Lost Wax Casting

Lost Wax Casting SBU

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LOST WAX CASTING SBU

The Fine Print Copyright ｩ 2005 – 2010 TechShop, Inc. and/or TechShop RDU, LLC. All rights reserved This manual is furnished under license and may be used or copied only in accordance with the terms of such license. The content of this manual is furnished for informational use only, is subject to change without notice, and should not be construed as a commitment by TechShop RDU, LLC. Except as permitted by such license, no part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, recording, or otherwise, without the prior written permission of TechShop LLC.

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These class materials are the copyrighted property of TechShop, Inc. and/or TechShop RDU, LLC and are intended for use in an instructional setting. Successful completion of SBU’s are REQUIRED for many of the products at TechShop, an instructor must sign off on this requirement. It is NOT enough to just read and follow these materials.

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Course Synopsis In this Safety and Basic Use class (SBU), you will learn how to create a metal object using the Lost Wax Casting method. Starting with a wax model, you will be taken through the steps required to duplicate the wax in alloy similar to silver. You will become familiar with the basic operations required to create a lost wax casting; how a wax is made, attaching the wax to a tree, setting up the flask, mixing, pouring and vacuuming the investment, the burnout cycle and finally, melting the metal with oxy/acetylene and completing the pour. The class project will be two or three charms or objects. Time Required: 5 Hours over two consecutive days

Casting at TechShop After this class you are welcome to set up and use the casting equipment at any time you wish. However, it is strongly suggested to cast with a partner, most importantly during the pour, one person does the melt and the other handles the flask. Given the amount of setup involved, proper timing and planning is necessary to accomplish an investment and burnout cycle and that you will be ready to pour the following day within a few hours of the furnace reaching the hold temperature status.

General Safety 1.Eye protection is required when working with all machinery and in the shop area. 2. Closed-toe leather shoes must be worn at all times. 3. Long hair or beards must be protected with a hair net/cap. 4. Long sleeved shirts must be worn when working with chemicals or molten metal. 5. Never leave a machine running or unattended. 6. Never make assumptions about the equipment. Inspect it carefully before use. 7. Know where safety equipment is located such as fire extinguishers, eye washers, first aid kits and the burn kit.

Casting Safety This list discusses some general safety concerns. Much of casting safety is about using correct technique and wearing properly fitting safety gear. The areas where safety is most crucial are mixing the investment, anything to do with the furnace and melting and pouring the metal.

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1. Casting is a two-person operation. We strongly suggest to never cast alone. 2. When investment is being used everyone in the area needs to wear a high quality dust mask. This includes the measuring, mixing, cleanup and breakout of the flask, as well as cleaning up the casting afterwards. 3. Always clean the investment tools and area using a h20 spray bottle, this will keep any potential dust down. 4. Molten metal can cause a steam explosion when combined with water, This is a significant hazard on its own, and can send droplets of hot metal flying. 5. Ensure you have a dry, non-flammable surface to work over. Dry sand is recommended during the melt. 7. Make sure all tools are completely dry before using them. 8. Make sure all metal is dry before adding it to the crucible 9. Small fires caused by spilled metal and hot tools are a common occurrence when casting. Don't panic, and extinguish them promptly when it is safe to do so. You may want to finish pouring your part and then put out the fire: this is fine, for small fires and minor spills, as long as nothing is threatening you or other people. Burn marks on the equipment are normal. The ONLY APPROPRIATE FIRE-EXTINGUISHING MEDIA FOR CASTING FIRES IS DRY SAND. Avoid pressurized fire extinguishers, water or other liquids. They can turn small problems into bigger ones. When working with the furnace make sure you have insulated gloves to protect from the intense heat. Make sure your tongs are in good working order and that you have a good grip on the flask before removing it from the furnace and placing it on the vacuum table. Remember that hot metal looks a lot like cold metal. Set hot tools on dry sand, a metal stand or table of fire bricks. Always set them down with the hot end away from you. When cleaning up finished parts use appropriate safety precautions. When sanding or polishing the surface and silica investment is still there is can be made airborne and inhaled as a fine particulate dust. This can cause silicosis, a chronic lung condition, especially with long-term exposure. Always where a high quality dust mask(and make sure anyone nearby does as well)

