Cutting sheet at 45 degrees? Fixture? [Archive] - Sawmill Creek Woodworking Community

Keith Colson

10-16-2014, 9:59 PM

Thanks for all the responses. Neil thanks for the fixture file, my only concern with the design is the acrylic will move near the end of the cut. It really needs some way to stop the acrylic sliding. I do want to cut the bottom end as it will have the easiest registration.

Anyway, I have decided to try something different being the diy'er I am. I ordered a gold silicon 150w rated 25mm mirror today ($20). I plan to mount it below the nozzle, mounted at 22.5 degrees. It should be interesting focusing and offsetting for the cut line. The cool thing is the sheet will stay flat and once set up it should be fairly repeatable. I only want to cut 5mm sheet so total cut depth is 5 x √2 = 7mm which is no problem for my laser. I wonder if there will be room with the nozzle on.

Cheers
Keith

Dave Sheldrake

10-16-2014, 10:13 PM

I ordered a gold silicon 150w rated 25mm mirror today ($20).

??? A Chinese lens Keith? Gold Si even from RMI / II-VI are only rated to 60 watts. Anything over 60 requires Mo or Cu mirrors.

It's not a good idea to put mirrors in the optical train after the final lens, they will get VERY hot and crack :(

cheers

Dave

Keith Colson

10-16-2014, 11:17 PM

Kevin Gregerson

10-16-2014, 11:49 PM

Thanks Dave, this is where I like this forum. You raise some great points. For 20 bucks it is not an expensive experiment. It sounds like I need to get the mirror really close to the lens if I don't want the diverged beam. I still don't understand though. Isn't the reflected energy going to be the same whether it is diverged or not? Doesnt the diverged beam spread the energy over more of the mirror so less of a hot spot? My laser is 60W so is OK for the mirror rating.

Yes, cheap Chinese mirror, haha.

Cheers
Keith

Gotta say I agree, with Dave. If you are trying to reflect it after the lens you are going to run into the hourglass convergence issue of reducing your power pretty quick. The 2.0 lens really only has a max usable focal dept of .4-.5

Keith Colson

10-17-2014, 5:48 AM

Sorry, I am being a bit of a dumb dumb today. I understand now that the beam gets more focused ~ 30mm from the lens thus creating a hot spot. I will try to mount the mirror as close to the lens as possible to minimse this. Hopefully the air assist will add a bit of mirror cooling too. Maybe I could 3d print a mirror holder. I also note that I will need to make sure there is minimal mirror rotation too. All fun stuff to play with. I will post an update either with a toasted mirror or some 45 degree cut acrylic. I hope luck is on my side.

Cheers
Keith

Dave Sheldrake

10-17-2014, 7:33 AM

Hiya Keith,

Think of the actual focussed beam as an hourglass rather than a triangle :) so while the further from the lens the mirror will be subject to greater power over a smaller area the total of the incident beams power doesn't actually change.
Mirrors have a yield point of watts per sq mm hence why on bigger machines that have a bigger incident beam but far higher power different materials are used.

If you have 3d printing facilities I'd be looking to create a fixture that will hold the mirror behind the final focal lens.

Air blast won't help with mirror cooling, the amount of thermal reduction available from air is way too low to be useful with the almost instant heating effect of a laser beam, a laser beam has no temperature as such but induces heat by molecular vibration in the target, but it does so VERY quickly.

cheers

Dave

ps: the depth of field of a 2" lens is 1.8mm

Clark Pace

10-17-2014, 4:29 PM

Sounds like you're onto it anyway.

I thought about this a while ago but did nothing.

I would like to bevel the edge, by cutting at 45 then trimming the sides so that its bevelled.

Slow and hot laser cut would give a more polished finish.

let us know how you go.

Table saw 45 degrees, sand then flame polish
---------------------
45 degree router bit, flame polish
-----------------------------------
jointer set to 45 degrees, flame polish

Andrew Holloway

10-19-2014, 1:42 AM

298628http://www.justaddsharks.co.uk/laser-cut-mitre-joints/
I'm sure you could clamp the material if you were worried about it moving near the end of the cut.

Michael Hunter

10-28-2014, 7:31 PM

Just came across a thing about bevels on Instructables in the laser section :

1 : A 45 degree stand for bevelling one straight edge at a time.

2 : A motorised turntable for doing circular bevels (the turntable was mounted on the 45 degree stand).

No. 1 is pretty obvious, but No. 2 is quite clever!

Andrew Holloway

10-28-2014, 9:41 PM

Very clever. For those who can't fint it. Search "Circular Laser Bevels on an Epilog" on Instructibles.

