24 – How to Change Your Laser Tube (43:05)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Engraving Machine. Thinklasers Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ explains and demonstrates the process of how to change a laser tube. He then covers the process of beam alignment by setting up the optical path.

How to change a laser tube
How to change a laser tube

Contents

  • Russ found some very small inconsistencies in his laser that would be fine for normal production work but not for test work.
  • Was sent a new tube made by EFR – a cheap but good quality tube.
  • EFR make 3 ranges of tubes
    • CL Series (stated life of 3,000 hours is questionable)
    • F Series (stated life of 6,000 hours)
    • ZS Series (stated life of 10,000 hours)
  • Warranty promises made by manufacturers are dubious
  • Doing the maths to compare life with cost shows that the bottom of the range tube chosen by Thinklaser is the most economical over time.

How To Change a Laser Tube – The Removal Process

  • Danger of stored high voltage electricity – leave the machine for at least an hour before starting disassembly.
  • Disconnecting the tube from the machine by snipping the cables.
  • Use of a standard terminal block to connect the wires.
  • Unclamping the tube.
  • Using a clean plastic bucket in case of leakage.
  • Clamping the tube and removing the water outlet pipe from back of chiller.
  • Using tape to keep the tubes high.
  • Blowing the water out of the tube.
  • Disconnecting the cathode cable.
  • Removing the tube.
  • Catalyst coating on discharge tube – seen as a pink colouration on the inside of the tube which is gold.
  • Cutting off high voltage connector.

How To Change a Laser Tube – The Installation Process

  • Installing the tube.
  • Making the electrical connections.
  • Using the silicon cooling tubing as an insulator.
  • Using silicon sealant – don’t use standard bath sealant (Editor’s Note: You need a type that doesn’t contain acetic acid – which is the chemical that causes standard sealant to be so smelly)
  • Fitting the water pipes.
  • Clamping the tube.
  • Replacing the water that was caught in the beginning.
  • Turning the machine on and checking that the water flows back through the tube.
  • Checking the tube with pulses.

How To Change a Laser Tube – The Beam Alignment Process

  • Using circular beam targets to check alignment.
  • Testing the beam alignment.
  • Lifting the tube to align it.
  • Checking the alignment with Mirror 2 and moving Mirror 1 to correct alignment.
  • Checking alignment with Mirror 3.
  • ‘Sighting Pulse’ and ‘Target Pulse’ to check beam is parallel with the primary axes of the machine.
  • Looking at various ways of getting the last part of the alignment correct.
  • Mirrors 1 and 2 less sensitive to small vertical errors, Mirror 3 less sensitive to small horizontal errors.
  • Removing the lens tube and doing pulse tests to check Z-Axis alignment.
  • Summarising the 3-step process:
    • 1: Move the mirror as far away as possible and make a ‘Sighting Burn’
    • 2: Move the mirror close to the previous mirror and make a ‘Target Burn’
    • 3: Then align the mirror to get the two burns coincident and repeat 2 & 3 as necessary.
  • Replacing the lens tube
  • Using another target to check the alignment of the beam with the beam tube’s nozzle.
  • Slightly adjusting the beam to get it into the centre of the target.
  • Using a large block of Perspex to check that the beam is vertical
  • Summary. The concept of adjusting the source of the beam or ‘catching the beam’. Now need to measure the performance of the beam. See the next video.

My thanks go out to Tom at Thinklaser for giving permission to embed these videos on this site. If you are looking for a new laser machine from a quality supplier, then I would suggest you check out their website: www.thinklaser.com.

