16 – What Can We Cut With a 20 Watt RF Laser Cutter?

The Tangerine Tiger Series with Russ Sadler

In this Series, Russ has purchased a new 500 x 300mm, 50W laser machine from eBay with a view to modifying and upgrading it. In fact, he rips out the glass laser tube and high voltage power supply and replaces them with an RF laser source and PSU from Cloudray. Find out how the expensive RF CO2 laser source performs as an RF Laser Cutter.

If you are considering purchasing an air cooled CO2 laser machine with an RF laser tube from one of the big boy suppliers, I would suggest you check out this series before making a decision!


Is my understanding of how PWM controls this RF tube flawed? I think there are major differences about the way PWM can be used in glass tube lasers and RF tubes. I compare the two technologies and demonstrate that with RF technology it is the raw PWM that is driving the beam switching.

Certainly, for a low power 20 watt tube, like I have, CW (100% power) is the only power I can ever imagine using and that means I am bypassing any PWM control. Cutting efficiency is dependent on 4 main factors. Assuming I use full power, they are: – lens focal distance, cutting speed, beam expansion factor and the correct application of air assist. All are demonstrated in this video

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Transcript for What Can We Cut With a 20 Watt RF Laser Cutter?

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0:00thank you for joining me in another session with my little tangerine tiger um

0:08look what i’ve done i put a big lump of wood on the back of my machine well actually

0:15it’s a silencer come duct that hopefully

0:21ducts the air right from the bottom up to here

0:26and it does make it quieter sort of you’ll also notice i’ve connected up the extractor fan as well

0:32so yeah we’ve got everything working more or less on this machine now i’ve decided to finish it off

0:38the other thing that i found wasn’t working quite properly was my air assist valve what i found was that this switch here

0:43wasn’t working properly at all when i came to try and sort the problem out

0:48because the ground i’ve already had something in it and i didn’t want to jam two wires into it i put the ground onto

0:56another place yeah there was a ground on here it wasn’t working now this really just comes back to

1:03something that i’ve long suspected and heard tell of but never personally come into contact

1:10with a problem myself that not only was this machine supplied with a b grade tube and a b grade power supply but it’s very

1:18likely that the most expensive part of it which is the rueda controller was also b grade as well

1:25now normally you would not find a problem the most likely reason for a b grade

1:31product like this is that there might be a missing memory cell somewhere that isn’t working properly

1:37and the chances of you finding that you might find one of your programs goes wrong for some reason or other

1:43but you know the chances of you finding a problem like that is very very small but it looks as though i found a

1:50non-operative ground on this particular controller which tells me that despite the fact that it’s

1:55got all these marks on it it probably is a b grade that’s failed final test while we happen to be in this

2:00controller i’m just going to point out to you something

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

2:05here which is a terminal called a n in this case it’s a n2 because it’s

2:11a second for a second tube um but in addition to that you’ll see that we’ve also got

2:18this one here which is the pwm output the question has to be asked why

2:23have we got both pwm and analog which is what the a n stands

2:28for output okay this brings me nicely somebody was very polite and tactful and

2:35advised me that i wasn’t fully understanding what pwm was all about i have no problem with somebody telling

2:41me that because as i probably mentioned to you before as a mechanical engineer once i get beyond

2:46ankle deep into digital electronics i’m going to drown so if anybody has got

2:52some good advice for me can tell me how this machine actually works with pwm

2:57i’m only too pleased to understand or learn so what i’m going to do is to give you

3:04what i consider to be my understanding of what pwm is all about then we’re going to go and do a little bit of

3:10investigation in the machine itself to see what goes into the black box

3:15and what comes out of the black box because that answers the question now i think i already have answered that

3:22question but i’m going to go back and check it again using a slightly different approach but

3:27something came to mind as i was considering whether or not i had misunderstood what this pwm on this

3:33machine was all about i’m going to take you through what i just mentioned

3:38on the controller the controller has both an analog and a pwm output why

3:44well if you read the manual it recommends that you use the analog output with a glass tube and it

