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Fórum » Only in English » Technologies » Laser produced Lithophanes. (Problems related to laser produced Lithophanes.)
Laser produced Lithophanes.
tweakie Dátum/Date: Vasárnap, 2012-12-30, 08:49 | Üzenet/Post # 1
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A question was asked, in the main section of the forum, if it was possible to produce Lithophanes using a laser.

The answer is “yes it can be done”, but from my tests the results were rather disappointing.

I am getting ‘noise’ (unwanted high spots) in the background areas where the pixel value is essentially all the same. The reasons for this are not yet clear so this thread has been opened to form an area for discussion, comments and ideas.

Tweakie.

Csatolások/Attachments: 5231305.jpg(21Kb) · 8379431.jpg(11Kb)


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tweakie Dátum/Date: Vasárnap, 2012-12-30, 10:50 | Üzenet/Post # 2
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Re: Posting http://hobbycncart.com/forum/17-82-10998-16-1356821204

Hi Steve,

Thank you for taking the time to look into this issue, it is much appreciated.

By using some toner I have been able to get a better picture of the material surface in the background area of the lithophane (the red circle is 3mm diameter).
Not quite what I was expecting to see but interesting nonetheless.

I am sure you are right with your suggestion of the effect of the overlap but I am sure it is much reduced by the position of the focal point (area of maximum laser power density concentration) being at a constant depth.

My laser cut lithophane was done some time ago so I will perhaps try another using different settings and see if the final results are similar.

Tweakie.

Csatolások/Attachments: 4858060.jpg(69Kb)


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picengraver Dátum/Date: Vasárnap, 2012-12-30, 15:14 | Üzenet/Post # 3
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Tweakie,
The more I read of your "adventures" with your big-boy laser, the more I want one (loud sigh goes here).

I am curious as to the material used. Have you looked at the surface with a magnifying glass? Corian, when spindle engraved, will deposit dust particles in some areas of a litho, although mostly in deeper areas, and they need to be scrubbed with a brass brush or a pot cleanser paste to remove. The dust shows up as black spots somewhat similar to what you show here. The dust seems to remelt from friction heat of the engraving bits. I wonder if something similar may be happening with your laser? Perhaps in your case the effect may be caused by small vapor bubbles.
John


I paint with a blue light beam.
 
tweakie Dátum/Date: Hétfő, 2012-12-31, 09:55 | Üzenet/Post # 4
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Hi John,

Thank you for your suggestions / ideas - they are most helpful.

The material is opal acrylic (unknown manufacturer) and I was using this because it sublimates easily at the CO2 laser wavelength. There is a fine powder residue created and I think this is the filler used within the acrylic to create the opal appearance. I was using a moderate pressure 'air assist' to clear this powder from the work surface during cutting but I am beginning to suspect that this powder may be the cause of the problems.

Perhaps, as you have said, some hand finishing is necessary so I will try a mildly abrasive cleaner / brush. If this removes the odd 'high spots' then I think I would be happy with the result.

I don't think I have any offcuts remaining of the original material used but I have a some opal plexiglas so will try that and also a different laser control technique and higher pressure 'air assist' etc. then see what transpires.

As always, learning as I go. biggrin

Tweakie.


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tweakie Dátum/Date: Hétfő, 2012-12-31, 14:02 | Üzenet/Post # 5
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Well... during the course of experimentation I have changed 3 things.

1) Using a known brand of opal acrylic (Plexiglas).

2) I have returned to using Pulse Repetition Frequency (PRF instead of PWM) for controlling the laser output power (The PRF varies between 0 and 12.5 kHz whilst the pulse width remains constant at 40uS).

3) In addition to the co-axial ‘air assist’ I have added a ‘tangential’ air supply which makes a much better job of clearing the powder residue during the cutting process.

There are still a few unwanted spots but they have been much reduced and I am sure that they will be removable by lightly scrubbing the surface with a mildly abrasive cleaner, as John has suggested. I am now (almost) convinced that it is the powder residue which has caused me the problems.
It is perhaps early days to be over-confident but it looks like ‘laser produced Lithophanes are go’. biggrin

Just a couple of notes;
Opal Acrylic has pretty good light transmission qualities, both this and the previous picture are only illuminated with natural background lighting by being placed in a window.
Lasers will never, I think, produce such high quality Litho’s as spindle engraving but who knows and as said earlier it is still early days. biggrin

Tweakie.

Csatolások/Attachments: 2142305.jpg(36Kb)


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picengraver Dátum/Date: Hétfő, 2012-12-31, 16:27 | Üzenet/Post # 6
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Tweakie,
Congratulations. Really good results.

If you get a chance, it would be good to see how the laser does on Corian. I will be glad to mail some to you if unavailable there.