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Transcript for How to Change a Laser Tube

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00:14

Now welcome to another Lightblade learning lab today we’re going to do

00:21

something a little bit different now just recently I detected some rather

00:25

strange performance characteristics in my 60 watt tube

00:29

I call them strange they’re strange to me for most in inverted commas normal

00:36

people and people that use the machine for daily production there would not be

00:41

an issue at all but because I’m using it for test work and for experimentation as

00:48

well as the little bit of work, I was finding some inconsistency which meant

00:54

that I couldn’t demonstrate some of the things that I wanted to demonstrate to

00:57

you easily and so consequently I had a few words with Thinklaser and they sent

01:02

an engineer down who looked at the problem and decided yeah it was worthy

01:07

of changing the tube so under warranty without any questions at all I have a

01:12

new tube now the new tube is not in there it’s in a box over there I’ve got

01:17

to fit it that was my choice because I felt that if I fitted that tube it would

01:23

give me an opportunity to show you how easy it is to actually fit your own tube

01:28

what I’m just about to say might sound like a bitch but it’s not Thinklaser

01:35

have supplied in this machine the 60 watt machine one of the cheapest EFR

01:40

tubes you can get now as I said that might sound like a bitch but in fact in

01:47

a strange sort of way it’s a bit of praise because first of all they’ve

01:51

chosen a very good quality tube EFR and EFR manufacture three ranges of tubes

01:59

they manufacture the CL range which is I suppose it could be called the basic range

02:05

which is something that’s been around for many years and it’s design has

02:10

gently evolved and it’s still called the CL range now that’s got a supposed

02:15

life of 3,000 hours they specify in here and I’ll read the words working life

02:24

3,000 now 3,000 hours is only four months, four months? No, it turns out from

Transcript for How to Change a Laser Tube (Cont…)

02:36

the information that I get back from Thinklaser that they’ve been told from

02:43

their contacts in China that this working life actually means shelf life

02:48

like most things that come out of China cynically he said we don’t necessarily

02:54

believe these numbers usually if it says 3000 hours

02:57

it means 2 hours 50 minutes in this particular instance I think 3000 hours

03:03

is a gross underestimate first of all I’ve already had this tubing here for

03:10

more than six months so first of all that numbers bombed out the water I’ve

03:18

got a machine over there which has got a tube life of supposedly 4,000 hours

03:23

when I bought it I’ve had it now in there for about 14 months which is over

03:29

10,000 hours so it’s already gone two and a half times its projected shelf

03:34

life so we can’t really attach a great deal of credence to these working hours

03:43

life because that working hours implies beam on and yet the information that

03:49

they get implies its shelf life who knows all I can say is that lots of

03:57

people have got evidence that tells us that these numbers are way way low if

04:04

it’s shelf life now as well as the CL range the next range that was developed

04:11

by EFR was an F series and the F Series has supposedly got a working life up to

04:18

6,000 hours now although they give the working life of 6,000 hours just like

04:26

RECI or RECI you say tomatoes I say tomatoes um both of these very large

04:32

reputable companies use rather weasle words when it comes to warranty

04:37

on the tubes I mean this 6,000 hours which is eight months has got a warranty

04:50

of 300 days but that’s about right but the first hundred fifty days from exit

Transcript for How to Change a Laser Tube (Cont…)

05:00

works date on the label they do a free of charge replacement if there’s a problem

05:05

but there’s all sorts of riders attached to that and then from the hundred and fifty-first day to

05:12

the 300th day there’s another set of conditions so basically the warranty

05:17

promises that you get with these tubes are to say the least vague the fact that

05:22

Thinklaser came in and just immediately said we’re going to replace

05:25

that under warranty probably didn’t mean that they were going to replace under

05:28

the tube warranty but under their warranty which is great news now there

05:33

is another series which is called the ZS series which is going to have 10,000

05:40

hour working life now there are also additional benefits to this tube as well

05:46

as it’s working life supposedly but in essence what it amounts to is and I’ve

05:52

got some prices and different prices down here if you buy them directly from

05:57

China for example with this ZS tube cost two hundred and seventy-five

06:00

dollars that’s the best price I could find but then again it was three hundred

06:04

ninety dollars shipped and then in addition to that you’d have to pay tax of some

