Chapter 7
Working with Metal
Here are three more “meta projects”—projects you build first, then use them to make other projects. These all use metals and metal-working processes in a fun way
The Desktop Foundry project makes a cool miniature foundry that casts tiny metal parts. It uses Field’s metal, a special, safe, low-temperature casting alloy. You could try substituting other low temperature alloys, but be careful. Don’t use an alloy that contains lead or cadmium.
I dressed up the Desktop Foundry with fancy brass parts I made using a process called photo etching. Even if you don’t etch any parts yourself, it’s interesting to read about the process and see examples of fantastically detailed parts made with it.
The last project in the chapter, the Yakitori Grill, is especially satisfying: it makes dinner. Everyone will love Ninja Chicken Sticks!
Desktop Foundry
Build this miniature working foundry and cast real metal parts safely, right on your desk. Make custom jewelry, tiny trinkets, die-cast-style game tokens—then remelt them and recast, again and again.
What makes it all possible is a special eutectic alloy—one with the lowest melting point—called Field’s metal, which melts at an amazingly low 144 ºF (about the temperature of hot coffee). Unlike other metals with a low melting temperature, this alloy of bismuth, indium, and tin contains no lead or cadmium and is safe and nontoxic.
The basic foundry is made from wood and metal along with a few scrounged household parts. If you’re up for a bit of a challenge, the second project in this chapter will show you how you can also dress up your Desktop Foundry with some snazzy brass trim and a twirling phoenix turbine.
Scan this QR code with your smartphone to see a demo video of the foundry casting a metal Makey Bot trinket!
Project Overview
You can vary the dimensions and features to suit whatever materials you have on hand. None of the materials or dimensions for this project are critical except for getting your hands on some Field’s metal. It’s a little pricey but you’ll only need a thimbleful or two of the stuff to have fun casting, melting, and recasting.
Fun fact: It’s named for its inventor, author and Make: contributor Simon Quellen Field!
Use Sugru, the super-easy-to-use silicone rubber material, to make the molds. It comes in handy small pouches perfect for this application. Find Sugru online, as well. Look for more details in the next project, Cast a Trinket.
I pilfered an alcohol lamp from an old chemistry set, but again, these are easy to find online and they are quite inexpensive. For the see-through crucible and storage vials, I used contact lens shipping bottles, but any small glass bottles will do. To make it easy to pour, use a bottle with the least “shouldered” neck.
The simple foundry design has a center shaft mounted vertically on a wooden base. The shaft swivels 90º to move the crucible from the heating lamp over to the mold. The cork handle swivels to tilt the crucible and pour the molten metal into the mold below. There’s also storage for molds, metal, and matches. This tiny foundry uses a thimble for a wick snuffer.
1. Make the Base
Start by cutting the base to size. If you like, use a router to add a decorative flourish to the edges. I used an ogee curve bit for a “desktop pen set” look. I also cut a 45º-beveled front face, but you can leave yours plain.
Mark and drill the holes for the shaft, bottles, and lamps. All holes are drilled 3⁄8″ deep, so use a drill press for best results. Drill a 1⁄8″ through-hole in the center of the recessed shaft hole. I also milled some recessed tray areas for storage of the snuffer, lamp, and extra molds, although you could use a router as well.
Make a mold holder using 2″× 2″ or any leftover wood scraps from your shop. I milled a small recess in the top to help hold the Sugru, but it’s not required. Cut some L-shaped supports, then cut bevels on the front. When glued in place in the center of the base they’ll keep the mold holder in position while casting.
Cut the 1″ dowel to 5″ length and drill a 1⁄8″ pilot hole in the bottom for the wood screw. Drill a series of 7⁄32″ holes for adjusting the height of the crucible (see sketch for details). Twist the dowel 90º and drill a 1⁄4″ hole—make it 3⁄8″ deep and 1⁄2″ from the other end of the dowel. I added some decorative rings using a lathe.
Cut three 1″ lengths of 1⁄4″ dowel and glue one into the hole near the bottom of the shaft. Place the large dowel in the center hole in the base and fasten the wood screw and washer through the bottom. Tighten the screw just snug so the vertical shaft can rotate in the hole. Add three stick-on rubber feet to the bottom of the base.