Keith Colson

11-02-2014, 5:36 AM

I modeled up the mirror (it arrived yesterday) and it looks pretty tight. The power that hits the mirror will be about double the pre-lens power, so I guess that means I should limit the power to 50% on my 60 watt. Here is what it looks like for a trial fixture. I will try to cut and assemble it soon. Thanks for all the feedback

"I'd be looking to create a fixture that will hold the mirror behind the final focal lens." I think you are right on here Dave. I think with a little work a mirror lens module could be made that could fit the existing ULS head. It would make the head about double the size on the y axis but might fit without any collisions.

299382

Cheers
Keith

Dave Sheldrake

11-02-2014, 5:13 PM

Going the above pictured route will cause a LOT of abberations Keith, the spot will end up being scattered to blazes. When redirecting a beam it MUST be worked on while in the incident phase and not the focal phase.

cheers

Dave

David Somers

11-02-2014, 6:45 PM

Keith,

I am no physicist, but I can see what Dave Sheldrake is saying about the beam going all widdershins on you if you have that mirror placed after the lens. Think about it. Before the lens the beam is coherent, or another way to say it is the light rays are all parallel to each other. The fact that there are so many mirrors used to move the beam from the tube to the lens is a testament to that fact. Once you pass through the lens though the light rays are no longer parallel and are either converging to the focal point, or dispersing from the focal point. Any mirror placed anywhere along that path is simply going to throw the light all over since the rays are coming from a whole slough of angles as they converge or diverge. They will each be hitting the mirror at different angles, and come off it as different angles. I just can't picture that working.

It really seems like thinking out an approach like Andrew suggested, a workhold of some sort where your piece is held at a 45 angle to the beam, would be the best approach. Assuming you have enough Z height to do that of course. You mentioned you were worried about the piece slipping as it cut? Design your work hold so the main piece can be held in place as the waste piece falls away. That might be done with a light friction grip from the sides, or with some suction cups, or some N52 magnets, or just simple double sided tape. Remember there is no measureable force being applied by the laser as it cuts. You just need to account for the changing weight of the object. I can think of many ways to do this provided you have the Z height to work with.

Then your main concern is the extra thickness you will face since you are cutting at an angle. Hopefully you can get a good cut with your machine over that thickness.

Dave Sheldrake....if Keith did something along the lines of what Andrew suggested would it be useful at all to put some tape over the acrylic where the cut is being made to reduce reflection off the shiny 45 degree angled acrylic surface? Or is that just not a concern?

This will be fascinating to watch as you play with this Keith. Thanks for continuing to bounce your thoughts and trials past everyone!!

Dave

Scott Shepherd

11-02-2014, 6:51 PM

My uneducated opinion is you'll fry that mirror pretty quickly with the beam being focused. I have nothing to support that statement, but that's what my gut tells me.

David Somers

11-02-2014, 7:02 PM

Scott....

He wouldn't be focusing on the mirror though would he? He would be using the mirror to change the direction of the converging beam well before the focal point so the focal point was placed at the surface of what he wanted to cut, and at the angle he wanted it. But with the optics of the beam as it converged or and striking an angled mirror it would just go woof. All over the place! The closer he got the mirror to the focal point the more the energy of the beam would be focused on the mirror. He can't get it very close to the focal point though or he won't have any distance left to actually get that focused beam onto the material he wants to cut. Or am I thinking wrong?

Dave (the totally inexperienced guy who ALWAYS asks tons of questions! <grin>)

Scott Shepherd

11-02-2014, 7:07 PM

Well, it's not at the focal point, but it's been through the lens. To me, that's enough to start causing issues. I could be 100% wrong. My guess is if you took a mirror, put it on a 45 under your beam, after it's been through the lens and cranked up the power, you'd smoke that mirror (along with putting your eye out ;) ). Again, that's just my gut, no science involved.

David Somers

11-02-2014, 7:11 PM

Scott Shepherd

11-02-2014, 7:56 PM

Oh my gosh!! You mean like a Red Rider BB gun Scott?

Don't go there Keith! Those things are dangerous! They will put your eye out just like Scott says! Ask your Mom! Or ask Ralphie from A Christmas Story!

<grin>

Dave

Exactly Dave!

Either that or I can hear "honey, I caught the cat on fire by accident with my laser".

Rich Harman

11-02-2014, 9:13 PM

I don't see why it wouldn't work. So what if all the photons are not traveling "parallel" to each other any more? Each one will leave the mirror at the same angle it entered, why would it scatter? You'll need a long focal length lens, and there will be losses from that and the extra mirror.

Here's an example. The mirror in a SLR camera is not at the focal plane, it is after the lens and before the focus point - just as Keith's mirror. But still we get a perfectly sharp image in the viewfinder.

Keith Colson

11-02-2014, 10:45 PM

It works! no more fiction haha, here are some real results My fixture all fit together perfectly on the first go but I will improve it now I have proven it works. First some pictures from my really bad camera.

