Laser Cutting, or Better Model Building through Science.

[DaKra]

Since Russ asked about what I do, I'm  posting a few ideas about laser cutting which might help conceptualize the tool, what can be done with it and how.   Hopefully it will give you some ideas about possible ways to make model parts using a cutter, or a cutting service.  There are a lot of variables to every laser cutting job, so I will just outline the basics.     

A laser cutter uses a tightly focused beam of light to vaporize material.   The light is reflected from a traveling armature onto the material so it can cut in a raster or vector mode.  The standard beam is about .007" wide, but different lenses can be used to narrow it further.   Tolerances are about .002"  -- give or take depending on a bunch of factors.

Unlike most other CNC equipment, a laser cutter works off of graphics software, the same way as a computer printer.   But instead of ink, it uses a laser beam to surface engrave material.   It will also work in a vector mode, like a plotter printer, for cutting through material.   It will cut a variety of materials, with limitations.  Most cottage industry lasers  won't cut metal.   Plastic is iffy. It won't cut glass but it will engrave and score it.  For cutting, its pretty much limited to organic materials like paper and wood, and acrylic (Plexiglas).  Fortunately there are so many varieties of wood, paper and acrylic, the limit on materials is not a problem. 

So, for model building purposes here are a few ways to conceptualize a laser cutter:

1) a robot micro router or engraver. 
2) a robot micro scroll saw.
3) a photo-etching machine that works with wood and paper instead of metal.

Ultimately, the laser is a tool, and just like any other tool, it relies 100% on operator input to make anything useful with it. Garbage in = garbage out.  So the most important part of the laser process is you. In order to get a good set of laser cut parts you need a good graphic, and above all, a good design.  If you can only draw with pencil on paper, you can hire somebody to do the graphic for you.  If you can provide a good design, clearly drawn out with exact measurements, you can have good parts made.

When designing parts for the laser, break down your finished piece into a set of flat parts.  The best way to learn about how to do that is by building, or at least studying, the high quality paper model kits from Central and Eastern Europe.   Those are superb demonstrations of breaking a 3d world into 2d parts, and then building it back into 3d.   The advantage of the laser is, the parts will be pre-cut, with score lines or surface engraving as needed, plus you can reasonably go much, much smaller with the dimensions and complexity of the parts!

But its not all 2d.  The laser has 3d capabilities, which are really more art than science, and definitely the least used and least understood of the machine's features.  In 3d mode, the laser uses the greyscale in the graphic to change the power of the laser beam as it engraves.  Black is 100% power, white is 0%.  So in order to make a dome shape, your graphic would be a circle with white at the center, and a smooth transition to black on the outer edge.   Results tend to be grainy, so a CNC router is often a superior tool for 3d cutting.     

That pretty much sums up how the thing works.  As I said before there are a whole lot of variables to it, material type, thickness, laser frequency, speed, power, dithering patternss, etc.  I've had my laser for a few years now and still learning what it can do.       

Dave

[finescalerr]

The most interesting part, then, is the gray area. That is apparently how you managed to design brick walls with three or more levels of "flat". Or wrenches with raised lettering and ridges. Excellent basic introduction. -- Russ

[DaKra]

Russ, the brick texture is part of the 3d capability, and that is really an issue of graphic artistry using greyscales (I can't take any credit for that, BKLN drew it for me).  

But creating raised letters inside an inset such as in the wrench handle is simple.  Everything but the letters gets engraved.   More than one depth can be cut in a single job.  In color mapping mode, the laser interpets colors to apply different power settings and/or speeds.   Higher power and or slower speed = deeper cut.

 

[JohnP]

Thanks for the intro Dave. A place I worked at cut control markings from a two-layer plastic sign material using a nice laser. They are unbelievable cool.

I will be needing some eyebars cut for the small Phoenix bridge I am building. I hope my questions will assist others too.

Do you accept custom jobs?

Can I email a file?

Do you accept .dxf? Or what is your preferred format?

