0:00welcome to our t-works Learning Lab
0:02today we’re going to take a look at two
0:05problems at least two problems that
0:07people have mentioned to me can I
0:09explain why one I can explain why and
0:13the other one I can’t explain why so
0:16we’re going to do a few experiments to
0:18see if we can come up with an answer to
0:19the question question number one is why
0:21does the beam drag if you don’t know
0:24what beam drag is I will demonstrate
0:26that to you in a minute the other
0:28question is I’ve got little rough edges
0:31on my acrylic cuts how can I get them
0:34nice and smooth now maybe some of you
0:36guys already know the answer for this
0:38question but the majority of people me
0:40included doesn’t know the answer at
0:42least one of those questions so what
0:45we’re going to do is just have a bit of
0:46a play here and we’re going to change
0:49one factor at a time so what we’ve got
0:52here is an eight millimeter acrylic now
0:54I’ve already measured the power out of
0:56my nozzle here and I know that I’ve got
0:58approximately 60 watts coming out there
1:01because I’ve got a one and a half inch
1:03lens in here I’ve got a distance away
1:06from the work of only about six or 6.25
1:09I think it is a quarter of an inch so
1:12I’m going to set my focus up first of
1:14all to sit right on the surface of the
1:18job I’ve got a pressure control valve on
1:20my machine but if you listen carefully I
1:22can turn the air pressure
1:28off or certainly right down so we could
1:33have it if I can get it just right there
1:38we go we can just hear a whisper there’s
1:41just enough positive air coming out of
1:42that nozzle to make sure that we don’t
1:44get any fumes back up on the lens so
1:47that’s about as weak as I can possibly
1:49get it so we’ve got several factors that
1:51we can play with it I play with speed we
1:54can play with power but it’s best to
1:56keep the power fixed and just change the
1:58speed we can change the airflow so that
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
2:01we can see what effect cooling or
2:04clearing of the fumes has and then we
2:08can change one other vital thing as well
2:10what I’m going to do is do a series of
2:12test squares I want to use acrylic so
2:15that you can see clearly what’s
2:16happening to the cut several other
2:18people have asked me what does
2:20through-hole do what’s through-hole
2:22power well I’m going to demonstrate here
2:25what through-hole power is I have set on
2:29my program through-hole power
2:32ticked and just above it there are two
2:34windows the top window is the important
2:37one because that’s when you start the
2:39cut why on earth you’d want one at the
2:40end of the cut I don’t know but when you
2:42start the cut you will see that the cut
2:44stands still for half a second because I
2:48program that to 500 milliseconds and it
2:51will pierce through and then it will
2:54move off so you will ever hold through
2:56before you even start moving and you
2:59will see that happening at the beginning
3:00of this square
3:09turn some extraction on
3:13now you can see the beam dragging there
3:21oh dear and it hasn’t dropped out so I’m
3:24going a bit too fast
3:27No so that was six millimeters a second
3:33now I think you can clearly see on this
3:36here how we’ve got striations it’s not a
3:40very smooth cut
3:42okay I’ve now reduced speed to four
3:45millimeters a second and we see what
3:47effect this has
3:51so it’s PS through and now it’s moving
3:54off it was a bit of a strange it’s still
3:56dragging look can you see that
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
4:03I would say we’re cutting through this
4:05time because all the fumes underneath
4:07but it’s still dragging even though I’ve
4:10reduced the speed
4:17and I would say it nearly dropped out
4:20look there we go if we look along the
4:25bottom edge of the cut you can see the
4:27little striations along the bottom of
4:28the cup there it’s not bad for 60% of
4:34the depth 80% of the depth
4:38but you can clearly see something’s
4:41going on on the last two millimeters
4:45okay now we’ve set to two millimeters
4:48the second
5:00beam is still dragging even though we’re
5:02going really slowly
5:07but the gas is coming out underneath
5:12I have got the merest whisper of gas on
5:15there at the moment
5:26I think you see the beam is not dragging
5:28quite as much
5:32but it’s still definitely dragging
