zero-kerf-laser-jigsaw

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Part 1: Using the Alignment Sled

Detailed walk-through with prepared example files

The sled has multiple uses. For this tutorial, we’ll demonstrate using it to make a zero-kerf photo jigsaw puzzle.

We’ll use these already-prepared files (click to download). (Part 2 will discuss how to create the files.) The bundle contains:

Materials needed:

(See Q&A at the bottom for product recommendations.)

Step 1: Lock down the crumb tray

Secure the crumb tray as described here.

Step 2: Attach a Three-Point positioning jig.

Solidly attach a Three-Point positioning jig (or equivalent) to the crumb tray. For example, I use this one. We want a Three-Point jig, not a right angle jig, because the sheets of card stock won’t always be perfectly square.

Position the Three-Point jig with its inside edges slightly outside (less than 5mm) the Glowforge cutting area. (This makes it possible to position the sled appropriately.)

inside edges slightly outside (less than 5mm) the Glowforge cutting area

Step 3: Decide whether to print your photo at home or to use a print service.

I’ve tried around 8 kinds of lab-printed photos and 10 kinds of inkjet photo paper. At the moment, I’m printing mine at home on a Canon Pixma PRO-200 inkjet printer using ProMaster Natural Watercolor Cotton Paper. The most important consideration is that the photo print paper must be compatible with the masking transfer paper, so you don’t tear off the picture trying to de-mask it.

Your needs may vary. Consider:

De-masking (“weeding”):

Appearance of edges: It’s nice if the puzzle pieces’ edges are less visible when viewing the completed puzzle. For all of the papers I’ve tried, Inkjet-printed photos have a slight advantage here over lab-printed photos. (YMMV depending on choices of photo paper.)

Finish: This is a personal preference. I prefer matte paper, not glossy, to avoid glare from overhead lights. It also looks more elegant, if you’re going to mount the completed puzzle. However, true matte photos from the lab (“Fuji deep matte”) will have lower contrast. The cotton inkjet paper I mention above also has lower contrast, but I think you’ll find it acceptable and superior to lab-printed matte photos.

Durability: Lab-printed photos seem more resistant to wear. I didn’t test this thoroughly.

Convenience: If ordering from a lab, order more than one copy to save turnaround time when you make a mistake and need to redo something.

Photo printer: If you’re assembling a puzzle cut from multiple sheets, make sure your printer gives consistent color from one side of the page to the other—my HP OfficeJet completely failed at this—and from one page to the next. (This is why my template includes color bars around the edges.) If you’re not ready to spend the money on a good inkjet photo printer, try using a lab first.

Step 4: Print the example file (tutorial-print.pdf)

Print it on a letter-size sheet of matte photo paper.

Printing to the expected scale can be challenging. Some printers may crop or automatically resize the image. It’s okay if you can’t print at the original scale, as we’ll work with the actual dimensions rather than the expected dimensions. Just make sure the black border is visible and not cropped, and is smaller than 261x198mm (to fit within the sled’s measurement area). The example file is set up to accommodate 6mm margins or a small amount of bleed.

If you use a print service, use the .jpg file, choose the option for no color correction. Depending on the amount of bleed, you may need to add additional margins to the .jpg file, so that in the final result, the black border is smaller than 261x198mm.

Step 5: Label the “Reference Corner”.

Mark the bottom-left corner of the page (oriented in landscape position) as the Reference Corner.

Step 6 Trim if necessary

Trim, if necessary, the bottom and left edges of the page (adjacent to the reference corner) so that there is less than 10mm between the black border and the edge of the page. (This is to avoid the photo print overhanging the sled.) Don’t lose the border. Example of trimmed print:

trim

Step 7: Mount the print

Mount it using your choice of backing board and adhesive. Make sure the board doesn’t extend beyond the edge of the photo paper at the reference corner.

Step 8: Determine cutting parameters and kerf adjustment

Using a separate scrap piece of identical photo paper and backing board, choose your cutting speed/power and run some test cuts to decide how much kerf adjustment you want. I’ve been using this strategy:

  1. Choose a slower speed, like 170. (For better accuracy.)
  2. Then choose the lowest power that cleanly cuts out all the pieces most of the time. (This is to reduce char, and also because weeding is easier if you don’t cut all the way through the masking paper.)
  3. Then make the test cuts, and choose a kerf adjustment that’s about halfway between “the pieces just fall apart” and “the pieces are difficult to pull apart”.

Step 9: Mask the print

Mask it with transfer tape (low-tack if you can obtain it).

If you’re using a lab-printed photo, or a good inkjet paper that’s compatible with the masking (such as the cotton paper I mentioned above), this is straightforward. Apply the masking, smooth it down avoiding bubbles, and press it down moderately with fingers or a rubber roller.

For a video of this, see Part 3: Masking and Weeding.

Step 10: Trim the masking

Use a paper slicer or exacto knife to trim the transfer paper so that the edge of the black border is left exposed. It should look like this:

trimmed-mask

Step 11: Make an initial estimated measurement

Make an initial (“estimated”) measurement with a ruler, to the outside edges (not the inside edges) of the black border, to the nearest millimeter.

measurement-with-ruler

Step 12: Alter the MAP sled template to match your estimated measurement.

Open the MAP-sled.svg design in the Glowforge interface. The diamond in the top-left corner, which you should find centered at (10mm,10mm), is the “Reference Corner”.

Select the precision error gauge on the right-hand side. Move it horizontally so that it is centered at x = (Estimated Width + 10mm).

