09 – RF CO2 Laser Source – Where Is The Magic?

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 CO2 laser source and PSU from Cloudray. Find out how the expensive RF laser source compares to a glass CO2 laser tube and prepare to get your hands dirty!

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

Contents

The way this technology has been hyped by the big companies, I was expecting to discover some magical properties from this type of beam control and generation. Glass tube technology allows control with just power and speed parameters. It is simple and intuitive for people to comprehend and use. RF technology adds frequency to this list of control parameters and power is no longer an intuitive parameter. The complex interplay between these 3 parameters now requires a degree of mental gymnastics to optimise performance. I can begin to understand why the sellers of these machines hide that complexity behind menu driven software. This video attempts to separate and explain the effect of each of these 3 parameters and then demonstrate how they mesh together to produce a predictable result.

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RF CO2 Laser - Testing the Response Speed
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Transcript for RF CO2 Laser Source – Where Is The Magic?

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0:01well thank you very much for joining me in another session about my little tangerine tiger

0:07now after the last session where we decided how the power was controlled i’ve done

0:14nothing more on the machine but i’ve done quite a lot of thinking can i start this session off with

0:19something rather shocking i think i’m going to have to reserve the right to change the title of my little

0:25machine from tangerine tiger to tangerine tabby cat i don’t think it’s

0:32going to turn out quite the way that i or you were dreaming that’s

0:37pretty bold statement but let me just begin to explain how this machine

0:43actually damages material and i think you’ll begin to see some of my

0:49disappointment now here in front of us we see the results of our mode burn

0:54now this is the mode burn from my 70 watt constant current machine this is the mode burn

1:02from the rf 30 watt machine running in more or less constant

1:09current mode 100 the same thing but this time it’s done

1:16with a beam expander which is three times this was two times beam expander this is

1:22three times beam expander now we talked about this last time but we didn’t really go into much of a

1:27discussion about it other than to say this was rubbish and this was more the sort of thing that i was looking for

1:34now i’m going to have to explain myself a little bit about that and why i want this rather than this ideally i’d like this

1:43but hey several things about this rf laser are different first of all coming out

1:49the laser the beam is not parallel it expands quite a bit more maybe two or three times more

1:55than that coming out of a glass tube machine that was disappointment number one and that in fact means that we put a

2:02beam expander in there like that to make the beam parallel

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

2:07okay now that automatically cost us to be found out last time two lenses in here cost us roughly four

2:14percent and four percent power so we’ve already lost power because we’ve had to adjust the beam

2:20i’ve had quite a few people ask the question why didn’t i use a three or four times

2:25beam expander because i’ve got plenty of room on the mirrors to do so it’s a difficult

2:30question to answer to somebody that cannot see what i can see they’re believers in what

2:37i call conventional lens theory and here we have a lens facing the work which is down here

2:44coming onto this lens we have parallel

2:49beings of light now that beam there happens to pass right through the axis

2:55of the lens this lens is designed to focus the beams i.e is trying to collect all

3:02the power into one spot so the beams that are on the outside here

3:09come in here and they focus say here like this

3:18now these beams are slightly closer towards the axis take a slightly different path and

3:24depending on the type of lens whether it’s a plano convex or meniscus if it’s a plano convex then

3:30they won’t take the correct path and they will actually

3:36focus a little bit further forward

3:42like that okay and the closer we get to center

3:48the further forward the focus point will move so let’s just take the extreme

3:54situation of this beam here that passes right through the axis of the lens

3:59where does that focus it’s a single beam and there is no other

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

4:08central focus only one the answer is really

4:15not eight meters away or eight millimeters that’s infinity it will never cross over itself

4:21because it is itself we’ve only got to move marginally away from the center and they will converge but where will

4:28they converge well the answer is probably a long way

4:33if we look at these rays and say well that ray is going over there that row is going out there this ray is

4:41going out here and this ray is coming out here what we’re finding is

4:46what you consider to be the focal point is this look we’ve got the line here which does that

4:56[Music] and that is what you would probably

5:01consider the spot size or

5:09the focal point so there is a footprint at the focal point

5:15through which all the rays will pass now that’s the important thing all the rays will pass it doesn’t mean

