Speed vs Power

[Ian Johnson]

I've had my laser for about a week (60w LG500 from Automation Technologies) and am still getting the hang of things. One thing I haven't found is a good explanation of the effects of power vs speed. I was originally under the impression that they were interchangeable, and that you could either reduce power, or increase speed and get the same effect. However in working with 1/4" melamine I'm finding that 100% at 8mm/s won't cut through reliably, but it will at 6mm/s. Once I'm down to 6mm/s I can drop the power to 50% and still cut through. It seems like there is a point of (swiftly) diminishing returns where more power won't gain more speed, only more smoke.

When you experienced users get a new material, is there a typical process you use of working through speed and power settings to settle on the most efficient combination?

[Bill Stearns]

IAN -
LaserBits Co. - on their site offers a "SETTINGS GUIDE" that might help you along the way. (laserbits.com). Also: I keep a notebook handy where I record settings for different materials and different types of projects - I've found this helps. You may just find some of this learning curve 'matter of trial and error. - Good luck.

Bill

[Kev Williams]

With my ULS and NH LS900 machines, they "seem" to output speed and power fairly relative to actual settings. Meaning, 40% laser power is 40% regardless of speed.

My Triumph on the other hand, doesn't seem to follow those rules. For example, I was engraving some anodized aluminum one day at 400mm/sec, at around 45 power. The result was a bit "hot", so to adjust, I increased the speed. However, even tho I didn't change the power setting, the power increased almost proportionally with the speed. The amp meter was giving higher readings, and the results were nearly the same. To get a "cooler" result I had to reduce the power.

Another instance I've found with this anomaly(?) is the fact the laser will fire as low as 4% using the 'laser' button, or engraving very slowly, but if I'm cutting or rastering at near 'normal' speeds, the laser won't fire when set below 9%.

It all ends up with the simple answer, 'no two machines are alike', and the only way you're going to know what your machine will do is to experiment with it! (which is half the fun!) ;)

[Chuck Stone]

Yep.. you've got some homework to do!
You'll end up developing your own chart. You can see other people's numbers, but only
in the most general way.. you won't end up using their numbers, but perhaps you'll
see their trends. One material uses lower power and faster speed... one uses high power
and fast speed.etc. You'll spot trends and be able to make educated guesses for your own
machine after a while.

Speed and power aren't really interchangeable, but they do work hand in hand. You can think
of it this way: There is a correct amount of total power you want for each material, for each
type of work you want to do. Sometimes you want to remove material. Go fast with high power.
Sometimes you want to remove the material AND leave a burned impression behind. So you need
to go slower and give the material time to burn. Go too slow and you have a charred mess.
So for the same material, you now have two different sets of numbers depending on what you
want to do. But someone else's numbers will only give you a starting point.. and probably won't
give you the results you want. But they'll point you in the right direction.

I just replaced resistors in my laser tube yesterday and now all of my numbers from Saturday are
no good to me. The same mirror I engraved Friday at 30 speed, 60 power engraved tonight at
70 speed, 30 power. But from that, I have a pretty good idea what my other numbers will be,
probably within a few points and I can test that on scrap. You'll be doing the same for yours.

[Mike Lysov]

When you experienced users get a new material, is there a typical process you use of working through speed and power settings to settle on the most efficient combination?


I always start with a maximum power of 90%-100% and then adjust speed until I can cut through and I am happy with cutting edge quality. This method may not work good with some plastic such as acrylic and you need to experiment. I mostly cut MDF or natural wood and I want to find power/speed combination for a new wooden material where I can cut through as fast as possible.

[Mike Null]

I am happy with cutting edge quality.

That's really the key to your settings. Speed or power are meaningless if you don't produce an acceptable result. I can cut .25" wood in one pass but I don't because I don't deem it to be acceptable.

I even use different settings for certain colors of laminated plastic of the same thickness.

[Keith Upton]

I've found that it really all comes down to exposure to the energy. It is going to take X amount of energy to cut through any a given material (X is really a range from the least amount of exposure to cut 100% through it all the way up to maximum your machine can output). So, if you decrease the power, you are going to have to decrease the speed as well to get the same amount of exposure. If you increase the power, you will need to increase the speed as well to have a similar results. Increase the power and keeping the speed the same will still cut though the material, but it is going to give a different effect to the material that is left behind.

[Ian Johnson]

I've seen a lot of mentions of edge quality but nothing yet on the characteristics it refers to. Do you mean the smoothness of the cut face? Or the edge between the faces? I haven't run into any problems with the edge yet, other than a tendency of the laminate to peel if the cut isn't thorough on the bottom. I've also been keeping an eye on how perpendicular the cut is, and I'm finding some variation within the piece. I know focus affects this, but given a fixed focus can speed/power affect whether the cut gets a slope? It's very slight, but I'm doing a lot of tab and slots so I'd like to keep them as straight as possible.

