FAQ (Frequently Asked Questions)

This list of questions are some which are frequently asked in e-mail and on the forum. Hopefully this list will save time for everyone especially those just starting out in metalcasting.

General questions

I'm new to metalcasting can you tell me what I need to do to get started?
Buy a good metalcasting book and read it. There is no "shortcut" to learning what you need to know. It is easy to learn but you need to still do your homework. There are several good books listed on the Metalworking bookstore page.

I'm new to metalcasting what type of furnace should I start with?
Melting metal is simple and if you are good at building things then you'll definitly have no trouble building a furnace. Most people say to start with a charcoal burning furnace (like the Flowerpot furnace I published a booklet about) because it is dead simple to use. But people who end up really enjoying metalcasting tend to advance toward a more convenient fuel such as propane. So they build a propane burner (similar to one described on my site) and a furnace similar to the "2-bucks" furnace detailed on my site. If you think you'll have a real interest in metal casting and you're willing to buy a propane tank and regulator, then just start with the propane furnace. If you're handy you should be able to buld a furnace and burner just from the information on the website. Making the actual sand molds is more challenging and i takes some practice but not too much. Get a book that describes the process and just get to it yourself. My sandcasting booklet is meant for complete beginners. But most importantly you have to actually practice the stuff on your own because that's when the real learning begins.

How long should I hold the molten metal outside the furnace before pouring?
As long as you don't over heat the metal you can and should pour it immedietly after removing it from the furnace and skimming the slag off. The only reason to hold the metal outside of the furnace is if it's been overheated and you're waiting for it to cool. Unless you have a pyrometer it'll probably take experience to determine when the "perfect" pouring temperature it. If you have good molding sand but the casting comes out covered with tiny sharp points that means that the metal was too hot. The tiny points result from the metal being so hot that it penetrates in between the sand grains on the surface of the mold before cooling. A proper pouring temperature results in the metal cooling right on the surface of the mold cavity and gives a fairly smooth surface. With some experience you can probably tell by the glow of the crucible etc. And you'll know how many minutes (or seconds with a really big burner) it take for the metal to be at pouring temperature after the last piece in the crucible melts.

Propane burners

Can I use a propane burner without a regulator?
It is possible but is is not recommended. The pressures inside the propane tanks can raise to levels far to high for the safe use of the propen burner. The regulator keeps the pressure of the gas entering the burner at a safe level.

Can I use the small regulator that goes to my barbecue grill for my Oliver-upwind burner or other blowerless burner?
No, they don't release propane quickly enough. Look at the rigging a propane system page for details on the right regulator.

Do I need a blower for my propane burner?
If the burner is designed to not use a blower then it doesn't need a blower.

You specify 1/8" pipe for the gas jet pipe, is that 1/8" the pipe's inside diameter?
The pipe is called 1/8" pipe but it is not really that size. Manufacturers just use the measurments as names (called the "nominal size") even though none of the pipes match that. I just used what is called 1/8" non-galvanized steel water pipe. The outside diameter is slightly more than 3/8" and the inner diameter is about 1/4". The length of it is not critial as long as it can extend through the main burner pipe as shown in the photos.

Waste oil burners

How does the Ursutz derived burner work?
Both burners work on the same principal but the newer one on the homepage is shaped a bit differently to improve combustion and it has a better air/fuel intake system. The burner is basically just a sheetmetal box lined with the same type of refractory that the furnaces are lined with. The refractory is about 1" thick. The inner chamber of the burner is rectangular about 6" long and 4" wide. The rectangular shape seems better than a circular shape because it produces more air turbulance which speeds the combustion. On the newer burner; the "Organic lipid thermal energy reactor" (OLTER) the blower is connected to a seel pipe and the oil line feeds straight into the air line. It works similarly to the venturi on a lawnmover engine. There is no oil nozzle and the oil is not pressureized (the system uses gravity to carry the oil). A valve simply controls the speed at which the oil drizzles into the airstream which blows the oil into a semi-mist for easier ignition. The burner is started with a nice hot wood fire (sticks, etc) in the burner's inner chamber. After about 5 minutes of the oil burning the burner is so hot that the oil fire is self sustaining. The flame exit port is just a sheetmetal tube lined with refractory with a 1 or 1-1/4" diameter tunnel runing through it to carry the flame.

Foundry tools and materials

Why do some people suggest not using iron or steel crucibles?
After a awhile the iron or steel crucibles begin to erode and flake apart. The molton aluminum (or bronze, etc.) can absorb some of this iron which will weaken the castings on a molecular level. It's usually said that on the typical backyard hobby quality this is no problem and is not even noticeable. But when attempting to keep the metals as pure as possible (i.e. when making high quality ingots, special alloys, or structural/mechanical parts) a ceramic crucible is best.

What do you make your crucibles out of?
Take a look at the building steel crucibles page.