2. Craft the Crucible
Cut a 14″ length of brass wire and wrap the center around the lip of the small glass bottle. Twist the brass wires to make a long handle, then cinch tightly with the vise grips. Thread the twisted brass wire through the brass tube. Put a collar over the tube, then slide the tube through one of the 7⁄32″ holes in the shaft.
Test the fit with the alcohol lamp in place: turn the shaft and slide the brass tube so that the crucible bottle is directly over the lamp’s wick. Hold the collar against the shaft and tighten the set screw on the collar.
Add the second collar on the backside of the tube and tighten it in place against the other side of the shaft. Drill a ¼″ hole in the center of a cork and twist the cork snugly onto the end of the wires and brass tube to make an insulated handle. The crucible should swivel as you turn the cork.
With the crucible positioned over the lamp, hold one of the 1⁄4″ dowel pieces vertically on the base so that it touches the 1⁄4″ dowel in the shaft. Mark that position on the base and drill a 1⁄4″ hole × 3⁄8″ deep. Glue the second 1⁄4″ dowel in the hole. This makes a positive stop to locate the crucible over the lamp.
3. Mount the Mold Holder
Next, swivel the shaft 90º counterclockwise and place the mold holder underneath so that the crucible will pour directly into it. Carefully place the mold supports on either side and mark their position on the base. Also hold a small dowel next to the dowel on the shaft, mark its position and drill a ¼″ hole × 3⁄8″ deep. Glue the third ¼″ dowel in place—that will make a positive stop for the shaft in the pouring position. Glue the mold supports to the base, too.
4. Finishing Touches
Cut a 10″ length of brass wire and wrap the center around the lip of the thimble. Using a vise grip, twist the brass wires tightly to make a handle as before. Drill a 3⁄16″ hole through a cork and thread it over the end of the twisted wires to make an insulated handle.
Finish the wood parts with a thin coat of dark wood stain to bring out the grain.
Drill some 1⁄16″ holes in each end of the two small brass strips. Cut a piece of striker material from the side of a box of kitchen matches. Place the striker on the base as shown and put the brass strips on each end. Mark the holes, drill 1⁄16″ pilot holes, and then gently tap in the small brass brads, holding the striker material to the base with the brass strips.
The basic Desktop Foundry is ready to use. The next project shows you how to easily make a mold and cast parts, but if you want to take your Desktop Foundry to the next level, skip ahead to the project on metal etching. You’ll see how to add some extra brass trim and a whirling phoenix turbine to make your Desktop Foundry worthy of your office or den!
Cast a Trinket
Use the Desktop Foundry to cast a metal part. By the way, you can also use this same technique and materials to mold lots of different items. Besides low-temperature alloys you can cast custom-shaped chocolates, resin figures, plaster shapes, novelty ice cubes, and more. Just about anything that you can pour as a liquid and then let set into a solid would work.
1. Make the Mold
Find a small coin, trinket, or object you’d like to mold. I sculpted a tiny Make: robot from a piece of styrene and added a dimensional letter M punched out from a plastic label-maker strip. Whether you sculpt your own shape, or use a found object as your pattern, be careful to avoid any major undercuts. Small ones are okay for this project, because the cured Sugru will easily flex when unmolding. Just be extra careful when you remove your pattern, and then gently reshape the uncured Sugru as needed.
Spray some non-stick spray onto the top of the mold holder (you don’t want the Sugru to stick to it). Open up a pack of Sugru and knead it, then press it into the mold base. Spray your object with some non-stick cooking spray as a mold release, wipe away the excess, then carefully press the object into the Sugru. Leave it in place for about 24 hours for the Sugru to firm up.
Carefully remove the object; you’ll have a mold with every tiny detail and surface texture reproduced in it. See how Sugru stays flexible and forgiving so that you can easily unmold your cast metal shape?
2. Cast a Part
Clean the oil from the mold and dust it with a tiny bit of talcum powder to help the molten metal flow better. Put your mold in place on the base.
Place a small quantity of Field’s metal in the crucible and swing it into position. Light the lamp. Gently twist the cork handle to swivel the crucible back and forth as the metal melts. When ready, swing the crucible over to the mold and twist the handle to pour the metal into the mold.