5:22to say they all focus at that point as you can see some of these rays are focusing

5:29way beyond the focal point now if this source of light here was uniform there

5:35would only be a small proportion of that energy which is focusing below the focal

5:40point and you would probably hardly notice it but that’s not the case with a laser beam because

5:46our laser beam has got an energy distribution [Music]

5:51which looks like that in other words we have got something like about 70 percent

6:02of the energy in roughly one-third of the width of the beam that means that

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

6:09we’ve got an extraordinary amount of energy concentrated around about the central axis of the

6:15lens now i’ve demonstrated this in several of my videos but there is a lot

6:22of power below the focal point that we can work with the reason why i’m telling you this is because the discussion about

6:30maybe using a beam expander to get a better focus i agree

6:37probably you would get a better focus so we’re going to take this gaussian distribution when it is coming out of the laser

6:45but by the time we’ve expanded it out to some other dimension what’s happened is

6:51our distribution is no longer like this it’s more

6:57like this in other words what we’ve done we’ve taken away the potential for this

7:04high energy which passes through the center and we’ve pulled it out away

7:10from the axis so that we can tame it and focus it and so we should be able to

7:17focus that beam a lot better if it’s bigger is that what i want

7:25i personally do not want that i want my beam to be untamed and i want this

7:32central core of energy because that is what i believe is going to do the damage to the material i’m not interested in this

7:39thing called a spot size or the focal point i want something else okay so that is why i have opted

7:46for exactly the opposite of this i’m trying to keep my beam as sharp

7:54as possible there we go we can prove that point there look

7:59opening the beam up makes it a lot blunter and if it’s blunter like this

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

8:07then we’re going to be able to focus it better that is how standard lens theory works and i agree with that completely

8:13it will focus it better but that isn’t what i want let’s go back to the pictures that we

8:19had last time where we saw we had control of the laser power

8:27with a square pwm signal what we have here

8:34is 30 watts every pulse is 30 watts we have no

8:41other wattage in this unit it always delivers 30 watts so how do you control

8:48the power here is one cycle now in that one cycle we have got fifty percent

8:56high and fifty percent low now when i say high and low

9:03i mean that is thirty watts of power and this is zero watts of power the

9:09actual rf laser is switching on and off and on and off all the time at varying frequencies

9:17which we talked about we can modulate the frequency but don’t worry about frequency because that’s not the issue

9:23the issue here is that we control power by [Music]

9:30changing this ratio here here we are percent power

9:37fifty percent power means we’ve got fifty percent on and fifty percent off ten percent power

9:43means we’ve got ten percent on and ninety percent off per cycle

9:48okay so 50 on and 50 off means that on average

10:00that bit there fills in this bit here what we’ve got is a total of instead of

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

10:0650 power we’ve got 50 of 30 watts so actually when we operate in this mode

10:14we’ve actually got 15 sorry we’ve got 15 watts [Music]

10:21because it’s only on for half of the time okay now let’s just take a look at how compare this to our

10:27constant power laser beam here we’ve got a surface

10:33here i’ve got my consonant power laser beam moving along at a constant speed so if i switch the laser beam on it will

10:40dig itself a hole because it’s constant power the hole will be

10:46like that and then it will switch off so it’ll make a hole like that now if i made that hole

10:55at say 200 millimeters a second

11:02and then i change the power on the laser beam to 100 millimeters a second

11:10what do you think would happen so i would probably expect to make a groove twice as deep

11:19because i’ve got the machine running so slowly that it’s able to do more damage before

11:24it moves on so this is a hundred millimeters a second

11:30of damage and this is 200 millimeters a second of damage so the depth of cut

11:36is proportional to the speed i’m going to put for cw which is constant wave which is when

11:44this machine operates at 100 percent

11:49or when we use a constant power laser this cw

11:59and our standard laser that we’re used to our glass tube which is on permanently

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

12:04and not pulsing would produce these shapes if we ran across

12:11at these speeds let’s assume that we said in both instances this is 100 30 watts

12:19and this is also produced by 30 watts with our glass tube

12:31they would both produce exactly the same result now i gave you some false information