How do you temper a clay/graphite crucible.
I've been successful by putting the new crucible in the furnace (on a disk of cardboard so it doesn't stick to the plinth block) and setting the burner for a small flame with the furnace lid off. This will produce about 250° F. in the furnace. I keep it at this temperature for one hour. Then I turn the burner all the way up to normal operating temperature and get the crucible red hot for about a minute and a half. Then I turn the burner off and let the crucible cool to room temperature while still in the furnace. It's now ready to use. If the crucible hasn't been used for awhile it may have absorbed moisture so it should be heated with a small flame to carefully dry it out. Or just put it in a hot furnace with the burner shut off allowing it to be heated and dried out as the furnace slowly cools.

Are there any substitutes for parting compound?
If you can obtain actual parting compound that is of course best but some substitutes that have been used by various hobbyists are; baking flour, talcum powder, baby powder and I've even heard of diatomacious Earth (from a gardening store) can be used. When using substitutes you may need to experiment because they may not work with certain molding sands (for example, it may work with oil bonded sand but not greensand) and they may be more sensitive to the moisute content of the sand.

Furnace building

What are some good dimensions for a hobby furnace?
The refractory walls should be 2.5" thick for a small propane furnace to be efficient and sturdy. The "2-bucks" furnace described on my website has a 6" diameter inner chamber (6" diameter temporary inner form) which equals 11" diameter steel container. For a very versatile sized hobbyist furnace find a 13" diameter container (or make one from sheetmetal) and go for a 8" diameter chamber. My personal rule is that the lid should be the same thickness as the walls. So 2.5" thick for that also with reinforing wire or rods in it. And I use a 2.5 or 3" diameter hole in the lid. That size is good so you can fit some scrap through the lid into the crucible. The base's drainage hole should be 1.5 or 2" diameter because smaller diameter holes can sometimes clog. And the golden rule; Always be sure that you have sufficient refractory to complete the job!

Can I use a ceramics kiln as a foundry? I have one in the garage.
I've read about several people who have used ceramics kilns to melt metal. Some of them used electric kilns and as-is and it took about an hour for the electric element to heat the kiln to the melting temperature. Other people have modified the kilns with gas burners and that resulted in very large capacity furnaces. I'm only guessing here, but this type of kiln may also work well as a burn out oven for "lost wax" casting.

How much heat can your refractory formula withstand?
I have not conducted any tests to determine the limit of the refractories effectiveness. I can only say that it withstands the heat for melting aluminum very well. But like most homemade formulas, it doesn't withstand heat as well as good quality commercially prepared refractories.

Is homemade refractory as good as store bought refractory?
In general homemade refractory does not last as long as storebought refractory. Homemade mixes usually contain common materials like clay, cement, sand a garden store perlite. These materials make a refractory that works well at aluminum melting temperatures, but temperatures above that (like for bronze or iron melting) cause the mixture to break down and the sand content often turns to a glass like substance. Store bought refractories usually contain "exotic" components like alumia, calciaum sulfate and other heat resistant hard to find materials. These are far more duarable in the higher temperature ranges.

Should I use a store bought refractory rated to 2,600 or 3,000 degrees F.?
This depends on the metal you're melting. If you'll only be melting aluminum and occasionally bronze then 2,600 degree rated refractory is fine. If you'll be meting bronze or iron on a regular basis the higher temperature mix is prefered. The higher the temperature rating of the material the heavier and more dense it is. It also allows more heat to pass through it so the furnace shell gets hotter. Lower temperature refractories are less dense so they have more air spaces which provide better insulation. But they are more easily chipped if struck.

What is fireclay and where can I get it?
Fireclay is a powdered clay used in furnace refractory (the heat resistant lining) and molding sand. It provides most of the heat resistance in the formulas. I buy it from a ceramic supply shop that sells materials to potters. Large masonry materials suppliers may also sell it. If they sell clay chimney pipe they may sell fireclay.

Is fireclay the same as furnace cement?
No. Furnace cement is a special heat resistant cenent which works like regular cement excenpt it resists a lot of heat. Fireclay is a component in some furnace cement.

What is bentonite clay and where can I get it?
Bentonite clay is just another type of powdered clay. It has more bonding strength (is stickier when wet) than fireclay. It is best used in molding sand formulas. The most popular sources for it as far as I know are pottery supply warehouses, some farm supply stores and well drilling outfits. A lot of people tell me they have trouble finding fireclay. I guess its just a matter of what part of the country you live in. Some people have used plain, fragrance free kitty litter which is made of bentonite clay. The only problem is that you'll probably have to grind it into a powder. Some people however get lucky and the kitty litter they obtain readily dissolves in water forming a smooth mush which can be dried out and used.

What grade of sand should I use for my refractory?
For refractory you can use the same type of sand used to make concrete or brick mortor. The low cost stuff.

What should I used for measuring out refractory components?
The refractory components are always measure out by VOLUME (like when cooking, i.e. cups, teaspoons, etc.). To measure out the parts you can use any container that you think is large enough to allow you to end up with sufficient material to fill the furnace shell. If you are making a small furnace such as my furnace built from two steel pails then a large coffee can (the 6" diameter type) will work. For a very large furnace you may need to use a bucket to measure out the parts.

