What focal length lens you use for cutting?

Discussions on optics for laser cutter/engravers

What focal length lens you use for cutting?

Postby educa » Thu Oct 04, 2012 11:38 am

Hi,

I was wondering. What kind of focal lens do you use for cutting?

I currently have a 50.8mm lens, but my 80watt reci tube will produce a 12mm diameter beam at its biggest, so I will have quite small DOF

Therefore I was wondering what laser wattage and what focal lengt you use to cut. (for engraving I know 50.8mm should allready be nice)

I have the possibility to mount a 100mm focal lens if needed.


Kind regards,
Bart
educa
 
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Re: What focal length lens you use for cutting?

Postby twehr » Thu Oct 04, 2012 12:56 pm

educa wrote:Hi,
I was wondering. What kind of focal lens do you use for cutting?
I currently have a 50.8mm lens, but my 80watt reci tube will produce a 12mm diameter beam at its biggest, so I will have quite small DOF
Therefore I was wondering what laser wattage and what focal lengt you use to cut. (for engraving I know 50.8mm should allready be nice)
I have the possibility to mount a 100mm focal lens if needed.
Bart


Cutting is a balance of power, speed, passes, focal length, and material to be cut. It is true that increasing to a 4" lens, instead of a 2" lens, will increase your depth of field, which may, in turn, reduce the number of passes necessary to get through thicker materials (depending on the material and thickness you are working with).

The increased DOF is, however, not free - it comes at the cost of effective power. That means your cutting with a 4" lens will require a slower speed (mm/s) than cutting with a 2" lens. Or it may mean multiple faster passes with the 4" compared to a single, very slow pass with the 2" lens. That is where the material thickness and passes really come in. If the 2" lens is requiring multiple passes, and the 4" lens will require only one, it may be that even at the reduced speed with the 4" lens, you will have a net time savings. It really comes down to exactly how you want to compare the effects of longer vs shorter.

The remaining factor is quality of cut. The quality of the cut edge is certainly different between a single slow cut and multiple faster passes.

Like I said, it is a balancing act.
tim
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Re: What focal length lens you use for cutting?

Postby educa » Thu Oct 04, 2012 1:31 pm

Well I mainly want to cut 3 and 4 mm plywood with PPI pulses so for me the width of 1 pulse is important.
Therefore I think that for me longer focal length combined with 80 watt laser will probably give me the smallest and most powerfull punches.

only minus point is that the beam is between 8 and 12 mm during my travel
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