3:51recommends that you only use the pwm with an rf tube both my light blade

3:56machine and my china blue machine which are glass tube machines both operate

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

4:02and we’re supplied with pwm here we have a very crude model of a glass tube system now the reader

4:09controller you can do two things with it you can press the pulse button and you can make

4:14the tube fire and essentially what that’s doing that’s switching this line here which goes into the power

4:21supply that allows current to flow through the tube so we physically switch the tube on

4:27and off in the same way that we switch a light bulb on off there are two other control lines out of here which are actually

4:34controlling the power that comes out of the tube now it doesn’t really control the power directly that

4:41comes out of the tube the power supply itself has got a specification up to maybe say 30

4:49milliamps so that’s quite a powerful tube probably 100 watt tube or something like that

4:55when we put in one percent power to the reader controller we get

5:01virtually zero milliamps out of the power supply and when we put

5:09percent power and if we can’t but we put 99 power into the reader controller what we get

5:16is 30 milliamps we get the full range so the percent

5:24power has got nothing to do with watts the percent power is all to do with

5:31a proportion of the output of the high voltage power supply it’s the current that will be allowed to

5:37flow through the tube so this power supply is doing two things

5:42it’s supplying extremely high voltage twenty thousand maybe thirty thousand in some instances

5:47depending on the type of tube to create the ionized nitrogen in the tube that lovely pink beam that you see once

5:54you’ve broken that nitrogen down from being a non-conducting gas it all of a sudden becomes

5:59very conductive and can pass huge amounts of current this power supply is performing two

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

6:05functions one is generating enough voltage to turn gas into effectively a wire that allows

6:13current to flow and then secondly it’s limiting the amount of current

6:18that you can allow to flow through that wire and so that’s what the secondary function of the power supply is to

6:24control the milliamps we start off with naught to 99 percent

6:32and what we then have to do is to send a signal to the power supply to tell it what we

6:38want do we want 100 power 30 milliamps to flow or nothing if we connect the analog

6:46signal to the in what we’re doing we’re sending a signal which is

6:52naught to five volts dc and that naught to five volts dc

7:00is equivalent to 1 to 99 power so we’ve already coded

7:08that power as a signal a voltage but this is a dc analog voltage

7:16which basically means that if we want say fifty percent power we’re going to output two and a half

7:22volts into the power supply because we want fifty percent power

7:31now the problem is [Applause] if i’ve got a five volt signal zero

7:38five volts and i want two and a half volts then i’m outputting a two and a half

7:45volt steady signal which is 50 of the power which is 15 milliamps

7:50to flow through the tube with 20 000 volts switching on and off rapidly we’ve got a

7:56hell of a lot of radio frequency interference that’s

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

8:02pervading the whole of the environment around this machine it’s very likely that our five volt

8:08signal here which is right next to this big rf generator could not look like

8:14that it may well look like this and if the input signal

8:22to here looks like this then the output signal from here your watts is going to look like that as

8:28well we want the most stable output that we can get there’s another route that we can take

8:33to sending that 5 volt signal into the power supply and that is from this route here goes

8:40into the same port and it doesn’t matter which one of these two you put in because there’s a filter inside there which sorts out whether

8:47you’re sending an analog or a pwm output now this is where the pwm

8:52is quite clever as we’ve seen before with a pwm signal that being zero that being five volts

8:59and if it’s on for fifty percent of the time and off for fifty percent of the time that means

9:05the net average through there will be 2.5 volts so hang on

9:14this now means i’ve got a digital way of encoding this signal so depending on the ratio

9:23of time that’s on in other words if i make it only 10 on and 90 off then i’m going to

9:30code a different voltage into the power supply now once it gets to the power

9:35supply the power supply doesn’t work on this square wave what it does it decodes it

9:44and turns it back into an analog voltage which is where it started off at but

9:49it’s basically digitized it to go down this line now look if i get a bit of interference

9:57on here and a bit of interference on here and a bit of interference on here like that it doesn’t make any difference

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

10:05because the decoding mechanism is looking for these massive changes it’s able to ignore