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Shop Etiquette Never talk to anyone while they are working on a piece of equipment unless the communication is in regards to the work you are doing together ie: (letting the casting partner know the metal is ready to be poured). Specifically avoid startling anyone while they are on the equipment. Leave the area you are working in cleaner than when you arrived Report broken tools to TechShop staff, so they can be replaced promptly. No broadcast devices such at radio, tv, Ipods, etc. Begin final clean-up and store your project 15 minutes before closing

The casting operation The lost wax casting concept is as follows: A wax model is created, either by filling a mold, carving the wax directly, constructing with wax wire and so on. Once the wax (or waxes, as a single flask can hold numerous individual waxes) is ready, it is “treed” up by attaching its sprue to the main sprue or trunk. When the tree is finished it is set in a rubber flask base. The stainless steel flask is set into the base. The next step is mixing the investment slurry, a silica based plaster like material, in a rubber bowl. Exactly measured investment powder is mixed with water using a hand mixer. It is vacuumed and vibrated to remove any air bubbles. It is then poured into the flask and vacuumed and vibrated again, then it is set to rest and allowed to gloss off and harden. Once hardened the rubber base is removed. The furnace cycle is chosen, and the flasks are set inside. During the cycle the wax will melt out and evaporate (or it can be poured off) and over the next 8-12 hours the investment is cured and brought to casting temperature. Finally the metal is melted with an oxy/acetylene torch using boric acid as a flux. When it is brought to the correct temperature and fluidity the flask is removed from the furnace, turned over to reveal the opening and set on the vacuum plate, the machine is turned on and the pour begins. The vacuum is left on until the metal starts to skin over, then it is released. After the metal solidifies completely the flask is removed from the vacuum machine and set on a firebrick to cool. After about five to ten minutes depending on flask size, the flask is lowered with a pair of tongs sideways into a 5 gallon bucket of water. The investment will bubble and pour out the sides and steam will rise. Eventually the flask will be let to sit in the water and cool. With the tongs gently removed the button and tree from the water.

Tools Required: Vacuum casting machine and accessories including bell jar, metal disks and silicone ring/sheet Alcohol lamp or wax pen

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Casting flasks 21/2” x 21/2” Casting bases – 2 1/2” Flask tongs Investment Scale and scoop Calculator Crucible and tongs Burnout oven programmable Ney Vulcan Rubber mixing bowl -1-1/2 quarts and Spatula Hand mixer Measuring beaker 250ml Sprue cutter Oxygen/Acetylene torch with melting tip Firebrick Carbon stir rod Heavy welding gloves Leather welding apron Face shield and #5 shade / safety glasses Leather closed toe shoes 5 Gallon bucket Used toothbrush Materials Required: 1 oz of “silver mine or alpacca alloy” casting grain 1 or 2 waxes and 1 piece 1/4”x 3” sprue wax #5 shade/safety glasses and safety shield Dust mask Investment for the flask (Kerr satin cast 20) Masking tape Boric acid Steno note pad Casting worksheet rubber gloves

Equipment Specific Safety Oxygen and Acetylene rigs pose the risk of fire, explosion and serious injury or death unless used correctly. Please follow ALL procedures strictly to ensure safety. BE SURE to check all connectors on the whole welding rig to avoid leaks and potential fire or explosion. If you suspect a leak, close the tank valve and notify TechShop staff immediately. NEVER USE OIL, GREASE, SOLVENTS, OR CLEANING PRODUCTS of any kind, on any part - of the OXY-ACETYLENE RIG.

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Gas Cylinders Compressed gases are under high pressure. Tanks should be kept upright and strapped or chained, and bottles should be capped or attached to a regulator. If you find any tanks in an un-secure condition, please notify TechShop staff immediately. COMPRESSED GAS CYLINDERS CAN CAUSE SEVERE PROPERTY DAMAGE, INJURY AND DEATH. STRICT SAFETY PROCEDURES MUST BE FOLLOWED. Only TechShop staff should move or change tanks. Notify TechShop staff if a tank is empty. Keep all sparks, heat, electricity and heavy activity away from tanks. Oxygen is under extremely high pressure in the tank, and can cause other materials to spontaneously combust and explode. Always make sure the tank is handled gently and is in a secure position. Acetylene, while not under high pressure, is very unstable and prone to explosion. It should never reach over 15 p.s.i. Hose pressure. Always make sure the tank valves are closed when not in use. Always wear shade safety glasses when melting the metal to avoid damaging your eyes.