12:38when i spoke last time i said to you imagine a candle flame

12:43and holding your hand over a candle flame now candle flame has got to come a constant output power and

12:50i talked about sharing power by moving your hand across slowly you share the power out a lot less and

12:58it settles in one spot more and you will burn your hand but if you move faster you can share

13:04that power out to such an extent that it doesn’t damage your hand i said but that wasn’t the case with

13:11this pulsing system because when you share it out you get a nice gentle beam like that

13:17and when you when you have a pulsing system every pulse would be the same power

13:26that was a bit of a misleading statement because now that i sit down and look at

13:31how this thing works it doesn’t work like that at all

13:37so for convenience again we’ve got fifty percent on

13:44and fifty percent off let’s just see what happens we know that this will always be

13:5230 watts of power it cannot change because the signal is controlled by

14:00this 5 volt value here and we’re not changing the value of this five volts at the

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

14:05moment okay this is the way in which it operates we change the power

14:10by changing the duty cycle of this square wave if we’ve got 30 watts here

14:17and it reaches this point here switches on and produces some damage in the surface

14:23switches off switches back on again switches off

14:30so we’re going to damage the surface like that if we have our constant laser

14:38running at 30 watts

14:44produce a groove like that not perforations but a continuous groove if this

14:51was running at 200 millimeters a second and this was running at 200 millimeters

14:56a second this little bit here and this little bit here

15:02is there any difference i’ve got 30 watts cutting that deep and here i’ve got 30

15:09watts from my glass tube cutting that deep

15:14there can’t be any difference because they’re both 30 watts so they both do the same amount of damage

15:22now come back to my burning hand principle the faster i run

15:30the more i will spread the power out and so consequently if i change this

15:36from 200 to 400

15:41[Music] my depth of cut is only going to be that

15:49deep [Music] because i’m running twice as fast therefore i’m spreading

15:55the same amount of 30 watts over the surface and i’m doing half as much

16:01damage because i’m running twice as fast does anything miraculously change with

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

16:06this system if i run this at 400 millimeters a

16:20second so i was totally wrong when i said that to you

16:26i’m not going to get little power pulses across my hand i’m going to get the same perforation

16:32pulses across there like that

16:38at the same energy density as i would if it was continuous you have to imagine

16:45that in this instance the candle flame is going on off on off on off at a rapid speed

16:52so all i would get is a perforated line instead of a continuous line with the same amount of damage

16:59or the same amount of hurt on my hand i’m puzzled at the moment as to whether this is going to do

17:04more damage it looks on the surface there as though i’m going to do half as much

17:10damage with this laser as i could do with 30 watts continuous i’m trying to

17:17work out what the advantage is of having a pulsing laser and of course

17:22this is assuming at the moment that the pit that we make is a dead copy of the

17:29on off it could well be that this pit is

17:37something like that because the power doesn’t get a chance to build up quickly it’s not a straightforward cut for

17:45instance if we had this at 10 like this

17:52[Music] what sort of shape pit would i make at 200

17:57would it be that depth or would it not get a chance to build up even and maybe i only got a little

18:03shallow cut these are all facts that we’re going to have to try and find out

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

18:10so undoubtedly this system can react a lot quicker than a glass tube system but it depends

18:16how you use the glass tube system you can’t emulate this process

18:22with a glass tube we’re gonna have to do some tests to find out about this

18:30how good is the relationship between this square wave here and the damage that we do i’m going to

18:37have to use this to start with because it’s the best way that i can see what’s going on

18:43inside there i can modulate this frequency along here if i change that to something like about

18:51500 hertz which i can do i’m allowed to do that because it says i

18:56can run it anything between 0 and 225 000. i decide to set the speed

19:03of my cutting to a thousand millimeters

19:10per second how long does it take to travel a millimeter so there’s one

19:17millimeter and there are a thousand of them in a

19:24second so that means that one millimeter actually

19:29equals one thousandth of a second which is one millisecond so every millisecond i

19:38travel a millimeter how long does it take for a single cycle if there’s 500 of those in a second