Happy New Year,
John


I paint with a blue light beam.

Az üzenetet módosította/Modified by picengraver - Hétfő, 2012-12-31, 16:27
 
tweakie Dátum/Date: Hétfő, 2012-12-31, 17:57 | Üzenet/Post # 7
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Hi John,

Thank you for the very kind offer but I have tried a scrap piece of Corian (off-cut from a counter top) with the laser but it did not sublimate well (It melts to bit of a goo similar to HDPE). I have ordered some high density polystyrene to try but I have the feeling that it may well behave the same.

There is something very special about acrylic (particularly cast acrylic) and CO2 lasers. The material acts as a wave-guide enabling what is essentially, in cross section, an 'hour-glass' shaped beam (with the focal point at the waist) to cut through acrylic whilst still maintaining, more or less, parallel sides. So far, I have not found any other material that acts in this same way.

Happy New Year to you and all our forum members and guests.

Tweakie.


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JJWMACHINECO Dátum/Date: Szombat, 2013-01-05, 12:47 | Üzenet/Post # 8
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Tweakie, WOW, that is amazing!! Lithos made with a laser is a first. respect

John, you mentioned having to clean your Lithos with a brass brush and it's most likely because of the sharp point of the tool your using. When I use a ball end mill, a blast of air from my compressor removes all the dust because there is no remelting. I also use Melin brand TIN coated carbide BEM from McMaster Carr which the coating most likely helps also and I run them at 45,000 RPM.

Jeff


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sanyi84 Dátum/Date: Szombat, 2013-01-05, 13:54 | Üzenet/Post # 9
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tweakie,
Very good, you can try it into plexi glass what would show? I would consider it interesting one if he would not burn the surface but the substance into himself the focus dot, this would be uniform reliefs would be. Sorry for the translator, I do not can in English.
 
tweakie Dátum/Date: Szombat, 2013-01-05, 14:26 | Üzenet/Post # 10
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Hi Sanyi,

The Lithophane effect only seems to work well with opaque material.

So far I have not been able to obtain a very good surface finish with Plexiglas - Hardwood is probably the best material for 3D relief's and one day I will have to give that a try.

Tweakie.


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Vasspisti Dátum/Date: Hétfő, 2013-01-07, 23:07 | Üzenet/Post # 11
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Hi Tweakie,

(tweakie)
I am beginning to suspect that this powder may be the cause of the problems.


The process is not perfect, there are fluidal and solid parts mixed with hot gases. They reduce the efficiency of the following Laser beam, so the surface will chaotic. The remelted materials make the surface crazy, as John and Jeff mentioned. So it is necessary to remove as many particles as possible from non-machined areas. The compressed air is a good solution. I think, three nozzles need for the better quality, two nozzles for X direction used alternately depend on moving X axis (one operates in +X, the other in -X) and one for tangential as you used. The angle between Z axis and nozzle is important. In my opinion the turbulent air is more convenient than laminar flow, but is only my intuition, I have not got any evidences.

The lithophane shown in #5 is perfect, congratulations. Only look at the picture, it is difficult to decide this is a spindle engraving or laser produced lithophane.

Vasspisti
 
tweakie Dátum/Date: Kedd, 2013-01-08, 07:59 | Üzenet/Post # 12
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Hi Vasspisti,

Thank you for your suggestion, I agree.

The existing tangential nozzle is directed at about 45 degrees to the surface of the work. I will fit another tangential nozzle (pointing in the opposite direction) and try pulsing the air alternately between the two nozzles and see if that improves the situation.

Tweakie.

Csatolások/Attachments: 9524929.jpg(40Kb)


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Vasspisti Dátum/Date: Kedd, 2013-01-08, 23:42 | Üzenet/Post # 13
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Hi Tweakie,

(tweakie)
try pulsing the air alternately between the two nozzles


I told about two X axis nozzles, but it is true only in that case when the X axis used for machined and Y axis used for stepover.
I think it would be better to show some pictures to correct my mistake.





So, Nozzle 1. and Nozzle 3. operates alternately depends on direction of machined and Nozzle 2. operates continuously.
I mentioned the turbulent air flow. Firstly I wanted to recommend a swirler to make it, but maybe the good settings of nozzles is enough (there will be turbulence when the air flows cross each other).

In my opinion the angle between Z axis and nozzles is important.



I think if the angle is small (the nozzle is close to vertical position) the force of the air flow is the biggest, but the horizontal speed of air flow is low, so the time between two Laser beams is not enough to remove particles. The cloud of particles will be giant due to high vertical speed of air flow.
If the angle is big (the nozzle is close to horizontal position) the horizontal speed of air flow is the highest, the cloud will be low. But the force of the air flow is very weak, a lot of particles will remain on the surface. The acceleration of particles is low due to low force of air flow, so removed materials can not reach the maximum speed until the following Laser beam arrives. The middle course usually is acceptable, maybe 45 degrees is a good choice.