10:13the rubbish that’s on the signal because this is a digital signal it’s no longer an analog signal

10:19so this is a very very clean way of making sure that we get nice smooth input signals to our power

10:26supply and once it’s inside the power supply itself it can be converted back into an analog voltage

10:32where it is used to control the current that’s flowing through the tube so in this particular instance the pwm

10:41is doing nothing more than producing a coded analog voltage inside the power supply

10:48so that we get a constant output and that’s what this whole glass tube technology is

10:55all about now rf technology as i described to you in one of the earlier sessions

11:00is no different than this at the end of the day we’re going to finish up with a pink beam

11:06that pink beam you can’t see because it’s inside a lump of metal and that lump of metal has got built

11:12into it some sort of power supply some sort of power supply but it’s not

11:17the same sort of power supply that we’ve got for the glass tube i didn’t think that the power supply was messing around

11:23in any way with the pwm signal in other words it was not trying to

11:29provide a constant current output because when i look at the big boy

11:35machines and look at the way in which their programs are written and when i look at the specification for

11:40an rf tube it says that i can use frequencies anything from one to twenty

11:46five thousand kilohertz it must mean that what’s being put through here

11:51is a signal which is a pulsing signal now

11:59if i vary on here the PWM for this glass tube system i mean if

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

12:06if my signal is like this

12:12and i’ve drawn it like that or like this

12:18that is the equivalent of saying do touch

12:26that big red eject button

12:35too late this one says hey don’t touch that big red button

12:42there’s a response time difference between the information that’s being sent down a

12:47slow frequency signal as opposed to a high frequency signal

12:53the data is still encoded like this as a square wave if you mess around with

12:58a frequency on a glass tube machine all you’re doing when you slow it down as you’re slowing down the response time

13:05of the tube to any change that you ask it to make so when you want to jump from one power to another power

13:12it’s going to take time now that has no real effect until you start doing things like

13:173d engraving or grayscale engraving or if you’re using special mode

13:25in special mode you’re relying on the pwm signal as your as your time base

13:30as far as a glass tube is concerned you don’t mess around with the frequency at all but when it

13:37comes to the rf tube we don’t have an on off signal

13:42for this rf unit all we have is this signal output here so therefore

13:50one has to assume that the switching takes place on this rising edge here or something

13:57once we get to a peak voltage because it is only the only signal that’s going into this rf

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

14:04unit as this square wave and so when you feed it with a square wave

14:09it outputs something in the way of watts now i’m assuming and i have yet to

14:16change my mind on this that when i see this signal here for my 20 watt

14:21tube that i’m asking for 20 watts

14:29just because i’ve got 50 on and 50 off doesn’t affect the fact that i’m getting

14:3420 watts out of this tube i might be getting 20 watts for 50 of the time

14:40so on average i’m getting 10 watts but i’m not doing a 10 watt burn i’m

14:47doing a 20 watt burn for a fixed period of time because this machine is so fast at turning on and off

14:55that i’m getting 20 watt pulses i’m not getting 10 watt pulses and

15:02that’s the way that i understand this machine to work my

15:07test pattern that i developed that looks something like this

15:19where these pixels allow me to switch the tube on and off very quickly because

15:25i’ve got a 0.1 pixel a 0.1 gap a 0.1 pixel a 0.1 gap and here i’ve got a 0.1 pixel and a 0.3

15:33gap so i’ve got the ability by looking at this pattern to be able to

15:38measure what’s happening to the power now up here i’ve got continuous lines

15:45now continuous lines as far as this machine glass tube machine means that i turn it

15:52on and even though i’ve got pixels six separate pixels in here like this

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

16:01those separate pixels are not read as separate pixels what happens is when i come to read that

16:07signal i see it turning black and it stays black until it gets to that point and while

16:12it’s turned on i get power

16:18on and then i get white which is power off

16:24and then it goes on again off on and i get a string here of on not a series of pulses

16:32so my point is that if i look at this signal that comes out of

16:38this power supply for a continuous line perhaps it’s not a

16:44continuous line it shouldn’t be a continuous line if the signal is continuously turning on

