0:00welcome to this rather extra special
0:02edition
0:03of my tangerine tiger as you can see
0:06this has already got the mirror 2
0:09and stiff motor bracket
0:12but somebody who’s fitted this up
0:15was saying that they’ve still got a
0:18fourth corner problem
0:20well hang on you can’t have a fourth
0:22corner problem because
0:23the fourth corner problem always seems
0:25to stem from the
0:27flexibility of that mirror we proved
0:30that many times before
0:32i mean many people have fixed the
0:35problem by
0:36sticking up their mirror bracket but in
0:38this particular instance
0:41it hasn’t fixed the problem so
0:44i have to admit that on one previous
0:47occasion i came across a machine which i
0:49could not fix and i still didn’t
0:52understand it
0:54now this second time round about a year
0:56and a half later
0:59makes me ask the question what is it
1:02that’s
1:02actually happening because i thought i
1:05understood it
1:06but obviously i don’t
1:09because if i did the problem wouldn’t
1:11exist
1:12my solution would be the solution here
1:16we are today
1:17and i’m going to try and get to the
1:18bottom of this because there are all
1:20sorts of myths
1:21about how you fix this fourth corner
1:23problem so at this point here
1:25on the fourth corner the head either
1:27appears to be up
1:29or down sometimes a little bit left and
1:32right but generally
1:33it’s up and down and that makes people
1:36believe that really the solution to the
1:38problem
1:38is to put packing shims under the rail
1:41here or something like that to fix the
1:42problem
1:44no this is a perfectly flat plane anyway
1:48because it’s been designed on a frame
1:50like this okay it’s not absolutely
1:53probably
1:53thousandths of an inch or 0.01 of a
1:56millimeter
1:57perfect but it’s certainly not two or
2:00three
2:00millimeters out as this would indicate
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont
2:04by putting a spot on here and then doing
2:06the same thing at the front
2:07this is definitely not a mechanical
2:09problem this is a beam
2:11problem of some sort where we’re getting
2:13a reflected beam
2:14which is not hitting the same place here
2:17as it is when it’s at the front of the
2:19machine
2:20so something is happening between the
2:21front and the back of the machine
2:23and up to now the general thing that
2:25seems to be happening
2:26now look you can see how this cable
2:28chain is raised up here it doesn’t want
2:30to go
2:31flat so if it does go flat then the
2:34curvature of this is exerting a slight
2:36upward twist
2:37on this bracket but hey this bracket now
2:40is so stiff
2:43you could probably stand on the machine
2:44and hardly move
2:46this mirror so we do not have this
2:49same problem that has existed on the
2:52naked and brand new
2:53raw machines although having said that i
2:56noticed the new machines are now
2:58now no longer using 16 gauge material
3:01here for this bracket
3:02but they’re using two and a half
3:03millimeter material which is why i’ve
3:06made this out of two and a half
3:07millimeter material
3:08and even stiffer by making a continuous
3:11l-shaped bracket people have suggested
3:13that it’s all to do with the
3:14squareness or levelness of your machine
3:17now people
3:18people interpret level as being
3:21water level so they get a spirit level
3:23out and they use a spirit level and they
3:24get their machine
3:25absolutely perfect no
3:28i think what’s implied by that is if
3:30your machine is somehow
3:32twisted in other words you could jack
3:34one corner of the machine up and get rid
3:36of the problem
3:37no you can’t i’ve already proved that in
3:40another session you can twist this
3:42machine as much as you like
3:43and it does not get rid of the problem
3:46so
3:47it’s not a mechanical issue it must be
3:49coming back to
3:50after we fix this number two mirror
3:52amount it must come back to
3:54something to do with the beam itself
3:57because
3:58you don’t get huge motions on here
4:01because of mechanical movement you get
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
4:03huge
4:03movements on your burn spot because the
4:06beam
4:07is not following the same path there is
4:09a problem with the beam alignment so
4:13i spent a long time thinking about this
4:15and the only thing that i can come
4:17to a conclusion on is that we the
4:20conventional beam settings method
4:24is not fully error-proof
4:27and that there are other steps that you
4:29need to take in that procedure
4:32to fix the fourth corner problem and
4:34what i’m going to try and do today
4:37is to first of all illustrate the
4:39problem
4:40and then how we’re going to fix it now
4:42this machine is already
4:43roughly set up it’s well it’s pretty
4:45well set up to be on
4:46the first thing we’re going to do is to
4:49set
4:50the y-axis and we’ve done that by