Vasspisti
 
tweakie Dátum/Date: Szerda, 2013-01-09, 08:01 | Üzenet/Post # 14
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Hi Vasspisti,

Excellent diagrams sir. cool

I have not tried it yet but I will be using an alternating, twin cylinder, air pump for nozzles 1 & 3 and they will be pulsed alternately (one cylinder per nozzle) during both +X and -X directions (nozzle 2 is continuous air).
The powder residue is extremely fine so once moved it may remain airborne for some time, certainly long enough to be collected by the fume extraction system.

Thank you for your suggestions, I will report back with the results.

Tweakie.


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picengraver Dátum/Date: Péntek, 2013-01-11, 18:30 | Üzenet/Post # 15
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Vasspisti,
I would also like to thank you for your information. You have convinced me that I need to add air nozzles to my lithophane machine as well. I will report back on this later when I get it set up (it may take me a week or so). I have a small solenoid air valve to use, which I am glad now I did not sell on eBay. smile

Thank you for sharing,
John Champlain
www.picengrave.com


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Vasspisti Dátum/Date: Péntek, 2013-01-11, 21:29 | Üzenet/Post # 16
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Hi Tweakie and John,

thank you for your kind words.
To tell the true, I did not think for the fume exhaust system, so I draw my suggestions for machining whithout this system. If you use vacuum dissipator combined with Tweakie's pulsation solution, the efficiency will be higher. In this case, the angle and position of nozzles maybe neccessary to change. The actual flow and mass flow capacity of the vacuum pump is important.

Vasspisti
 
tweakie Dátum/Date: Szombat, 2013-01-12, 11:52 | Üzenet/Post # 17
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Hi Guys,

Thanks to Steve for the air nozzle suggestions the results have been much improved.

I also owe John an apology regarding Corian – it appears that the initial off-cut I was given to try was not genuine Corian but an EU manufactured impostor.

I have now managed to get a few small pieces of real Corian and it is just perfect.
Unfortunately it was ¼” thickness and had to be machined down to 3mm but it lasers extremely well with little, if any, particle dust and overall it is a beautiful material to work with – it is just a great shame that it is not commonly available here in the UK.

In conclusion Laser produced Lithophanes are quick and easy to produce (generally without any alterations to the contrast ratio’s of the original image being necessary) and because there is no Z axis movement I was able to use a constant velocity of 4000mm / min for the X axis (excepting the acceleration and deceleration zones for each line scan).
The final work does need backlighting (unlike opal Plexiglas) so it looks like I will be making a few of Johns LED / diffuser light frames when I get a chance. biggrin

Tweakie.

Csatolások/Attachments: 2637718.jpg(63Kb)


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picengraver Dátum/Date: Szombat, 2013-01-12, 13:34 | Üzenet/Post # 18
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Tweakie,

That is simply amazing work. The level of detail is far better than I get with rotary engraved lithophanes.

Corian is not inexpensive. The last I purchased (two years ago) was about $300US for a .25 x 30 x 96 inch sheet, which is the smallest thickness and largest sheet size it is produced in. Dupont will not sell it except to an authorized, factory trained installer, so getting it wholesale is near impossible. I purchased mine from a small local cabinet manufacturer.

Please post what size your example is, and engraving time. At over three times the speed of my router, I am now extremely interested in obtaining a CO2 unit myself. Did you have to use full laser power?

Thank you so much for sharing this.

John


I paint with a blue light beam.
 
tweakie Dátum/Date: Szombat, 2013-01-12, 15:24 | Üzenet/Post # 19
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Hi John,

The Litho is quite small at 65mm x 43mm (as I only have small scraps of Corian).

Physics determines my smallest laser dot size (typically 0.03mm) which is probably not any smaller that a jewellers rotary bit but my sides are a lot steeper and without the blended axis movement (X and Z axis) it may be capable of producing finer detail (although I still doubt that lasers can make a better job). The advantage is probably just down to the speed as this little piece took approx. 30 minutes to complete.
The actual laser power is difficult to quantify as settings may not be linear but my tube is rated for an absolute maximum current of 20mA and this piece was cut with a peak, (average) pulsed (12.5kHz) laser current of 7mA so perhaps 1/3rd power.
Obviously the quality of the focus lens and mirrors can make a big difference here and mine were all manufactured in the USA.

I still have a way to go with this but I think I am now on the winning side. biggrin

Tweakie.


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Vasspisti Dátum/Date: Szerda, 2013-01-16, 20:00 | Üzenet/Post # 20
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Hi Tweakie,

this litho is wonderful and the machining time is very impressive.

Vasspisti
 
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