16:50and off and on and off and on and off i should see breaks or pulses

16:58in that continuous line that clearly shows me that this machine

17:04is not operating in the same way that an ordinary glass tube

17:09machine works we’re not taking the pwm signal and converting it into an analog signal

17:14so that we get a nice smooth steady output we’re leaving this pwm as a raw

17:20pulsed signal so that we can produce a pulsed output and that’s the whole supposed

17:27magic of the rf system the further i get into this the more i realize that

17:32there is no magic just a simple pulse signal so if i’ve got 20 watts here to start with and i’m only using it for 50 of the time

17:40yes i have got a degraded 20 watt signal because i’m only getting on average 10

17:48watts but as i said i’m not getting 10 watts what i’m getting i’ve got 20 watts

17:5320 watts 20 watts 20 watts 20 watts I’m getting a pulse 20 watt signal

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

18:00and so what i want to do today to start with is to make sure that we are seeing those pulses and it’s not

18:08in some magic way producing an average power obviously

18:14the greater the frequency the smaller these pulses will be just to put some numbers on it if i can

18:21run this machine at a thousand millimeters a second

18:28and i’ve got a 254 ppi pattern which is what i’ve got

18:37then it means every one of those pulses is 0.1 of a millimeter but if i run a thousand

18:44millimeters a second then technically every millimeter one millimeter

18:51happens in one second divided by a thousand

18:57which equals one millisecond so i travel a millimeter in a millisecond

19:03so if i’ve got 0.1 pixels

19:09my pixel is going to be traveled over in a tenth of that time ie it’s going to be

19:15100 micro seconds 0.1 of a millisecond so if my if my pulse is

19:23100 microseconds it should just about cover a single pixel which is the some of the

19:29stuff that i’ve been playing with up to now and i have been changing them to get half decent pictures

19:35so i know that i’ve got control of something and i’m still convinced that it is

19:41control of the pulse length itself because i’m working with raw pwm signal there is of the part of

19:48the specification for this tube which claims to tell you something about

19:53the rise and fall time of a pulse now in the glass tube system it’s completely understandable

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

20:00this power supply has got a specification which says you will get 90 of your demand

20:06in less than one millisecond and there are two things that have to happen first of all we have to get

20:13through the electronics so the electronics happens very very quickly so we switch this signal on

20:19and it goes through the electronics here but this electronics can switch on very

20:25quickly but it can’t make the current rise very quickly

20:30once you switch the tube off the voltage has disappeared there is a substantial amount of time

20:36and that’s what this one millisecond is all about we have to get this charged up to make the beam pink which

20:43then allows the current to flow you know we switch the signal on and at the same time as we switch the

20:49signal on the voltage or the power starts to rise so we want 50 watts of

20:55output but the time one millisecond has passed like this we may or may not

21:03have reached 50 watts

21:09we may or we may not have done all right it depends on the response time of your

21:15power supply i happen to have a very good power supply in both my machines and i know that i can get to that value

21:22in around about 0.25 milliseconds how do i know that well because i can

21:29get this little spike here although we’ve got a one millisecond

21:34time period i’ve got this little burst of energy which is just enough

21:40to produce a dot and then it disappears although i’m asking it to print a pixel

21:46i’ve got a little squirt of power that is so slow coming on

21:51that i just about get to the end of the pixel and i get a little pulse of power to burn a dot

21:56whereas with the rf it turns on instantly i get my power instantly and i get a

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

22:02line and not a dot that’s the difference between these two systems right now

22:08you can play with this speed here if i run too fast

22:15with my linear speed i do not give this response time

22:21enough time to build up to give me a single pulse it will give me

22:28a line but what will happen is that line might start off faint and then become solid

22:35and that’s not the same so it appears with this rf machine although people are quoting

22:43at me 100 microseconds rise time and 100 microsecond delay

22:50off so therefore i’ve got 200 microseconds

22:59now if this was true how come i can see

23:07dashes like that where each one of these dashes is in itself 100 micro seconds