[Keith Upton]

The effects on edge quality are going to very from substrate to substrate. With acrylic too high of speed will show the "facets" that make up the circle. Slowing the speed down allows the excess heat to polish (melt) the edge just enough to smooth it out some. On woods, the biggest effect will be the burning or charring of the edges. More power (or less speed) then needed will put more heat into the wood, there by charring it. Sometimes you want that burned look to the edge, sometimes you don't.

My wife scrapbooks and buys these laser cut wooden embellishments all the time. Once I got the laser I decided I could cut there for her. One day I went to a counter top place to pick up some Corian to try on the laser and they had all these different little counter top laminate samples. They had all kinds of colors and patterns. I thought they would make great embellishments for her. I though a couple on the lase and found I had to use full power and very slow speeds to cut all the way though the tops of them. The thin wood behind them only needed a fraction of that power though. So, if I cut them all the way through, the edges would char badly and left a thick coating of soot on them! Not at all something she could use because of the edge quality.

[David Somers]

Keith,

Am curious what thickness Corian that was? I think you can get it down to 1/4"? I think countertop thickness for that is 12mm?

Just curious.

Dave

[Keith Upton]

Dave, I did not have a project in mind for it, I simply wanted to try engraving it once. As such, I just asked them for a scrap I use to mess around with. It is in fact 12mm. They told me they would sell me scrap for their cost of $12/Sqft. I said thanks and would keep them in mind... but I will not be buying any from them as I'm sure I can find a place that will just want to get rid of scraps.

[Ian Johnson]

Does charring depend on the wood? I've only been cutting 1/4" melamine MDF so far, but there isn't a setting that will cut through that doesn't leave a black edge. Would that be more on the density of the wood, or is it going to be impossible to cut above a particular thickness without putting enough energy in to char it no matter what? Can you cut the energy in half and do multiple passes and avoid charring that way?

Also I am currently masking the wood to keep the burn marks off. I have a kind of giant double tape dispenser that I can push the boards through to apply the tape so it isn't too much of a hassle. Even so is there a way I can avoid staining altogether? Some approach to settings or cutting surface maybe (I'm currently using the standard honeycomb)?

[Bert Kemp]

I find the easiest way to avoid staining is to seal the wood. You'll get some degree of stain or smoke residue but it will just wipe off with a damp rag.

[Chuck Stone]

Does charring depend on the wood? I've only been cutting 1/4" melamine MDF so far, but there isn't a setting that will cut through that doesn't leave a black edge.

Hitting MDF with a laser beam produces lots of soot and CO2, both of which hamper the
laser's effectiveness. And once you make one pass, the incomplete cut is full of soot that
smokes and maybe flares up on your second pass. And each subsequent pass is less effective.
I might get 90% through on the first pass, only 3% on the second pass, another 2% on the third etc..
I'd do all I could to get through it in one pass, but I've come to the conclusion that my laser
just can't handle MDF. (30W)

[Dan Hintz]

One thing I haven't found is a good explanation of the effects of power vs speed. I was originally under the impression that they were interchangeable, and that you could either reduce power, or increase speed and get the same effect.

Move a lit match in a large circle under a piece of paper... if you move it fast, no matter how long you keep that match moving the paper will not catch fire. Slow the movement to a crawl and the paper will quickly burst into flames.

The effect is the same with a laser... you can not simply trade power for speed.

[Ross Moshinsky]

Engraving cutting boils down to speed : power. So if you break things down to actual units of measure watts:ips, you'll find that you can ballpark settings pretty accurately regardless of laser. I've never believed in "my laser is unique so my settings are different". The same thing has been said forever in the car world and it's simply not the truth. There is a shred of truth to it, but for the most part 10 of the same laser are going to be more alike than not.

With all that said, I can't speak specifically to how Chinese lasers control their power and speed. As stated in this thread, it seems they are a bit unpredictable and lack a linear result that you see from Western/DC type lasers.

[Rich Harman]

...but given a fixed focus can speed/power affect whether the cut gets a slope?

Yes. Think of it this way - if you cut just a bit too fast it will not quite cut all the way through but it may be enough to free the pieces. The top of the kerf will be wide but the bottom will be zero, so you have a slope. As you slow the cutting speed the bottom of the kerf opens up. You should be able to find a speed so that the top and bottom of the kerf are the same. I haven't tested this but I believe this process is easier if you are focused on the surface. I always cut full power (except for really thin stuff), always single pass and focus on the surface and can get perpendicular cuts on up to 3/4" material. Actually 1" if you count foam, that's the thickest material I have cut so far - and in that one case I focused half way into the material, the edge was vertical and very slightly convex.