299426299427

My calculations showed that the power hitting the mirror would be double what the mirror would normally see, so I set the power to 50% and the mirror looks perfect after a few cuts. When I get a spare mirror in stock I will try 100% power. The cut edge looks perfect too, the picture doesn't do the edge any justice. Its got a nice polished look all the way along. The top left of the "cut picture" almost shows the finish. Cutting 5mm acrylic took 50% power at 2% speed for a rough calibration.

On a safety note the laser points to the back of the machine so viewing is "reasonably safe" as the honey comb should eat most of the light, I still stand to the side when cutting as it is good practice.

Cheers
Keith

Rich Harman

11-03-2014, 12:14 AM

Geez Keith, you kinda took the fun out of debating whether or not it would work... :-)

Kev Williams

11-03-2014, 12:45 AM

I've just been waiting to hear you say "it works!", very cool.

Jerome Stanek

11-03-2014, 7:38 AM

So much for the experts

Bill George

11-03-2014, 7:44 AM

I am curious as what a non glass mirror, such as one made from a hard drive disk would do?

Dave Sheldrake

11-03-2014, 8:57 AM

Good stuff Keith, when you go for the 100% power maybe an idea to use a Mo mirror to avoid the chance of cracking / shattering.

You will be losing a lot of the incidents power due to scatter but if the end result is still what you need that's academic anyways.

Bill, should be a bit stronger, I'm not a huge fan of sticking $2 modifications into $20,000 machinery though given the cost of real mirrors being so low.

cheers

Dave

David Somers

11-03-2014, 10:12 AM

Keith!

Wooooooot!!!!!!!! <big grin> Delighted to be proven completely and totally wrong! Very cool! And an enjoyable process trying to reason out what might happen as well! Looking forward to seeing 100% power now!

Dave

Bill George

11-03-2014, 1:04 PM

Rich Harman

11-03-2014, 1:16 PM

You will be losing a lot of the incidents power due to scatter...

Why would it scatter? When the converging beams bounces off the mirror it will continue to converge - just like the photons bouncing off an SLR's mirror will continue on in an ordered path to the viewfinder.

Ross Moshinsky

11-03-2014, 1:51 PM

Instead of putting the 3rd mirror at 45 degrees, couldn't you put it at 67.5? Then put a 4th mirror parallel to the 3rd and a lens after the 4th? A bit more complicated but then you don't have to worry about cooking the mirror...

Dave Sheldrake

11-03-2014, 2:57 PM

Why would it scatter? When the converging beams bounces off the mirror it will continue to converge - just like the photons bouncing off an SLR's mirror will continue on in an ordered path to the viewfinder.

it's a gaussian curve Rich not a straight line

cheers

Dave

Rich Harman

11-03-2014, 3:12 PM

it's a gaussian curve Rich not a straight line

Ok, that explains everything.

Dave Sheldrake

11-03-2014, 3:12 PM

Keith I predict some enterprising business either US or Chinese will copy your idea and there will be one on the market in a few months. I don't think its able to be Patented however because you posted on a public forum.

I think it's either AP or HX do similar Bill but they stick two more mirrors in and have adjustable angles.

cheers

Dave

Keith Colson

11-03-2014, 3:20 PM

I cut some prisms last night and the quality is surprising. I can actually look at a text image through the prism and it is still very legible. I just wanted to to turn led light so that's a give in.

Rich, you are right, it won't scatter to any detrimental amount. Reflector telescopes have been reflecting prior to the focal point of the hour glass since they were invented and I can see the moon okay with out any scatter. It is effectively the same model that I am using. My focal point ends up with a slight elliptical distortion but not a scatter as it is 22.5 degrees and not 45 like the image below.
299449

Yes, Bill I should make the final version, test it really well and then sell it. Good idea.

Dave, are you calling my quality work $2 worth? haha.

Building a unit with the mirror before the lens would be the proper way to do it as there would be no power issues. It just requires the last laser mirror to be pitched by 45 degrees. The mechanics get a lot harder and head collisions would then be possible too. I can keep that up my sleeve if my current system has any downsides. I quite enjoy experimenting.

Thanks for all the feedback everyone.

Cheers
Keith

Scott Shepherd

11-03-2014, 3:35 PM

Keith I predict some enterprising business either US or Chinese will copy your idea and there will be one on the market in a few months. I don't think its able to be Patented however because you posted on a public forum.

I think you have that backwards Bill, someone in China is saying "If you do this, some guy in New Zealand will copy your idea" :p

https://www.youtube.com/watch?v=HAZX_fn0EQ0&feature=youtube_gdata_player

Rich Harman

11-03-2014, 3:43 PM

Rich, you are right, it won't scatter to any detrimental amount. Reflector telescopes have been reflecting prior to the focal point of the hour glass since they were invented and I can see the moon okay with out any scatter. It is effectively the same model that I am using. My focal point ends up with a slight elliptical distortion but not a scatter as it is 22.5 degrees and not 45 like the image below.