23:16long so if the dash is only 100 microseconds long

23:21if this were true i wouldn’t see anything at all the first test we’re going to conduct is based on

23:28this set of numbers here frequency of five thousand we’re on fifty percent on and fifty

23:33percent off now what that means is that the amount of on

23:38distance is 0.1 which is exactly the size of one of my pixels and the pitch is 0.2 that’s the distance

23:46between the pixels let’s predict what we might see on a continuous line the lines on my

23:53pattern are like that and then occasionally there’s gaps with two

23:59and then maybe a four and then maybe a three there’s all different lengths of lines

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

24:05on there with different numbers of pixels in a dot a gap a dot

24:11and a gap that’s what i expect to see when i look at that line we’ve got point

24:16one pixel and 0.2

24:22pitch so we should be producing

24:28pixels which look like this now in reality what we’re going to get

24:33is pixels that look like this we’re going to get a brown dash but then

24:38we’re going to get the beam and i don’t know what width the beam is but whatever the width of the beam is

24:44we’re going to get half a beam width hanging out the end of each pixel now we can measure the

24:49line width and make sure that what we’re seeing is correct that’s what i’m expecting to see if we are dealing with a raw pwm signal

24:58if we’re not dealing with a raw pwm signal then i shall see a straight line now to carry out this

25:05test i’m using some red card this card i’ve found to be

25:10very useful as a tell-tale material i can take the die out of the material and leave a white

25:16wood pulp behind so we get quite a nice contrast on this material i’m using the compound

25:22blends to get the finest possible dot that i can now i’m afraid you have to put up with a little bit of noise because i’ve got the

25:29uh the cover off the back of the machine at the moment before the next part of this exercise i want to carry out and just so

25:35that we have a record of the settings 1000 millimeters a second 50 50 power

25:42we’re on scan mode we’ve got 0.1 pitch and we have got the frequency set to

25:515.005 in other words it’s 5005 hertz because if you remember five

25:57kilohertz is exactly the so-called pre-ignition frequency and that seemed to interfere with the pulse

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

26:03pulses so we’ve moved it just above five kilohertz

26:08[Music] okay so we’ve got what i expected i

26:13never have a problem with somebody calling my knowledge into question because remember my knowledge has been

26:19gained by practical experience and i could be misinterpreting what i see but i don’t think i’m

26:26misinterpreting this i know the signals that we put in and those signals are exactly what we’re

26:32seeing here now the other question is about 100 microseconds 100

26:37100 microseconds rise time and 100 microseconds fall time just doesn’t make any sense at all

26:42because here we’ve got 100 microsecond pulse 100 microsecond gap 100 microsecond

26:48pulse and 100 microsecond gap if we had a hundred mic in second rise time and a hundred micro second full

26:54time we wouldn’t be seeing any of this so to all intents and purposes this machine

27:01has got a pretty instantaneous rise and fall time and i think that’s all

27:07because it’s got it’s already sitting there at the top of the pre-ionization zone

27:13ready to switch the beam on at the instant that the electronics tells it to there is no electronic delay

27:20so there’s no physics involved with this in the same way that there is

27:25physics involved with switching on and off a glass tube through the power supply so this is all good news because it does

27:33mean to say we can now progress further knowing that we understand exactly how the pwm works on

27:38this machine i mean i’m doing a thousand millimeters a second here so this is running pretty fast and it’s

27:44still switching on and off instantly enough to show that i’ve got virtually

27:50no if you like power build up there is a little teeny weeny bit of power build up here because look you can

27:56see the beginning of the pulse if you like to regard that little white bit in the bottom there as being

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

28:02maximum power then you can see that it is slightly shorter than probably 100

28:09microseconds but the overall pulse width here is about 100 microseconds well we’ll just

28:16do one more test because that’s all we need [Music]

28:21and that will be to leave the frequency exactly where it is but this time we turn it on to 100

28:28power 100 power should now produce continuous lines and

28:36lo and behold we have exactly what we expected look we’ve got a continuous line this time we’ve got no interruption