[Mike Lysov]

I've seen a lot of mentions of edge quality but nothing yet on the characteristics it refers to. Do you mean the smoothness of the cut face? Or the edge between the faces? I haven't run into any problems with the edge yet, other than a tendency of the laminate to peel if the cut isn't thorough on the bottom. I've also been keeping an eye on how perpendicular the cut is, and I'm finding some variation within the piece. I know focus affects this, but given a fixed focus can speed/power affect whether the cut gets a slope? It's very slight, but I'm doing a lot of tab and slots so I'd like to keep them as straight as possible.

Hi Ian,

I meant charred sides by edge quality but it is not about level of charring. For example I can cut through 16mm thick MDF with the maximum speed of 800mm/min, however even though it is completely cut through edges are not perfectly smooth. It has some imperfections on an edge close to the back side. If I do the same cut with 600mm/min it makes a smooth edge. Straight edge depends on how thick is your material and what lens you are using. I have found some website where depth of field has been calculated for each lens. As far as I can remember 4" lens can give you maximum of 7mm depth of field.
I have no problems doing 18mm thick MDF with 3" lens but I set focus for wood from 12mm to 18mm deeper into the wood. It is not completely straight but I would not say it is really noticeable.

[Mike Lysov]

Does charring depend on the wood? I've only been cutting 1/4" melamine MDF so far, but there isn't a setting that will cut through that doesn't leave a black edge. Would that be more on the density of the wood, or is it going to be impossible to cut above a particular thickness without putting enough energy in to char it no matter what? Can you cut the energy in half and do multiple passes and avoid charring that way?


I do not think so. I have cut a lot of different types of wood. It always comes with charred edges. Multiple passes make it even worse because you get charring after the first pass and the second one makes this part of completed first pass even more charred.

You can get rid of residue at the back and at the front if you use a good air assist and you raise material above a cutting table. It works for me on my Laser Pro Spirit and all MDF cuts come very clean. However my other laser even with 65PSI of air assist sometimes leaves some residue at the top of cutouts. I believe it happens because my air compressor cannot keep recommended 70PSI all the time and pressure drops to 45-50PSI after compressor works 2-3 minutes. Anyway it leaves residue only at the piercing point so it is not really hard to clean.

The back of cutouts is kind of tricky on my 280W laser. I am using blades as a cutting table in this laser. I raise material about 2mm above the blades. But because the blades are dirty with residue when beam hits the blades it generates some flame at the back. That how I get some smoke stuck to the back of cut outs. Anyway it looks much better than cutting with material placed on the blades directly. If it is sitting on the blades I am getting reflections from the blades plus some residue stuck at the back.
I tried to cut with material hanging between blades but I was experiencing another problem. When cutout was complete and starting falling down the beam was still hitting it and was making some unexpected burns on them.

[Morris Mac]

There is a relation between both of them. When you cut a straight line there is no problem machine give you power and speed from the settings. Now when machine comes to a corner or do a small intricate cut, if machine keeps same power same speed you will see big burn on corners and because the machine have to slow down to make the turn is were software come in play to tell the laser to reduce power so you will not see those burns on corner. Machine can turn a corner or process geometry only as the mechanics allow, (is like driving your car around a corner with 100 miles an hour) sometime mechanical is not possible. Machine have to accelerate and de-accelarate and power of laser need to adjust as well.

[Allen Rawley]

In my experience, the following factors (in order of importance) will reduce charring when laser cutting quarter inch and thicker wood:
1. Reduce the nozzle orifice size the smallest acceptable diameter. Typical diameters are 2 mm and less.
2. Increase nozzle air pressure to maximum available (good settings start at 30 psi, and go up to 70 psi). By having a small diameter nozzle the velocity increases tremendously.
3. If more than one laser is available, then choose the one with the highest power as it will cut fastest and minimize the time to char.
4. Add a pierce or dwell time to penetrate the wood, then optimize speed for the cutting. In other words, it takes longer to first cut through the wood and if you maintain that power while cutting then you are simply adding unnecessary energy into the wood while cutting and increase charring. You Lasercut users have this feature accessible in your parameters setup--learn it and implement it. Older Lasercut users--the parameter for delay it is accessible in your syscfg.ini and found by using your text editor and searching delay and changing the value until you get it.
5. Industrial alcohol and charcoal lighter fluid are excellent to remove soot afterwards.
6. If nitrogen is available, then use it in place of compressed air (without oxygen there is less charring).

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