Introduction: Casting Rings - From Startup to Finish
Second Prize in the
3D Design Contest
Who has the budget for a customized, unique engagement ring? I certainly don't, especially being a college student. Heck, I had no idea how rings were even made. It wasn't until a friend of mine told me about how he designed his own engagement ring for his wife. This really intrigued me and so I started doing some research on how this process is done. Pretty soon I discovered how relatively easy it is to make your own ring (or any other small metal part) using materials from the hardware store, jewelry supply shops, and a few online vendors. So here I've put together a comprehensive step-by-step Instructable on how to put together all the tools necessary (and quite inexpensively) for casting rings.
I am not a professional jeweler, nor am I going to school to be one. I am a mechanical engineering student, which gives me many benefits and insights into building the tools necessary to make successful castings; however, no part of this process requires you to have an engineering degree, or any prior knowledge in making jewelry.
A FEW WORDS OF CAUTION:
1) SAFETY FIRST! There are a few steps involved in this project that can be dangerous, so use caution and common sense! I assume no responsibility for anyone injured by following my Instructable.
2) The material cost of all parts and consumables used in this project will be approximately the same as a decent engagement ring. However, you will then have all the tools needed to make more rings - so in the long run you will be ahead!
3) As I said, I am not a jeweler. I have not had training or much experience with jewelry making until beginning this project. There are many ways to go about making jewelry that I do not discuss in this Instructable. If you know of a better way to do something, feel free to deviate and experiment (but make sure to let me know how it works!).
Step 1: Some Background and Overview
The method that I have used is called the Lost Wax Investment Casting process and is probably the most common way that professional jewelry is made today. This process has 5 basic steps that are followed:
- Create a version of the part using a melting/burning material (such as wax or certain plastics).
- Place the part into a heat-resistant cementing material using sprue channels.
- Heat up the cemented mold such that the part melts/burns out through the sprue channel.
- Melt down the metal to be used and force the molten metal into the mold through the sprue opening.
- Cool the part down and clean as appropriate.
There are different ways and materials that can be used to perform each step; I will only be showing what is called the Centrifugal method (another popular method is the Vacuum method). This involves using a centrifuge to force the molten metal into the mold via centrifugal/centripetal (lets just call it centrifᵫtal to make everyone happy) forces.
Step 2: Making the Kiln, Part 1: Gathering Materials
The kiln that I built is based off of another Instructable by Wolfgar77. However, my kiln has a PID temperature controller which is used to regulate the temperature, allowing me to walk away and do other things while it is running.
- Soft fire bricks, 9"x4.5"x3", 2600 degrees C (K26) (x7)
- NOTE: these will make a chamber that has a cavity of 3"x4.5"x6". These dimensions can be adjusted to your needs by either slicing the bricks or by finding other sized bricks. Adjust the steps accordingly.
- Angle iron (~10 ft.)
- 5/16 coarse threaded rods (~12 ft.)
- 5/16 coarse nuts (x18)
- PID temperature controller
- Type K thermocouple
- Kanthal A1 heating coil (> 15" long)
- Zinc plated or Aluminum sheet (x2, at least 9"x9" each)
- Steel coat hanger
- Steel "staples" or paperclips
- Kaowool ceramic fire wool (1" thick, 6"x6", optional)
- Small hinge (x2, optional)
- Screws (optional)
- Small deadbolt (optional)
Variable speed controller (optional)
- A band saw, skill saw, miter saw, hack saw, etc. (whatever you have lying around)
- Wire cutters
- Wire strippers
- Hand router (a knife will work too, though a little messy)
- Tin snips
- Face mask
Step 3: Making the Kiln, Part 2: Heating Chamber
Steps to making the heating chamber:
- Take one of the fire bricks and cut it in 1/3. This will be used for the back. Caution: I am unsure about the health effects of breathing in particulates from these bricks. I know that they are asbestos free, but I would strongly recommend using a breath mask when cutting them.
- Take the Kanthal heating element and stretch it slightly so that the coils are not touching each other (see image). For a kiln of this size, you will want approximately 720 watt heater. To figure out the amount of coil needed, use Ohm's law for power: P = V*I = V^2/R, thus R = V^2/P. Since V = 120V (from a standard outlet) and P = 750W, R should be around 20 ohms. As a check, make sure that the current doesn't exceed the wall outlet's maximum (typically 10 amps). So, using Ohm's law again: V = I*R, thus I = V/R = 120/20 = 6 amps. This is perfectly fine.
