Speed vs Power

[Bruce Dorworth]

What is better, when cutting wood or anything for that matter? High speed and high power or Slow speed and low power.Through trial and error I have come up with a speed of 12 and a power of 50 to cut 1/8" Baltic birch on my 80watt laser. That is fine for one or two pieces. So does that mean that if I use a speed of 24 and a power of 100 I can cut twice as fast?

Then there is 1/4" Baltic Birch. I can cut through in one pass with enough power and a slow enough speed, but the edges get really charred. Would it help to do this in two passes? If you did do it in two passes would you lower the focus on the second cut?

Thanks in advance for all the knowledge answers I am going to get..............:)

Bruce

[Michael Hunter]

With my 60W I cut 1/4" baltic birch at slow speed and mid power in one pass.
The key to minimising the char is to adjust the ppi or frequency (not familiar with your laser and what controls you have) - high enough that you get a continuous cut (as opposed to perforations), but low enough to reduce the excess energy going into the wood. On my machine this works out at 1000Hz, but that figure is pretty meaningless if you are not using an Epilog!

Some people will advise two passes. My own findings suggest that if you can't get a clean cut with one pass, then two will make it worse.
You need to vapourise the wood, not burn through it!

With 1/8" 3-ply I get a light tan coloured cut which is clean (no brown comes off on my hands).
With 1/4" 5-ply I get a slightly shiny darker brown coloured cut and the brown will come off a bit if rubbed. No ash or black soot though, except where there were glue pockets or bad knots in the inside layers.

Baltic birch is notoriously variable. For best results get the best grade you can find (normally B/BB) with INTERIOR grade glue.

[Rodne Gold]

More speed will always be better, processing times are shorter and the faster you can go thru the material the less chance areas adjacent to the cut have of being overheated.

[David Fairfield]

Yup, agree with Rodney. I work at the highest acceptable speed for any given task. But speed, in effect, reduces power. And for very fine work, speed reduces accuracy (jiggy curves, etc). So speed setting must account for those factors.

[Richard Rumancik]

What is better, when cutting wood or anything for that matter? High speed and high power or Slow speed and low power.Through trial and error I have come up with a speed of 12 and a power of 50 to cut 1/8" Baltic birch on my 80watt laser. That is fine for one or two pieces. So does that mean that if I use a speed of 24 and a power of 100 I can cut twice as fast?

Not all materials behave the same. For polymers, generally twice the power = twice the cutting speed (for given thickenss.) But you have to realize that for most lasers a power of 100 is not twice the power of 50. That is unfortunate, but the laser manufacturers have not made the relationship between % and outout power in watts a linear relationship. You probably won't be able to determine the shape of the %-power curve. You have to treat the power level much like an a radio volume knob that has no markings. You adjust it until you get satisfactory results. If you try to read too much into the % you will just get confused.

For thickness changes with polymers, if you double the thickness it will be much harder to cut and you will usually have to reduce the speed by much more than 50%. Conversely, with half the thickness you might be able to achieve 3x the speed. But this is not a constant relationship - as to get to thicker substrates the relationship levels off to a more linear relationship.

I don't know if this relationship applies to wood in a similar manner as I have not seen similar charts for wood. And with plywood, which is not a homogeneous material, it is anybody's guess how a thicker material will behave.

The problem I find with two passes on wood is that the first pass creates a lot of carbon at the bottom of the cut; the second pass reflects off the carbon and I get a lot of sparking and not efficient cutting.

[Mike Null]

I am one who uses two passes for a cleaner more complete cut. I do not get charring. I always use air assist when cutting.

It is critical to be sure that the Baltic birch is flat--sometimes it is not.