Give the mold some gentle taps to help the molten metal flow into any details and to release any bubbles. When cooled, flex the Sugru to unmold the metal part. You’ve cast a real metal treasure! You can remelt and recast again and again.
3. Create Jewelry
After you’ve tried casting a few parts, why not add a few jewelry findings to make something really special—custom jewelry!
After you’ve poured the molten metal, but before it cools, carefully add an earring post and hold it there until it cools. You made an earring!
Similarly you can add a pin back to create a cool lapel pin.
To make a charm, make a small wire loop and add it to a molten casting. When the metal cools, use a few jump rings to add the charm to a necklace or bracelet.
Photo-Etched Metal Parts
While working on the Desktop Foundry project, I was surprised to learn that my local shops with CO2 laser cutters wouldn’t cut brass. It’s too reflective and can damage the lens. What to do? Instead, I thought I’d try to create the intricately detailed brass parts using a different process: photo-etching. Better living . . . through chemistry!
Photo-etching is used to make parts for small-scale model trains. This 1:48 scale model helicopter from Czech Republic comes with a sheet of photo-etched brass parts. Czech out the exquisite detail! Those tiny bolt heads are only 0.010″ in diameter.
British designer Sam Buxton has created some spectacularly clever art pieces for his line of Mikro men. A single flat piece of etched stainless steel is bent and twisted to create a miniature 3D world. My favorite is a bubble-helmeted space man taking his pet Mars rover out for a walk, holding a robotic pooper scooper. There are also half-etched details of textures, lettering, and markings.
Some of the pieces I photo-etched for the Desktop Foundry project were simple, flat, decorative brass trim, but two parts were bent and folded to create a 3D, phoenix-shaped turbine.
If you’ve ever etched your own circuit boards you may already have most of the required materials. If not, consider using the excellent Pro-Etch kit from Micro-Mark. It has everything you’ll need in one box: all materials and chemicals, and an excellent instruction manual.
The process (shown on the next page) is similar to etching a printed circuit board, except there’s no board. In short: Print your image on clear film and place it over the photosensitized brass. Expose it to a light source and place it in developer. The areas covered by the black image wash away, leaving an acid-resistant pattern. Place the brass in ferric chloride solution to etch away the unprotected areas, leaving your etched part. Here are the details.
1. Create Your Image
Photo-etching can create very small details and features, down to a tiny 0.010″ or so. However, the smaller the feature, the more care you will have to take in keeping the image razor sharp and the exposure blur-free. Also, the finer the detail, the more vigilant you will need to be when developing and etching. Create your image as a bitmap in Photoshop or vector art in Illustrator, or even just go old school with hand-drawn images. Add dotted lines to aid bending or folding the finished shape. Connect all of the parts and shapes with thin lines so that when etched they stay together and don’t fall off into the tank of acid. Leave a generous border of unetched brass around the parts to act as a frame to hold it all together while etching. Print out your image on clear film with dark black ink. The clear parts of the image will not etch—those are the resultant metal parts.
Unlike etching a PC board, in this process the acid will etch through both sides of the brass at the same time. You can choose to have a solid area of resist to protect the back, resulting in a simple part. You can also have slightly different images on the front and back. Where the areas of the images are the same, the brass is etched completely through, making a hole. Where the images are different, etching only happens halfway into the metal and only from one side, making an engraved feature like the tiny bolt heads or markings in the above examples.
2. Transfer to Metal
First, prepare the surface of the metal. It must be grease-free and perfectly clean. Scrub with a moistened polishing pad and handle the metal by the edges only—no greasy fingerprints! Peel off the protective carrier and adhere the photo-resist film to the metal with a little water. Smooth out any trapped air bubbles and excess water. Repeat for the other side. Then place the film-brass-film sandwich in a protective paper-cover sleeve and run it through the laminator. The heat and pressure adheres the photo film to the brass.
3. Expose to Light
Place the printed image over the film, clamp between plexiglass, and expose to UV light. Use the bright noon sun for 15 seconds or a 100W bulb with a longer exposure time of up to 15 minutes or more. When the resist film is properly exposed, you should see a dark purple image, the negative “shadow” of your artwork. Repeat the exposure on the backside, in my case with no image (solid resist).