- Take a multimeter and check the resistance from one end of the wire until you read just above 20 ohms. Cut the coil at this spot.
- Take the coat hanger and cut 2 sections that are about as long as the thickness of the back of the kiln. Take the rods and rap one in each end of the coil so that they are tight - these will be used to prevent the coil from overheating and breaking near the tips.
- Lay out the firebricks that make up the 2 sides and the back of the kiln. Take pieces of string and lie them down on the bricks in the approximate pattern that you want the heating coils to make. Be sure to include a groove in the sides that allow the coils to pop out the back. Pencil in the outline on the bricks and then use the router with a 1/4" bit (or just using a knife), cut out a groove following those lines to a depth of 1/4".
- Take the string that you used and lie them end on end. Stretch the heating coil so that it is about an inch longer than the total length of the string.
- Cut the angle iron into 4 sections 14" long and 2 sections 9" long. Also, cut the threaded rods into 8 10" long sections.
- Set the long angle iron on end to make 4 corners, then insert the 4 threaded rods apply nuts to hold the base together. Also, set the smaller angle iron pieces on opposite ends to make a base for setting the firebricks.
- Start placing the firebricks onto the stand. Put in the heating coil into the grooves.
- Take some steel paperclips and cut them in 2 so that they make 2 "U" shaped pins each. Use these to pin the heating element in place.
- Place the top firebricks on and insert the final 4 rods into the angle iron, nutting them in place.
- Take a 9"x9" piece of sheet metal and cut out the 1.5"x1.5" corners. Draw lines at 1/2" and 1" from the edges on the tabs (see images) - these will be your bending points.
- Bend along the lines with your fingers and a table edge until you have 2x 90degree bends on each side. Snip off a little bit if necessary to allow the edges to mesh better.
- Figure out the alignment of the door with respect to the kiln; make marks on the metal leg and on the door where the hinge screws should go. Remove the leg and drill holes at those points.
- Screw the hinges in using long wood screws for the kiln side, and use nuts and bolts to hold in the door side.
- Take the 1" thick, 6"x6" piece of Kaowool and insert it inside the door
- If you are making the bolt lock, then go ahead and screw it into the fire brick in the desired location. Then, drill a hole in the door where the bolt will go, making sure to keep it a tight fit.
Step 4: Making the Kiln, Part 3: Electronic Control
At this point, you will be working with wall voltages and decent currents, so make sure you consult someone with enough electronics know-how to be safe. For the most part, you will need to consult the electrical schematic for all the wiring steps. I've included a few pictures of the circuit that I made.
- Drill a hole in the back of the kiln just large enough to fit the thermocouple - angle it slightly downward and located near the top of the kiln. Slide the thermocouple in and check that it protrudes enough inside the kiln.
- Take the other piece of sheet metal and fold it as shown in the image above. You want the flat parts to be just wide enough to fit the PID controller when fully bent in place. Only bend half way at this point.
- At the flat section that will become the bottom, screw in the Solid State Relay. Make sure the the "+" & "-" terminals and not the "~" terminals are facing toward the location that the PID controller will be.
- Use the wire strippers and cut the power cord receptor end off. Cut off an additional 15" of the cord and completely strip this section. Strip only the end of the remaining cord.
- Using the schematic above, wire up all the wires. I found that the Green, White, and Black wires corresponded to "Ground", "Hot" and "Neutral" respectively on the prongs.
- Connect the thermocouple. At this point fold the sheet metal all the way to make a shell for the electronics and a fin that attaches to the kiln.
- After drilling holes into the sheet, mount it onto 2 of the protruding threaded rods on the kiln body. Fasten with additional nuts.
- Caution: Before testing the kiln, use a multimeter to check for any short circuits on the kiln.
- Plug in and test the temperature settings.
If there is no door on the kiln, a small block of fire brick can be used to block the chamber. Make sure to test the maximum temperature you are using before leaving to do other things. My kiln can easily get over 800 degrees Celsius!