06:08

sort when it arrived in your country so you know at the end of the day that’s

06:13

five six vertually six hundred dollars plus tax for a top-of-the-range

06:18

ten thousand hour tube the middle of the range tube the best I could find was

06:27

including shipping at one hundred and seventy-five dollars plus three hundred

06:30

and thirty one which again is about four and eighty five hundred dollars so it’s

06:35

five hundred six hundred dollars for ten thousand our five five hundred dollars

06:40

for a six thousand dollar

06:46

and here we’ve got something like about $300 total including shipping for a

06:52

three three thousand our to you now at the end of the day three thousand hours

06:59

as we said it’s rubbish it’s substantially more than that and to be honest I

07:05

believe that Thinklaser have actually made the most economic choice by putting

07:11

this bottom of the range tube in, look whether it’s a mini a Ford or a Ferrari

07:16

sixty miles an hour as sixty miles an hour there is no difference in

07:22

performance only how quickly you get there and the luxury with which

07:27

you do it the one thing that really can’t change with a machine like this is

Transcript for How to Change a Laser Tube (Cont…)

07:31

sixty watts so I’ve been supplied with a bottom of the range tube which I believe

07:37

is the most economical and the best tube for this machine and I suspect that this

07:43

tube is going to last me anything from eighteen months to two years which

07:46

nobody’s going to complain about that bearing in mind Thinklaser don’t have

07:51

years and years of experience with these tubes it’s very much here so they are

07:57

taking this bit at face value and what they’re saying is at the end of their

08:01

one-year warranty they will supply you with a brand new tube now that’s a

08:06

fantastic offer but it does mean to say that either you’ve got to pay them to fit

08:11

it or you fit it yourself and that’s what I’m going to show you today how you

08:16

fit it yourself because it is a very very simple task

08:20

now I’ve already taken the protective cover off here as you can see and now

08:24

I’ve opened the lid and you can clearly see what it says on the end of this tube

08:28

danger, there’s 25,000 volts or more at that end there now if you’ve recently been

08:36

running your machine or had it powered on I ernestly advise you to turn the

08:41

Machine off and leave it walk away for an hour because there’s possibly still

08:47

some dangerous voltages stored in capacitors and various other things in

08:51

the power supply now I don’t know and I can’t be absolutely sure because I’m not

08:56

an electronics expert or an electrician but it’s a general safety precaution to

09:01

let any high voltage leak away now do not disconnect your machine from the

09:07

power supply while you’re doing that because it probably needs the little way

09:11

to earth somewhere if you disconnect it from Earth

09:14

it might not leak away so only when you get to the point where you’re going to

09:19

mess around with this should we disconnect the machine now down at the

09:24

bottom there it’s clearly marked with a 220 volt input disconnect that plug and

09:35

now you know the machine is completely safe so before you start you need to

09:38

disconnect the tube from the machine now I’ve done that by brutally snipping the

09:47

cables because the connector that was in there I couldn’t really replace so I’ve

09:54

got several options one of them is very easy and straightforward the second one

Transcript for How to Change a Laser Tube (Cont…)

