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Which color laser?

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et...@whidbey.com

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Oct 19, 2016, 4:19:24 PM10/19/16
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I must be looking in the wrong places because I have not yet been able
to find out which metals absorb which frequencies of light best. I am
looking at heating various metals with a laser so I need to know which
laser will work best for which metal. Anybody here have any pointers?
Thanks,
Eric

David Billington

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Oct 19, 2016, 5:13:20 PM10/19/16
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I don't know if it'll be much help but my local laser profiling company
mentioned that they had been warned off cutting copper based alloys
because the main mirrors in the laser cutter were highly polished copper
and cutting copper based alloys could send enough energy back to
overheat the mirrors and damage them. They do cut copper based alloys
but limit the thickness cut to something that doesn't threaten the
mirrors. I was in the past involved with a laser activated optical
emission spectrometer so will have a look to see if I have any details
that might be useful but don't hold too much hope as I recall the
project worked but was abandoned due to issues such a short laser
longevity etc. .

Larry Jaques

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Oct 19, 2016, 7:50:26 PM10/19/16
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Eric, I was reading an article the other day in a signmaking mag about
an engraving/cutting laser, and they were mentioned using a coating to
assist in this. It wasn't detailed, but you might do a search re:
this.

--
If government were a product,
selling it would be illegal.
--P.J. O'Rourke

Bob La Londe

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Oct 19, 2016, 7:53:59 PM10/19/16
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"Larry Jaques" <lja...@invalid.diversifycomm.com> wrote in message
news:jm0g0cd4q3jmjnull...@4ax.com...
> On Wed, 19 Oct 2016 13:22:48 -0700, et...@whidbey.com wrote:
>
>>I must be looking in the wrong places because I have not yet been able
>>to find out which metals absorb which frequencies of light best. I am
>>looking at heating various metals with a laser so I need to know which
>>laser will work best for which metal. Anybody here have any pointers?
>
> Eric, I was reading an article the other day in a signmaking mag about
> an engraving/cutting laser, and they were mentioned using a coating to
> assist in this. It wasn't detailed, but you might do a search re:
> this.

Could that be coating the metal so that it didn't reflect the energy instead
of absorbing it? I seem to recall having seen that sort of thing a few
times when watching How Its Made.



gghe...@gmail.com

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Oct 20, 2016, 10:22:34 AM10/20/16
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Heating to how hot? ~60-100 C or heating to 1000 C,
or laser melting and cutting?

George H.

et...@whidbey.com

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Oct 20, 2016, 12:44:55 PM10/20/16
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Up to about 200 C.
Thanks,
Eric

dpb

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Oct 20, 2016, 1:33:55 PM10/20/16
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On 10/20/2016 11:47 AM, et...@whidbey.com wrote:
> On Thu, 20 Oct 2016 07:22:11 -0700 (PDT), gghe...@gmail.com wrote:
...

>> Heating to how hot? ~60-100 C or heating to 1000 C,
>> or laser melting and cutting?
>>
>> George H.
> Up to about 200 C.

And what volume of a specimen of what size do you intend to heat?
Lasers are quite local in their application of energy, "not so much"
when it comes to bulk effects.

Applications like surface heat-treating rely on scanning a laser over
the surface and surface heating the local area to a very shallow depth
leaving the bulk material temperature essentially unchanged. It's
self-quenching into that cool reservoir that's the hardening mechanism
as opposed to bulk immersion of a heat-treated part in conventional heat
treatment.

What's the end objective here, really???

And, what specific materials?



et...@whidbey.com

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Oct 20, 2016, 2:05:55 PM10/20/16
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I dunno which metals yet, It depends on which ones can be easily
heated. Steel, copper alloys, zinc, and tin are ones I want to try
though.The laser will be scanned.
Thanks,
Eric

Carl Ijames

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Oct 20, 2016, 2:24:38 PM10/20/16
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wrote in message news:38th0c11govejia8s...@4ax.com...
=====================================================================

Eric, if you have access to a good library look for books by W. W. Duley.
He wrote a few on the effects of lasers on solids. I have his
"Co2 Lasers: Effects and Applications (Quantum electronics--Principles and
applications)" because that's the best if you want to build a CO2 laser (and
I did, :-)), but he wrote a few and they do a great job of covering the
physics of laser heating (heat capacity, thermal diffusivity, absorbance,
thermal conductivity, etc). I know at least one of his books had some nice
data on a list of different metals that should give you what you need but it
has been 20+ years since I was up on that stuff so I can't recommend a
specific book, sorry. Amazon has a pretty good selection, too. They date
from the 1970's to maybe 2000 so they don't include all the great solid
state high power lasers available now on the laser side, but the target side
was well covered.

