Metrix Create:Space

Overview

The 50 Watt CO₂ laser can cut and engrave a variety of materials with the power of light. It is a precise but destructive process, so care must be taken when making a project. It's one thing to make a mistake on a piece of 1/4" birch — it's another to burn a hole in a MacBook Pro. We prefer to cut materials we stock, but we will cut custom material as well. Any custom material that is not immediately identifiable may require a burn test to determine its chemical makeup. We reserve the right to refuse to cut unidentifiable materials. Materials that smell bad but are otherwise relatively harmless, including most plastics, have a stink surcharge.

HOWTO

The laser cutter requires a HPGL .PLT file, which is a common format for vinyl cutters and plotters. We can take standard format EPS or SVG files and convert them to PLT for you. If you have text in your file, please use EPS so the font is embedded in your file.

We have run into issues converting SVG, mostly concerning scale or curve during conversion. You should put a 1cm square box in a corner of your drawing so we can be sure that the conversion is correct (we can delete it before cutting). You will also want to look at the converted file carefully, as curves can be converted to line segments and will need to be fixed in Lasermate before being sent on to the cutter. If it looks wrong in the print, it will look wrong when it's finished.

Inkscape is a popular package used to design for laser-cutting.

If you're using Google Sketchup (and want to export face cuts), note that Sketchup does not export PLT, SVG, or EPS natively, so you will need to install a plugin to export SVG. Once you have an SVG file, it is a good idea to take a look at it in Inkscape to make sure everything went smoothly.

Because programs are often finicky about sharing data (even between different versions of the same app), and output options can be confusingly or counterintuitively named, it's a good idea, once you have a final design (especially if you're doing the actual design work elsewhere) to supply several different candidate files. One recent project, for which the design was created in Inkscape under Linux, worked best when saved as a PDF and imported through CorelDraw at the shop; your mileage may vary.

http://code.google.com/p/sketchup-svg-outline-plugin/

No matter which program you're using, we find that designs import best if all line weights are set to hairline (or .001 if possible) and if there are is no fill to the line.

Take a look at your print before you cut.

Before we run a design on the laser, we can print an 11x17" proof if you would like. We know your LCD is accurate, but you should always see how things look on paper before you cut your materials.

MATERIALS

We can cut

• Acrylic (up to 1/4")
• Wood (up to 1/4"; not pressure treated, stained, or finished)
• Stamp Rubber
• Paper/Cardboard/Illustration Board
• Cloth
• Leather (up to 1/8")
• Polycarbonate plastic (very thin sheets only; thicker polycarb will simply smoke and melt)

We cannot cut

• Anything containing halogens (fluorine, chlorine, bromine, iodine, astatine, and ununseptium). This includes vinyl and many plastics (including teflon), as well as Moleskine notebooks or anything 'pleather.' If you’re not sure whether what you’ve got contains chlorine, you can check on the MSDS (if you can't find it there, ask the vendor or manufacturer directly) or do a burn test to check.
• Metal
• Glass cutting. It etches OK, but we can’t cut it with the laser.

We will not cut

• ABS and other styrene plastics
• Stingray and most other animal hides

See this post for more information.

KERF

The laser gets rid of material along the line you give it. You should account for kerf (that is, the width of the cut) in your artwork. It is dependent on material. This number is the width of the cut in total; half of it will be on each side of your line. Additionally, the laser beam is slightly conical rather than a perfect cylinder, so your cut will be gently tapered (about 2°).

Optimizing your design for the laser cutter

The laser cutter can do three different types of cuts: 1) It can cut straight and curved lines. 2) It can do vector engraving, which is similar to outlining. 3) It can also do raster engraving. Raster engraving cuts away large portions of material, leaving raised and lowered areas; this is good for rubber stamps, woodblocks for printing, and edge-lit signs.

Cutting and vector engraving are both very fast. A very cut heavy design will probably take less than 30 minutes to finish. The rated speed for cuts depends on the material in question, but is usually in the neighborhood of 4 to 20 mm/second. Hard turns require the laser to slow down and speed up, which reduces the effective speed.

Raster engraving takes quite a while, and raster heavy designs can take an hour or more to finish. With this in mind, you can minimize your cost by reducing the amount of raster engraving you do. You can reduce rasters by cutting things out instead of rastering them wherever possible.

If you want several types of cut in your design, simply make them each a different color. Cuts and vector engravings follow the lines in your design. Raster engravings fill an outline, so you can engrave inside of any closed curve. When exporting your design, please make sure it is a line drawing with hairline line widths with no fill properties. Since Inkscape can't do hairlines, make the line widths .01 mm or less.

For more information, see http://www.pololu.com/docs/0J24/5

Care of your laser-cut design

When you get your lasercut materials back, they may be covered in char marks or dust. Several things can be done about this, depending on what material your design was cut from.

• If your design was cut from acrylic, it may be covered in vaporised acrylic from the cutting. This can be cleaned up with a water-damp paper towel. If you clean it with alcohol, you will get tiny cracks near the edges.

• If your design was cut from wood, there may be discolorations on the sides of the cuts. This can be quickly sanded away with some coarse sandpaper.

• If your design was cut from stamp-rubber material, there may be some bits of rubber clinging to the finished piece; it wipes off easily with a moist paper towel.

Workshops

We offer Inkscape for Laser Cutting on a regular basis. Please check our calendar for dates.

