After I made our large round dining table (see Instructable) it seemed our old vinyl plastic coasters did not really fit in anymore. I decided to make some simple wood ones from some of the scrap cut-offs. I wanted something simple and quick to make, but also something that fit the look of the dining table.

Step 1: The Design

The design is relatively simple. I made the coasters square, so they could be stacked on their sides when not in use (I intend to make a small storage 'rack' for them later) and they are large enough to hold our largest diameter mugs. I also wanted them to stand off the table a little and thought an arched cut on the bottom side, leaving just the corners in tact would give them a little more elegant look. I opted for 3.75" (95.25mm) square by 3/8" (9.525mm) thick coasters. The circular (3.5"/88.9mm diameter) cut-out on top would just be roughly 1/16" (1.5mm) deep and the 'legs" on the bottom side the same. There are no critical dimensions here, almost anything would be fine.

Most of my measurements are shown in imperial units, but my drawings have metric on them as well. My routers bits are all in imperial sizes, but anything close or suitable would do.

Coaster - Square.PDF
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Step 2: Materials and Tools

Tools:

As always, safety first: Ear muffs, safety glasses and a dust mask are a must.

Table Saw to re-saw rough blanks (or a band-saw)
Drill
Jig Saw
Random Orbit Sander
Router Router bits (core box bit, large diameter bottom cutting bits or a dish carving bit)
Clamps (bar clamps)
Drill bits
Measuring tape, rulers, squares, marking tools
Sandpaper ranging from from 120 to 320 grit
Light (maple coloured) wood filler
Brushes for finish coating

Materials: The wood I used was from the scrap corner pieces after cutting out the turntable circle for my dining room table. They were large enough to cut 3.75" square blanks from and at 1 1/4" thick I was able to re-saw two 3/8" thick blanks from each scrap corner piece.

Some thin material to cut templates from (thinner than coasters) and some thicker plywood (or other stock to make a fixture). I used 1/8" (3.175mm) thick HDF for the templates and 3/4" (19.05mm) plywood scraps for the fixture.

Polyurethane (I used Varathane, Semi Gloss, Oil Based)

Step 3: Cutting the Blanks

The rough blanks were cut to size (3.75" square) using a cross-cut sled on the table saw with a stop block set to provide consistent cuts. The blade was raised only enough to cut through the block.

The thick blanks were then re-sawn to 3/8" thickness on the table saw. The blade was raised to a little more than half the width of a blank and they were cut in two passes. An auxiliary fence (just a sturdy piece of plywood) was clamped to the fence to provide more support. It also kept my fingers further from the blade as I pushed each piece through with a push-stick.

There were 10 finished blanks in total, but two of them had cracks (boards had checked while drying) and fell apart after re-sawing. I glued those back together to see if they might still be of use.

Step 4: Cutting the Bottoms

First I made a template to guide the cut. I wanted the bottoms to have an arc on the sides and so I made a large circular template (from 1/8" HDF). The diameter of the template circle is basically twice the "diameter" of the bottom cutout minus the diameter of the router bit used to make the cut. The cutout on the bottom is not a true circle, it is more of a rounded diamond shape. I wanted about 1/2" (12.7mm) of material left at each corner for a leg and the core box bit was 1/2" diameter, so my template circle was 7.5" (190.5mm) in diameter.

The circular template was aligned to the table mounted router using the cut out. A 1/4" hole was drilled into the cutout and a 1/4" rod was mounted in the router. The cutout was fit over top of the of the rod and the template spaced around it using whatever bits I had nearby with 1/4" shafts (various router bits).

During cutting, the router bit will not be contained within the perimeter of the coaster at all times and can come out the sides. Using a push block is the safest way to do this. Also clearing the dust often helps keep the depth of cut consistent. The core box bit was used to cut the perimeter (to give a nice curved edge) and then the flat bottom bit was used to clear out the center. In hindsight, I should have just gone out to buy a dish carving bit and done this all at once. Changing the bits and trying to get the exact same depth of cut was tricky and time consuming.

Step 5: Cutting the Tops

To cut the tops I made a fixture to hold the square coaster pieces, since I wanted perfect circular cutouts on the tops. I used one coaster blank (one of the glued ones that had cracked) to make an outline on a piece of 3/4" plywood and cut a tightly fitting square hole though it (jig saw and then some rasping). I used the same coaster blank with a small divot at its center to help position a piece of HDF that I used to cut a new circular template. In this case the circle had to accommodate the diameter of the router base as well. I wanted a 3 1/2" cutout on the top of each coaster and my router base was 6 1/2", so a 10" diameter circle was needed. When cutting this circle, remember to account for the router bit diameter. I forgot that the first time.

Each coaster had its top routed out. The last piece I routed was the one which was was repeatedly pressed into and out of the fixture to correctly size it. It did not fit very snug anymore and I was using an up-cut spiral bit. The router lifted the piece out of the fixture and cut right through it, so it really wanted to be scrap after all.

Step 6: Sanding and Finishing

Some pieces had some small amounts of tear-out, because the scraps I used had some wild grain patterns. I filled those with the maple coloured wood filler and sanded the parts. I used the fixture to hold the parts so I could sand as much as possible with a random orbit sander and then the rest by hand. I used a belt sander to round over the corners (best guess on the fillet radius).

I then finished the pieces with 3 coats of semi-gloss polyurethane, lightly sanding between coats.

Step 7: Final Notes

The coasters can be made any size (or shape) really. I made one piece with a square cut bottom (rather than arched) and it does not look as good. So ,I am rather glad I chose arched bottoms. I still wish I had used a dish carving bit, as it would have made everything much easier.

The goal was to make them from scrap pieces and if I had some of suitable thickness I could have saved myself the re-saw work. It was suppose to be a quick project and only took a couple of days (finishing add more time).