mechanicals, drives, etc. Will start with Mach3 because I am familiar with it and see how we go in the longer term.

No experience with lasers. I will have a lot of questions but will start with this one about optics or more precisely the carriers for them.

Which laser head and mirror mounts?

Going to build with room for a 60w tube, but will start with 40w tube and a 60w power supply. So optics must be capable of 60w.

On ebay there are a lot of mirror and lens size options. (Laserlands and others)

20mm mirror & 18mm focus lens
20mm Mirror and 20mm Lens
25mm Mirror and 20mm Lens
30mm Mirror and 25mm Lens

Any advise on that would be great.

Planning on a moving table so I assume that adjustable height lens carrier that is typical of these heads is not important.

However I am guessing that the length of the air assist nozzle is. Looks like lenses come in various focal lengths. What focal length should I be thinking of?

The typical ebay head has a fixed nozzle length. Is this an issue?

I want to get this head ordered. As this is the bulk of what must fly back and forth, when I have it in my hand I can get a better feel for gantry design. Otherwise I will overbuild it.

Any wisdom from forum members will be gratefully received.

Greg

[bdring]

Most of the optics can handle either power level. The diameter is not that important. Get what fits the mounts. A larger machine might need a bigger diameter due to divergence, but don't build a machine that big (trust me).

The typical lens focal length is about 50mm. Most lasers like you are building use that length.

A shorter focal length yields a proportionally smaller spot size. I have a calculator page here.

http://www.buildlog.net/cnc_laser/laser_calcs.htm

[Greolt]

Thanks very much bdring.

No the machine will not be too big. 900 x 450 should be enough for a first machine.

Went ahead and ordered a head with 20mm lens (63.5mm focal length) and 25mm mirror. Mirror mounts the same 25mm.

Looked at you calculator and all it told me is, I have a lot to learn.

I will have many more questions.

Greg

[Greolt]

Had another look at the calculator and now, after a lot of forum reading, it now makes sense.

This may be a dumb question but....here goes......

The lens has what looks to be a flat side and a convex side. Which side faces the tube..... or up ?

Greg

[TLHarrell]

Curved side faces up.