Using the laser to cut a jig has been documented in many other projects- basically you just use the laser to cut a template that your desired "object d'etch" will either sit in or be held in registration while you run the job. However, what if you have a bunch of irregular objects that need to be etched?
Obviously it's incredibly time consuming and a general pain to individually level each piece, focus the laser, and run the job... then repeat... then repeat... this Instructable shows a quick way to construct a compression jig that holds irregularly shaped work pieces at a similar height. For this example, we are engraving a logo onto tumbled river rock (which is mostly granite or marble).
Step 1: Make a Box With an Open Side
Here I used some scrap MDF-core plywood and a scrap piece of 1/8" acrylic in a sweet shiny translucent red. The translucent plastic helps you see the position of your work pieces underneath.
The one constraint here is that your laser system will need to have enough clearance for this box to sit on the bed, so size it accordingly.
Step 2: Cut the Jig
It is *very important* that you push the wooden frame of your box squarely against the upper left corner of the laser bed, or else registration will be off when you load up the box and attempt to engrave your objects. I also marked the laser bed with blue tape where the edges should meet, and slightly oversized my aperatures for the etching.
Step 3: Gather Your Materials. and a Little Bit of Info About River Rocks.
A slight aside: a few quick things about these kinds of rocks and laser etching.
- You aren't going to get a deep etch of any great quality. You *can* get a really nice quality light etch.
- Basically you will be blasting the tumbled polished surface away, so your design will etch as white regardless of the color of the rock.
- I was using power settings of 60% power, 70% speed at 300DPI for these rocks on a 120W Epilog. Too much power and you will actually blast bits of granite off the surface and make a really nasty etch (and a big mess). It's similar to the crystallization that occurs when you etch glass at too high a temperature. If you want a slightly deeper cut, two passes at lower power is the way to go.
- For the 'contemplation stone' type tchochkies, a very soft sandstone is usually used which is then sandblasted through a mask that is laser cut. That makes for a nice deep cut which can then be filled with enamel. You can find instructions and materials for this online with a quick web search.
Step 4: Load Your Material Into the Box
Load your material into the inside of the box with a decently flat face towards the acrylic. With a nicer jig you may not need all the masking tape to hold them temporarily in place, but the rocks were heavy and liked to slip around before I secured them.
You may also need additional support if any of your material is undersized relative to the aperture in the acrylic. Ideally all the material would be larger than the hole, as you are about to apply back-pressure to hold it all in place.
Step 5: Foam Party!
The foam needs to be stiff enough to be supportive of the work pieces, but also squishy enough to press around the contours of the work material.
Step 6: Shims and Compression
Alternately, you could use more foam here, but the shims allow you to adjust the tension as the height of the work materials changes.
In the future with a more permanent setup, I plan on making a back piece for my compression jig box that attaches with spring latches to squeeze the box contents tighter.
Step 7: Place the Jig in the Laser System, Focus, Register to Upper Left Corner, and Etch
Now focus the laser to the height of your material inside the aperture (which roughly the same height as the bottom face of the acrylic) and push the box squarely into the upper left corner to recreate the same registration as when you cut the jig.
Step 8: Unpack the Materials From the Box, Reload, and Keep Going
If you have more to do, then reload the jig and keep on truckin'.