Determining what to bridge

Here are three quick ways to determine what portions of your design need bridging.

In Illustrator:

  1. Select All
  2. Object -> Compound Path -> Release

This converts all of the closed paths of your design into their own objects. Now we can clearly see which pieces will be left on the laser bed, like so:

In Acorn, Photoshop etc:

  1. Eyedropper the color from your image
  2. Flood fill the background

All of the white portions need bridges.

To see what will actually be cut out, as with the Illustrator version:

  1. Use the magic wand to select the background
  2. Select -> Inverse (note: menu items may differ in Photoshop)
  3. Edit -> Fill
  4. Clear the selection

Kerf widths, inside cuts and Illustrator

Cutting art with fine details requires accounting for the kerf of the laser beam. The laser beam’s center follows the center of the vector path. Some material will be burned away; the width of the removed material is called the kerf.

The kerf depends on a few factors, including the size of the lens, the type of the material, and the speed of the cut. For example, when cutting cardstock with a 1.5” lens a ULS 4.60 there is a 0.003” kerf on straight cuts and a 0.007” kerf on round cuts. Since the beam is centered, we only need to account for half of the kerf. In practice I’ve found that a 0.003” addition to the art allows for a good approximation of the original art.

Normally in Illustrator CS4 I use the appearance palette to add a Path->Offset Path… to account for the kerf. However, this doesn’t work correctly with inside cuts.

For example, from this art:

we would like to end up with a frame.

However, the kerf (purple) will cut from the exterior and interior, leaving a frame with a narrower width than intended.

Original art (two nested squares)

Desired cut (inner square cut from the outer, leaving a frame)

Frame narrower than intended

With Offset Path… only, both paths become larger.

The final frame is bigger all around.

Squares shown scaled up

Narrow scaled up frame

One easy change is to set the outer square to a positive offset, and the inner square to a negative offset. However, with complex artwork it is tedious to select every inner and outer cut separately.

Instead, select the cuts and use Object->Compound Path->Make. Then with the compound path selected apply the Offset Path.

Now the kerf is correctly accounted for and the desired frame is achieved.

Outer square has outer outline, inner square has inner outline

Final correct frame

Candyspotting specializes in laser-cut paper. Contact me for a free estimate.

Illustrator graphic styles for ULS

Here’s a set of graphic styles you can use in Illustrator to take full advantage of the ULS print driver.

  1. Download Illustrator graphic styles for ULS laser
  2. Move them to ~/Library/Application Support/Adobe/Adobe Illustrator CS4/en_US/Graphic Styles
  3. In Illustrator, open Window->Graphic Styles
  4. Open Graphic Style Library->User Defined->uls

The top row of styles is for etching, the bottom for scoring and cutting. Once the job is in the ULS Control Panel you should see the same colors that were used in the document. If everything displays black instead, double check that the document is using RGB (File->Document Color Mode->RGB Color). If it’s not, change it to RGB and reapply the styles to the document.

When testing a new material I use every color to test as many settings as possible at once, like so:

Illustrator screenshot with 7 vector settings

Rastering the setting numbers takes extra time but it creates wonderful documented samples.

Laser cut felt showing the settings used