-----
Regards,
Carl Ijames


gghe...@gmail.com

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Oct 20, 2016, 3:51:27 PM10/20/16
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It's not anything I know much about. Most metals are reflective,
which makes it not only hard to heat but scary if you are bouncing
a high power laser off it.
I quick google search found this
http://www.me.mtu.edu/~microweb/GRAPH/Laser/SPECMET.JPG
from here,
http://www.me.mtu.edu/~microweb/chap4/ch4-0.htm

So how about iron and ~800 nm - 1.1um... on issue with the near IR is you
can't see it which makes it more dangerous for your eye... no blink reflex.

George H.

nob...@nowhere.com

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Oct 20, 2016, 9:13:48 PM10/20/16
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I remember seeing a CO2 gas laser used to machine threads into a
ceramic bolt. They kept that monster in a separate room and no one was
allowed inside the room when it was working. there were occasions the
beam reflected around the room and damaged things.

gghe...@gmail.com

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Oct 20, 2016, 9:54:55 PM10/20/16
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I've no idea what Eric is doing, but my cast iron frying pan
looks like it absorbs pretty well in the visible too.
CO2 is useful because you can get a lot of power.

George H.

et...@whidbey.com

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Oct 21, 2016, 12:15:52 PM10/21/16
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Thanks Carl, I'll head to Seattle soon and check to see if they have
these books,
Eric

et...@whidbey.com

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Oct 21, 2016, 12:16:40 PM10/21/16
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Thanks for the links George. I'll check them out this wekend.
Eric

rangerssuck

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Oct 22, 2016, 10:50:31 AM10/22/16
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On Wednesday, October 19, 2016 at 4:19:24 PM UTC-4, et...@whidbey.com wrote:
I've done some looking into laser etching circuit boards. Apparently, it reflects so much IR that it's virtually impossible with IR or visible lasers. There ARE machines that do it, but insanely expensive (quarter-million dollar range) with UV lasers. I have not looked much further other than to have read various dire warnings about the dangers of UV lasers - "you'll shoot your eye out" sort of things. One day, I'll find the time to get back to this.

Martin Eastburn

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Oct 23, 2016, 9:27:13 PM10/23/16
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How big a board are you talking about ?
Will a cnc machine do the job - there are companies that make enclosed
lasers.
Martin

rangerssuck

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Oct 24, 2016, 2:19:34 PM10/24/16
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On Sunday, October 23, 2016 at 9:27:13 PM UTC-4, Martin Eastburn wrote:
> How big a board are you talking about ?
> Will a cnc machine do the job - there are companies that make enclosed
> lasers.
> Martin

No particular size, though my work usually fits in 8" x 10" or so. This was more of an exploration into the practicality of producing quick protos in my shop rather than sending them out and paying big bucks or waiting a long time for them to come back.

when you say "cnc" I assume you mean milling machine. That would work for some boards, but I don't know what kind of resolution you can get that way, I find it hard to imagine 6 mil traces and 6 mil spaces from a milling machine, though I haven't looked in that direction recently.

Another possibility is using a laser to remove a resist layer applied to the board. People are getting promising results that way, but it's not easy to control a chemical etching process with such small features. It would seem (to my uneducated mind) that it would be easier and more repeatable to dial in the parameters for a laser etch than for chemicals.

The machine I saw a price for was from LPKF. I did not find an online price, but I did find a public record contract from a college in the Pacific Northwest to purchase one. Delivered and installed, with a day or two of training, the prices was around $250K. A bit out of my price range.

I do have access to a 40W laser cutter at the local makerspace, and I may take a whack at the etching of a chemical resist (most likely black Krylon) when I get some free time.

Jim Wilkins

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Oct 24, 2016, 6:13:41 PM10/24/16
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"rangerssuck" <range...@gmail.com> wrote in message
news:a63a4e3b-c910-40f8...@googlegroups.com...
=========================================

I used these with generally acceptable results:
http://www.t-techtools.com/store/

At the time, the 1990's, 6 mils was difficult but possible for them,
IIRC 10 mils was easy. The Z height adjustment of the tapered
engraving cutter relative to an adjacent foot that pressed the board
against the platen set the space width. It was capable of milling a
GPS receiver. I used Mentor's PADS for PCB design .

--jsw



rangerssuck

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Oct 25, 2016, 1:49:12 PM10/25/16
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interesting. They say they do 4mil trace/space, which is pretty damned good. I'll be contacting them for system pricing, though I'm guessing it aint cheap.

But still, I'm thinking about this more as a diy project.