Thanks Keith. I think the only reason for the elliptical distortion is because the beam is hitting the acrylic at an angle, not because it is being reflected.

The Newtonian reflector is a good example. You could use any telescope that uses a star diagonal as example too.

Chris DeGerolamo

11-03-2014, 4:03 PM

Nice Keith!

Dave Sheldrake

11-03-2014, 5:48 PM

Dave, are you calling my quality work $2 worth? haha.

nooooooooooo if it does what you want then actual cost is achademic Keith, I meant the idea of butchering up HD platters to make mirrors when genuine mirrors are only a few dollars from China.

Keith Colson

11-03-2014, 8:17 PM

Sorry Dave, I need to comprehend your posts a little better. Maybe its that sneaky cat face that biases my comprehension. hehe.

On another note I ordered another mirror today and have started the next design which will clip on to the laser head in a few seconds. I also measured the 45 degree angle and it's better than 0.2 of a degree, best I can measure. Now to work out how to cut in the right place depending on the Z height.

Cheers
Keith

Dave Sheldrake

11-04-2014, 11:33 AM

Honestly guys, my biggest limitation is time (or lack of) the differences between scattered multiwavelength ambient light and coherent narrow band / frequency laser light are different worlds. You simply cannot apply the fundamental principles of one to the other past the involvement of "photons". It's like comparing laser resonators to LED's in reality.
If I had a LOT more time on my hands I'd happily post about the need to keep tubes at a keen level to the first mirror or why semi focussed beams scatter but being hand on heart truthful the time involved would be colossal, maybe if I retire early I'll post a lot more in depth stuff but for now I'll just do what I can in the time I have.
Please please don't think I'm being smug or elitist but the subject matter is mind warpingly complex involving quite a few first principles that even when you understand them cause headaches.

cheers

Dave

Maybe its that sneaky cat face that biases my comprehension. hehe.

my other love in life Keith, Cats :) 20 so far and counting :)

David Somers

11-04-2014, 12:22 PM

Now Dave,

Just because you are trying to remodel an entire castle (abbey?) run a very large business and have a family life with wife and kids and 20 cats and have friends and do fun and interesting things on the side is no reason to give short shrift to SMC. What is all that free time for after all? <friendly grin>

Dave

Scott Shepherd

11-05-2014, 8:54 AM

If I had a LOT more time on my hands I'd happily post about the need to keep tubes at a keen level to the first mirror or why semi focussed beams scatter but being hand on heart truthful the time involved would be colossal, maybe if I retire early I'll post a lot more in depth stuff but for now I'll just do what I can in the time I have.
Please please don't think I'm being smug or elitist but the subject matter is mind warpingly complex involving quite a few first principles that even when you understand them cause headaches.

Or.......you could mock one up, put it in, push start, prove it works, and avoid all that wasted time :p

Dave Sheldrake

11-05-2014, 9:08 AM

A nuclear device will also crack wallnuts Scotty :)

Scott Shepherd

11-05-2014, 9:25 AM

Prove it :)

Kev Williams

11-05-2014, 10:27 AM

Keith I predict some enterprising business either US or Chinese will copy your idea and there will be one on the market in a few months. I don't think its able to be Patented however because you posted on a public forum.
Who gets a patent isn't necessarily determined by who gets to the patent office first, it's typically determined by who can prove they had the idea first. Posting an idea on a public forum is actually proof of the idea, and its date.

Paul Phillips

11-05-2014, 11:04 AM

A nuclear device will also crack wallnuts Scotty :)

See Dave, this is why I appreciate your incredible level of knowledge, every tidbit you share with us mere humans is savored and digested with the utmost appreciation of being able to further our knowledge of the mysterious complex inner workings of the laws of physics how lasers do their thing! Thank you for the time that you do take to throw some crumbs from the masters table! :D

Scott Shepherd

11-05-2014, 11:10 AM

Who gets a patent isn't necessarily determined by who gets to the patent office first, it's typically determined by who can prove they had the idea first. Posting an idea on a public forum is actually proof of the idea, and its date.

Sorry Kev, that's dead wrong. Posting your idea on a public forum will not provide you ANY protection at all. If you want to invent something, you should NEVER post it anywhere until you have filed for the patent.

The U.S. Patent system is a "First to File" system, not a "First to prove anything" system.

Dan Hintz

11-05-2014, 4:17 PM

Who gets a patent isn't necessarily determined by who gets to the patent office first, it's typically determined by who can prove they had the idea first. Posting an idea on a public forum is actually proof of the idea, and its date.

