Laser Cutting, or Better Model Building through Science.

[JohnP]

Dave,

I am going to try to convert my CAD into a vector or other compatible file. Maybe that could be part of your class. If I can't I will send you a dimensioned drawing. They are very simple parts. For the small Phoenix bridge that uses the post in my resin thread I will need eight of the same eyebar, so it is perfect for laser work in plexi or styrene. I'll see what my software puts out and/or look for freeware.

I wonder if SketchUp converts somehow? I could draw it there.

Thanks, John

[DaKra]

John, I can work from a .jpg or TIFF scan.  Even the drawing you posted would be sufficient if I had the exact measurements.  I just import it to Illustrator and trace.   For something as simple as this, it only takes a couple of minutes.  Thickness is the issue here, as I'm limited to stock material, or layers of it.   

[JohnP]

I know my TurboCAD converts to .jpg so I will draft what I need and send it your way maybe tonight. I'll figure out materials too. Thanks a bunch!

John

[JohnP]

Dave, I sent you an email with files attached. One is a .svg (scalable vector graphic). Maybe Illustrator will open it.

Thanks, John

[lab-dad]

This is an excellent learning opportunity!
Please continue to share.
-Marty

[DaKra]

I've gotten the files from John and will photograph the part making process for a SBS on the forum.  Meanwhile here is a link to a laser kit maker in Germany, MBZ. 

http://www.mbz-modellbahnzubehoer.de/produkte/index.htm

MBZ's line is an example of the superb realistic work that can be done with a laser commercially, when the domestic customer base isn't fixated on kitsch.   All their surfaces are 3d engraved, in particular, check out the 3d engraving on the roof treatments. 

http://www.fotos.mbz-modellbahnzubehoer.de/4_2/index.htm

Dave

[DaKra]

And here is my attempt at 3d engraved shingles. 



Here is the graphic I used to make them.  The laser interprets greyscale to adjust the amount of power applied to the material.  The darker the shade, the higher the power, the deeper the engrave depth.    Notice I randomized a few shingles so it wouldn't look lifeless and computery.



And here is a photo of the raw output.   The laser leaves a grainy surface, I sanded it down a little.   Then brush paint, followed by an oil wash and finished off with an airbrush dusting of a second grey color.     

[finescalerr]

Does the time required to add texture add significantly to pricing? A friend who does laser work charges by the minute and says cutting bricks or doing other things where the laser makes a lot of passes is "not cost effective". He charges immense rates for such work. -- Russ

[DaKra]

Russ, yes, 3d engraving is ponderous and since parts are priced according to machine time, it adds significantly to the cost.   I've wondered how MBZ are able to do this cost effectively.   For one thing MBZ kits aren't cheap, and for another they have a customer base in Germany willing to pay for accurate, realistic scale models.  So I suppose they can sell enough of these machine-time-intensive kits and parts to invest in additional machines and have them running simultaneously.  2 machines make parts twice as fast as one.   I don't think the American market could support an economy of scale like that, for realistic kits of that calibre.   

[JohnP]

I've seen enough automated process assembly lines to say that one could set up a laser with a moving line through it. You could load a stack of material and let it run continuously except for material movement. Maybe MBZ does it, maybe not. I did see a large-ish arch bridge for over 900 Euros in 1:48 so the comment about customers willing to pay for the best seems correct.

Dave, your roofing is exquisite. The rough texture is perfect for typical shingles. A weathered blend of colors and streaking due to rain would bring it out more. And thanks for posting the art for the roof. That makes the partial laser power use clear. It must have taken a while to process even that size though.

John

[eTraxx]

Found this link this morning - reciprocating laser cutter - interesting read. Heck the responses are too. It's always fun to read intelligent responses ..

[Malachi Constant]

Notice I randomized a few shingles so it wouldn't look lifeless and computery.

Indeed, that's where art meets science!  (Hello, Science, my name is Art) 

Those artistic touches add greatly to your work ... just made a plug for your gears on another forum.  Looking forward to ordering more of your goodies.

Meanwhile, glad to see you're so keenly aware that there are times when "perfect" looks fake!  The gray-scale cutting seems to work very nicely too.

Cheers,
Dallas

[DaKra]

 Hey Dallas, thanks for the plug.  Until I'm ready to invest in magazine adverts, I depend mostly on word of mouth advertising.   And you are right about perfection being imperfect.  Perfect imperfection is what we're after!   