Using Bell Jars Safely For an optimum seal keep the bell jar rim and vacuum table clean of investment debris; never use a chipped or damage bell jar, it could implode. Never press or hit the jar during vacuum. It's under tremendous pressure and can implode. This could result in serious injury from flying debris.

Vacuum Casting Machine The vacuum machine is a dual use machine for vacuuming air out of the investment during mixing, after the investment is poured into the flask and again the flask is vacuumed during the metal pour to help pull the metal into all the fine detailed areas. The machine we will be using has a vibrating table for vacuuming the investment both in its rubber bowl and the flask filled with investment. The vibrating table helps agitate the investment to remove air bubbles. To facilitate the vacuum the work is done under a bell jar. The other side of the machine has a spot to drop perforated flasks in or adapter plates for solid flasks to sit on to be vacuumed during the pour. There is a silicone ring and a silicon sheet with a hole in it for the flasks to sit on to help create the vacuum.

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Before turning the machine on make sure it is level, all the surfaces are clean to create a proper seal and look through the site window on the side of the machine to check the oil level. Low oil will cause damage to the pump unit.

Caution before mixing investment Always test the vacuum seal between the jar and pad before mixing investment. To test the vacuum seal, moisten the underside of the bell jar rim with a clean sponge. Place the bell jar over the vacuum table and rubber vacuum pad. If needed, apply slight pressure around the rim of the jar. Never apply pressure to the top of the bell jar. NEVER push down on the top of the bell jar during vacuuming. This can cause the bell jar to break and implode. To operate the machine for investment vacuuming in either the bowl or solid flask first make sure the vacuum pad is in place on the vibrator table, then set your bowl or flask on the table. Position the bell jar squarely over the bowl or flask taking care to follow the same instructions as above with regards to the care and handling of the bell jar. Such as TO NEVER PRESS DOWN ON THE TOP OF THE BELL JAR. If necessary to make a good seal you can press down lightly on the rim ONLY. Then turn the handle to the investment position and turn on the machine. Vacuum investment until proper vacuum is achieved (investment slurry should bubble, rise & fall during this step). This operation should take about 90 seconds. To release vacuum, move the toggle switch to the cast position, then turn the power off. PLEASE NOTE: The vacuum gauge should indicate full vacuum in usually less than a minute. Investment in the bowl will crest at this time and begin to release air bubbles.The precise mercury reading stating full vacuum depends on your altitude. At sea level, full vacuum is reached at 29" of mercury. The gauge registers approximately .9" less mercury for each 1000 feet of altitude. Vacuum casting machine

Equipment Controls The primary controls you will use on the Vacuum Casting Machine are the handle that dictates whether you are at the vacuum table, vacuum release or casting chamber. Also there is an on/off button which is only used when the vacuum is fully released.

PROJECT DESCRIPTION Copyright ｩ 2005 – 2010 TechShop Inc. All rights reserved

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For this class, you will be given 2 waxes, a 3” piece of tree wax and 1 troy ounce of silver mine casting grain (an alloy that looks and works just like silver but costs a fraction of the price, it is usually used for sample lines in commercial mfg) . First you will tree up the waxes then mix the investment slurry to fill your flask. Next you will vacuum the flask to remove any air. Finally on the first day we will program the furnace for the burnout cycle. In our second session you will melt the metal, pour the metal into the flask and finally you will breakout the flask and retrieve your cast object from the water bucket.

Getting Started What is casting? Casting is the method of creating an object by pouring a liquid material, that later will harden, usually metal, , into a cavity or mold. There are many ways of creating the negative space for the metal to fill. Primitive castings were made in chiseled rocks. Sand casting has also been done for millennia. Low temperature metals can be cast in steel molds or heat resistant rubbers. Cuttlebone, and even carved charcoal blocks can be used. The most popular form is lost wax casting. A wax model is set inside a flask and a special plaster is poured around it. Once hardened, the flask is placed inside a furnace to melt the wax and harden the plaster. The melted wax leaves an exact hollow of the original. Metal is heated to liquid stage and poured into the flask with the help of the vacuum to pull metal into every little space.