10:00

is a practical solution for most people because they won’t have these things to

10:06

hand now these things happen to be crimp connectors and they will allow me to

10:16

join two pieces of wire together inside that insulated sleeve which is

10:21

fantastic but you might not have the ability to do that so what we’re going

10:28

to do is show you a possibly an alternative way and the alternative way

10:32

is to use one of those now I’m going to destroy this because I’m going to cut

10:37

cut one piece off and then very carefully without cutting my fingers off

10:45

I’m going to slice the back off like that okay now with a screwdriver

10:52

I should be able to push that metal connector out now that’s got two screws

10:57

on it which will enable me to join the wires together because most people have

11:03

got these little connector blocks somewhere in their workshop so that’s

11:08

stage one preparation there is another important stage that you need and

11:14

that’s to get some sellotape or some masking tape now stage two is to unwrap

11:20

the tube so take the clamp screw out it may or may not come out but don’t lose

11:32

the screw and this flexi clamp lifts up a long way the tube is completely free

11:44

except that the water pipes are still connected but there’s a good reason for

11:49

that and that is the fact that we’ve got water in this tube here now before we

11:55

start the next stage we need again to prepare we’ve got a little bucket here

12:02

nice clean plastic bucket and we need to stand that underneath this return pipe

12:11

here there’s a possibility that we’re going to get a bit of leakage out of

12:16

here when we take this pipe off or at least when we start emptying this tube

12:19

well I’m now going to follow this pipe here and this is the water outlet pipe

12:24

and it comes all the way down here there’s a label on here that says water

12:29

outlet so follow this water outlet pipe back to the chiller and now we’re going

Transcript for How to Change a Laser Tube (Cont…)

12:36

to remove this pipe from the chiller but before the pipe comes off make sure you

12:41

clamp the pipe tight, there we go we don’t have any loss at the moment but

12:47

keep that bucket under there because it is likely that when I hold keep it

12:53

clamped now I’m up in the air I can undo it let go of the clamping and this is

13:00

where I need the sticky tape because I’m going to have to put this pipe up here

13:10

and that makes sure that the water can’t run uphill ok now I’m going to take it

13:17

off for a moment because the next trick is to actually blowi into it and what we’re

13:23

going to do we’re going to blow the water back along here and down

13:28

into the reservoir and that’s when we might get an overflow

13:45

there we go you can probably hear the water flowing now because that’s a

13:59

sealed bottle down there I suspect that what’s happening as I’m

14:04

blowing I’m actually blowing some more water up here but at the moment the tube

14:10

is virtually empty so I’ve got rid of the water out of the tube and now I can

14:14

stick my tube up here so that it doesn’t leak anywhere then we should be able to

14:19

now remove there is just a little bit of water in there but it’s not going to

14:25

cause us a problem I’ll now take that one up as well I’m going to connect this

14:35

end back down onto the chiller now because it is empty and I’m now going to

14:42

remove this one from here just in case I’m going to take that one up there as

14:49

well as you can see here we have one more cable that’s connected and that’s

14:58

this cathode cable from the cathode end of this tube so let me disconnect that

Transcript for How to Change a Laser Tube (Cont…)

15:11

just a tie wrap there and probably a crimp connector underneath there as well

15:18

now this end doesn’t have any high voltage on it at all this is this is

15:26

completely low voltage this end and we’ve got a bullet connector on there

15:31

which is probably okay but if you don’t have a bullet connector in other words

15:38

once you’ve broken that you might not be able to replace that, again what you can

15:44

do we can use one of these connectors a screw connector and that’s what I’ll do

15:50

inside that piece of insulated sleeve so now that I’ve disconnected that black

15:54

wire the tube is completely free and we should be able to lift it out

16:11

okay now I’m just going to put a piece of white paper behind this tube because

16:20

I want to show you something now starting with the most expensive tube

16:26

one of the things that they claim on here is long lifespan catalyst coated

16:32

discharge tube okay now that’s normally something you only find in the long life

16:38

tubes so let’s go back to the 6000 hour and here it says long life the catalyst

16:46

coating on discharge tube that’s the key thing a catalyst coating so when we get

16:52

to the cheap tube the 80 watt tube catalyst doesn’t say yes doesn’t say no

17:00

with the 1200 CL tube which is the one that we’ve got here it clearly says

17:06

catalyst yes and I can see that can you see that pink tube in the middle there

17:14

the fact that it’s pink tells me that it’s been flash coated on the inside

17:19

with gold and that gold flashing is an indicative feature of a long life tube

17:26

it helps to recombine any free oxygen with the carbon monoxide to keep the co2

Transcript for How to Change a Laser Tube (Cont…)