4:52putting a target on the mirror
4:54it’s not easy to see what’s going on at
4:56this first target here so
4:57i’m looking at a reflection in a mirror
5:02so there we go we’ll put our mark on
5:04there so let’s just try
5:06see what it’s like at the front here and
5:10it looks as though we’re not lined up we
5:13need to move the mirror
5:15so that the burn comes closer to this
5:18direction
5:21that looks better let’s repeat that test
5:23again because that’s the first
5:25of our several iterations we probably
5:27need to do this at least
5:28probably three times if you’re setting
5:32up from scratch
5:33if you’re doing it from a position where
5:35you’re pretty close to perfect then you
5:36might only need to do it twice
5:46it’s not far off center let’s go down
5:50here again and check it see what’s
5:51happening at the front
5:57i would say that that’s good enough to
5:59move on with
6:00you need to make sure that your mirror
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
6:02is clean because every time you burn the
6:04target on there you get a little bit of
6:05a
6:06condensation or halo of fumes and we
6:08need a different sort of
6:10target now and these two holes here the
6:12funny shaped holes
6:13press onto the screws that project out
6:15from the springs
6:17so you just pop them on there like that
6:19so there we are with with the target in
6:21place
6:21i’m not going to bother to move the
6:22camera so i’m going to move the target
6:24close to mirror 2 and i’m going to put
6:26a reference burn on there a target burn
6:29now you’ll see what i mean about it not
6:30being perfect
6:31and spot on but don’t let that worry you
6:34we’re now interested in getting a dot to
6:36match that dot
6:38so let’s have a quick pulse and see if
6:40we can find out where we are
6:45okay that’s probably not far out we’re
6:48very lucky because this machine is more
6:49or less set up
6:50what we’re going to do is we’re going to
6:52move this to the back position
6:54and now we’re going to see what sort of
6:57burn that we’ve got on the fourth corner
7:03well it’s not bad it’s probably about
7:06a millimeter or so forward now that this
7:09is the problem
7:10i’ve got a slight fourth corner issue on
7:13this machine but i think that it all
7:17comes down to
7:18the accuracy with which you manage to
7:21spot your x
7:22and your y settings
7:25now i’m not criticizing the way that you
7:27set the machine what i’m saying to you
7:29is
7:29that on a small machine like this you
7:31don’t get
7:32much distance much leverage if you like
7:36to do your setting i’m going to now
7:38do something that i’ve never ever
7:41recommended before and that is that we
7:43go back
7:44to the beginning i’m just going to turn
7:46over now because you can use these
7:48twice first of all we’re going to
7:51go across to the left hand side
7:55and right at the back of the machine
7:57we’ve got a burn reference mark in
7:59a new target mark and there we go
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
8:03so now we’ll check where it is at that
8:07end of the stroke not bad
8:15so it’s difficult for me to get a fourth
8:17corner problem on this machine
8:20but if i come to the front now and try
8:22the same thing i have got a small
8:26problem look
8:27you can see that it’s not lined up bear
8:30in mind we made the target mark
8:32right at the back left hand corner
8:35okay so we’re now just about as far away
8:38with this mirror as we could be
8:42from where we made the original target
8:44mark
8:45we don’t normally make a target mark on
8:48mirror 3
8:49at the back left hand corner
8:52but this is what i think probably should
8:55be the final stage
8:56of setting and that’s to do a diagonal
9:00setting across the machine from the back
9:03corner right close to the mirror with
9:06mirror three
9:08and then we go back to mirror one
9:12and we adjust this error out
9:15diagonally across the machine not x and
9:17y but diagonally across the machine
9:20so what we’re going to do now we’re
9:22going to change mirror
9:24one and try and push this mark further
9:27towards
9:28me at the front of the machine here
9:32now this is quite complicated in terms
9:35of
9:36imagineering because we’ve got
9:39reflections going all over the place
9:41and it isn’t quite what it seems
9:44if you want to move the burn across
9:46towards the front of the machine
9:48you would tip your mirror that way
9:51so i’m going to put a small amount of
9:54adjustment
9:55on mirror one now
9:59and i want it to go towards the front of
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
10:01the machine
10:03which means basically i’ve got to move
10:05it across
10:08mirror 2 towards the front of the
10:10machine
10:12which means i’ve got to
10:15remove a little teeny weeny bit of
10:18motion
10:18off of mirror one very very small amount
10:21of
10:22adjustment on mirror one and now we’ll