Jim Wilkins

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Oct 25, 2016, 2:45:37 PM10/25/16
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"rangerssuck" <range...@gmail.com> wrote in message
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Mechanically the T-Techs I used consisted of a smal high-speed motor
plus 1/8" shank engraving cutter on an X-Y bridge mount. The head was
spring-loaded down and located in Z by a foot resting on the board,
which compensated for warpage, until a dull cutter began raising
burrs. A solenoid raised it. Blank boards were located with dowel
pins, so they could be accurately flipped, and held with masking tape.

To some extent you could do the same job manually on a mill with the
high speed motor or Dremel spring-loaded below the spindle. I think
the main difficulties would be translating the PC artwork vectors and
adjusting the cutter depth to the intended width of cut precisely
enough.

A Gerber file consists of line endpoint pairs with an associated track
width, originally meant to be photoplotted with light through a round
aperture. You could have undercutting at corners if you only made the
tool paths the track centerline plus/minus half the track + space
width.

--jsw


rangerssuck

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Oct 25, 2016, 7:00:45 PM10/25/16
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So, the foot is spring loaded towards the board and the router to foot distance is controlled by a solenoid? That seems pretty easy to rig up. I'm not sure why you'd (at least I'd) need to vary the Z axis at all. The range of widths in their bits seems to be only a couple of mils. Seems like if you're (I'm) drawing outlines of copper, a cut's a cut. If I need a wider cut, why not just take two or more passes? The software for that would be pretty simple once the rest was done.

I doubt I'd be able to find it in my archives, and if I coupld, it may very well be on an 8" floppy, but actually, years ago when I used a layout service in Canada to design boards, and all I had was a single-pen plotter, I wrote software to read Gerbers and draw the outlines of actual-width traces. Of course, I was younger and smarter then ;) Seriously, though, once you have the picture in your head, it's just a matter of drawing rectangles with rounded ends. Not a very big deal at all.

Now, I'm in danger of actually doing this. I have a couple of X-Y mechanisms kicking around and a 45Krpm handpiece...

Dammitall, I still have actual work to be doing!

Jim Wilkins

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Oct 25, 2016, 11:24:37 PM10/25/16
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"rangerssuck" <range...@gmail.com> wrote in message
news:0a44b165-7671-490c...@googlegroups.com...
On Tuesday, October 25, 2016 at 2:45:37 PM UTC-4, Jim Wilkins wrote:
> "rangerssuck" <range...@gmail.com> wrote in message
> news:a2d52121-0a5b-4684...@googlegroups.com...

So, the foot is spring loaded towards the board and the router to
foot distance is controlled by a solenoid? That seems pretty easy to
rig up. I'm not sure why you'd (at least I'd) need to vary the Z axis
at all. The range of widths in their bits seems to be only a couple of
mils. Seems like if you're (I'm) drawing outlines of copper, a cut's a
cut. If I need a wider cut, why not just take two or more passes? The
software for that would be pretty simple once the rest was done.

=======================

I don't exactly remember how the head operated. IIRC a stop screw set
how far the vee shaped cutter extended below the foot when the head
was down, maybe pulled by the solenoid? It could also drill the holes
with a longer stroke.

I planned jobs such that the board fab time didn't delay the project
and didn't use the T-Tech any more than I had to. Since it only made 2
layer boards without plated vias it wasn't that much better for
prototyping than perfboard, and tended to require a lot of inspection
and hand deburring. I usually needed 4 or 6 layers with internal power
planes, or RF microstrip on Duroid.

--jsw


rangerssuck

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Oct 26, 2016, 9:43:28 AM10/26/16
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Their hottest looking machine has a tool changer to do drilling & other width milling, and auto-zeros in the z-axis. The also have (not inexpensive) hole-plating & multilayer stuff. I could do without the tool changer, and the auto-zero would be pretty straightforward. Many of my boards are far less demanding than the 6x6mil I said before. even 12x12 would be good enough to get a lot of work done. I don't do microwaves, I do mostly industrial controls and that stuff tends to be bigger. many of the parts I use are available on breakout boards (generally for robotics hobbyists) and sometimes as arduino-type shields. Given that, and the fact that I'm rarely constrained by small enclosures, I usually don't need the high precision. I'm starting to think that I really could do this with an x/y positioned dremel and a two-position z axis.

et...@whidbey.com

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Oct 26, 2016, 11:24:37 AM10/26/16
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The problem with the Dremel is the way excessive runout. But if you
can fiddle with it to get the runout down to just a couple tenths then
it would work. The runout has to be tiny at speed, not just when
turning by hand, and it needs to be pretty good over the length of the
cutter. With a limber spindle runout can cause the spindle to describe
a circle as it spins at speed so that your .002" dia. cutter mills a
.004" wide slot even though the tip is perfectly concentric to the
spindle axis. You can buy carbide engraving cutters that have very
small points so getting small spaces between the traces would be no
problem. If you can tame any runout.
Eric

Jim Wilkins

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Oct 26, 2016, 12:51:59 PM10/26/16
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"rangerssuck" <range...@gmail.com> wrote in message
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>...I'm starting to think that I really could do this with an x/y
>positioned dremel and a two-position z axis.