Working with wax. For this class we will start with a pre-made wax. These waxes were made with a wax injector, a pressurized tank that is heated to liquify the wax, the mold is pressed against the nozzle and filled with hot wax. There are many types of wax, each specialized for a specific task. The properties determine the waxes use, flexibility and hardness, opacity (good for checking for flaws) melting and injecting temperature(lower injectable temp = less shrinkage), carving, modeling and specialty waxes like sprue, sticky, transparent , wire and sheet types. The first thing we do with our waxes is make sure there are no problems with them such as pinholes, dents, hollows, etc. Then clean off the mold marks with a file, razor, etc and fix any problems we see at this point. This can be done with a tool heated over an alcohol lamp or with an electric wax pen. When we are satisfied with the quality of the wax then we attach it by its' sprue to a thicker wax rod called a tree. Using a heated tool we place the sprue at the point where we want it to sit on the tree, then melt the two waxes together. The tree is a wax column that allows for the wax to exit the investment and the metal to enter, it is thick enough to be a feed source of liquid metal for the pieces we are casting.

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1. It is important that the wax is placed facing at an upward angle on the tree (facing away from the base). They need to be “downstream” from the sprue button and important that there are no “uphill” flows required. A part that is “uphill” would require a second or third sprue to feed that spot. When the metal is poured the flask is upside down, so the metal will flow with gravity into the spaced made by the wax. The connection of the wax sprue to the tree needs to have a smooth transition to avoid causing turbulence in the metal flow. A way to think about this is imagine filling the flask with water (once the wax is melted out) are there any places where a bubble would form? Once the tree is secure in the flask take apiece of 1” masking tape and wrap it around the top of the flask twice. Casting waxes

Weighing the sprue and the tree. Once all the waxes are attached to the tree, the entire wax construction needs to be weighed to compute how much metal is required for the pour. The scale must have troy ounces or grams. Be sure to record this information for later. I.e Flask A sprue construction = 12 grams. To determine how much metal is needed for the cast multiply the weight of the wax construction( your wax on the tree) by the specific gravity of the metal you are casting with. Sterling silver has a 10.40 specific gravity so if your waxes weighed 1 gram you would need 10.4 grams to make up the waxes and another 20-25% for the button metal. The button is thick and stays fluid longer than the patterns, this metal feeds the pieces as they cool and keeps downward pressure on them. If the sprue and button are too thin when the metal cools and shrinks they will actually pull metal from the object. This will result in porous castings. Now that the wax is weighed, the tree is inserted into the rubber base. Alternatively there are bases that do not use “tree sprues” but have a large hole that is filled with modeling clay. The individual wax sprues are set into the clay. When cast the large button formed by the clay space feeds the pieces the same way the tree and button does.

Rubber base

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The Investment Procedure After the waxes are in the base, the stainless steel flask is set in. Next measure and mix the investment slurry. A dust mask must be worn to avoid inhaling investment which is silica based. Investment is a plaster used to fill the flask and surround the waxes. There are specialized investments for type of metal, temperatures and stone in casting. The first step is calculation. The investment manufacturer has suggested ratios for standard flask sizes. It is important to keep notes on every cast in case something goes wrong, you can see what was done. It also allows one to accommodate for different casting situations. In this class we will use Kerr “satin cast 20” - this is what I used in my casting shop . Our flask is 2 1/2” x 2 1/2” which will require 8 oz of investment and 91 ml of water. This is a 40/100 ratio. The steps are as follows: 1. weigh the investment and leave in the scoop 2. measure the water in the measuring beaker 3. put water in rubber bowl first, then add investment 4. mix the slurry for 3–31/2 min, by hand or mixer until very smooth. 5. Place the bell jar over the bowl and vacuum for 20 seconds AFTER the slurry starts to boil. (which should be about 25” of mercury) all the time shaking the vibratory table, then release the vacuum and remove the bowl from the chamber 6. Pour investment slurry into flask 7. Place flask on the investment table and cover it with the bell jar and vacuum and shake for 90 seconds, it should boil most of that time. 8. Release the vacuum and turn off the vacuum pump. 9. Remove the flask from the machine and place it on a level surface and allow it to set up. This will take a few minutes, then the investment will “gloss off” (water is fully absorbed) 10. After at least an hour remove the masking tape and with a spatula scrape any investment that is above the edge of the flask 11. Remove the rubber base by gently bending and peeling it off the flask. Then mark the bottom with your initials. Make sure no investment crumbs fall into the hole. Place in the furnace and start the program. Investment drum, scoop and rubber bowls