17:33

up to a reasonable level it delays the death of this tube and so this is a

17:38

hallmark of a very very good tube now you won’t find that catalytic tube in

17:44

most economy tubes should we call them okay now sadly the first thing I see is

17:52

I’ve got to be a bit brutal with this tube because it’s got a very very nice

17:55

connector on it which is a proper high voltage connector but I don’t have the

18:02

mating female connector that goes on the other side of it so I’m gonna have to

18:07

cut that off there and make the connection as per we

18:10

discussed so obviously this Red end the red cable

18:14

a high voltage cable goes to this end because that’s the way that we took it

18:18

out this cable here is to come down oh

18:26

they’ve already supplied me with a little connector there which is great

18:31

they’ve already supplied me with a bullet connector well that’s good news so I

18:39

haven’t got a fiddle with that end so there’s absolutely no reason why this

18:46

needs to be fully protected this end

18:51

there is no, there’s no voltage here at all and current well current is very

18:59

minimal it’s only somewhere in the region of around 25, 22 to 25

19:04

milliamps so we can lose that back inside there and that’s that end made off

19:10

we’ve got a fair amount of tube here and that’s good because what I want to do is

19:17

to nick something like about 2 or 3 inches of that tube and we’ll plug that

19:29

back on there and we turn it so that it sits at 12 o’clock and we push it back

19:39

as far as it can go because I need a reasonable gap here to do my tests so

19:51

somewhere in the region of about 40 millimeters I’m gonna leave here I will

19:56

try and just take the end off of it with a cable cutter

Transcript for How to Change a Laser Tube (Cont…)

20:07

and as you can see there’s a plastic coating inside it’s double thickness now

20:15

I don’t think I should be able to get that layer off because it’s bonded on to the

20:21

cable inside is it not taking a huge amount of current it’s just taking a

20:28

huge voltage so that’s one end now as I said, sad to say I’ve got to be brutal

20:38

with this end so I’ve got a nice tight screw clamp connection on there so just

20:53

to be doubly doubly sure before I put over a high voltage connection now that’s

21:00

cleaned it out nicely we’re going to pop that on there like that before I connect

21:12

this side up there we are a nice positive connection it’s only got to

21:19

carry a few milliamps as I said the problem is trying to keep the very very

21:23

high-voltage electricity away from the air because if there is any dampness in the

21:27

air effectively what we’ve got is the potential for lightning between here and

21:31

the chassis somewhere ground and so what we have to do is make sure that we

21:36

completely isolate it that’s why I’m using this thick silicon tube it makes a

21:41

fantastic insulator and we can slide that inside the tube like that and what I’ve

21:50

got here and you can buy this from places like Maplin now this is a white

21:58

silicon sealant and adhesive it’s not bath sealant whatever you do don’t use

22:04

bath silicon because bath silicon has got chemicals in it which you can smell

22:09

and it will corrode the joint in there so you need to go and get non-corrosive

22:16

silicon right there we go we put some in that end like that now as you

22:22

can see that is very nicely sealed off around this cable and the inside of the

Transcript for How to Change a Laser Tube (Cont…)

22:30

tube so there’s no chance of any air getting in there it will probably take

22:36

half an hour to an hour to dry now I’ve put the cable tie on the other end

22:41

because I thought it was going to run right the way through but it hasn’t

22:50

it’s horrible stuff if you get it on your hands and there we go we put a cable tie back on

22:57

this end as well so there we go I’ve just wrapped that round here and it’s

23:04

in its ,this is sitting right in fresh air so there’s no chance of any

23:08

discharge to anywhere and I’ve just tied wrapped it against itself so we can put this

23:13

water pipe on here at the end there’s only one place to put it because there’s

23:23

only one connection free so we will just check that we’ve got clearance on the

23:30

end of our tube when I put the case on so we just put the case on just test the

23:36

case on there and yes it looks as though we’ve got about 3/4 of inch to an inch

23:42

clearance which is fine. We’ve got our cathode connected, we’ve got our anode connected,