Proving you invented something first (but not disclosing it to the public), was the way it used to work (up until about two years ago). Now, it's whomever files first.

Dave Sheldrake

11-05-2014, 4:31 PM

See Dave, this is why I appreciate your incredible level of knowledge, every tidbit you share with us mere humans is savored and digested with the utmost appreciation of being able to further our knowledge of the mysterious complex inner workings of the laws of physics how lasers do their thing! Thank you for the time that you do take to throw some crumbs from the masters table! :D

My life would be a lot easier if I didn't post at all Paul ;) no gain or loss to me either way :)

Rich Harman

11-05-2014, 5:30 PM

My life would be a lot easier if I didn't post at all Paul ;) no gain or loss to me either way :)

What bothers me Dave, is that you are a self proclaimed expert on lasers, indeed many other proclaim your expertise too. Yet, you post things that are not true, have it pointed out that they are not true, then evade.

I will cite post 140 of the Chinese laser tips and tricks thread where you tell someone that their problem with not being able to get a good alignment is that their tube is not level - which is hogwash. Eventually in that thread you sort of admit that you were dumbing it down. In this thread you make a reference to the importance of the tube being level, maybe because I questioned your advise there too.

Then in this thread you tell someone that their idea won't work - yet they prove it does. Then you talk about mind warpingly complex ideas that you don't have the time to explain to us, that we should just trust you and not question.

As an expert and an authority you have the responsibility (IMO) to make sure that you are sharing information that is not only correct, but applicable.

Rich Harman

11-05-2014, 9:15 PM

My life would be a lot easier if I didn't post at all Paul ;) no gain or loss to me either way :).... Poof! and just like magic the shop keeper dissappeared

How can I interpret that in a non-negative way?

I do not think I am unique when I say that I contribute to a forum in order to share what I have learned and to learn things myself. I enjoy learning (that's a gain for me), and I enjoy helping others (another gain for me). Sometimes people are impressed that I know some things (that gains me some sort of status, and strokes my ego), other times they may think I am a dolt (loss of status, not good for ego).

If someone truly gains nothing by participating, or loses nothing by not participating, what is the point of participating? I can't speak to what Dave feels he gained but I am certain that his participation at the very least has gained him status in this forum an an expert.

If his sig line is true, I guess Dave's life just got a lot easier. So that is something positive.

Dan Hintz

11-06-2014, 6:50 AM

What bothers me Dave, is that you are a self proclaimed expert on lasers, indeed many other proclaim your expertise too. Yet, you post things that are not true...

Even the best people get things wrong at times (I know I do). The trick is to use logic and work through the scenario... more often than not the correct answer comes out at the other end. I try to admit when I'm wrong, but I stick to my guns when I think I'm right (until proven wrong). It's not a comfortable feeling realizing someone had the answer and it wasn't you, but we all deal with it in different ways.

Scott Shepherd

11-06-2014, 8:23 AM

I certainly hope Dave hasn't disappeared. He's contributed more to this forum in a short time than anyone else I can remember. I also know, first hand, how willing he is to help offline. He gladly gives out contact information and offers help. He's got more time behind a laser than 99% of the people on here. Small lasers, big lasers, Galvo's, Gantry's, and everything in between. Dismissing his knowledge because you don't agree with something he said in 2 posts is silly. I don't see where he said anything incorrect in this post. What He said was the beam would scatter. I suspect that's a fact. What Rich seems to be reading that as, as proof Dave was wrong. However, what Dave did not say was that a beam that is scattered can still cut just fine, it's just not the ideal beam structure, which is probably 100% true by anyone's standards.

To take that sort of nitpicking and try to run someone off because of it is a real disservice to this forum, in my opinion.

Dave Sheldrake

11-06-2014, 8:43 AM

As an expert and an authority you have the responsibility (IMO) to make sure that you are sharing information that is not only correct, but applicable.

A valid point Rich and I can see what you mean but a couple of things that leaves out,

The reason for a tube being level to the plane of the beam is important, the problem is the explanation of why it is important is at point C, if the person asking is at point A then that requires explaining point B before going to point C, that's where time comes in.
In the thread you mention it is far easier to just let somebody stick the tube in at an angle as while there are problems associated with it the chances are they are unlikely in the real world to cause any safety issues or readable benefits. This thread itself has issues with using semi profiled beams onto a reflective surface, it will cause scatter (I have a 4 inch long scar on my chest as testament to that) but in reality the risks associated with it are small. It comes down to chosing between what people can get away with safely and a long technical explanation of what is and isn't correct when the benefits of 4 hours writing still achieve the same thing.