28:43because we’ve asked for 100 power which is the pwm on all the time

28:48and what we can see at the bottom here as again what we expected we’ve got 100 microsecond pulses not because we’ve set

28:55100 microsecond pulses because the pixels are switching them on and off at 100 microsecond

29:01intervals but what we have got down here now is the width of the beam hanging out the end

29:07of the 100 microsecond pixel so we’ve got a joined up string of pulses we no need to go any further and

29:12investigate this when we talk about pwm in the future i hope that we will all understand what’s

29:18happening with this machine i’m going to expl i’m going to be exploiting this most of the time because we need maximum

29:25power for cutting if i had a 60 80 or 100 watt machine maybe i’d be using some pulsing system

29:33but for 20 watts i might even be able to chop up smoke rings because it’s that quick how much thicker

29:39than tissue paper or thin card will it go with 20 watts i never go about using 20 watts in a

29:46conscious manner on the glass tube machine because 20 watts happens to be right at the top end of the

29:53pre-ionization frequency where i’ve got huge spikes of power and high very very high frequency so i’ve

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

30:00effectively got something that looks like this for cutting card and it works extremely well so our first

30:08test is going to take place at five millimeters a second 100 power i’ve left the frequency at

30:145.005 because it doesn’t matter about the frequency if we’re using 100 power there is no frequency involved

30:21when you’re using the power continuously

30:26well the good news is the smoke is coming out underneath [Music]

30:31that means it’s cutting

30:39that was five millimeters a second well the edge is very black and the

30:45underneath there’s a little bit of color underneath that generally tells me that we can go

30:51quite a lot faster so i don’t even want to step up in little increments i think we’ll go up

30:56to 10 millimeters a second next coming out the back again

31:03it’s an interesting surprise you can probably see the color difference there

31:09we’re getting lighter which means that we can go faster because we’re still too brown

31:17well surprise 15 millimeters a second i think

31:23you can clearly see there the change in color as we go across the three of them we’re getting to the point where we’re

31:29nearly there now still getting smoke out underneath wow and the color is even lighter 19

31:36millimeters we’re still getting smoke out underneath but it’s not falling out this time

31:48no it doesn’t want to i would regard that as being

31:54no good we’ve hit a rock there at 17 millimetres a second that’s not bad now I’m going to test my

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

32:00theory and reveal my secret for these tests i’ve been using

32:06something that people have been asking me to do the times 3 bean expander

32:13which gives a bigger beam size my argument all the way along is the

32:19theory that i don’t want a bigger beam size i want the smallest beam size i can get because

32:24i want to exploit one of the weaknesses of lenses and that is the central axis

32:31the closer you can get to the central axis the less the beam focuses not more

32:38and the less the beam focuses i believe the better the cut will be so i’ve now

32:45swapped this times three for a times two we’ve seen where times

32:51three bounces off the wall in fact it bounces off the wall here at 18 it won’t deal with 18.

33:00let’s just have a look at what happens now when i continue this run

33:07times three [Music]

33:14now i’ve done nothing else other than change the beam expander i

33:20haven’t reset anything except

33:27that’s 20 millimeters a second

33:44and that’s 27 which will not push out so the only other cutting lens i would

33:49contemplate using on this machine is a two inch lens and that’s what i’ve got in here now i’ve got a two inch

33:56plano convex this is normally set to seven millimetres

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

34:03and i would expect this to be able to do [Music]

34:0810 millimeters a second i’m getting confident now because this is a doing a bit better than i expected to be

34:18honest well that made it

34:24it’s already sort of a pale brown so it can’t go a lot faster than that let’s try 12.