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Some Investment tips Storage Always store investment in a dry, cool environment. After using get rid of all the air in the bag and close the lid tight. Mixing The investment should always be added to the water in the recommended water / powder ratios. Working Time is the time it takes the investment to harden after water is mixed with the powder. Depending on room temperature it takes 3-5 minutes or so. Water temperature: Water should be 70f – 75f and should be measured with a thermometer to insure consistency. Colder water extends working time, warmer shortens it. Investment temperature: The investment powder should be stored at the same temperature. If the temperature changes season to season, the working time will change as well. IE; colder investment extends work time, likewise, if the investment is warmer it will shorten the work time. Mark your flask: Always mark your flask, use your initials and a number afterwards IE; CB1 and if you are casting flasks in different metals then add a S for sterling, G for gold, B for brass and C for copper.

The Furnace and the burnout ; Once the flasks have been filled with investment and they have been allowed to dry. (a minimum of one hour for small flasks and up to three or four for the really large ones) they are ready to go into the burnout furnace. Remember that this furnace can reach temperatures above 1400.f, and can give you an very nasty burn, so except when cold, NEVER TOUCH THE FURNACE WITHOUT GLOVES. The furnace also needs to be vented because of the gases that are created from the wax. Also very important is the thermocouple inside the furnace, a small piece of wire covered by a special ceramic that reads the temperature inside the furnace. The thermocouple is VERY FRAGILE, a bump with a flask can break it and the cost to replace it is high, so be very careful when placing or taking flasks from the kiln. Before placing your flask in the furnace, remove the rubber base and mark the investment with your initials.

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The furnace we will use is an electric model with a built in controller. A furnace without a controller will require the user to be present the entire burnout cycle which is from 8 hours plus preheat time for small flasks up to 31/2” x 4” up to 24 hours for extra large flasks 6” diameter and larger. A manual furnace requires the user to change the temperatures instead of a controller. The burnout cycle consists of a preheat, a ramp to wax melt stage, an intermediate ramp, the wax vaporization temperature, temperature to cure the investment then back down to the casting hold temperature. Because the wax is being vaporized the furnace needs to be vented to the outside in some manner. Also the temperatures reached are incredibly high, so the unit must be set on a non flammable surface and the surroundings must be safe with such heat . You must also wear heavy furnace or welding gloves to protect yourself from the intense heat. A typical 8 hour cycle is as follows: Preheat the furnace to 300.f. Then program it for 2 hours at 300.f, 2 hours at 700.f, 3 hours at 1350.f then 1 hour at 800.f and then hold at 800.f until ready to cast. I prefer to allow at least a one hour hold after the 1 hour at cast temperature). Some controllers allow you to set how fast the heat ramps up, say from 300.f to 700.f in 20 minutes, or 300.f to 700.f in one hour. Others have a built in ramp program that ups the temperature at a set rate. Raising the flask temperature too quickly can cause the investment to crack. Going over 1450.f will cause the investment to actually break down. If the flask temperature is not brought to casting temperature and held there long enough (at least one hour) the metal will stay molten too long and the castings will have porosity problems. The first ramp of 300.f is to heat the water in the investment slowly, steam is created at 212.f and the steam is released through the pores in the investment. If it is heated beyond 400.f to quickly the steam expands during its escape and can ruin the cavities made by the wax. Between 200.f and 300.f most of the wax is melted out, above that temperature the steam helps to clean most of the remaining wax off the walls of the patterns. It usually takes about an hour for the wax to melt out – to “become lost” as the name of this type of casting is called. The next temperature is a stepping stone on the way to 1350.f. Any wax that has not already melted and flowed out turns to carbon at 1000.f The carbon is completely eliminated at 1400.f by mixing with oxygen in the air. For this reason, it is very important to have your furnace ventilated. Except for very detailed castings such as filagree, going over 1350.f is not necessary. The final temperature is the casting temperature. This furnace ramps down to 800.f and holds it for at least an hour. You can choose a hold as long as you need until you are ready to cast. But instead of holding for a long time, most controllers allow for a delayed start, so you can have your flasks holding for 1 ½ Copyright ｩ 2005 – 2010 TechShop Inc. All rights reserved

