Mixed-media medallions

woodeditordave, posted on Feb 25, 2020

I was looking for a unique way to sign the gifts I build for others, and was inspired by the technique for making the metal inlaid medallion in the Arts and Crafts occasional cabinet in issue 265 of WOOD magazine. My initials are D and C, which, in all capital letters, look kind of symmetrical. Here's how I made my medallions; obviously, you'll want to make them your own by using a different design and materials. Soft metals, such as brass, copper, and aluminum, cut easily with your regular woodworking blades, so explore some place like McMaster-Carr to find out what shapes, thicknesses, and shapes are readily available.

 

The basic process is to insert lengths of metal into a metal tube in an organized manner, and then fill in the gaps around the inner parts with casting resin. After the epoxy cures, slice medallions off the end of the tube like bread slices, then inlay them into your project. 

Materials or Supplies

Materials or Supplies

1" o.d. general-purpose aluminum tubing 3' long
5/8" o.d. brass tubing 3' long
Two-part casting resin
Sandpaper and polishing compounds as fine as you can get
disposable mixing cup
disposable stir sticks

Make a simple fixture to secure the tubing

The "D" and "C" in my initials are made from a single length of brass tubing ripped down the middle. To keep the tubing from rotating during cutting, I made a simple jig from scrap plywood about 4" wide. I used my tablesaw to cut a V-groove down the middle of the piece about 20" long, well more than twice the 6" length of the tubing I wanted to rip. Then I crosscut the jig in the middle.

 

With the groove facing up, I used my bandsaw to freehand-cut a kerf down the middle of each V groove. This kerf transfers the location of the groove bottom to the outside of two pieces of the jig.

Brass sandwich

Next, I sandwiched the brass tubing between the two pieces of the jig and snugged it all together with brass screws. (The extra wedge in the top V-groove is the result of cutting the grooves too deep. I had to fill in with a thin scrap to keep the tubing from "floating".)

Let 'er rip

Next, I went to the bandsaw and cut through the tubing, keeping the blade in the kerf cut in step 1. When the tube is cut completely through, it may fall back into the center, closing up the gap between the two tubing halves. So I stopped just short of cutting completely through to prevent that. You could also wait until the bandsaw blade comes to a complete stop before pulling the blade back through the jig.

Nice rip

You can see the halved brass tubing here.  

Remove the tubing

After disassembling the jig, I removed the tubing and completed the cut with a hacksaw.

Straighten the edges

The cut edges of the brass were a little rough, so I clamped a flat file into my vise and filed the edges of both halves nice and flat. 

Glue them back, back to back

To remove any manufacturing oils and other impurities from the brass tubing, I carefully wiped it with lacquer thinner using a paper towel. (Remember, those cut edges can be sharp!) I then put a few drops of CA ("super") glue on one half of the tube and glued the piece together as shown. I only had to hold it for a few seconds.

Cap one end of the tube

To infill it with casting resin, I needed to stand the aluminum tubing on its end. I capped the end by boring in a scrap of wood a shallow 1" hole that matches the diameter of the tubing. It doesn't need to be deep, just enough to capture the end of the tubing. I'll "seal" it in a moment.

Secure the core

Using a dab of hot-melt glue, I adhered the brass assembly in the center of the cap. The glue keeps that end centered and is flexible enough to allow adjustments at the top end of the tube to make sure the brass parts stay centered through the length of the tube.

Seal the tube

I slipped the aluminum tubing over the brass core parts and sealed the aluminum to the cap with a bead of hot-melt glue around the outside.

Before the pour

You can see the edges of the "D" touching the inside of the aluminum tube, while there's a gap on the edges of the "C". I can center this with a small shim or a dab of hot-melt glue at this end before I pour the casting resin.