10:25see what effect
10:26that has had
10:32well it’s brought it more or less in
10:34line the only thing that we have to do
10:35now is
10:36raise it very slightly so to raise it
10:38i’ve got to lift
10:39the mirror up very slightly
10:41anti-clockwise
10:43just i don’t know a tenth of a turn
10:46or less okay so what we do now
10:51we’ll put a new target on so we’ve got a
10:54target burn
10:55at the on mirror three at the back left
10:57hand corner of the machine
11:07and we’ll see how close we are now with
11:10our target
11:14still a little bit low
11:20and there we are i think we’re now just
11:22about spot on
11:24what we’re going to do we’re going to do
11:25this one here we’re going to make a mark
11:26here
11:29we’re going to go to the back of the
11:30machine and see how close
11:33we are with our mark
11:36and there we go we’re just about spot on
11:38now
11:39and that’s at the back corner so it
11:42looks as though we no longer have a
11:44fourth corner problem
11:46we’ve tuned it out by adjusting very
11:48slightly adjusting
11:49and i do mean very slightly adjusting
11:51mirror one
11:54but because we’re adjusting mirror one
11:56over a much much
11:57longer distance and referencing it to
11:59mirror three
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
12:01we’re actually making the setting much
12:04more accurate
12:05so if we now go back and check what
12:07we’ve done
12:08to the x and the y settings just clean
12:10that mirror again because as you can see
12:13it’s got some crap on it
12:18you can see i’m not doing anything
12:19special with these mirrors these are
12:21molybdenum mirrors
12:22you could be quite abusive with them i
12:24would suggest you normally use toilet
12:26tissue or something to clean them
12:28um not normal kitchen roll or anything
12:31like that
12:32because kitchen roll has got an abrasive
12:34kale in it that stiffens it
12:36um but ordinary toilet tissue is just
12:40basically wood pulp and it’s very soft
12:44if you want to be really fussy you use
12:46lens tissues
12:48so i’ll make a target burn on our y-axis
12:51right close to mirror one
12:58it’s a bit of a weird burn doesn’t it
13:03you see so it’s not hitting the hole in
13:05any way at all see what’s happened
13:07to our y-axis adjustment have we messed
13:10around
13:11with it in any significant way
13:20and the answer is no
13:24so has it affected our x-axis alignment
13:32and the answer is we haven’t
13:35so what we’ve done we’ve put an extra
13:38layer
13:39of accuracy into the setting procedure
13:42by doing one final extra
13:46move we’ve seen that we’ve not affected
13:48x and y
13:51so we go back to the far back corner
13:54again
13:55see how good our burn is
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
14:05pretty good and now we’ll go to the back
14:08corner of the machine
14:10and we do a fourth corner check at the
14:14back
14:16and there we go so
14:19just one extra procedure at the end of
14:23setting x and y
14:25before you go to setting z will
14:28triangulate
14:30and reduce the errors that you produce
14:33by doing
14:34x and y separately now we can go to z
14:37and for z we need to drop the nozzle
14:39down so that it’s below
14:41this step here
14:46because we’re going to use this third
14:49target
14:53which is this one i’m going to put it so
14:55that the
14:56hole sits in the corner we either move
14:59the mirror
14:59in and out for y or the head up and down
15:03for x to try and get our
15:06theme right in the center of the cross
15:09check where our beam is in relation to
15:11the central axis of the lens tube
15:16what can i say you must do two other
15:20checks
15:20one you must make sure that mechanically
15:23this
15:23is sitting square to your table in both
15:26this axis
15:27and that axis and we put a burn on here
15:33like that drop the table down maybe four
15:36inches
15:37we then tweak number three mirror to
15:39make sure that we get the
15:41beam running true perpendicular to the
15:44table
15:46so it’s a repeat of the x and the y axis
15:48but we’re doing it in the z
15:49axis and then finally
15:53once you’ve done that you do the check
15:55that i’ve just done
15:56which is to make sure that the beam is
15:58actually trued up to the
15:59axis of the lens tube purpose of today’s
Transcript for Laser Beam Settings To FIX The 4th Corner Problem (Cont…)
16:03session is all about trying to find out
16:05and solve
16:06what the fourth corner problem is and i
16:08think
16:09at last we’ve solved it
16:13because i don’t think it’s anything any
16:15longer to do
16:16with mechanical things i think we’ve
16:18fixed all the mechanical issues on this
16:19machine
16:20go forth experiment and play and if it
16:22doesn’t work for you
16:24well keep it to yourself thanks for your
16:26time and patience
16:28and i hope i never hear from you! bye for
16:30now