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hours when you are ready to pour. Casting temperatures (what the flask must be at for a good cast) Silver, brass ….. 800.f - 850.f. W. Gold, thin...1050.f – 1150.f

Bronze..............900.f thick 900.f - 1000.f

Y. Gold Filigree...1050.f – 1150.f thin...900.f - 1000.f thick...800.f – 850.f. Melting temperatures Sterling silver 1640.f

Fine silver 1761.f 14kt Y gold 1615.f

14kt W gold 1825.f

Bronze 1743.f

Preparing for the melt

Brass 1710.f

carbon rod

When you are finally ready to melt your metal for the pour the first thing to do is get all your tools together. You will need flask tongs and heavy welding or furnace gloves to take the flask out of the furnace and to melt the metal. The vacuum machine needs to be on the “cast” setting, the silicone mat with the hole for the vacuum flow needs to be set on top of the metal plate made for this purpose. The next step is to measure out your metal, gather your torch and safety equipment and start melting the silver. For the melt you will need an oxy/acetylene rig, a torch with cutting tip, a flint striker, a foundry brick for resting the crucible on, #5 shade goggles or shade face shield, leather apron and welding gloves, heavy leather boots or shoes, long pants and long sleeves. You will also need sand in case of any small fires. To melt the metal you will need a crucible and handle, borax flux and a carbon stir rod to remove slag and up to an ounce of sterling silver casting grain and a scale to measure it out in. If you were using scrap silver or a button from a previous cast you would need some fresh grain and some alloy replenisher. Last thing we need before we can start the melt is the breakout bucket, a 5 gallon plastic or metal bucket with water about 7/8 full. We will start by measuring out the casting grain. The scale has troy ounces ,

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pennyweights (dwt) and grams which is what we will measure in. A troy ounce has 20 pennweights and 31.1035 grams. 1 dwt is 1.555 grams. If our wax construction weighed 2 grams, we then multiply 2 x 10.4 which will give us 20.8 grams, or 13.374 dwt, a little more than half a troy ounce of silver. We then add the 10% for the button, 6.687 which gives us a total of 20.1. So we will use a full troy ounce for a 2 gram wax weight. So now we begin the melting procedure 1.Put on your safety equipment, apron, gloves, shade goggles. 2.place your metal in the crucible and add a pinch of borax.

3. To start the torch, we do the following: Make sure the tanks are upright, securely chained and the regulators are securely fastened.The oxygen tank has a green hose and pressure numbers that reach 4000. The acetylene tank has a red hose and numbers going to 500. Check all the connections, making sure they are all tight. The gauge needles should be all the way down, registering no pressure. Check the hoses for burns or cracks. The torch itself should have all valves fully closed (fully clockwise). 1.check to see that all knobs on the torch are turned fully clockwise 2.Open the Oxygen knob on the torch body fully (counter clockwise) 3.Point the torch away from you & anything flammable. Open the acetylene knob on the torch just a little(note: you may detect a garlic odor,this indicates the Acetylene is flowing). 4.Click the striker and light the torch 5.Adjust the Acetylene knob until the turbulent part of the flame is approximately ONE INCH from the cutting tip. 6.Turn the pre-heat Oxygen valve on the cutting attachment counter clockwise until all secondary flames disappear. This is called a Neutral flame and it is what you want to use to melt your casting grain. The torch should sound quiet, with no hissing.

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4. Position the torch near the material until is first starts to melt. Move the flame around the metal to warm it all up, do not stay in one place too long or you could actually burn the metal. Move round and round in a continuous fashion, to keep all the metal heating up. With new casting grain you will not have any slag to remove unless there are remnants in the crucible, but you still need to stir the metal with the carbon rod to see if it is fluid enough. About half way through add a little borax or boric acid to keep it flowing well. When the metal is heated properly it will be entirely fluid and moving around quickly, not boiling but completely fluid. When you see it once you will clearly recognize it again.

5. Once your metal is ready to pour, your partner will remove the flask from the furnace with furnace gloves and tongs. When the flask is removed it will have the button or pour side facing down(this is where the wax melted out). Place the flask on a fire brick and then turn it over with the tongs. Now that it is turned over, pick it up again with the tongs and place it button side up on the silicone pad, centered on the hole.

