Constellation Coasters With Copper Inlay

These coasters are made from slices of hardwood inlaid with short lengths of copper wire. The inspiration for them came from two other Instructables, Constellation Coasters and Stand (Laser Cut) and How to Make Drinks Coasters With Nails Inlay. I wanted to create starry patterns with the same effect as the nail-inlaid coasters, but unlike the author of that ‘Ible I don’t have access to a table saw that’s capable of cutting though steel nails – or even copper wire. So I came up with a glue-free method of inlaying the copper stars into the coasters instead of hammering nails into a block of wood that is then sliced up. It involves annealing copper wire to soften it, then hammering it into blind holes in the surface of the wood.

You can have fun selecting your favourite constellations, or those with a special meaning associated with when they are visible where you live. A set of coasters featuring the zodiac constellations for the birthdays of all the members of a family would make a great present.

Choose a dark-coloured wood with a fine grain for this project, such as teak, mahogany, rosewood or walnut. And if you can’t get hold of 3mm copper wire, pick a size near to that - AWG 9 is close – but you’ll need to find a drill bit to match the diameter.

You will need:

• 3mm copper wire – a 30cm (12”) length will go quite a long way.
• A length of hardwood at least 10cm (4”) wide and 1cm (3/8”) thick
• A saw – a tenon saw, or even a hand saw, will do the job if you’re accurate, but a mitre saw will make the job easier and a table (circular) saw easier still
• A Dremel rotary tool with a metal-cutting disk, or a hacksaw with a fine blade, or a jeweller’s saw
• Metal files – ordinary type and needle type
• A vice
• An old stainless steel spoon
• A gas cooking hob or blowtorch
• A drill (preferably a pillar drill) and a 3mm bit
• A hammer
• A pin punch, or a nail with a 3mm diameter shaft
• Sandpaper from coarse to fine, and a sanding block
• Wood finish (eg Danish Oil or varnish)
• Safety glasses – wear them for every process involving tools or heat

plus things that everyone has around the house: pencil and paper, a couple of pieces of scrap wood, a bowl of water, a vacuum cleaner and rags or a brush for applying the finish.

Each coaster should be about 9.5-10cm square and 10-12mm thick. So you need to slice up a block of wood to achieve that, with the grain running across the face of the coasters rather than the endgrain showing.

Assuming your piece of hardwood is thicker than the coasters will be, decide which is the best face and then rip an 11-12mm slice off that face. (“Ripping” means cutting with the grain, not across it.) Then rip the slice down to about a 10cm (4”) width, and crosscut it to make square coasters. But if you’re sawing by hand you might prefer to make the crosscuts first (across the grain) in a mitre box (or using a mitre saw) to get short lengths with perfectly true ends that will then fit into the mitre box for ripping. Doing it in that order, you’ll need to take care to get all of your coasters the same thickness.

Either way, rip as many slices are as needed to make all the coasters you want, rip the slices to the right width and chop them to length to match the width.

Save at least one offcut of the same thickness as a coaster to practise with in Step 3.

Sand the coasters smooth, decide which is going to be the top face of each one and put a very slight chamfer around the 4 edges of that face with sandpaper.

Find constellations online (eg StarDate’s Constellation Guide) or in a book. When you’re selecting them, bear in mind that they need to fit into a square without any two stars being too close together – constellations with a fairly even distribution of stars look best. I used the Plough (aka Big Dipper, part of Ursa Major and therefore, strictly speaking, an asterism not a constellation), Cassiopeia, Auriga the Charioteer, Lyra and Cancer.

Adjust the size of each constellation to fit on a coaster without any star being closer than about 10mm from an edge or 15mm from another star, to minimise the risk of the wood splitting when the copper inlay is hammered in.

Trace off your re-sized constellations (or just print them from a computer) and transfer them to the coasters, making a pencil mark for each star. Orientate the constellations to avoid more than one star being on the same grainline, especially if they are relatively close to each other, again to minimise the chance of the wood splitting along that grainline.

Drill a 3mm hole for each star to a depth of 3-4mm (about 1/8”). Take care to make them all the same depth by using a depth gauge on your drill or sticking a piece of tape around the drill bit. Lightly sand the surface of the coasters to remove any roughness around the holes. Tip the sawdust out of the holes and vacuum them clean.

Drill lots of holes to that same depth in the practice piece(s) you kept in Step 1, positioning them randomly but not too close together. Then work through Steps 4 to 7 with pieces of copper wire of slightly different lengths, hammering them into the practice holes, to work out what the ideal length should be. Repeat with as many other practice stars as you feel are necessary to get comfortable with the process.

Cut (or saw) a generous length of copper wire off the reel. It needs to be at least 15cm (6”) long, even for just a few stars, or it will be too short to hold when cutting and filing. Straighten it as best you can by hand, or by laying it on a flat surface and hitting it repeatedly along its length with a mallet while you rotate it.

We’re going to cut lengths of wire to whatever length you decided in the previous step was best for the inlay, probably about 1mm longer than the hole depth. The easiest way to do this is with a Dremel fitted with a suitable cutting disk, but you can also use a junior hacksaw or a jeweller’s saw. Clamp the wire between two pieces of scrap wood in the jaws of a vice for sawing (the wood will develop a groove when you close the jaws tightly on the wire the first time, use the same groove each time), or just hold it down against a piece of scrap wood if you’re using a Dremel – but hold it well away from the cutting area, it will get hot!