4. Strip
Remove the clear protective films from both sides and immerse the brass in a diluted bath of sodium hydroxide developer. The unexposed areas will soften and wash away, exposing the bare brass. Gently brush the surface to help remove the softened film until you have crisp edges on all the smallest features. Rinse clean with water.
5. Etch
Immerse the brass completely in a tank of ferric chloride. Use a support clip to periodically lift the part out of the tank to check on its progress. The etchant is nasty stuff, so wear protective gloves and goggles and work in a space with good ventilation. For best results also use an aerator in the tank—the gentle bubbling agitation will ensure a flow of fresh etchant.
Periodically lift the part from the solution and check the progress. Carefully brush away spent etchant over small details to speed up the process. Depending on the amount of metal to be etched and the level of detail, it may take 20 minutes or more to completely etch your design.
When all the exposed brass is etched away and small details are clearly etched—it’s done!
6. Clean, Trim, and Assemble
Rinse the finished part under warm water to remove all the etchant. Double-check the finest details and return it to the etching tank if it needs more time. When it’s done, dip the finished part in a tray of undiluted sodium hydroxide to dissolve and remove the purple resist material.
Gently brush away any stubborn resist, then rinse in clean water. Done!
Trim the parts from the supporting brass runners using a tiny snips or an X-Acto knife. Carefully burnish with a polishing pad for a shiny look.
I did a second etch to make the phoenix and some other trim pieces. I tapped the center with a center punch to make a slight dimple to act as a bearing.
Then I folded it to make the wings and head of the phoenix, and twisted the blades to make the turbine fan. When assembled the phoenix/fan rests on a sharpened rod and spins freely on the slightest bit of rising hot air. See it in action two ways!
Look in the corner of this book and use your thumb to flip the pages quickly: the turbine spins over the flame!
Scan this QR code with your smartphone to see a demo video of the spinning turbine.
Hack a Yakitori Grill
One of the most memorable and delicious aspects of travel is sampling the local foods. A trip to Japan gave me a chance to enjoy favorites like takoyaki (octopus fritters), okonomiyaki (cabbage frittatas), and other Asian eats in their native setting. A new (to me) treat was yakitori, a simple bar food snack of grilled chicken.
In the Tokyo neighborhood of Shinjuku, I saw (and smelled) enticing restaurants featuring sizzling streetside grills. Unlike big American grills that cook anything from burgers to ribs to steaks, these scaled-down grills are designed to do one thing, and one thing only: skewers. Short skewers loaded with chicken, asparagus, meatballs, and other simple ingredients spanned the narrow troughs of red-hot coals. The suspended foods cooked quickly and without burning or sticking to a grate or grill surface. And the offerings included nearly all the parts of the chicken, from succulent breast (torinku) to crunchy cartilage (nankotsu) and delicate, crispy chicken skin (torikawa). Yum!
Back home, I wanted a way to cook yakitori myself, so I came up with this easy-to-make grill design and some specially designed roll-proof, double-crook skewers. Use them to try delicious yakitori recipes.
The basic design is simple: a single piece of sheet metal is rolled into a half cylinder to serve as the trough for the coals. The cake pans help form the trough. The grill stands on metal legs with insulated cork feet. Pop rivets hold it all together.
1. Prepare the Sheet Metal
Sand any sharp edges or burrs on the aluminum sheet with 100-grit sandpaper. For extra safety, wear gloves when handling the sheet metal.
Measure and mark a series of 5/32″ holes that will serve as holders for the skewers. Make a line ½″ below the 24″ edge of the aluminum sheet. Starting 3 inches from the end, measure and mark the holes on 2″ centers. Use the center punch and hammer to make dimples to keep the drill bit from wandering when you drill. Then drill all 10 holes.
Drill 5 holes along each end of the sheet. These holes will be for connecting the pop rivets to the rims of the end caps. Draw a line 1″ from the edge, then measure, mark, and punch the position of a hole at the center, 6″ from each side. Then do the same for holes 1″ from each side, and holes 3½″ from each side.
2. Prepare the Pans
Find the center of the pan, then mark it and punch. Draw a line from the center to the rim of the pan.
Use this line to center the L-strap legs as shown, and carefully mark the location of the L-strap holes on the cap.