Take Michelle (I think it was) asked about metal cutting machines, thankfully she seems to have taken it at face value that the chinese metal cutters are dangerous without needing a long explanation of the different parts of the chinese machines that won't pass safety inspections and the intrinsic electrical problems associated with using exothermic gasses in machines not really designed for them.
In effect I said that the machines are a fire or explosion risk and in essence that's true, all it will take though is somebody to pop along and say "But Oxygen isn't flammable" and they would be right so calling into question the entire statement that Oxy assist machines present a big fire / explosion hazard.

Getting back to the angular settings on a tube, there are issues with it, do I have 4 or 5 hours to write up the issues and the why of those issues when in reality it won't make a lot of difference to the end user unless an unlikely set of conditions is met? probably not.

As to being an expert....not me....X is an unknown factor, Spurt is a drip under pressure. I don't list professional qualifications, I don't list the machinery I have or use and with good reason, I don't want anybody to accept something at face value because it's me or because I seem to have a lot of machines. What I want more than anything is people to be safe, happy and get what they want done when they want to do it without making some of the mistakes I have in the past.
You are quite correct, I do dumb down answers sometimes simply because an answer somebody doesn't understand is pointless and achieves very little and certainly doesn't help them.

I'd love to spend 8 to 10 hours a day on this and my own forums answering questions and posting data, the reality of life means I simply don't have that sort of time if I want to stay married, keep my job running and have a social life so I'll try to help as many people as possible in the time I have spare. I'm no smarter than anybody else (hell I know as much about woodwork as most people know about nuclear cross sections) and my social skills are limited (I'm autistic) so if I come across as cold or arrogant or eliteist I apologise, it's not intentional.

cheers

Dave

Rich Harman

11-06-2014, 1:02 PM

In the thread you mention it is far easier to just let somebody stick the tube in at an angle as while there are problems associated with it the chances are they are unlikely in the real world to cause any safety issues or readable benefits.

This is the problem. You say that it is important, too complicated to explain why, but then admit that it wouldn't make any difference. I say that, even if in the most technical way it is correct, it is not applicable. In that thread about the tube being level you tell me to model it in 3D and I would see why it wouldn't work. The thing is, modeling it in 3D shows that it does work. Which makes what you said wrong. But you maintain that it is right, and that you don't have the time to teach me why.

May I suggest that if you don't have time to explain these things that maybe you could provide some keywords on the concepts you are referring to so that we can Google the matter on our own, or better yet provide a link. Certainly this knowledge (if correct) can be extracted from other places.

I do dumb down answers sometimes simply because an answer somebody doesn't understand is pointless and achieves very little and certainly doesn't help them.

Having someone spend time making certain their tube is perfectly level, when it does't actually matter, does not help them. They may have a job and family too, time is valuable to many people.

You shot down Keith's idea saying this:

Going the above pictured route will cause a LOT of abberations Keith, the spot will end up being scattered to blazes. When redirecting a beam it MUST be worked on while in the incident phase and not the focal phase.

To me that sounds like you didn't think it could work and were citing reasons why. Someone less motivated may have read that and given up on the idea. After all, those words came from someone with an understanding of the mind warpingly complex field of lasers. What was the point of that comment if not to discourage him from wasting time on the idea?

I think I will not say any more about this. Most likely it will only serve to make me look (more?) like a hair splitter or "nitpicker". I've made my point as best as I can. At the very least maybe some additional care will be taken in the future with regards to expert advice.

Paul Phillips

11-06-2014, 1:55 PM

My life would be a lot easier if I didn't post at all Paul ;) no gain or loss to me either way :)

Dave, I hope that I did not come across as disrespectful, I was trying to use humor, but was absolutely serious about being very appreciative of your help and I for one have learned much from your posts and hope you will continue to share your knowledge because it would be our loss if you didn't. :)

Kev Williams

11-06-2014, 2:07 PM

Sorry Kev, that's dead wrong. Posting your idea on a public forum will not provide you ANY protection at all. If you want to invent something, you should NEVER post it anywhere until you have filed for the patent. The U.S. Patent system is a "First to File" system, not a "First to prove anything" system.

Canada, the Philippines, and the United States had been among the only countries to use first-to-invent systems, but each switched to first-to-file in 1989, 1998, and 2013 respectively.

DEAD wrong? Give me a little credit. Sorry my 90 hour work schedule has been interfering with my law studies...

Scott Shepherd

11-06-2014, 2:10 PM

DEAD wrong? Give me a little credit. Sorry my 90 hour work schedule has been interfering with my law studies...

Is there another way to say that what you told people to do is incorrect by 100% and will actually get you in trouble if you were trying to file a patent? Because it was.

Dave Sheldrake

11-06-2014, 2:38 PM

To me that sounds like you didn't think it could work and were citing reasons why.