Step 5: Making the Vacuum Chamber
- 1/64th" thick steel plate, 8"x8"
- Rubbergasket, 6"x6"
- 1/2" thick block of wood, 8"x8"
- 1/4" ID plastic tubing
- 1/4" male NPT to 1/4" MIP 90 degree elbow
- 1/4" FIP to 1/4" OD barb
- 3/8" MIP to 1/4" OD barb
- Vacuum pump (cheaper substitute: hydro aspirator)
- Rubber cement
- Hose clamps (x2)
- Screws (x4)
- Glass bell-jar (a sturdy Tupperware container could work too)
- Gas sealant
- Saw, skill saw, band saw, etc (whatever you have lying around)
- Drill, drill bits, and screw driver
- Caulk gun
- Drill a hole about 1.5" from one edge of the steel plate large enough to be able to thread the elbow joint into.
- Thread the 90 degree elbow into the hole, using the National Pipe Thread (NPT) side until it protrudes less than the thickness of the wooden board. Attach the female barb to the other end.
- Caulk around the hole with the gas sealant. Rub with finger or object to get into the crevasses.
- Cut a rectangular notch into the wood to accept the barbed part. Set the plate onto the wood as shown.
- Cut a hole into the rubber gasket so that it lines up with the protruding threaded pipe on the top of the plate. Take rubber cement and apply it to the rubber gasket and then press the gasket onto the steel plate (keep pressure on it until it dries; it will want to curl). CAUTION: Rubber cement produces fumes that are not good to inhale - use proper ventilation when using it.
- Attach the MIP barb to the vacuum pump (or use a hydro aspirator) and then attach the plastic tubing to the barb on both the pump/aspirator and use the hose clamps to tighten the seal.
- Wet the edge of the bell-jar and set it onto the rubber gasket. Turn on the pump (or the water spigot for the hydro aspirator) and admire your new vacuum chamber! This chamber gets around 25 in Hg of vacuum depending on how well it is sealed.
Step 6: Creating Your Ring - 3D Print or Hand Carve?
There are really 2 different ways that you can make rings for casting:
- Wax working - The process of taking a wax blank and subtracting and/or adding wax to make the shape of the ring by hand. This is the traditional way and takes many years of experience to perfect.
- 3D Printing - With the revolution of the 3D printer, printing a ring is a great way to integrate complex geometries without too much effort or skill, as long as you are somewhat familiar with CAD (Computer Aided Design) software.
Because I am a mechanical engineering student and have access to both quality CAD software and 3D printers, and because I really suck at hand carving geometries more complicated than a simple band, I chose to go the second route. For those who are not engineers and are familiar with CAD, DON'T STRESS! You can still go this route if you are willing to spend a little time learning a new program. Also, with the rise of online 3D printing vendors, you just have to send them a digital file and they will send you a completed part.
For a CAD program, I ended up using Creo (formerly known as Pro/ENGINEER). Solidworks is another high-end program. If you are really into making rings with CAD, I've heard that Rhino has an add-on specifically for jewelers. If you are looking for some free software, try either DesignSpark Mechanical, Google SketchUp, or FreeCAD.
I had school access to a Stratasys Objet260 Connex (think big, expensive, high resolution printer). The resolution on this sucker is plenty for making nice, smooth geometries. However, because the resin used in this printer is not designed to be able to cleanly "burn-out" (more about this process later), this is not the ideal way to make a plastic ring. A great printer to get fantastic resolution AND compatible resin would be the Formlabs Form 1+ printer. This printer eliminates a difficult step in the casting process, making things much more streamlined. Plus, it is within the price range of hobbyists!
Designing and creating a ring is not what this Instructables is about (you can find plenty of resources online for help with this) so I've thrown a few images of how I've made some rings just to give an idea of the process.
Step 7: Optional Rubber Mold and Wax Injection (for Saving Your Design)
This is an optional step that can be done to save and assembly-line the process of making multiple copies. The reason why I used this step in my process was because I did not have easy access to a lost wax-compatible printer; all the rings I printed were of a material that had dirty burn-outs and didn't turn out so well. By converting to wax, I could get cleaner burn-outs. The ideal fix for me would be to get a 3D printer (like the Form 1+) which has compatible resin thus saving me from needing to do this step which is difficult for complex parts.