Select the precision error gauge on the bottom. Move it vertically so that it is centered at y = (Estimated Height + 10mm).

sled-template-in-interface

Glowforge interprets the SVG file assuming 96dpi. If you're not using a Glowforge, you may need to adjust the scale. The diamond in the corner should be centered at coordinates (10mm,10mm). The height of the error gauge at the bottom (see picture above) should be 6mm. The width of the error gauge at the right should also be 6mm.

Step 13: Fix the cardstock in the jig

Place a sheet of heavy card stock in the Glowforge cutting area, snugly against the three-point jig.

️Do not rush this step! Assure yourself that you can remove and replace the card stock in exactly the same position. Make sure the edge of the card stock is stopped against the three-point jig — not slipping underneath. If it keeps slipping under, try slightly bending up the edge of the paper.

Carefully, without moving it, tape down the corners with painter’s tape.

cutting sled

Step 14: Cut the MAP sled.

For heavy card stock, I use speed 240, power 30. Don’t use the highest speed, as it will be less accurate.

Step 15: Align the sled to the photo.

Set the masked photo on the table, face up, with the reference corner at the bottom left.

Remove the cut sled from the Glowforge, and flip the sled upside-down, so that its reference corner is also at the bottom left.

Align the guide holes along the left and bottom edges of the sled to the left and bottom outside edges (not inside edges) of the black border.

align the guide holes 2

As best you can, get the edge of the border going right through the exact center of the guide holes. Then use painter’s tape to tape the sled to the photo print, using the two round holes in the center area. After taping, double-check the alignment.

aligned-magnified

Step 16: Fine-tune your initial measurement

The error gauges, at the top and the right of the sled, let you tune your “estimated” dimensions to a precision of 0.1mm or better. The gauge’s small measuring circles are arranged in increments of 0.1mm. Remember you are measuring the outside edges (not inside edges) of the black border.

error-gauge

(Note, this is the step in which the photo’s dimensions are directly mapped to Glowforge’s coordinate system. The “real world” coordinate system, as defined by your favorite ruler, is actually irrelevant.)

reading-error-gauges

Step 17: Flip and place the photo for cutting.

Flip over the taped-together photo/sled assembly top-to-bottom, so that the reference corner is in the top left, and the photo is resting face-down on top of the sled.

Do not rush this step: Place the assembly back on the crumb tray against the Three-Point jig, with the sled in the exact same spot as before. The sled should be resting directly against the Three-Point jig. (If you can’t do this because the photo/board is overhanging the sled, then you forgot to trim the photo/board. Start over at that step.)

Carefully pin it down without moving it.

place-assembly-in-cutter

Step 18: Load the cutting file (tutorial-cut.svg) into your vector editor.

Make sure your editor is set to use units of millimeters, not pixels.

Step 19: Adjust the cutting file dimensions

In the editor, “Select all” (rectangular boundary and pieces) and:

  1. Flip the whole thing upside-down (Important: we’re cutting upside down! After flipping, the reference corner is at the upper left).
  2. Resize it (width and height) to the corrected dimensions you measured using the error gauges. (Important: unlock the aspect ratio when doing this!)
  3. Move it to position the top-left corner at (10mm, 10mm).

Step 20: Apply your kerf adjustment

Apply the kerf adjustment to the pieces—but not the rectangular border!—including the four “canary pieces” in the corners.

Tip: use slightly less kurf adjustment (individually) on more delicate whimsy pieces, to prevent breaking during disassembly.

In Affinity Designer, it’s the “Contour” tool

affinity-designer-contour

In Inkscape, this is the “Outset” or “Dynamic Offset” tool

I’m not familiar with Inkscape, sorry

In the Glowforge interface it’s the “Create Outline” tool

I can’t get this to work correctly.

Step 21: Load the design into Glowforge.

Save/export the design from your editor in the usual way, and upload it in the Glowforge interface.

“Select all” and verify the position and dimensions.

verifying-cut-in-interface

Step 22 (optional but recommended): Cut two canary pieces

Go ahead and cut two opposite “canary” pieces to check the alignment. While holding the piece down in the GF so that it doesn’t move, carefully pry out the canary pieces with a knife. You should get an accurately-cut red or green piece.

canaries

Step 23 Cut the pieces!

Ignore (don’t cut) the rectangular border. Cut the pieces.

After the cut, you will see that a sliver of the image remains around the holes. That’s because the printed piece’s outline is made larger than the cut piece’s outline by 0.5mm, to allow for slight misalignments.

In this example, the cut wasn’t quite perfectly centered, but it was off by only 0.1mm, which is acceptable and typical. For single-page puzzles, the error disappears anyway, because the relative error between adjacent pieces is small.

final-cu2

Step 24: Discard the paper sled

For the next job, print a new one. (This is because Glowforge’s coordinates can drift over time.)

Step 25: Remove (“weed”) the masking paper and clean the edge char.

You can weed the masking in the ordinary way (using bits of Gorilla tape to pull off the masking paper from each piece). But see Part 3: Masking and Weeding for an trick to make it easier.

You can tumble the pieces in a jug of Kosher salt to clean the char. But I find this to be less important if you choose the right materials. With my recommended plywood and inkjet paper (see Product Recommendations below), I don’t really find it necessary.

Step 26: Replace bad pieces

If there are any bad pieces (failed cut, face charring, photo torn during weeding), this method lets you cut individual replacements. Or, more simply, cut another copy of the whole puzzle to get a full inventory of replacement pieces for future copies.

Note that pieces cut from a separate sheet sometimes won’t be perfectly aligned, but they will usually be good enough for the puzzle player not to notice.

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Q & A

Product recommendations?