Nooo, I said it will cause abberations leading to scatter, scatter in any ionising beam is dangerous, sometimes minimally so, sometimes very much so. The point of the comment is not wanting to see a nice guy end up setting fire to his cat or wife's furniture or finding himself with a very hot mirror / broken mirror. Point any laser at pretty much any surface and it will reflect, refract or backscatter, white paint for example in the home has been responsible for eye damage in the groups where people use small 1w 532nm lasers but at least they have a blink reflex to protect them, the human eye has no blink reflex to IR lasers so by the time Bert,Bill or Harrys uber death ray has gone awry it's usually too late to help them.
If I believed or had a reasonable suspiscion that the angled mirror idea wouldn't work I'd have simply said "That won't work" and provided reasons why.....I didn't, I simply said it will cause abberations and scatter.

Having someone spend time making certain their tube is perfectly level, when it does't actually matter, does not help them.

Then go waste a few days reading up on Phase Cancellation, Uncontrolled Mode Changes and the effects of Multi Mode Laser Beams in industrial and semi industrial environments, maybe a look at Professor Shaol Ezekials series of books and lectures may help or some of the printed / posted works by Dr Sam Goldwasser in understanding the effects. Modelling it out in 3D also requires taking into account non linear abberations caused by any reflective surface's effect on a laser beam as well as the base mode of the beam, granted at TEM00 the effects of having a tube out of line won't be noticed but as yet I haven't seen any lasing source outside of a lab approach a single mode TEM00 beam profile.
Another source of useful reading is the published works around the NIF and the methodology they used when aligning resonators. In reality a laser can be pointed at a lens and fired and it will cut, however when you are dealing with the close to minuscule powers of small format lasers anything that sucks those photons is important, losing 2% on a 7kW resonator isn't going to be noticed,losing a base line of 2% on a 30 watt RF tube can make the difference between a job working and failing.

At the very least maybe some additional care will be taken in the future with regards to expert advice.

At no point have I said or suggested what I offer is expert advice, if you want real experts I can name 6 to 10 people easily that make what I know about lasers seem like chump change, that said if I'm going to have to write half a books worth of information down to justify and explain every post I make then it's just easier for me not to post. If the tiniest detail really is that important then there are many seats of learning round the world that offer courses that can help with that as well as a huge volume of publications at post grad level that will provide details to boil the brains of the most avid learner.

Dave, I hope that I did not come across as disrespectful,

Not at all Paul :), although at this point in time I'm leaning toward not bothering with posting here anymore, when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

cheers

Dave

Scott Shepherd

11-06-2014, 2:52 PM

Not at all Paul :), although at this point in time I'm leaning toward not bothering with posting here anymore, when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

cheers

Dave

That would be a real shame Dave. Don't stop posting because one or two people make comments. Think of the 100's of people that have replied positively to you and your help. Don't punish us for something he did ;)

Besides, if that's all it took, there'd be no one left on the forum :)

Rich Harman

11-06-2014, 2:59 PM

...when Rich takes the time to drag up a post from ages ago about tilted laser tubes that kind of tells me all I need to know.

I give up, but I would like to point out that it was you Dave, that dredged up the subject of tilted laser tubes in post #44 of this thread.

Wilbur Harris

11-06-2014, 3:16 PM

Deleted this post because what I wrote about is none of my business...

Keith Colson

11-06-2014, 4:08 PM

Not to beat a dead horse here, but I cannot see any optical "scatter". When I run the red targeting laser through the system with the lights off I cannot see any red light other than the target dot. I used to measure optical scatter when I was testing retro reflectors in my last job (miniature digital camera and optical ranging design) and it's very easy to see when it is present. Note that you will not get refraction from a first surface mirror either as you need a change in transmission media to enable that effect. I am meeting my optical scientist friend at lunch today and will discuss this further as I am always keen to learn. He was the one that told me to add the 22.5 degree mirror to the system, a really clever guy.

Dave its funny you mention 1 watt lasers in the house on painted walls. I have a blue one mounted in my lounge amongst many other lights. I scan it using a laser printer mirror. I added a monitoring circuit that shuts the laser down if it is not scanning (unsafe). With a smoke machine I get a blue sky effect, it looks pretty cool.

Cheers
Keith

Dave Sheldrake

11-06-2014, 5:26 PM

Not to beat a dead horse here, but I cannot see any optical "scatter". When I run the red targeting laser through the system with the lights off I cannot see any red light other than the target dot.

Red dot is already focussed Keith (or in some cases with diodes just collimated), you can either work with an incident beam or a focussed beam but adding a mirror into the optical train of a laser mid focus causes scatter given that the reflected beam will always travel at an equal angle to it's initial. True you won't get refraction from a first surface :)

Remember coherent laser light and ambient light (as in the case of photography and telescopes) are two very different animals, if not none of us would have thousands of $$$ worth of resonators, we would all just being using lots of LED's ;)

Dave its funny you mention 1 watt lasers in the house on painted walls.