19:45it’s one divided by 500 point zero zero two seconds

19:52one second divided by 500 increments two seconds point zero zero two which

19:58equals two milliseconds

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

20:04so we’re going to travel one

20:09plus cycle and one minus cycle i should be able to run at a thousand

20:15millimeters a second and 500 hertz and

20:20produce a shape on the surface which looks like that where that’s one

20:26millimeter that’s one millimeter and that’s one

20:31millimeter that should be very very very very visible and that will tell me exactly what’s going on so in the

20:39previous diagram we showed that you could reduce the depth of cut

20:45on the rf and the constant power laser by

20:52changing the speed spreading the power out over more time over more distance

21:00whatever it is you could spread the power out and reduce the effect of 30 watts whether it be

21:07from an rf or a glass tube so even though i’ve still got the low speed

21:12200 millimeters a second if i reduce the power from 30 watts to 15 watts with a glass tube

21:19i can make the cut half as deep so i have two ways of adjusting the cut depth on a glass

21:26tube laser do i have the same options on the rf laser

21:32well the answer is no look i’ve got 30 watts here

21:38and i’ve always got 30 watts even if

21:43i make this into 10 and 90 all i should finish up with doing

21:50is producing a hole like that it will be the same depth because i’ve

21:56got the same amount of power 30 watts so i cannot change the depth of the cut

22:02with power you say well yeah look you have just reduced the power i’ve reduced the average power i haven’t

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

22:10reduced the specific power in a pulse the average over time

22:16has reduced but not the power per pulse so the only way that i’ve got to

22:24adjust the depth of cut with an rf laser is speed

22:33if i increase the speed i should decrease the depth of cut now that’s a very important fact

22:41and a big difference between the two systems now i’ve got no idea why the big boys

22:49decided to choose an rf laser other than the fact that it’s not chinese they may or may not have

22:57realized the mechanics of engraving

23:02when i watch their videos i have to say they do not understand the process that

23:07they’re selling now it sounds a bit arrogant and i’m going to explain why and you can go and look at some

23:13videos and demonstration videos and you’ll see exactly what i mean you need to understand

23:19the basic principles behind engraving it’s not even engraving it’s

23:25material damage so here we’ve got a surface

23:30and i’m going to fire a laser beam at the surface now bear in mind it’s a laser beam which is

23:35focused down to a point and that means that i’m going to put an incredible amount of power

23:41into the surface of this material now we won’t talk about the material for a minute we’ll just call it

23:47a material the first thing that’s going to happen is we’re going to produce

23:53a little bit of damage there and that little bit of damage is going to convert solid material

24:01into gas or vapor if i gave you a cup of water and you boiled it and didn’t have any

24:08windows open in the room that you boiled in that cup of water would

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

24:13fill the room with steam you know intuitively that vapor takes up a lot more room than

24:19solid obvious fact but one that everybody seems to ignore when they’re working with these machines

24:27if you convert a small amount of material into a vapor it will do

24:33exactly what this is shaped like and it will produce vapor

24:42which explodes upwards like this if you try and tunnel down deeper you’re

24:47converting material much more material into vapor but

24:53hang on this vapor here is in the way of the vapor that wants to expand up

24:58there as well and so it doesn’t what it does it expands out sideways like this because it can’t

25:06go upwards because there’s so much vapor going up that’s in the way

25:11and so consequently you get a lot of sideways spread the more you try the more

25:17material you try and convert the more you’re going to get this sideways spread a sideways explosion

25:22of expanding gas because it can’t physically move up quick enough and that is the stuff

25:30which if you happen to have stuff that’s blowing down onto the surface which

25:37i hasten to add when you look at the the big boy machines they always have air assist on their

25:44engraving they say it blows away the fumes no it doesn’t it blows the fumes back down

25:49onto the work where they condense and produce the horrible brown surface that you see on their work

25:57they do not understand this very simple mechanical principle it’s not even chemistry the basic principle engraving

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

26:04is very simple and i’ve i learned this a long time ago if i’m trying to engrave a letter like

26:10that which is solid click click click click click click like this that’s the last thing i want to do

26:17i am going to scan across there but what i really want to do i don’t have the option on a glass tube

