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

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