I estimated that I could build the mechanical part from surplus
Thompson rod etc without too much difficulty. In college I built a
wooden animation stand with similar x, y and z motions for a
film-maker.
https://en.wikipedia.org/wiki/Animation_stand

The snag would likely be having to code design rule checking to ensure
that the cutter never violated the overlapping exclusion zones of all
nearby design and drafting features. You couldn't just outline each
line segment independently, they are meant to be created by an
additive process that allows them to overlap while milling is
subtractive. It was hard enough to properly define all the widths and
clearances in the pad stacks when the program did the checking,
although I had more layers to attend to on a board with inner planes,
solder masks and silkscreens.

--jsw


Jim Wilkins

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Oct 26, 2016, 1:03:04 PM10/26/16
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<et...@whidbey.com> wrote in message
news:q6i11chungm2ake60...@4ax.com...
Manually jog the cutter along the margin of the board and measure the
cut width with a magnifier. I don't remember graduations on the Z
adjustment of the T-Tech I used.
--jsw


Martin Eastburn

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Oct 26, 2016, 10:58:42 PM10/26/16
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CNC isn't a milling machine. LPKF has all sorts. I was certified with
them.

CNC is computer numeral control. e.g. commands sent.

CNC laser driven to expose trace and then in the box or outside develop
and etch.

I used to use Ruby and blue tape for IC's. Then PCB's then CAD came and
early cad used a CNC laser to draw on the wall to make large film
sheets. In those days we were into 18x24 many layer. Later we went
large square and special material with fluid cooling on both sides...

The small LPKF I used was to make protype test boards to spec and one
day after the Cad design was completed.

Martin

Jim Wilkins

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Oct 28, 2016, 9:14:42 AM10/28/16
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"Jim Wilkins" <murat...@gmail.com> wrote in message
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I faintly remember another technician showing me a board on which the
T-Tech had fully outlined each track segment, resulting in arcs and
circles milled through the tracks at every pad, corner and junction.
He may have drawn the tracks as overlapping graphic lines instead of
named electrical nets and the compiler didn't recognize that the pads
and track segments should be left connected.

I quit planning how to build one when I realized that the programming
effort to check spacing and detect all overlap conditions would more
than nullify the time saved not waiting for etched boards.

--jsw


edhun...@gmail.com

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Oct 28, 2016, 9:58:00 AM10/28/16
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On Wednesday, October 19, 2016 at 4:19:24 PM UTC-4, et...@whidbey.com wrote:
> I must be looking in the wrong places because I have not yet been able
> to find out which metals absorb which frequencies of light best. I am
> looking at heating various metals with a laser so I need to know which
> laser will work best for which metal. Anybody here have any pointers?
> Thanks,
> Eric

Hi Eric. This doesn't directly answer your question but it may give you some ideas. Cutting lasers for fabricating work are mostly of two types -- first, CO2 lasers, with a light wavelength of 10.6 micrometers, which don't work well at all on highly reflective metals. The light is just reflected back, screwing up the mirror and other components.

Fiber lasers, with a wavelength of 1.064 micrometers, are effective on copper, brass, stainless steel, and other reflective metals. YAG lasers produce the same wavelength and they're used mostly for engraving and marking, rather than cutting.

You'll note that these wavelengths are at opposite ends of the infrared range. In the course of writing about these lasers for the past five years or so I've often asked the experts if the light frequency has anything to do with absorption in different metals. The usual answer is "no." The reason that fiber lasers are more effective on reflective metals, they tell me, is that the shorter wavelength allows a much more concentrated focusing spot -- power is much more concentrated -- and that fiber lasers have less trouble with reflections. I haven't dug into it more deeply than that, but the people at Trumpf, Bystronic, LVD-Strippett, Amada, or others who make both types of lasers may be able to give you more info.

I'm skeptical that laser *color* has much influence on the heating. Reflective metals tend to reflect a very broad band of frequencies. But it's not an issue I've investigated, so take this for what it's worth.

--
Ed Huntress
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