26:23machine of being able to go blip blip blip blip blip blip

26:28like that now the way that i achieve that on a glass tube machine is

26:35to take that letter there but i will convert it into a bitmap i will make the black into grayscale

26:45and i will make the grayscale into mid gray

26:54why well because mid grey when it’s converted into a dithered

27:00image and i know this sounds a long way around but when you convert it into a dithered

27:06image i get this 50

27:11black and 50 white i get dots like this hang on

27:23isn’t that what we’ve got here the ability to produce dots

27:28of course it is the rf laser does something in a simple way that i i have to approach in a very

27:34complicated way on the glass tube machine now why am i doing this

27:40you might say well hang on you’re going to produce a gray letter no i’m not i’m going to produce a black letter

27:45because the dots are always one color it’s just that it’s not going to be a continuous line it’s going to be a

27:51series of dots like this which to the naked eye will look like a solid line the advantage is

28:00that all i’m going to do with these dots is to produce little teeny weeny

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

28:07explosions like this and my fumes will go upwards now if i’ve got my air

28:14management through the machine sorted out properly those upward fumes will not be blown

28:19down because i’m not going to use air assist on engraving they’re carried away

28:24by the high velocity airflow that i have over my work they do not get a chance to settle down

28:30this is particularly useful when it comes to engraving some really dodgy materials like leather leather

28:37produces huge amounts of fumes the oils and the the organic products in the surface it

28:44just absolutely cakes the place with brown if you do continuous scan lines the only way you

28:51can engrave leather in any way shape or form is to convert it to a bitmap and dither it but you dither it to fifty percent white

28:59and fifty percent black meet gray then you can produce a nice clean image on leather or wood

29:06or any other material you choose to use which produces nasty fumes and acrylic is one of them

29:12the fact that this rf tube can produce small controllable dots

29:18at high frequency has got great potential as far as i’m concerned

29:24for engraving it might be crap as a cutting machine but it has potential as an engraving

29:31machine if it’s understood how it works and you utilize it properly now i’ve not seen any evidence

29:38of proper utilization when i look at some of the demonstration videos on youtube they talk about resins

29:46and saps being pushed up and flowing and how you clean them up

29:52afterwards with a with just a damp sponge no you don’t clean up with a damp sponge

29:58you don’t even let them settle we have found a big positive

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

30:04maybe for an rf laser the first one now here’s our standard pwm 25 kilohertz

30:12and we’ve got it set at the moment to 50 percent power 50 on 50 off so we’ve actually got

30:1915 watts going into our job but as i said we haven’t got 15 watts

30:25we’ve actually got 30 watts going into every pulse but the pulse length is 20 micro seconds

30:32long that’s not very long 20 microseconds so a question we ask is how much damage

30:39can we do with 20 microseconds of 30 watts of power

30:44now that’s a difficult question to answer if it’s a piece of wood maybe it can do that much damage

30:53if it’s a piece of leather it may be able to do similar sort of

30:59damage if it’s a piece of acrylic the chances are

31:04it may be able to do that much damage if it’s a piece of glass it may be able to do that much damage

31:10mdf is very similar to acrylic

31:17i know this because of all my experimentation the materials themselves do not respond

31:23in exactly the same way for instance acrylic has got a melting point of 160 degrees

31:29c that’s pretty low and it boils at 200 degrees c so you said well

31:36they’re very very low temperatures i mean wood for example you have to be

31:41maybe 200 degrees c to to make it scorch and probably about

31:48350 degrees c to effectively start burning it and then you have to be about 4500 degrees c

31:57to burn away the carbon 4500 degrees c wood is easier to damage than acrylic

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

32:04which has got a threshold of disappearance of only 200 degrees c it’s all to do with the

32:10atomic structure of the material and how this 10.6 micron wavelength is

32:17able to excite the molecules in the material these molecules here are easily

32:22excitable whereas these molecules here are much more difficult to excite so it requires more power to cut acrylic

32:29and mdf than it does to cut wood or never 20 microseconds on wood

32:34might work and produce that amount of damage how do we get the same amount of damage

32:42onto acrylic but the answer is we’ve got to allow more damage time that might have to