23:47

we’ve got our water outlet connected and we’ve got our water inlet

23:52

connected we’re basically done I’ve set this gap here to about 40 millimeters

23:58

which is what I need but if you want to set it closer you can do so now we’ll

24:04

just clamp the tube back up now because these tube clamps have not been moved

24:10

basically I would expect the tube to be fairly well aligned it might need a

24:17

tweak, the beam alignment but that’s all just a tweak and that’s it the tube is

24:25

fitted it’s no more complicated than that 4 wires

24:30

and two water pipes and a little bit of care about how you connect it up it’s

24:36

the method rather than the difficulty one final little job to do so I’ll just

24:45

cut the bottom off of an old water bottle and make myself a temporary

24:50

funnel otherwise this could be a little bit of a messy job job done and that’s

Transcript for How to Change a Laser Tube (Cont…)

25:13

the final little task so we leave it for a few hours now just to let the sealant

25:18

settle around the HV connection and then we can give it a try well we should plug

25:24

the power back in now and we’ll turn the machine on so we’re going to have to

25:29

make sure the tube fills up with water to start with. Here comes the water

25:40

through the tube

25:44

and it’s cleared the bubbles absolutely perfectly so the first thing I’m going

25:51

to do is set max power make sure it’s about 25% which it’s not at the moment it’s

25:56

70% and now I’m going to press the pulse button and we’re just going to check

26:01

what happens there we go look we’ve got a beam very nice okay now in the past

26:11

I’ve used these target holders that we’ve made to sit on the mirrors and the

26:18

targets but if you happen to be unlucky enough to have a machine and you haven’t

26:26

made these then you can’t use that sort of target so what I’ve got here is

26:33

something, a slightly different approach which maybe even Thinklaser can supply

26:39

with the new tube and that’s these little targets here

26:43

so we’ve pull one target off and we’ll go round to mirror one what we’re going

26:48

to do is we’re going to pop this into the mirror orifice and I’m just going

26:56

to hold it in place with a little piece of tape across the top like that now I’m

27:02

going to turn the power down to 15%

27:07

I would say it looks as though that beam has got to go up by about two

27:13

millimetres now how do I get the beam up by two millimetres I want to lift both

27:19

ends of the tube up by the same amount i.e. two millimetres we’ve got these

27:25

screws on here and underneath here we’ve got like a locking collar now that

Transcript for How to Change a Laser Tube (Cont…)

27:35

locking collar can lift up and down

27:39

it’s an adjusting collar twist it down so that it sits on the top of the pillar so

27:46

I happen to have a piece of Perspex here which is two millimetres thick what I’m

27:51

going to do now is once this collar is sitting down on the top of this pillar

27:56

and I’ll make sure that the one at this end is the same I’m going to undo these

28:00

two screws here which will allow me to lift the beam up and I put that spacer

28:08

underneath there and I will lock the screws back up and I’ll do the same at

28:17

this end undo the screws

28:27

lift it up by two millimeters and re clamp it and now it’s gone too high so it

28:39

probably only wants to go up by a millimeter okay well I’ve got a piece of

28:43

one point one millimeter thick material so I can undo the screws again and let

28:53

it drop down onto that piece of material and tighten up the screws

29:04

now that looks to be pretty well spot-on so let’s just run it once more and

29:10

that’s not looking bad at all okay so we’ve driven mirror 2 right to

29:15

the front edge of the machine we’ll put a target into mirror 2

29:26

what we can see that it’s quite a long way out on mirror 2, height is not bad

29:32

this mark is what I call a sighting mark so what I’m going to do is to tip

29:38

mirror one very slightly okay now that’s not far out it does not have to be

29:45

perfect it has to be more or less on center but you know a millimeter

29:50

either way is not probably we replace that target and this time we’ll bring

29:56

the head right to the back of the machine, this burn is what I call a

Transcript for How to Change a Laser Tube (Cont…)