What color or layer name for the edge cuts i.e. through the material?

How should I define a light engraved mark (lower power) - with a different color or different layer?

What is the offset to account for kerf width?

What is your supply of acrylic or sign type plastic materials? Can I specify a thickness?

I know I'll have more questions later, such as about the gray scale cutting. It might look good for the bridge constructor plates. Thanks.

John

[DaKra]

Hi John

I take custom jobs, bit too much to do at the moment.  Files can be emailed.  I do all my work in Adobe Illustrator, most lasers are optimized for Corel.  Anything complex like CAD is a problem, at least for me, since I don't have the software to support it.  I believe some laser operators work directly from CAD software. 

An edge cut would be vectored.  In the graphics software the laser interprets a "hairline" (as Corel calls it)  or .001" or smaller stroke as a vector to trace.   Any line .002" and up gets engraved.  The standard lens cuts a .007" kerf so your offset would be +.0035" to compensate.   Might be best to leave kerf compensation to the laser operator, as lenses vary.   

Any area filled with black gets engraved.   Or, for jobs with more than one different depth engraving you can fill with a different color and assign it a depth.   

Regarding engraving depth, its not a mechanical system, so depth is achieved with power/speed settings on the material in question.   Experience is helpful here.

My standard materials are very strong cardstock in  .0145" and .01"
Birch plywood in .035" and .2"
Basswood in .04" and .1" 
Plexi in .07"

What's an eyebar?   

Dave

[JohnP]

Thanks for all the information. I'll have to see what I can do about conversions. Maybe there is something in my software that converts to a vector file. I am interested in your special cardstock. I'll have to design something just to see what occurs. Or buy some of your stuff!

I put a .jpg of an eyebar set below. They are the tension members on a pin-connected bridge. Single thickness parts. They are made by heating an iron bar and "upsetting" the end to the diameter with the hole. There are tables in old books about how long to cut a piece of bar to get the ends just right after upsetting.

Thanks, keep up the information. How about some photos of the machine, the laser head and the unit in operation?

John

[DaKra]

Hi John

Those parts look optimal for laser cutting, how thick do they need to be?   If a piece doesn't need engraving and there aren't any fine details such as these,  they can also be done in thin sheet styrene.   

There are photos of the cutting lens and a short video showing the machine in operation here on the manufacturer's web site:

http://www.epiloglaser.com/laser_cutting.htm

Here is a link to one of their testimonials, Ben Animek who works in Z scale.   

http://www.epiloglaser.com/cs_animek.htm

And here on Ben's website is a scan of a typical laser cutting graphic.  He's using color mapping here to change the settings or cluster groups of cuts during the job.  Looks like the graphic is shown in actual size.

http://animekmodels.com/images/MRoyal_plan.jpg

Dave

[marc_reusser]

Great info and interesting thread. Thanks.

M

[Ray Dunakin]

How thick can you go with styrene sheet? Is it possible to laser-cut thin brass?

[DaKra]

My laser won't cut metal.  It won't even cut the thin foil embossed on Christmas cards. The beam just reflects off it.  Metal cutting can be done with an industrial laser, I've seen it used to make model parts but the edges tend to be relatively rough.  It may be possible to use my laser to remove a layer of laquer, or similar resist, from sheet brass, then acid etch it to make photo etched parts.  Its something I've been meaning to try but haven't gotten to.

On sheet styrene, I've cut up to .08" but the thicker the material, the less detail and sharpness I can achieve. Styrene is not really a good material to laser because the material doesn't fully vaporize.   The edges tend to melt away from the beam, then the material flows back into the opening and "reheals" slightly as it cools.   It also produces a slight lip at the cut.  This problem increases with thickness and or complexity of the shape being cut.  One solution is scoring the material, then the end user snaps the pieces from the sheet.   Another is to use special type of styrene designed for laser cutting, unfortunately its not as rigid as the usual stuff and costs more.  There are other ways to improve cut quality of styrene.   I can produce very acceptable results in many cases.   But a good laser operator will know when the limits have been reached and recommend other materials.     