Got a couple of programmable galvo display lasers here :) great fun when the day job gets tedious and drives my cats mad :) I still have the ocular limits papers here somewhere from my last LSO course, it's quite surprising how little it takes to do permanent eye damage :(

A little bit of useless information, a 1 watt blue laser (445nm) shone into space can be seen with the naked eye by the crew of the ISS :)

cheers

Dave

Rich Harman

11-06-2014, 8:28 PM

but adding a mirror into the optical train of a laser mid focus causes scatter given that the reflected beam will always travel at an equal angle to it's initial.

If the reflected beam always travels at an angle equal to it's initial, how does that lead to scatter? (this is my original question BTW) Scatter would be a beam being reflected in an undesired way - reflecting at the same angle it entered is what is desired.

Dave Sheldrake

11-07-2014, 8:59 AM

see my earlier reply Rich, it's a gaussian curve once it hits the focal lens, making changes to a part focussed beam changes the profile of the beam leading to abberations and scatter. Similar in some ways to fitting a meniscus lens lens upside down, a lens fitted backwards will cut and in some cases will appear to have a longer focal length but in reality all it is doing is scattering the beam giving a slightly larger spot and strays providing the illusion it cuts better (or deeper).

It can be done using curved (convex) mirrors to re-profile to some extent but the distances involved mean needing a VERY accurate set of spacings (much like a 3 lens collimator does)
This is the big difference between laser optics and visible optics, the curved nature of the beam profile and requirement for the cleanest modes available is what makes it so dang awkward to get right, if you work with the incident beam as far as possible you are dealing with a *rod* of light, that can be manipulated by a 1,000 different methods before hitting the focal train but once you get into the focal train the nature of focussed lasers makes things that much more difficult as any movement (such as heat expansion) moves the relative position of the reflecting surface in relation to the focal state of the gaussian curve.
If the part focussed beam was just a simple V shape then no problems and Keiths idea would work without any problems.
It's the fundamental reason on a lab laser everything that needs to be done is done before the final focal modification even if there are other optics like expanders / combiners etc in the train.

cheers

Dave

Bill George

11-07-2014, 12:27 PM

Well its clearly working in the initial tests, but just wondering long term IF the highly focused beam will burn a hole in the mirror or at least make it dark enough to render it useless.

David Somers

11-07-2014, 12:48 PM

Dave and Bill and Rich,

Would it be safe to say that in this case, the problems Dave is referring to are there, but that our laser systems have enough slop in them that the loss is relatively meaningless to us, while in a lab system or a more high power system that Dave has in his business it would be more critical. The important thing here being that Keith's mod is working well enough to accomplish his job and it was a mod that was low cost and relatively low effort. It might be that he needs to keep an eye on his mirror for damage over some period of time. Or maybe things are sloppy enough in our lasers that it wont make a difference? It is an inexpensive mirror to begin with as well so he can enjoy the learning process without worrying about the costs if something goes woof.

Either way though, I would certainly appreciate it if Keith doesn't mind continuing to tell us how his next efforts at mods goes! And if you guys don't mind continuing to debate and discuss what he is finding. It has been fascinating to follow and a great learning experience!!

Thanks Keith!!! And Dave and Rich!

Dave

Dave Sheldrake

11-07-2014, 2:29 PM

it's a gaussian curve once it hits the focal lens

To clarify...once it EXITS the focal lens

Bill George

11-07-2014, 3:03 PM

Dave Sheldrake

11-07-2014, 3:20 PM

I guess my question might have be interpreted as being critical, was not intended. It was merely wondered out loud if the mirror or any glass mirror could take that focus beam for long? That I why I was wondering early on if one made from metal as a HD platter would last longer?

The cheapest *glass* mirrors (K2) are pretty poor quality glass with a gold PVD coating, renown for going pop even in 30 watt DC lasers, The Si Glass mirrors again Gold PVD will stand much more (up to 60 watts incident) without too many problems but above that you need to move to either Cu (Gold coated copper) or Mo mirrors. Mo will take 300 watts without trouble but as the resistance to heat increases the reflective index decreases, The cheapest gold glass mirrors have the highest reflective index and the ultra tough Mo mirrors have the lowest...it's only a matter of 1 - 1.5% difference so in real terms not a lot, all of them are in the high 98% + range and once they get slightly dirty the difference in RI really doesn't matter.

My only concern with HD platters would be their resistance to corrosion and possibly heat distribution as I understand they are a lot thinner than the 3mm standard stuff??

Mo mirrors are the beasts, you can drop them from low orbit and they just don't break :)

cheers

Dave