32:49extend out to say something like about 60 microseconds

32:55now if it requires 60 microseconds of energy 30 watts to do that amount of damage

33:02that means the only way that we can get 60 microseconds

33:07is to change the frequency we’ve got to reduce the frequency from

33:12say 25 kilohertz to and bear in mind we’re now going to go from 20 which is the damage

33:18cycle to 60 so we’ve got to go three times as long or roughly one third

33:25of that frequency so we’ve got to come down to about eight kilohertz and at eight kilohertz we shall have

33:32sixty microseconds on and sixty microseconds

33:38off if we had to be using 50 percent power we could achieve 60 microseconds

33:45by choosing a different frequency and a different relationship in other words not 50 we could use a

33:52slightly higher frequency 12 maybe and use maybe 60 on

33:57and 40 percent off we’ve got all sorts of combinations that we can use but that’s

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

34:03why we’ve got control of the frequency and the mark space ratio or the duty

34:09cycle that’s why you need to understand the difference between duty cycle and modulation because at the end of the

34:15day it’s the pulse length the amount of time that you allow the beam on that’s going

34:22to cause the correct amount of damage for the material that you’re using it’s got nothing to do with this

34:29average power it’s all to do with the pulse power in one single pulse

34:39and because it’s so important i’ll try and sum it up very quickly in a few words average power

34:46has got nothing to do with pulse power

34:52you control this machine with pulse length and pulse length comes

34:58from a mixture of duty cycle and modulation the frequency so that’s

35:05enough theorizing well a lot of it’s not theory it’s fact the only thing that we don’t know is the

35:11relationship between this fact of the electronics and what happens in

35:17the real world what is the physics response to that electronic signal how quickly can the light generate

35:25enough photons to damage the material in relation to this signal i think the answer is

35:31we probably won’t notice the difference the only thing that we shall notice is actually this problem here the

35:38difference between the materials and we’re not using the best material in the world acrylic to start with

35:43but it’s the only material that we’ve got that enables us to look through the edge and see what’s

35:50happening so let’s go to the machine and see whether we can make this happen okay now look i’ve

35:55drawn a line here which is 20 millimeters long and here are the parameters i’m going to

36:00set for it we’re going to set it a thousand millimetres a second [Music]

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

36:0650 percent power now remember 50 power isn’t 50 percent power is fifty percent

36:12average power where i’ve got fifty percent high thirty watts and fifty percent low zero watts

36:21okay so i’ve still got thirty watts here for fifty percent of the time that’s the important thing to remember

36:28when you see these numbers i can go in here to advanced settings now so i’m going to set the modulation

36:33now by ticking this and i’m going to choose instead of 500 hertz which gives me one millimeter

36:41pulses i’ve chosen 250 so that it gives me two millimeter pulses

36:48this line is not very long and i’ve asked for a thousand millimeters a

36:53second now i haven’t messed around with the accelerations on this machine at the

36:59moment so it’s going to accelerate quite slowly and it’s not like scanning this it won’t

37:05accelerate and then produce a line and then decelerate this is not scan this is cut so what we shall see on this

37:13here is likely to be a start off from zero which means we should have quite a deep

37:20cut because the speed is zero remember even though we’ve got long pulses we shall also have

37:28slow speed which means we should get a deep cut to start with and as this speeds up and

37:34gets towards the middle of the line and hopefully by the middle line it will have reached a thousand millimeters a second and then

37:41it will slow down again so we should see deep cuts maybe

37:46some nice two millimeter pulses in the middle and then we should see some deep cuts again at the end

37:56and there we go it was as interesting as that so this image is basically the line tipped up at 45

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

38:03degrees so that i can see what’s happening you’ve got a reflection internally

38:08within the perspex of the image so the one at the top is the reflection the one that we’re

38:15looking at is the bottom image and there you see we’ve got our acceleration from zero

38:21where we’ve got a lot of cut depth gradually the cut depth gets shorter as we accelerate and then we move up to

38:29some sort of speed which is not a thousand millimeters a second and look we’ve got some pulses but those

38:36pulses are only three quarters of a millimeter apart so they’re not running at the correct