A good plastic substitute is acrylic (Plexiglas) its glass smooth, glues with liquid cement, and comes in a variety of thicknesses and colors.  It cuts and engraves nicely as the material is almost completely vaporized by the laser.  I can cut up to about .25" Plexi.   Some fairly complicated shapes can be cut from it, but the material is very brittle, unlike sheet styrene. 

[finescalerr]

Dave, how did you get into lasers and learn so much about them? You are like a professor. -- Russ

[DaKra]

Hey Russ, I got into laser cutting because I figured it would be an awesome tool that I could use for my hobby, and also make enough commercially to pay for itself, so it would be win-win.   That's the theory, but developing products and finding customers for them isn't nearly as easy as the laser sales brochure made it out to be!   It is a very tough market.  Subject for another thread someday.

Nearly all my information is covered in the instruction manual that comes with the machine.  Most operators probably don't read much past the quick start guide.   I wouldn't have, but I'm mostly working on the edge of the operating envelope where the default settings don't work well!   

[finescalerr]

Please continue to push the envelope. Your laser work has transcended skill to become art and I find it immensely inspirational. I know a couple of other guys very skilled with lasers but they have not achieved your level.

Personally, I find my ability with a computer to be a little stronger than my manual skills. I also find I have more patience to deal with detail on the computer. So my ideal project would be something I could conceive and design in CAD, translate to laser cutting and 3-D printing, and assemble relatively simply by hand. That's why I find the threads on lasers and 3-D printing so amazing.

Finishing is another matter entirely. I used to love working with an airbrush, stains, washes, and textures (and despised cleaning up). But the potential for disaster always lurks and my own paranoia detracted a lot from my enjoyment. So I decided to see what I could do with an inkjet printer. Some things work well, others just don't. Paints, stains, dyes, chemicals, and pastels still seem to yield the best results. But I must speak to my therapist before tackling the next project.

I might point out that I'm finding the same inspiration and limitations in music. Computers and instrument samples are great ... up to a point. But you need to record a human playing one or more real instruments along with them to bring the music to life; otherwise it has a synthetic quality. It's exactly the same as modeling.

Please keep the information coming and post photos of your laser work.

Russ

[JohnP]

I suspect we are creating a little of this concept here on the forum: http://www.emachineshop.com/

We have discussions about CAD solid modeling, Print-A-Part rapid prototyping, Dave's advanced laser work, the resin casting thread, metal etching and so on. I wish we had a US based etcher that is positively modeler-friendly for small runs. We need more info on that.

Keep it up Dave, you will find your niche and sell to it.

John

[DaKra]

Russ--

Totally agree.  High tech has a place in any craft, as long as it does not become a case of the tail wagging the dog, where the craft becomes a lame excuse to use the tech.   

One example I see over and over in our hobby is the misuse of fancy frilly fonts in signs.  Just because I can use a computer to make loud, elaborate multi-colored store signs, or easily laser cut individual letters in a modern calligraphic font for a rooftop signboard, does not mean I should.   Its not prototypical, I won't do it, as much as it appeals to the masses. 

Your music analogy nailed an important issue regarding the unrealistic, synthetic quality of high tech.   Computer  software has an irritating tendency towards "perfection" built into it.  For example, it is a very simple matter to line up a row of perfectly identical cobblestones, perfectly spaced, in a perfectly straight courses.   The result is completely unconvincing and  lifeless, as you said.  When imperfection is desirable --and it so often is-- adding this human element to a graphic is painstaking because the software is always working against it.   So, even in the virtual world, there is still no substitute for manual labor. 

It really boils down to having respect for both the art form and the potential and/or limitations of the technology.

John--

If you post or email me the specs for the parts you posted above, and its something I can do with materials on hand, I'm willing to try to cut sample finished parts, as a SBS demo for the forum.  They look pretty simple.   No charge for samples. 

Dave