For traditional carvings, this is a pretty useful step since it helps to save your design in case you mess up later with the casting.
- 2-part liquid silicone (I found that Castaldo LiquiFast ICE worked well)
- Aluminum bar (for the frame)
- Acrylic (or metal, plastic) sheet (x2)
- Heat source (ie: propane torch)
- Metal air piston (for injector)
- Barb attachment for injector (1/4" MIP)
- Metal funnel
- Container (for mixing and vacuuming)
- Piece of rubber (such as from an eraser)
- Baby powder
- Lamp/light source
- Table vice
- Vacuum chamber
- Metal bender or vice
- Metal bottle opener
- Using a metal bender or vice, take the aluminum bar and bend 2x 90 degree bends in it so that it forms a flattened "U" shape approximately wide and tall enough to fit the ring and sprue with some space (don't make it too tall or wide so that you don't waste a lot of liquid silicone). Glue a small block of rubber to the bottom inside of the bar.
- Take the ring and add a sprue in an acceptable location on the ring. Attach the other side of the sprue to the top of the rubber such that the sprue is vertical.
- Clamp the 2 sheets of acrylic to the open sides of the metal U using the C-clamp.
- Using the 2-part liquid silicone, mix equal parts into the mixing container (measure out the amount that you need to properly cover the ring but not so much that you will waste). There is about a 15 minute working time - I spent about 7 minutes stirring and 6 minutes getting the air bubbles out with the vacuum chamber. The rest of the time is needed to pour the liquid silicone into the mold casing. Do this by letting it run down the side of the container and not onto the ring. It may take a little while because of the viscosity of the silicone.
- Allow to sit for a few hours until it is properly cured. At that point you can remove it from the mold case.
- Clamp the metal bottle opener to a table so that it can be used as a 3rd hand for prying the mold open. With plenty of light, take the scalpel and start opening the mold by cutting around the edge in a way that will allow you to pull out the ring without damaging either the ring or the mold. There are a few online videos that show the basic process of opening the silicone mold.
Once the ring has been removed, setup the injection system. There are commercial versions of wax injectors that run hundreds of dollars, and other ways of making decent injection systems. However, I wanted to be minimalistic here, so I simply took an air cylinder from my local surplus store and used it as an injector:
- Invert the air piston onto the vice. With the barbed tip removed, place the metal funnel with scrap wax over the injection hole. Heat up the funnel and piston so that the wax melts and flows into the piston. Caution: This type of wax is not good for you to breath in - well ventilate the area and use a mask.
- While heating the piston, screw on the the barbed tip. This will act as the injector nozzle.
- Use a very small amount of baby powder on the inside surfaces of the rubber mold. This will help remove the wax part.
- Once the wax inside the piston is warm enough to flow easily, take the 2 sheets of acrylic that you used earlier and place the closed mold in between them. Using your fingers to keep the mold together, place the hole over the injector nozzle. With a fair amount of force, push the piston so that the wax flows into the mold. Do this for about 4 seconds. Then allow the mold to cool for about 30 seconds.
- Remove the wax part carefully and check for defects. Inject again if necessary.
Step 8: Investing Your Ring
Now it is time to begin turning your wax ring into metal! What you will need:
- Flame/heat source (such as an alcohol lamp)
- Flask (I use a 2.5" diameter steel flask)
- Rubber sprue bottom (sized to flask)
- Fine metal tool
- Dish soap (for debubbleizer)
- Hydrogen Peroxide (for debubbleizer)
- Cotton Swab
- Investment compound
- Gas mask
- Measuring cup
- Vacuum chamber
- Mixing cup
- Attach a small sprue to your ring. Do this by taking a small rod of wax and fusing it onto the ring in a non-critical location. Use multiple sprues if necessary for larger and more complex parts.
- Measure the mass of the wax and sprue. Record this number down somewhere for future reference. You will need to measure out your metal based on this quantity.
- Affix the sprue and ring to the rubber sprue base. Keep the sprue as straight up and down as possible.