30:02

target burn okay now that’s our marker it’s actually not bad move back to the

30:08

front of the machine and now what we’ve got to do is got to make a mark that

30:14

matches that one we’ve got to adjust the mirror so that the two marks are

30:22

coincident as you can see it very slightly to the right so I need to take

30:27

a little bit off that mirror too much

30:36

and that looks pretty good now not only do they line up with each other they’re

30:41

also more or less on center now it means that the beam is actually lined up with

30:49

this y-axis in both the horizontal and the vertical plane now we’ve got to get

30:56

the beam on to the centre of mirror 3 so we will first of all

31:05

go for our sighting there is another size in here which is a slightly

31:11

different sized target which we shall need to use for this particular

31:14

situation now which will definitely need a small piece of tape on this one

31:20

because there is nothing behind it there’s no mirror behind here to hold it

31:25

so what we’re going to do is we’re just going to drop that into the hole

31:28

okay so I’ve now got the head pushed as far away from mirror 2 as I can get it

31:34

and we’ll do a sighting pulse well

31:44

it’s not terrible but it’s not brilliant but not to worry at the moment because

31:51

what we’re going to do is we’re going to do a target pulse and so here we are

31:58

right up against Mirror 3 (means mirror 2)

32:08

and that’s our target pulse. Sighting pulse,

32:12

target pulse and then alignment is the procedure that you’d go through for each

32:17

one of these axes so that’s our target pulse let’s see where we are

Transcript for How to Change a Laser Tube (Cont…)

32:31

well I would say we’re possibly just about half a millimeter high so we need

32:38

to just drop that very very slightly I now just tweaked that mirror

32:49

I would say that that’s probably just about spot-on and this is where people

32:55

get, can get very confused and why I personally believe that these machines

33:00

are not really designed to make it easy for beam-setting I personally think that

33:07

mirror number two should be a static mirror and then this one should be an

33:14

adjustable mirror because what we want to do now is to move that head to catch

33:20

the beam on that Center we can’t adjust the mirror anymore

33:24

because we’ve already got the mirror set up so that it is the beam is running

33:28

horizontally and vertically true to this X but of course as soon as I twist that

33:34

mirror through 45 degrees look what happens to it it shrinks its height

33:41

changes and it’s no longer 23 millimeters tall it’s probably only

33:46

about 13 or 12 millimeters tall we’ve got to be very accurate with the

33:51

alignment of our beam in this up and down vertical axis how are we going to

33:56

get that beam down well we could go right the way back to the later tube and drop

34:02

it down but hey we just raised it by two millimeters to get it central on the

34:07

other mirrors well the other mirrors are twisted this way so they are a lot less

34:16

sensitive in the height position than mirror number three

34:23

so I’ve got two choices there are some adjusting screws on here which will

34:31

allow me to adjust it this way by a small amount which I could certainly use

34:35

to get this in but I’ve got no adjustment up and down on this head

34:41

other than to put some packing pieces underneath there in other words I could

Transcript for How to Change a Laser Tube (Cont…)

34:51

shou the head up a possibility but a bit of an ugly solution so what I’m going to

35:01

do is go right the way back to the back and drop the beam down by the millimetre

35:06

that I lifted it up fortunately I left the collar set that’s only a matter of

35:14

loosening those screws and dropping it down onto the collar tightening the

35:19

screw up and doing the same at this end and let’s see what effect that’s had on the

35:26

position of that beam hopefully the beam should have dropped down a

35:29

millimeter. And there it is

35:45

and that’s back to spot-on now what it does mean is that the other mirrors are

35:52

very slightly compromised because those mirrors are twisted this way I’ve got to

35:59

be accurate in the horizontal plane less so in the vertical plane so it isn’t a

36:05

big issue this one is absolutely essential now it is very very slightly

36:11

maybe half a millimeter out of position in this direction but again because this

36:18

mirror is tipped this way I can afford to be very slightly out in this horizontal