6. Your partner will now turn the vacuum machine on and the needle will begin to rise. When it reaches a steady point it is time to pour. Keep your flame on the metal until the moment before you are ready to pour.

7. Bring your crucible over to the flask and in one smooth movement, pour the molten metal into the flask. Leave the vacuum running until the metal skins over then release the vacuum and turn off the machine.

8. Turn the torch off, first the acetylene knob, then close the oxygen knob. Remember that the torch tip is very hot so place it down in a safe spot.

9. Place the crucible on a fire brick 10.

With the flask tongs, remove the flask from the silicone pad and also place it on a firebrick. The flask needs to rest so the metal can solidify for up to five minutes. When the color of the metal is no longer red/dark and is looking like darkened silver, it is ready to breakout.

Breaking out the flask You will need the flask tongs, safety glasses, dust mask, rubber gloves and the 5 gallon bucket of water This will get a little messy, depending on the temperature of the flask, the water

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will boil and spray a bit. We did this outside when possible. With the flask tongs, hold the flask firmly and horizontal, the open ends perpendicular to the floor. Very slowly lower the flask into the water, resting the tongs on the bucket edge, if the water and investment pouring out comes too fast back off a little, once you are 3/4's of the way in let it rest for a bit. Then lower the flask towards the bottom and turn it so the button and tree slide out without falling too far. A tree falling from the top of the bucket could damage or break fragile parts of a casting. Give the water a few minutes to cool an then with rubber gloves or the flask tongs remove your flask and the casting tree from the bucket and dry it off.

Troubleshooting and Tips: The two most common problems with castings are porosity and incomplete castings. Porosity is when minute particles of investment or gases are trapped in the molten metal when it is poured into the mold. The result can be surface pinholes or blemishes or sometimes the surface looks fine until it is polished, and the defects are then visible. Here are some reasons porosity may occur: the sprues are too small or cause turbulence in the pour. Too much flux during the melt overheated metal Incomplete cure of the investment or overheating of the investment It is important to keep very good records during your cast. This way if and when problems occur you can figure out why. For instance, how much of the metal was “old” - this should be in your notes. What was the burnout cycle? If there was actual missing parts in the casting you may need to heat your metal higher, or maybe your flask temperature was too low. Casting problems will occur, what is important is what you do when it happens. Some problems can be repaired by soldering or other hand methods.

If you have ANY questions about any operation or task, be sure to ask your instructor or another TechShop staff member before proceeding.

Cleanup time

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It is extremely important to double check on the oxy/acetylene rig, the furnace and the vacuum caster that when you are finished they are turned off properly because damage or dangerous situations can occur if not. All the tools that have been used such as tongs, crucibles and such need to cool completely before they can be put away. The water bucket with the broke out investment needs to settle at least overnight before the water can be poured off and the investment can be disposed of in the trash (double bagged). All other hand tools need to be put in their specific place. Sweeping the area where you have worked keeps techshop safe for you and the next person using this area.

COOL LINKS http://www.ganoksin.com/index.htm http://www.lost-wax-casting.com/index.htm http://www.metalcastingzone.com/ www.riogrande.com http://metalliferous.com http://jewelrymaking.about.com/od/makingcastmetaljewelry/ss/100507.htm http://www.homemodelenginemachinist.com/index.php?topic=4816.0

OTHER LEARNING RESOURSES The best book is Centrifugal or Lost Wax Casting by Murray Bovin http://www.amazon.com/Centrifugal-Jewelry-Casting-Tradesmen-

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Craftsmen/dp/0910280053 another good one is http://www.amazon.com/Handbook-Lost-Wax-InvestmentCasting/dp/0935182284/ref=pd_sim_b_2/188-3981578-6622810

WHAT’S NEXT? [ After successfully completing this Lost wax casting SBU, you might be interested in these classes: basic aluminum sand casting Blacksmithing general metal shop In the future I am hoping to offer classes in rubber mold making , wax carving, jewelry soldering, finishing and more. Don’t forget to join the TechShop RDU Forum at http://TechShopRDU.com/Forum and the Group Meet-ups (see the class calendar for dates). Get ALL the answers!

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