Adding an engraved pattern to the rim of a turned wood bowl can add to the natural beauty of the bowl and lend a subtle indication of your intended purpose for the bowl, in this case; wrapped Christmas candy. I engraved this bowl at the Techshop,www.techshop.ws San Jose, CA.
Step 1: Measure the Rim Diameter and Foot Diameter
You need to know you rim's outside and inside diameter in order to fit your pattern and also in order to make a paper mask. Choose an image you want to use and step and repeat the image as necessary to complete a circle that will fit on your bowl's rim. In this case I chose to engrave with a vector pattern, but the same would apply for a rastered pattern.
You need to know the foot diameter in order to make the positioning fixture. This simple fixture will hold the bowl in position so that you can use the paper masks to check your pattern, without the risk of moving the bowl.
Step 2: Create Paper Mask
In Corel, or your drawing program of choice, create an outline drawing for a paper mask that is used to "proof" the engraving design prior to actually engraving the bowl rim. Use the outside diameter to draw a circle and add four tabs to the circle. The tabs will be bent over the bowe edge to position the mask.
Use a "vector" setting and cut a couple of masks out of paper. Plain copy paper works fine, but if you have a larger bowl you may want to use "butcher paper" or brown wrapping paper. The mask is going to be used to check your pattern, size and placement, so use good (clean and not wrinkled) paper.
Step 3: Create Positioning Fixture
Use 1/4" MDF, particleboard or plywood to create a positioning fixture to hold your bowl in position while you use the paper masks to check your pattern and for actual engraving. The board needs to be wider and longer than the bowls largest diameter. Mark a spot approximately centered in the "X" plane and far enough down in the "Y" plane such that the bowl can be placed there without being outside of the laser's path.
Put the marked board on the laser bed, tight up against the upper left corner of the laser bed. Disable the X-Y drive on the laser and use the red dot to position the laser over the mark you made on your positioning fixture board. Set this position as "Home".
In your drawing program create a circle slightly larger than the diameter as the foot of your bowl; about +.010 should do. Set the line width to "hairline" and the laser to "center engrave" and cut the circle out of the positioning fixture.
Check that the positioning fixture is snug to the upper left corner of the laser bed.
Step 4: Add Bowl to Fixture.
Disable the X-Y drive and move the laser head out of the way and put your bowl in position in the circular cut-out. Lower the laser bed, so you don't crash the laser head, and bring the laser into position to focus on the rim of the bowl. Adjust as necessary to focus. Leave the X-Y drive disabled.and move the laser head out of the way.
Step 5: Place Mask on Bowl
Take one of the paper masks and bend the four tabs down and place the mask on the bowl. Touch "reset" on the laser console to return the laser to the "home" position previously set. Prepare to print your pattern, but make sure the POWER is SET LOW. You only want to trace an image on the paper, so increase the speed and cut the power. If you don't see an image on the paper after the first "run", increase the power, or slow the speed a bit and try again. Remember, the whole idea is to check your pattern before you start burning wood.
Step 6: Are You Happy With It?
If you first attempt didn't come out the way you planned, make the appropriate changes to your drawing and put a new paper mask in place and try again. Once you're happy with the looks of your pattern, size and placement, you're ready to engrave your bowl.
Step 7: Engrave
Remove the paper mask and reset your power and speed parameters and engrave your bowl rim.
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