5:47okay let’s take a look at this one now
5:51I don’t know when you can see the edge
5:52this time it is not bad at all going
5:56slowly we’ve got a lovely smooth mirror
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
6:02polished edge on there now and I can
6:04feel that this piece is hot
6:06the edge is hot and that’s because we’ve
6:09going so slowly that the heat was
6:11actually flame polishing the edge as it
6:13goes we’re improving the edge cut and
6:17the depth of the cut the quality but
6:25something that you might notice on there
6:27if we can catch it in the light right
6:30let’s just see if we catch it in the
6:31light guy
6:33and that’s that these edges are not
6:35really upright
6:40and he what I wanted to show you there
6:42really was because we’ve got through
6:44power on to start with nothing to pierce
6:47the hole to start with it doesn’t make a
6:50lot of difference we’re getting beam
6:52drag even though we’re starting off with
6:54a nice clean up right cut now I’m going
6:57to change the program and we’re going to
6:59go for just a straightforward 25
7:03millimeter square
7:05ok so now we’re going to do 4
7:07millimeters a second with no start no
7:10through-hole to start with
7:27you see we’ve got being dragged across
7:29the front there quite significant
7:40and the lacer should start immediately
7:45hasn’t
7:47so why is there a delay there and on
7:49delay and I still got my 500
7:52milliseconds in there
7:54through hole
7:56I reckon I have that’s what the problem
7:59is I’ve still got 500 millisecond delay
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
8:02in there before I start the cut well
8:06that’s interesting
8:09so they’re going to be careful of that
8:11it could be useful it could be annoying
8:14like I’ve just found out so I’ve got to
8:17go back and edit the program now and
8:18take that 500 millisecond out and make
8:20it zero even though I haven’t got the
8:22through-hole ticked it delays the onset
8:25of the beam now that we’ve taken that
8:29500 millisecond delay out we’ll try a 25
8:33millimeter square
8:36there we go that was quite an
8:39interesting observation
8:42so let’s take a look and see what this
8:43beam is doing as it travels across the
8:45front here
8:49four millimeters a second it’s not quite
8:52this draggy but it’s definitely dragging
9:02and it dropped out let’s hung up on a
9:05corner because the beam is dragging it
9:08didn’t quite cut the bottom corner
9:13and again if we look carefully we shall
9:17find that the edges are not exactly
9:20upright they’re not square
9:25surface is not too bad but we’ve
9:28definitely from two millimeters away
9:30from the bottom we’ve definitely got
9:33some some striations now I just turned
9:38the extraction off and what I’m going to
9:40do now turned it off so you can hear I’m
9:45going to turn the air pressure on four
9:48so that we can see what effect
9:50increasing air pressure has
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
10:02I would say looking at that across the
10:05back it’s even more dragon
10:08oh yes
10:11it’s very dragging out
10:21dropped out
10:24there’s actually a slight improvement
10:26but the edges seem to be very out of
10:30square
10:37now I’m going to try something slightly
10:39different
10:48cool now definitely dragon
10:51you’re seeing a reflection at the bottom
10:53there that’s why it’s a sort of a bitter
10:55v-shape okay are we coming across the
10:58front end
11:08see what I was doing here
11:12I was playing
11:14with the focus
11:17so what I’m now going to do because that
11:19was rather interesting I don’t know if
11:21you observed it but I certainly saw
11:22something
11:24I do have a piece of 3 millimeter
11:27material here
11:37okay so we know three nine inches off
11:39the surface which means we’re about
11:40three and a half millimeters into the
11:42job with the focus point
11:57being dragged at all
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
12:08we have a lovely polished edge
12:17now what I’m now going to do is try
12:20something else
12:24I’m now going to increase the speed back
12:27up to six millimeters a second
12:30remember all the tests we’ve done so far
12:32six millimeters per second has not
12:35dropped out
12:38Oh being dragged six millimeters a
12:40second
12:49just about did it
12:52we’re getting a small hint of striations
12:54across the bottom again
12:58if you go slower
