Custom Coasters as Christmas Gift

A project by:

Gabriel B. Soares


Date:

December 2014


Build Time:

Three Weekends

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Finished Coasters

This past Christmas I decided to take advantage of my membership at the Techshop and instead of buying everyone gifts, I decided I would try to make a few more personalized gifts. These coasters are what I made for my grandmother. The etched Japanese characters have a significance which I will explain shortly. These are regular-sized coasters, made out of Bubinga wood, with a thin cork bottom.

My grandmother published a book last year with poems that she has written over the years. For each one of the poems, she had a calligrapher in Japan (who is also one of our family members) to make custom characters which translate as closely to the title of the poem as possible. I took the characters from a few of my favorite poems and decided to make these coasters for her.

The following page describes all the steps I took to design and make the coasters.

Design and Laser Cutting:

Luckily for me, while my grandmother was working on the book, she had sent me scanned copies of most of the Japanese characters that were in her book, and so all I had to do was dig up the email which contained those attachments and pick out my favorite ones. With the scanned images, all it took was a bit of image manipulation with Adobe Illustrator and CorelDRAW to get them in the necessary format for the laser cutter. The first image below shows the negative image of what I then sent to the laser cutter.

For this project I wanted to work with an exotic wood that I haven't worked with in the past. During my search I found that Bubinga is a hardwood that is often used by guitar makers, has a beautiful grain pattern and color variation. The wood is also fairly easy to work with when dry, and can be finished in a number of ways (stains, oils, wax, polyurethane, etc). You can check out all the details about the species here.

Since I have never worked with this wood before, the first step in the process was to run a whole series of tests on the laser cutter to figure out what parameters I was going to use in the final etch. I therefore cut a thin strip of the bubinga sheets I bought and played around with the power, speed, and resolution settings until I could get the depth and resolution that I wanted. The second image below shows my test runs, where I've annotated a few of the parameters for each pass. For each of the tests that I ran, I wrote on a text file what settings I was using and wrote my observations. One of the characteristics of bubinga is that it is an oily wood and unlike a lot of other woods, when laser cut it will scorch and char, which means you have to always keep an eye on the cut/raster and make sure you don't see any flares or flames when the laser hits oily patches.

The final settings I used for the wood are as follows (which produced the second to last character in the test strip):
- Vector Cuts: 75% power; 10% speed; 300 ppi (points per inch)
- Raster Etch: 30% power; 100% speed; 500 ppi; quality=6

The last image below shows a test piece I ran using the parameters defined above to make sure everything would look ok.

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Sanding, Routing, Sealing:

Once I worked out the settings and ran a couple of test jobs on the laser cutter, all I had to do was hit <ctrl>+p, set the parameters I had worked out in the step above, and just let the machine do its thing!

The coasters that come out of the laser cutter have quite a bit of char that needs to be sanded, and lucky for me the Techshop has a belt sander which makes quick work of what normally would take hours to do by hand. I started with 600 grit sandpaper, and worked up to 2000. Once they were nice and smooth to the touch, I took each coaster to the table router set with a 1/4" rounded bit, and rounded the top edge. The first image below shows the coasters after they have been sanded and routed.

At this point, I wasn't going to be able to complete the whole project in a single weekend, and so in order to avoid the coasters from warping from one week to another, I decided to seal the wood. This prevents the wood from absorbing or releasing moisture into the air which is what causes the wood to warp. If the coasters warped even slightly, they would develop a wobble and become useless.

As a sealer I used Danish oil which also helps the grain of the wood to pop. Danish oil is commonly used for indoor furniture where you might want to highlight the grain of the wood rather than hide it under a dark stain. I applied about 3 coats.

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Powder Coated Inlay:

This section describes a technique that I have not seen anyone else use in the past and I tested specifically for this project without knowing whether it would work or not. To my surprise it worked quite well!

When people talk about powder coating, the mediums they normally use are metals. This is because in order to use a powder coating gun and set the paint, you need a material that can be heated to moderate temperatures (typically around 400F) and can hold a charge. A piece of wood can't do either (if you heat up a piece of wood to that temperature it will dry out, warp, and burn.

However, I had just taken a powder coating class around the same time I was tackling this project, and decided to try to do an inlay on wood with powder paint in order to get the etched characters to pop.

So what I did is as follows:
- I put some of the powder on top of the etched characters and worked it into the etched part using a business card. I made sure the powder was only present on the etched part and cleaned it off the surface of the rest of the wood.
- I then took the board to a Hot-Air Reflow station (a piece of equipment essential in electronics for soldering and removing certain surface mount components), set the temperature to 400F and lowest air-flow setting, and patiently heated only the powder coated section of the coaster until I could see it settling and change from a powder state into solid glossy surface.

Because I had sealed the wood prior to this step, and kept the heat very localized to the etched characters, the wood wasn't losing moisture and didn't develop a tendency to warp. I found this method to work really well, and will be playing with it in the future (different powder colors on different types of wood)...

The first two images below show a coaster where the top character was powder coated and the bottom wasn't to show the created contrast.

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Finishing and Cork Bottoms:

I decided to use a high gloss polyurethane finish on these coasters as an extra protection from the elements. These coasters could be used with hot or cold liquids, and the polyurethane will further help protect the wood and give it shiny finish.

For this project I applied three coats of Minwax Helmsman Gloss Varnish (spray form), lightly sanding with 2000 grit sandpaper in between coats. The final result is shown below.

The last step to complete the coasters was to add some sort of bottom that would help with grip and cushion. I though about using rubber strips or felt pads, but in the end decided to go with a cork bottom. I went online and purchased a 1/32" thick cork roll for $8.00 (+$8.44 shipping), laser cut them to size and glued them to the bottom of the coasters using gorilla glue. These gave the coasters a nice cushion and a decent grip.

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Conclusion:

This was a fun project to work on. It was a simple build, but still took quite a while to complete. It allowed me to experiment with a new wood type and try inlay techniques which I had never done before. I love the way the grain of the wood stands out and how easy it is to work with. I will definitely be playing around with Bubinga again in the future.

If you are wondering whether my grandmother liked her gift, then just look at this photo.

These last images show each coaster with it's character as printed in the poetry book.

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