Cost Structure

Prototyper (usually best value)

$2/min + material
No labor charge (unless it's really excessive)

Small Run

$1/min + setup + material
Labor is $50/hr, billable in half hour increments. Minimum labor is $25.

Flat rate specials

11x17 paper cuts for stencils and origami are a maximum of $20 + material

We now carry 5mil Kapton for solder stencils!

Surcharge for Acrylic and Leather (and other especially malodourous materials)

$.50/min

Discounts

Discounts are available with membership.

We have also introduced a Thingiverse discount. See the blog for details.

Laser Cutter Basic Info

The laser cutter apparently came without any sort of documentation. That's okay, though, because it's actually a pretty straightforward machine.

The Y-axis motor is mounted to the laser cutter body. The Y-axis motor is linked to the Y-axis shaft via a single timing belt. The Y-axis shaft is linked to the Y-axis crosshead via two timing belts, one on either side of the shaft. The X-axis motor is mounted on the Y-axis crosshead, and moves itself up and down the crosshead via a timing belt. The laser tube is mounted on the lower-right side of the machine, and shoots a laser into the laser cutter head and down onto the workpiece via three mirrors - one mounted on the laser cutter body to turn the bean towards towards the crosshead, one mounted on the crosshead to turn the beam towards the head, and one mounted on the head to turn the bean downward to the workpiece.

Exporting from EAGLE CAD

You will export the 'cream' layer (tCream or bCream) to an EPS file. The cream layer is a property of each part (including being automatically created for SMD pads in library packages/devices that you create).

Adjusting for kerf

The cream layer defined by a part is usually the same size as the SMD pad. The laser cutter will actually make a hole a little larger than what's in your file, due to some combination of laser kerf and melting of the stencil material. You need to update the cream layers on your board, making them slightly smaller than the pads themselves. From your board, open the DRC (Design Rule Check). Click on the Masks tab, and set the Cream Min and Max to 0.05 mm or 2 mil (depending on the units you are using). Click Apply. Your board's cream layers will be updated. Yes, this is surprising since it's labeled as a 'check' activity but does actually adjust the layers. You will, of course, need to do this for each board. Also note that this has no effect on parts with custom cream layers.

Generating the EPS file

From the Board, choose File/CAM Processor. (You should be familiar with this as it's what you use to create files for a board house.) Make the following settings:

• Device: EPS
• File: .eps
• Layer: select tCream (or bCream) and make sure no other layers are selected

Click Process Job. Your file will be created in the same folder as your board file, with its base name and the .eps suffix.

This works great as written for larger surface mount parts. However, it starts to break down for very fine pitch packages like TSSOPs, TQFPs, QFNs, and similar ones designed for the compulsively masochistic. The problem is that, for unknown reasons, the stencil openings are wider than specified in the Y direction and narrower in the X direction. It's a tiny effect, but significant for 0.5mm pitch packages with contacts on all sides. Poking around the Pololu FAQ for laser cut stencils indicates they have a similar problem and solved it by shrinking each opening more in the Y direction than in the X direction. There's no way that I know of in Eagle to do that on a per-board (instead of per-package) basis. However, there is a way to do it at the Gerber level.

Adjusting and exporting the Gerber

Each pad in a gerber file is defined by something called an aperture. The apertures for a well-formed gerber file are defined at the head of the file. SMD pads are almost always rectangular, and they are defined by lines of the form:

ADD<aperture #>R,<X dim>X<Y dim>*

There's no provision for rotation; the same pad in different orientations is defined by multiple lines of that form. Therefore, it is trivial to shrink the Y dimension more than the X dimension. Having modified your gerber, you can then open it in a program that can export it as an EPS or PDF file. The latter is more common; GerbView can do this, but costs money.

Setting up the cutter & the Kapton film

The Kapton film must be stretched tight over a frame in order to cut well. There is a small wooden frame for doing this behind the counter. Stretch it flat over the frame and secure it with blue tape. Set the laser up with the standard settings for Kapton and single directional raster cut. This, along with the above described adjustments, will produce usable stencils.

Exporting from gEDA

You want the paste layer; most likely the front/top paste. You'll also need Inkscape installed and the package which includes the program ps2eps, which is, unsurprisingly, called "ps2eps" in Debian.

As mentioned before, you'll need a EPS, SVG, or PLT file. As of Sep 2011, PLT export is not working.
You should be able to print the Gerber directly from gerbv to a Postscript file, but it mangled some pads. So here are some steps that worked:

1. In PCB, do "Export layout…" to PS which prints the multi-paged printout; disable all the printout options (align-marks, outline, and show-legend). Also, recommended to shrink the pads by 2mils, so enter "-200" in the ps-bloat box. Don't forget the negative sign! Finish by pressing okay.
2. Open the printout and print the paste page to its own .ps file. I used `gv` and "Saved marked pages…" (after marking the paste page, of course). Other options include using whatever standard viewer you have available and print just that page to a .ps file.
3. Then convert the .ps to EPS by running `ps2eps myboardpastelayer.ps` with your filename in the appropriate location. It creates the file myboardpastelayer.eps in the same directory.
4. Open the EPS in inkscape.
5. Ctrl-A, Ctrl-U, Ctrl-Alt-C (could run a long time on the last step). This sequence of operations is Select All, Ungroup, and Stroke to Path. This is necessary to create the outline for the pads.
6. Save as EPS again (my uniconvertor fails if you try to make .plt after using Stroke to Path in step 5 — perhaps future users will have better luck). Probably could also save as SVG if desired.