Mark the length you want to achieve on a piece of paper and use it as a measure to make a pencil mark on the wire for the next length after each cut. It’s easiest to file the end of the wire flat (ordinary file then needle file) and de-burr the circular edge before cutting each length (but after marking it). Don’t bother making it perfectly smooth, you’re going to be hitting it with a hammer shortly.

If you’re using a Dremel to make the cuts, reduce the pressure you’re applying to the minimum when the cut is nearly through and stop as soon as you see the almost-cut-through piece start to bend. Bend it on the workbench to break off the piece you want. This stops short lengths of wire from flying all over the room and getting lost.

Only one end of each piece of wire needs to be flat and clean, but de-burr the other end after cutting and make it approximately flat (remove the high points), holding it in a vice between two pieces of scrap wood as before. Don’t file off too much material, the finished length of each wire needs to be a little longer (say 0.5mm) than the hole depth.

The cut lengths of wire should just fit into the star holes in the coaster if you have removed all the burrs around the bottom edge and your drill bit is the same size as the wire. It doesn’t matter if the inlay pieces are very slightly loose, because hammering them in will fatten them and shorten them, but it does need to be possible to hammer them in without squashing them before they even get into the holes. So if they seem too tight either enlarge the holes a little or file a bit off the outside of the lower part of the wires (the part near the not-so-good end) to ensure that the wires will enter the holes straight and can then be knocked all the way in.

We need to anneal the lengths of wire to soften them so that they will fill deform to fill the star holes and stay put without the need for messy, fiddly gluing. Annealing involves first heating the copper to a dark red colour, which can be done on a gas stove (even one burning methane) or using a blowtorch. I did it by placing the inlay pieces in an old stainless steel teaspoon and holding them in the hottest part of a gas burner’s flame, while using an oven glove to hold the spoon’s handle. It didn’t take long before they had all turned dark red. (The bowl of the teaspoon went red too and has never been quite the same since, so don’t use your best cutlery!) With a blowtorch you could lay the inlay pieces on a heatproof surface such as a brick or concrete slab and play the flame over them. Have a bowl of cold water ready and tip in the inlay pieces (or sweep them off the heating surface into the bowl with an old spoon or table knife) as soon as they reach the right colour. Wear safety glasses to protect against any spits of steam.

Fish out the pieces of wire (they should be cold after their dunking) and dry them. Lightly file the flatter, smoother end of each with a needle file to restore its shine. (Filing will work-harden the surface, so don’t do any more than is necessary.)

The standard way to test whether copper is annealed is to strike it with a metal object to see if it makes a ringing sound – if it does, the annealing hasn’t worked. But these short lengths of wire are too small for that, and they are so small that it can be hard to judge their colour when you are heating them. Fortunately, annealing is a process that can be repeated so move on to the next step and, if the first “star” doesn’t appear to squash into its hole easily, re-anneal.

Lay a coaster face up on a flat surface that’s covered in something firm that will cushion the wood a little and prevent the underside from being marked, such as a cork mat, a hard piece of rubber or an offcut of plywood.

Place a star in position on the coaster, in one of the holes near the centre – make sure the “good”, shiny end of the wire is upwards – and hammer it into its hole, being careful not to strike the wood. Tap it in quite lightly at first to get it to go in full depth, then harder to squash it in and make it fatten out. When you feel that you are in danger of marking the wood if you hit it again, use a pin punch of the same diameter as a star to drive the copper flush with the surface. (If you don’t have a pin punch of a suitable size, fashion one by cutting the tip off a nail squarely and filing the cut end perfectly smooth. I used a clout nail because it was the right diameter and because they have a large head which makes it easier to hit them squarely.)

Inlay the remaining stars, working outwards from the centre on each coaster.

It’s important to avoid driving the stars below the surface, they won’t look good. But if, despite your practice piece, you find the lengths of copper inlay are too short when you come to use the first one for real, don’t despair. Just pack out the bottom of the star holes with small pieces of hardwood, even pieces cut off a cocktail stick will do. When you drive in the inlay it will compress the wood into the base of the hole and you should be able to get the copper flush with the surface.

The pin punch may raise small burrs on the surface of the copper. Carefully remove them with a needle file held perfectly parallel with the surface of the coaster. Turn the coaster frequently as you’re filing so that, if the file does touch the wood, it’s not all in the same place. Any inlays that are slightly proud of the wood surface can also be made flush by careful filing.

Using fairly fine sandpaper (say no. 120-150) wrapped tightly around a block, sand the surface of the coaster in the direction of the grain to remove any minor marks left from filing. This will also smooth the copper to some extent and minimise the scratches left on it by the file.

Wipe the dust off the surface of the coasters using a rag moistened with white spirit (aka mineral spirits) or a barely-damp cloth. When they are dry apply several coats of the finish of your choice. I used Danish Oil.

Further ideas:

• Use pyrography or laser etching to draw in the lines between stars to make the constellations more recognisable, like Constellation Coasters and Stand (Laser Cut), and/or write the name of the constellation across each coaster.
• Inlay with copper wire of varying diameters to represent stars of different brightness, or use a mixture of copper and brass wire. (Brass can be annealed in much the same way as copper.)
• Stick felt or cork on the underside, either over the whole surface or just in the corners.
• Use the same principles at a larger scale to make table mats or a teapot stand.