34:40well just about i suppose so i’m now she’s going to show you another trick and it just reinforces

34:49what i keep telling you about air assist and the efficiency of

34:54air assist now i haven’t got much air assist on here i’ve only got a little teeny weeny motor if you look carefully just down the back there

35:01i’ve got my motor hanging inside the machine so it’s actually suspended by

35:08some tie wraps in fresh air it’s only a very very small motor it’s probably only delivering about 50 or 60 liters a

35:14minute i’ve already got the focus set seven millimeters i’m now going to push the nozzle down by

35:20the thickness of that washer which i’ve made out of mdf three millimeter mdf so i’ll put that over the collar over

35:26the thread there and i’ll put the lens tube back on so now i’ve increased

35:31the distance between the nozzle and the the nozzle and the lens

35:36so instead of a seven millimeter gap now i’m gonna have to set this to a four millimeter gap we haven’t changed

35:43the focus at all all we’ve done is decrease the gap between the nozzle and the work to improve the efficiency of the air

35:50getting into the kerf just about made 12 millimeters

35:56well as you see that more than just made it

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

36:0112 a a air assist

36:07we’ve already got air assist on there but we’ve just improved the efficiency of the air assist let’s go to 15.

36:16so we try 18 17 let’s try seven

36:26now i’m just going to gently tap that and that’s 20. getting to the point where i think it

36:32won’t do much more we can try 22 but i think 22 will fail

36:41it’s still on the edge of okay staggering isn’t it all i’ve done is brought the nozzle

36:47closer to the work i haven’t changed the focal distance the speed or anything all i’ve done is increase the efficiency

36:54of the airflow through the curve to blow the smoke away the smoke is absorbing the energy

37:00and if you don’t get it away quickly underneath the job we haven’t got any extra air assist

37:05we’ve still only got about probably three at the most four psi but what we’re doing we’re

37:11using it more efficiently we’ll try 24 i think we’re struggling now

37:20yep we are so 24

37:28five okay it’s quiet again now so we can have a quick summary because i think this really is the end of this session

37:35we started off with a boring bit about pwm but the case has proven so we can leave that behind us now

37:40i have to say i was pretty surprised about the cutting capability of this

37:46machine with 20 watts i thought i was only going to be able to cut tissue paper and but it seems as though

37:51three millimeter plywood has been a surprise to me with the in compound engraving lens

37:58we were able to get up to 17 millimetres a second with a three times beam expanding i can

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

38:05say is to those people that thought i was being mad when i changed to a two times beam expander what do you

38:12think now my case is proven i can do 17 millimeters a second

38:18with a times 3 and 25 millimeters a second with the times two

38:24because i think i understand one of the weaknesses of lens theory and that’s the rogue

38:31beams as i call them that go right through the center the more you spread your beam out the more you’re making it opportune

38:38to condense the beam into a nice spot for engraving but the tighter you keep the beam the

38:45less you can control those rogue beams right down the center and they go right through the middle and

38:51they give you extra power for cutting they don’t just stay on the surface for engraving and it subscribes towards the

38:57principles that i was working with in my rdx learning session where we were playing with

39:03a seven and a half inch lens here and a two and a half inch lens here and managed to get a 30 percent increase

39:11in cutting ability because we were expanding the beam but

39:16because we were condensing the beam before it went through

39:21a two and a half inch lens so i think this general idea about compressing the beam to put it

39:29through a lens to make it more efficient at cutting it’s probably something we shall further investigate and prove

39:36as a real possibility because hey if you can get 30 more speed out of the same tube by just changing

39:43your lenses it’s much cheaper to buy two lenses than it is to buy a big expensive tube

39:49and then the real surprise i suppose was the efficiency that we managed to get out of the two inch lens two inch lens

39:56well we got up to twelve millimetres a second but with a little bit of a fiddle to improve the efficiency of the air

Transcript for What Can We Cut With a 20 Watt RF Laser Cutter? (Cont…)

40:03assist we racked it up from 12 millimeters a second to 22 millimeters a second

40:09so we more or less doubled the capability of the lens by just reducing the air gap

40:16from seven to four millimeters now that’s not unique to this machine

40:22that’s something that’s unique to all machines you don’t need high pressure air assist what you need

40:28is efficient air assist we have established beyond any doubt that this machine

40:34works on raw pwm pulses so thanks for your time and your patience today and i’ll catch up with

40:39you in the next session

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Last updated April 25, 2024


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