My charcoal burned really quickly and the metal didn't melt what's the problem? If the charcoal was ignited well but burned away before the metal melted then the fuel is burning too quickly. Either your blower is too powerful or the charcoal you used is poor quality. My first guess would be that the blower may be a little to powerful. A blower that is too strong can blow the flames and heat out of the furnace before the metal can absorb it. If you can't replace the blower then consider moving it further back from the furnace so less of the air pressure reaches it.

Another potential problem could be the charcoal. Some people have found that their foundry only works well with quality name brand charcoal briquettes like kingsford.

Metal sources

Can I use soda and/or beer cans as an aluminum source?
Yes you can but there is a "trick" to using them successfully. Since the cans are so thin they easily burn and oxidize rather than melt. For this reason many people say they should not be used. But if you already have a good pool of molton aluminum in the crucible then the can can be melted efficiently by crushing them (top to bottom) and dropping them into the pool. If the dry cans are pushed below the pool's surface they will melt and be less likely to oxidise. This aluminum is almost pure (unlike car cyclinder heads which are alloys). So the metal will usually shrink more when cast. but it is extream;ly shiny making it good for small decorative castings.

What are some good sources for scrap aluminum?
Potentially any aluminum obect could be a source. The best alloys for casting machine parts are old aluminum machine parts. Some examples are, car cylinder heads, transmission cases, water pump housings and pistons. This is a strong alloy which usually doesn't shrink much. More common sources are lawn chair frames, storm door and window frames, beverage cans, foil, disposible turkey and pie pans etc. The second group of aluminum sources are known as extruded aluminum (as opposed to cast aluminum) because of the way the products are manufactured. It's more of a pure aluminum so they are shiner when cast making them good for decorative castings. But they are weaker and the castings usually shrink more while cooling. Machining charactoristics are often not as good either.

Can I melt gold with the homemade equipment on your site?
The equipment and methods detailed on backyardmetalcasting.com are not designed for precious metals. Special crucibles are needed for these metals to keep losses to a minumum. The furnace may reach the proper temperature to melt the gold or silver but without a special crucible and other materials the metal losses from oxidation etc will be expensive.

Do you know of a place that sells ingots?
Try www.budgetcastingsupply.com

Can I melt iron in the flowerpot furnace?
Probably not. This furnace is designed to be simple and quick to build with low cost "everyday" items to get you introduced to metalcasting as fast as possible. It won't hold up to melting much more than aluminum and small amounts of bronze.

Will the homemade greensand work for iron casting?
It will work for iron casting but it is not the best for this purpose. The higher temperatures of molton iron will wear out the molding sand much quicker than aluminum will. This is caused by the clay in the mixture being vitrfied (like fireing pottery in a kiln) causing it to lose is bonding ability. Molding sand used for iron casting often uses different clays than the regular fireclay and often has powdered coal added to it which is said to improve the surface quality of the castings. Also the heat of the iron is more likely to turn the silica sand to glass.

I'm having trouble with the flowerpot furnace, it's build just as you describe
1) The crucible is too large (there should be at least 2.5 inches all around the crucible to fit a good amount of charcoal all around it). And there should be a good bed of charcoal under it.

2)The gap that you found between the flowerpot and the metalpot may have cause exces heat to escape since there wasn't insulation in there.

3)The metal you were melting. Try to melt a solid chunk of aluminum first. When you melt thin material like soda cans or rain gutters then sometimes the metal can oxidize before melting and form slag. But a chunk of aluminum with automatically form a molton pool of metal and then the thin material will safely melt in the pool creating less slag.

Can melting metal cause heavy metal poioning?
Since brass is an alloy (combination) of copper and zinc it can (and almost always does) produce zinc fumes when it melts. This is caused by the zinc vaporizing at the high temperatures. The fumes look like thin smoke coming off the surface. If inhaled in a large enough amount they can cause cold or flu like symptoms which some people call "zinc fume fever" amongst other names. Simply avoid the fumes just like you'd avoid smoke from a fire. Last month I melted about 12 pounds of brass/bronze mixture and avoiding the fumes was simple. I had no trouble. The dirt and other debris found on the surface of scrap metal (which is what most hobbyists use as their raw material) floats on the surface of the molten metal forming "slag" or "dross" and must be skimmed off with a steel spoon or similar tool. It is best to skim it off just before you pour the brass or bronze because the slag layer helps slow the release of zinc fumes.

Can the HobbyMelter™ furnace be adapted to melt iron and/or steel?
Melting iron may be possible with a larger burner. But the burner mount would have to be modified since it is designed for the smaller stock burner. Also a refractory with a very high heat resistance rating (about 3,000 degrees F.) would have to be used. Melting steel is very unlikely to melt since it's melting point is well above iron.


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