13:01you will flame polish the edge better
13:03and if you push the focus point into the
13:06material you will get more depth of cut
13:09but you also get a smoother finish all
13:12the way through your cut
13:14okay now finally I’m going to do
13:15something very strange first of all I
13:18put the speed back to four millimeters a
13:20second and I still got the nozzle set
13:22three millimeters above the surface but
13:24I’m going to start the cut off right in
13:26the middle of that previous square when
13:29we started looking at these and saying
13:31well the the edge looks as though it’s
13:32you know not cutting square it’s
13:34completely off angle I realized that
13:36there was a problem that I needed to
13:37show you
13:45quite a nice cleanup right cut
13:53now I’m going to do something strange
13:55I’m going to set the speed on my machine
13:58too
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
14:00sorry I’m going to send it to four
14:02millimeters a second
14:04I’m going to change the power max power
14:07to
14:10sixty
14:12five percent which is what I was cutting
14:14the programmer
14:16okay so I’ve now set my manual speed
14:19controls
14:21and what I’m going to do I’m going to
14:22hold the pulse button down
14:25and I’m going to drive the head manually
14:31and I’m doing a manual cut now
14:35now I’m going to take it down this way
14:41cutting across my
14:43workers underneath there
14:47I woke up back
14:59and I’ll go up
15:03so I’ve done a manual cut there without
15:05going anywhere near the programming
15:06system
15:09so there we are we’ve cut our
15:14we’ll cut our piece of material like a
15:16jigsaw puzzle
15:17let’s have a look at this carefully if I
15:20push those parts together like that
15:22that’s obviously not the cut because if
15:25I pull it one way that’s twice the
15:28thickness of the cut and if I push it
15:31together that’s not the cut but if you
15:33look at the way in which the shapes
15:35don’t match up both of them are actually
15:40going the opposite way to the shape of
15:43the beam the beam is necked but the
15:48center of that cut halfway through the
15:50material has actually got bigger and
15:54then if you look carefully at the bottom
15:56of the cut you’ll see the bottom that
15:58cut is touching but the top of the cut
Transcript for Acrylic laser cutting: beam drag and flame polishing (Cont…)
16:01there’s actually a gap at the top
16:04there’s a very short focus of only
16:06something less than a millimeter I think
16:09on this machine with my 38 mil lens the
16:15focal distance is very very short and
16:18after that the beam starts diverging and
16:21getting out of focus and as it gets out
16:24of focus obviously the beam gets bigger
16:27in diameter and it’s effective density
16:29power density gets less which means it
16:32has less and less cutting power the
16:35further we get away from the focus point
16:37but that then accounts for why we
16:39haven’t got such a cut at the bottom
16:41there look the power is disappearing the
16:43cutting power is disappearing at the
16:44bottom of the cut and so consequently
16:49that’s why the bottom of the cut is
16:51actually narrower than the top of the
16:53cut just because the edge is not square
16:57doesn’t necessarily mean to say that the
17:01beam isn’t square it’s all to do with
17:04the heat radiation and the shape of the
17:07beam and the power of the beam at a
17:08specific point through the cut so those
17:12of you would 2-inch lenses for example
17:15will have less of this problem you will
17:17be able to focus up better and probably
17:19have a straighter cut when you’re
17:21cutting thicker materials but then again
17:23you won’t be able to cut such thick
17:25materials because your power density is
17:26lower so we’re into a bit of a circular
17:29situation here
17:31you know but if you’ve got a lot of
17:32power 60 80 watt machine then you should
17:35be able to cut 8 millimeter with no
17:36problem at all and probably get
17:38reasonably straight edges better edges
17:39than I can get it cook because we cut it
17:42very slowly
17:43it’s a superb quality edge all I’m
17:47saying to you is although the edge isn’t
17:48up right
17:49don’t run away with the idea that
17:51there’s something wrong with your
17:52machine because there probably isn’t
17:54it’s all to do with the way in which the
17:56energy density in the beam is affecting
17:59the material that you’re cutting