Use a block of wood as a support inside the pan. Center punch and drill all three holes. Do the same thing on the other pan so that they’re identical.
Use pop rivets, with washers on the inside, to fasten the L-strap leg to the outside of the pan. Repeat with the other pan and leg.
Gently roll the aluminum sheet to the 6″ diameter curve. Don’t try to bend it all in one pass; just slightly curve it against a tabletop and slowly and gradually roll the sheet to bend the curve as you go. Check your progress using the pan.
Now “dry fit” the parts. Place the curved trough inside the pans. Do this on a flat, even surface; make sure all 4 feet are level and touching at the same time. Hold the pans tight against the curved edge of the sheet and mark the location of the holes in the sheet on the inside of the caps.
Now use the holes already drilled in the trough to mark the locations of the matching holes in the end caps. Use a marker to carefully mark the position of each hole on the inside rim of each end cap.
Strike the marks gently with a center punch, then flip over and punch the same marks from the other side to convert them to dimples on the outside of the rim. That will make it easier to drill from the outside. Support with a wood block inside and drill the matching 5⁄32″ rim holes.
3. Assemble and Paint
Line up the holes on the trough and connect it to the pans with pop rivets. Use washers to back up on the inside and to ensure snug riveting.
Mask off the inside surfaces with paper and masking tape. Then paint with two coats of high-temperature stove paint. Let dry overnight.
Drill a 1⁄8″ hole through the axis of 2 corks. Use a small flathead bolt to fasten the cork to the center hole on the end plate, with a washer and nut on the inside. Tighten the nut very snugly to pull the flathead flush with the cork—you don’t want to touch the metal bolt when you pick up the grill by these insulated cork handles.
Use a hobby knife to make a slit along the length, but not all the way to the end of a cork, as shown. Carve out a little more cork material to make a slot that will fit snugly on the edge of the foot. Make three more cork pads, one for each foot. If the corks are loose, use some wire to poke through the cork and the hole in the leg. Twist the wire to secure.
4. Make the Skewers
To make the double-crook skewers, cut stainless steel rods to 14″ lengths. Use vise grips or pliers to make the bends shown. Dimensions aren’t critical but make the bends into a zigzag shape.
Drill a 3⁄32″ hole through the center axis of a wine cork and drill a second shallow 3⁄32″ hole between the center and the edge of the cork.
Thread the cork on the short end of the skewer. Use the needle-nose pliers to make a very tight U-shape bend at the end of the wire.
Then slide the bent end into the second hole on the cork. This gives the skewer an insulated handle that won’t spin. Make as many skewers as you like.
If you don’t want to make these special skewers, you can use any kind of skewers. Look for flat cross-section bamboo skewers if you can find them—they’ll rest on the grill edge without rolling when you flip them.
Cook!
Put the grill on a fireproof surface away from any flammable vegetation or structures. Use crumpled paper and make a mound of charcoal in the center of the grill. For best flavor use binchotan (special Japanese high-carbon-content “white” charcoal) or mesquite, and avoid chemical starters. Light the coals and let them burn until uniformly covered in white ash—about 30 minutes. Can’t wait? Use your Shop-Vac with the hose on the outlet as a blower to fan the flames. You’ll have red-hot coals in just a few minutes, but be very careful—don’t blow hot embers all over; go easy!
Recipe for Ninja Chicken Sticks
(Sounds like more fun than yakitori chicken on skewers.)
1 lb boneless chicken thighs, with or without skin
¾ cup mirin (sweet rice wine)
½ cup soy sauce
½ cup sake
¼ cup sugar
Skewers
Combine mirin, soy sauce, sake, and sugar in a small pan and boil over medium heat until slightly thickened.
Cut chicken into bite-sized chunks or strips. Thread the meat evenly on the skewers, centering on the skewer to fit inside the grill. If you’re using bamboo skewers, soak them in water first to prevent burning.
Spread the hot coals to make a uniform layer along the middle of the trough. Insert the skewers into the holes. Rotate the skewers every few minutes, brushing on more sauce. Repeat until golden brown.
You can “yaki” more ingredients besides chicken. Kushiyaki fare includes ikada (scallions), butabara (pork), piman (green pepper), asuparabekon (asparagus), and more.