36:24

direction and so I’m not going to go hunting any further for the problem at

36:31

Mirror three that’s as good as I can get okay now we’re into the final stage of

36:35

setting this beam up which is trying to make sure it comes down here vertically

36:40

to get to the lens now to do that I’m going to remove the air assist and we’re

36:49

going to remove the lens tube itself

36:57

now I’m going to sit that target on there and I’m going to raise the table

37:03

not too much and only guess roughly where the centre is it doesn’t matter

37:16

too much let’s just show you what I mean I know it’s not on center but that

37:28

doesn’t matter because what I’m going to do is to drop the table down by about

37:35

two inches this is the same three-step approach that we used for the mirrors

Transcript for How to Change a Laser Tube (Cont…)

37:51

this is our target pulse well I think you can see that the difference is nil

38:03

which means that that beam is coming true right down the center there because

38:09

it hasn’t deviated in X or in Y that’s about as far as we can go the beam lines

38:16

up with everything as we require it now we haven’t had to do a great deal but

38:21

the one thing I just reinforce to you again is the 3-step principle that I use

38:26

it’s taken half an hour because I’m showing you what I’m doing it would

38:30

probably normally take me no more than about five at the most 10 minutes to

38:34

fiddle around with this three simple steps remember move things as far away

38:40

as you possibly can and get a burn so that it’s approximately in the area

38:46

where you want it that’s what I call the sighting burn then we move this mirror

38:50

close to the other mirror that we’re trying to set up and we then do a target

38:58

burn then we move it back far away and we align the mirror onto the target burn

39:06

those are the three simple steps once you’ve done step one two and three you

39:12

only need to keep repeating steps two and three two and three and you

39:17

shouldn’t have to do that more than about once or twice and you should have

39:21

the beam perfectly aligned with the axis that you’re working on okay let’s put

39:26

this back together now we can now use our what I endearingly called the laser

39:32

thermometer

39:47

this is the final test because we don’t want the beam to clip the edge of the

39:52

orifice otherwise we should be losing power and it does look as though the

39:56

beam is sitting down here at about 6 o’clock so we can really do with trying

Transcript for How to Change a Laser Tube (Cont…)

40:04

to tweak that beam up to a slightly different position now we know that

40:10

they’re all in the same position so we don’t have to go around and check every

40:13

other because we don’t have to check all the positions again so all we need to do

40:19

is just check it in one position

40:33

and there we go dead center so that’s the final check to make sure that the

40:39

beam is not clipping the nozzle it’s got to be in the center of that target give

40:46

or take about point two or point three of a millimeter now unless you have a

40:51

big block of perspex like this you won’t be able to carry out this final test but

40:57

this is something I like to do and I put this right towards the edge

41:09

I’m holding the pulse button on

41:18

okay so that’s the beam going down in relation to a set square I think you’ll

41:26

see that it’s pretty well up right and then if I check it in the other

41:30

direction

41:38

it’s not too bad either well I can remember the feelings that I had the

41:43

very first time I started fiddling with my mirrors was I ever going to get the

41:49

machine back into working order again I hope today’s session has done two things

41:53

for you one it’s given you sufficient confidence that you will be able to dive

41:57

in and change your own tube and if as a result of that you find that you need

42:02

to adjust your mirrors to get the beam back into good alignment then I hope I’ve

42:07

taken the mystery out of that for you now this very simple three-step

42:11

procedure for each axis as I’ve explained it to you is a foolproof

42:15

method it will work every time but you have to think about whether you’re going

42:21

to move the source of the beam or catch the beam today I think I demonstrated it

42:28

would be good and simple to catch the beam but we’ve come up with a compromise

42:36

which works perfectly well on this machine and I’m very happy that this

42:40

machine is completely set up now that we’ve got the machine back into good

42:44

working order in the next session what I need to do is to establish just how good

42:49

that new tube is so we need a record of its performance today

42:54

Brand new. I’ll be going through that process in the next session so until the

43:00

next time thanks for your attention

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Last updated August 26, 2021

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