38:41speed and then we slow down again and you can see the depth getting deeper

38:47and we get to the end of the cut so that was pretty unsuccessful really wasn’t it apart from proving the point that the

38:54cut depth is dependent upon velocity now to ensure i get a thousand millimeters a second

39:00i’ve done two things first of all i’ve been into my vendor settings and set raised the limit from 500 to 1000

39:06millimeters a second so that when i get to this layer here i can actually use a thousand millimeters

39:12a second now i thought i was doing that when i did the single line but i think i might have made a mistake

39:19always admit to my mistakes because hey that stops you making the same ones maybe

39:25so there’s nothing wrong with this now scan because i’m going to use scanning and i’m going to put lines that

39:32are one millimeter apart so i’ve got about four or five lines in there one millimeter apart

39:38that should give us an idea of whether or not we’ve got good separation and good response time um

39:47if they did the line test look what i put in there 250 that’s not 250 hertz look what it

39:56says here 250 kilohertz there we go so my two grow cells let me down again

40:03they didn’t quite spot the fact that it said kilohertz so if we want 250

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

40:08in fact we’ll go to 500 which is what we originally thought we’d do which will be 0.5 kilohertz

40:17500 okay just check that it’s accepted 0.5

40:25yeah it’s happy to accept 0.5 so we should have one millimeter space one millimeter line if we’ve got all our

40:32calculations right and if the material responds

40:37at a fast enough rate it’s not going to be very exciting but hey let’s go for it

40:48look what we’ve got i think we have to be pretty impressed

40:53with that haven’t we because not have we got a thousand millimeters a second out of the machine so it tests the

41:00machine accuracy because we’ve got exactly one millimeter gap and one millimeter spacing

41:06across there it also tells us that we’ve got an incredibly fast

41:11response time switching the pulses on and off

41:17and the our acrylic is not as dead as i thought it was going to be if we try and go deeper we might not

41:24have completely square corners but i’m pretty impressed so far the only way that i can make that pulse

41:30deeper is to compromise on the speed

41:36so if i run at half the speed i should get twice the depth but still get one millimeter spacing we’ll now run

41:43this at 500 millimeters a second

41:50it’s under the microscope to see what’s happening but i can assure you that it’s very very interesting now

41:57these are the pulses at a thousand millimeters a second

42:02and you can see that i’m looking through the edge of the material and tipping it up okay so

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

42:09we’ve got you can see the depth of the pulse there and it’s looking

42:16pretty good so there’s the depth but when i tip it up you get a

42:22reflection but even so they’re looking pretty crisp

42:28now when we halved the speed here’s what we got

42:35they’re quite sharp edged pits they’re not quite as rounded as i expected them to be they’re

42:41sharper than i expected them to be but they do look shorter now why would

42:47that be what did i not think about so if i halve the speed from a thousand

42:54to five hundred millimeters a second my one millimeter per millisecond

43:00is going to change down here to 0.5 millimeters per millisecond

43:11so therefore i’m only going to see a one millimeter

43:25because i’m going to have half up half a millimeter up and half a millimeter down so if i keep the frequency the same

43:31i’ve got a half the distance which is what this is telling me but in addition

43:37to halving the distance what it’s also done has doubled the depth

43:42because we’ve kept the pulp because we’ve kept the pulse on longer so if i want to go back to two

43:49millimeter spacing i’ve actually got to change the frequency to

43:55250 hertz not 500 hertz i hope this little demonstration of my

44:00mistake shows you how heavily related that speed frequency

Transcript for RF CO2 Laser Source – Where Is The Magic? (Cont…)

44:09mark space ratio are intertwined together i ran exactly the same tests on a piece

44:15of poplar plywood all the same settings

44:21then on a piece of mdf and then on a piece of glass all very interesting and actually quite

44:27a lot better than i thought they were ever going to be having started off asking the question

44:34am i going to be disappointed i think we’re coming up with a slightly better answer there is no magic

44:41there’s a lot of complexity but i’m quite actually excited again for the future so on that

44:47happy note i thank you for your time because my head hurts i don’t know about yours

44:53and I’ll catch up with you next session bye for now

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