Build a pressure pot

My first attempt at making medallions resulted in a tube full of voids and gaps because I didn't evacuate air bubbles that develop while mixing the resin, trapping them permanently. After a little research, I learned that placing the freshly filled tube in a low-tech pressure pot would force those bubbles out for a void-free pour. I made mine from an inexpensive paint sprayer using a technique learned on YouTube

Mix the resin and fill the tube

After my failed first pour using two-part epoxy, I also switched to a slower-curing casting resin to further assist with air-bubble evacuation. Mix it in a disposable paper or plastic cup as directed by the manufacturer, stirring it thoroughly. I also added some black tint to create contrast between the resin and the shiny metal parts. People who do more casting than I do suggest pouring the mixed resin into a different cup before pouring it into the top of the tube to avoid any un- or undermixed components contaminating the resin. Seems like a good idea. I poured the resin in the tube slowly to minimize bubbles and filled it until the resin crowned slightly over the top of the aluminum tube. 

Under pressure

I pressure-tested my hacked pressure pot the night before my pour and discovered it didn't maintain the 40 psi pressure very well by itself, so I simply connected it to a small air compressor set to 40 psi and left the pot's inlet valve open. That made the compressor tank and pot like one big pressure pot, and when the pressure fell below 40 psi in the whole system the compressor would fire up and maintain the correct pressure.

 

So, after the pour, I placed the filled tube inside the pressure pot, sealed the lid, and turned on the air compressor. I left the whole system sealed and pressurized for about 24 hours to give plenty of time to work out the air bubbles.

It worked!

When I depressurized the pot and removed the tube, I discovered that my crown of resin had become a valley instead. That means the pressure pot had done its job and the now-void represented the amount of air bubbles that were no longer in my pour.

Ready to slice

I wanted to be sure that the epoxy had thoroughly cured all the way through the 6"-long tube, so I let it cure for more than 7 days before taking it to the bandsaw. I chose a 3/8" carbide-tooth blade.

Trim the plug

To make sure my cuts were perpendicular to the tube, I pared down the plug so one edge would rest flat on the bandsaw along with the tube. 

Close up the gap

A zero-clearance throat insert would be a good idea, but all I really wanted to do was make sure that a thin slice of the blank wouldn't drop in and get trapped between the blade and the slot, so I just added some blue painter's tape against the offcut side of the blade and in front of the teeth.

Best thing since sliced...

Using a miter gauge to keep the cut square, and a length stop (the wood in the lower left corner) to ensure the discs were the same thickness, I began slicing off discs. Even with a vacuum hooked up to my bandsaw, bits of hardened resin went everywhere.

Not bad!

I had to take a few slices to get past the void at the end of the tube, but these are the first void-free medallions straight off the saw. I'm starting to get excited about this process!

Sand and polish in bulk

The medallions are too small to handle individually for sanding and polishing, so I tacked them to a scrap of plywood with hot-melt glue so I could do them all at once.

Sand to smooth the faces

I sanded the medallions with 180-, then 220-grit paper on a random-orbit sander. I probably could have gone higher with sandpaper, but I didn't have any higher grits for my ROS.

Then switch to polish

At this point, you could switch to progressively finer automotive rubbing and polishing compounds. I had some compounds left over from cleaning up the scratched headlight lenses on my daughter's car, so I used a cordless drill and the polishing pads and compounds that came with that kit to work toward a glossy finish. 

The final product

After polishing, I carefully popped the medallions off the scrap. I was worried about breaking the thin bond between the resin and the aluminum ring, so I was careful to not separate them during the process. Also, the hot-melt glue worked better than expected, and I found it a little difficult to remove from the back of the medallions. Some cheaper consumer-grade glue sticks might have cleaned up easier. 

 

To install the medallion, I simply bored a 1" hole as deep as the medallion in a hidden part of the project and used CA glue to secure the medallion in the hole.

Tip of the Day

Ripsaw Found Wood With This Stock Box

Have you ever found a beautiful chunk of burl or crotch wood in the forest but didn't know how to... read more