- Using a 50/50 mixture of Hydrogen Peroxide and Dish soap, apply generously to the wax ring (cotton swab is useful here). Allow to dry for about 10 minutes. This is the "debubbleizer" which prevents air bubbles from forming in the investment compound and ruining the part. After it drys, dunk in water to remove excess residue and to check for any bubble formation. Repeat as necessary until bubbles no longer form on part.
- Attach the sprue base to the flask. Apply a ring of tape to the top edge of the flask to prevent spilling.
- Using a measuring cup, measure out the amount of water you will need for mixing with the investment. Do this based on the manufacturer specifications of the powder you use. For my powder and flask size, I needed 100 ml of water with 150 g of investment. Keep a little bit of water on the side for fine tuning the mixture.
- Put on your mask! At this point you will be working with investment, which contains silica. You REALLY don't want to breath this in (it would be like sanding down your lungs and destroying them over time!).
- Using a balance, measure out the amount of investment you need into the mixing cup.
- Add the water to the investment and start the timer. There is an 8 minute working window - don't go over. Here is the suggested process for the powder I use:
- 3.5 minutes mixing by hand in the cup. You want the mixture to be thin enough to be able to pour into the flask and surround the details of the ring, but not too thin. Fine-tune by adding bits of water or investment.
- 1.5 minutes degassing the investment (in the cup) under vacuum. This will help remove air trapped in the investment. Shaking/vibrating the chamber a little can be done to improve results.
- Pour the investment into the flask, running it down the inside and not over the ring (you don't want to knock it out of alignment).
- Remaining time is used degassing the investment (in the flask) under vacuum. Shaking/vibrating the chamber a little can improve results.
- At the 8 minute mark, put the flask in a convenient location to sit for 2 hours and harden.
Step 9: Casting of the Ring
- Centrifugal caster
- Centrifuge crucible
- Slab of wood
- Large cardboard box
- Dual-gas torch - combines oxygen and MAP/propane
- Oxygen canister
- MAP/propane canister
- Carbon rod
- Metal to cast (Zinc, Silver, Gold, etc)
- Bucket of water
- Fire resistant gloves
- Drill with screwdriver
- Cinder blocks (optional)
- Safety glasses
- To prepare the centrifuge and keep it safe to use, take the wood sheet and screw the centrifuge to the center. Use the cardboard box to create a barrier around the centrifuge to block any flying objects from escaping without impeding the centrifuge motion (the more enclosed it is, the safer). Affix with glue/caulk.
- Measure out the amount of metal you need. For converting from wax, take the mass of the wax and multiply by ratio of densities between the wax and the metal (for Sterling, the ratio is about 10.4) then add a little extra to make sure there is enough (some might fly off, not go into the mold, burn off, etc).
- Balance the centrifuge out with the metal and flask (without rubber base) in place. This will help prevent molten metal from flying everywhere (as I incidentally found out) and give a better cast.
- Take the flask and place it into the kiln so that the hole is facing down. Turn on the kiln and begin the burnout process. Based on my experience, the investment I use, and the suggestions by bcyrjewelry, this is what I do:
- 1 hour at 150 degrees C
- 1 hour at 370 degrees C
- 2 hours at 700 degrees C
- 1 hour at casting temp (550 degrees C for Sterling)
- Wind up the centrifuge to its maximum number of turns. Use the locking mechanism (mine had a pin) to keep it wound.
- Start heating up the centrifuge crucible without any metal inside - this will help significantly with melting. Caution: Oxygen + Propane flame is HOT! Using MAP + Oxygen is REALLY HOT! Use common sense and get help if needed when using the torch. Be safe (tip: never start the flame with the oxygen on). You want a relatively "reducing" flame (one that is oxygen deficient) when working.
- Once the crucible is warmed up, add your metal. Heat up until the metal starts to glow red (such as for Sterling) then add a small pinch of borax powder. This will help prevent too much oxidation of the metal. Keep heating the metal and stir with the carbon rod to distribute heat. Note: for Sterling, any green flame is Copper being burned away - try to avoid too much of this.
- Hopefully the kiln is near by and you can quickly grab the flask and put it into the centrifuge while still heating up the metal. Use help if needed.
- Once the metal melts down, keep heating for about 30 more seconds. Then, release the mechanism and let it spin! Caution: Be safe at this point - expect metal to fly off, so wear safety glasses and make sure your barrier is in place to stop flying objects.