Today I cut the bridge parts for John P.   It was a pretty straightforward job, so its a good demo of the process.  I'm sorry the plot isn't very suspenseful.   

First John sent me some files, which my computer could not read.  That is totally typical.  I use 2d graphic arts software.  Anything that originated from CAD makes my computer burp.   John's second try worked OK (mystery to me).  He included a really good diagram of the part, with measurements.   Which is a great for checking the finished work.  If necessary I could work from that alone, or a even a pencil sketch with the dimensions. 



But since John's drawings were in a vector format, I had very little set up work.  I made sure the vector graphic matched the measurements supplied, and checked the kerf offset was "about" right. (I say "about" because a laser beam is conical, so the part will be a little wider at the bottom than the top.  Its a very slight difference bottom to top, but it is a factor.)   Then I sent his file to the laser and loaded the material. 

In this case we decided on Plexiglas because it was about the right thickness and has a smooth surface.   I chose black plexi for John's parts. Better than clear because if a bright light strikes the finished part, it won't shine through and spoil the illusion of solid metal.   

Then I pressed "go" and just stood around making sure the stuff doesn't catch fire.  That's always a risk, especially with plexi.  It has a nasty reputation of igniting during a moment's inattention!    I've never actually witnessed it, but I have seen photos of completely burned out machines.   The machine should never be operated unattended. 

Here is a photo of the machine doing its work.  I'd like to be able to say the weird colored orbs are sparks thrown off by the laser, but they are actually just reflections of Christmas lights I keep strung up in my workspace.

 

Another action photo.  Notice there is no visible smoke.  That's because a blower exhausts the smoke to the exterior.   



Finished parts.  Paper is still on the plexi.  For a simple part its better to keep the paper on, as it protects from smoke stain on the front, and "reflection" on the back.  Reflection is when the laser beam reflects off the table grid, and causes annoying little tic marks on the rear of the material, especially if the power is set too high.   The paper will absorb this excess energy.  For more complicated parts, I remove the paper, so it does not become a nuisance to pick little pieces off.   



Last picture of a finished piece removed.   Note the fine sawtooth pattern on the edge (exaggerated here due to the reflection off the shiny black plexi).  The laser does not fire in a continuous mode, rather it fires in rapid pulses.  In effect its shooting .007" holes through the material, close enough together to form a continuous cut, and that's what you see here.   Unfortunately it leaves the end user with some clean up work.  This is really only a problem with  thicker materials, and especially plastics as they tend to liquefy around the beam in a sort of ripple effect.  I'm told its possible to polish the sawtooth pattern out of plexi with something called a "flame polisher"  but I'm way more comfortable with a file and putty!     



Finally the parts get packed up and go in the mail, and then its all up to John to build a stunning model bridge!

[finescalerr]

This presents still more critical information for us to absorb and illustrates the abilities and limitations of laser cutting. Very useful, even for those of us with some experience in this arcane science. -- Russ

[DaKra]

I didn't really mention the economics, but its really one of the great advantages of the laser.  This custom job for John cost under $20.  The files were ready to print (computer burp notwithstanding) so there was very little set up involved.  The material cost a couple of bucks.  The fee reflects mostly machine time, but this was a quick job for the machine to process.   

The ideal machine to make these parts would be a vertical mill.  A machinist could make these parts from plexi or stainless steel, or whatever.  They would be absolute perfection, but the price would be considerably higher.  Maybe astronomical.  So we have a nice compromise with laser cut parts. 

Another nice thing about the economics of the laser is, if there was an error in the design or execution, its not a big deal to make a correction to the graphic and sent it back to the machine.     

With a photo etched part, there is a whole layer of process between drawing and etching, so a lot of work ends up in the bin if an alteration needs to be made.   Not so with the laser. 

Finally, while I am comparing etching to lasering, the laser can cut thicker sheet material much more efficiently than photo etching.   There is a certain grey area in photo etching where the parts are a little too thin to be realistic, or the cost to etch thick material is too high to be effective, and that's where a laser starts to become a good alternative.   This is around .01" and up.   I've found the .0145" card material I use to be totally ideal for my applications, just as good as brass and sometimes better because it accepts glues and paints beautifully.

None of this is meant to imply the laser is superior to machining or etching.  That is absolutely not the case. There are no substitutes for those methods.   But for every application there is an ideal tool and the laser is ideal for a whole bunch of applications.