- Allow the centrifuge to slow down to a relative stop. Pull out the flask without inverting it. Let it cool until you can no longer see any red glow from the protruding metal, then take the flask and dunk it in the bucket of water, shaking back and forth. The ring will fall out to the bottom. Once cooled, go ahead and pick out the ring and flask and clean them off. A dark grey oxidation layer is common and can be removed easily in the next section.
What this does is both allow the wax to "burn-out"/melt-out of the flask and also heat treats the investment so that it is much stronger. Once you are about ready to pull it out of the kiln, begin setting up the centrifuge.
Step 10: Cleaning and Finishing
- Mini Crock-Pot
- Ultrasonic cleaner
- Plastic fork
- Small metal pick
- Mini grinder with flex shaft
- Disk cutter for flex shaft
- Buffing compound
- Buffing wheel/brushes for grinder and flex shaft
- Tumbler (optional)
- Dish soap (optional)
- Burnishing compound (optional)
- Metal shot (optional)
The first thing you need to do after casting is to clean off the excess investment from the ring. Start by using a small pick to get chunks out. Then, run the ring through an ultrasonic cleaner to get the finer chunks removed. After that, take the Crock-Pot and heat up some water, adding a small amount of Sparex. Don't touch the sparex or solution with your bare hands. This creates a "pickling" solution which helps to remove oxidation from the surface of the ring. Allow the ring to sit in the solution for a couple hours to remove any final oxidation. When you pull it out, use a plastic (not metal) fork. At this point you should have a white coating over the ring that can be removed by using a coarse brush attachment on the mini grinder. Once you get all the white compound off you can begin to use the buffing compounds and buffing wheels to polish the metal to the desired luster.
As an optional step the rings can be burnished (a type of polishing) using either a homemade tumbler, or one that was purchased. The burnishing process is performed by pieces of metal shot rolling over the piece of jewelry and therefore both work hardening and removing many of the minor defects.
- Fill the container with shot until the bottom is just covered.
- Fill the container with water until the shot is just covered.
- Add either a pinch of burnishing compound or a single drop of dish soap.
- Place the rings in the container and close it up.
- Run for somewhere between 2 hours and overnight (depending on how much is needed) making sure to replace the water every 2 hours
Do any final polishing at this point.
For the engagement ring I made, I ended up going to a professional jeweler and having them set the amethysts and diamond - I didn't feel comfortable with my skill level making sure the diamond didn't fall out. However, for less expensive stones, I could certainly set them myself. This is a whole art in of itself.
Step 11: Tips and Tricks
- Clean and dry the flask right away after quenching - it will be easier and you will prevent rust from forming
- Balance the centrifuge before putting the flask in the oven. Use the metal that you will be melting down as well.
- Oxygen tanks will run out quickly (around 20 minutes of use) - keep a few stockpiled
- Start off using Zinc - it is much cheaper and easier to melt than silver. Zinc is the primary metal in newer pennies
- Only add a little bit of Sparex to the hot water for pickling (not the whole container)
- Make thicker and longer stone setting prongs than what you think you need - they can always be cut down and filed
Things I would do different/add:
- Add a handle to the kiln door that won't be hot to the touch
- Make the safety shield around the centrifuge a little taller
- Add a relief valve to the vacuum pump to quickly remove the lid
- Use a 3D printer with compatible resin for lost wax casting - this removes the need to convert to wax and the risk of dirty casting
- Purchase a better quality torch
- Instead of using a centrifuge, you could make a sling that you place the flask in and attach it to a long piece of string/cable. Melt down the metal over the hole of the flask and then swing the flask around really fast to get the centrifugal force
- I've occasionally cut the kiln time from 5 hours to 3.5 hours total and had some decent castings
- Use Zinc instead of Silver or Gold
- For the Tumbler, you can take a plastic bottle, cut a hole in the bottom, glue a screw through it, and attach it to a drill in a vice to get the tumbling motion.
- You can use propane instead of MAP - lasts, like, forever, but doesn't burn as hot
Let me know if you have any suggestions, tips, questions, answers, or if you made any rings yourself. Good luck!
Oh, and she said YES!!!
We have a be nice policy.
Please be positive and constructive.