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    • CommentAuthorsundog
    • CommentTimeMay 14th 2009
     
    Hi All,

    Here's how I go about making my foam patterns for casting.

    First I examine the drawings of the part, to figure out how to build it up from flat pieces of foam and/or carve it from a block. If I can assemble it from flat pieces, I re-size the drawing to 5% larger than it's real size, to allow for shrinkage. I then print out the drawings, and cut them out with scissors or an Xacto knife.

    I then cut my foam into pieces slightly larger than the drawing pieces. I typically use 3/4" blue or pink insulation foam. I either plane it down or glue pieces together to thin or thicken the piece. I use a razor knife to cut the large pieces of foam. I use hot glue sparingly to join the foam pieces together, sometimes with sewing pins or bits of toothpick to help hold it together.

    Once I have the "blanks" of foam, I use a few sparing drops of Elmer's glue, spread with a wooden stick (popsicle stick works well) on the foam. I then place the cut out drawing and let it sit for awhile for the glue to dry.

    Once the glue is dried (usually the next day for me), I use a hotwire saw to cut the foam to the outline of the drawing. Unless there is a specific need, I keep the cutting wire perpendicular to the cutting table.

    Once all the pieces are cut, I then glue everything together using hot glue (sparingly). Once that's done, I add a sprue, generally 3/4"x3/4", 4-5" long. Bigger patterns require bigger sprues. The function of the sprue is to channel the molten metal into the pattern, but also to provide a reservoir of molten metal for the pattern to draw on as it solidifies and shrinks. If the finished casting shows dimples, hollows, or similar defects, increase the cross section of the sprue. if that doesn't help, add a shrink bob near the problem area. The shrink bob is just a small volume of foam that fills with metal when casting, and provides liquid metal for the cooling area to draw from, helping to prevent shrinkage defects. You'll see what I mean when you start casting, and how these things help the problem.
    • CommentAuthorsundog
    • CommentTimeMay 14th 2009
     
    Dipping the pattern in a slurry helps improve the surface finish because it's surface is far finer than the sand the part is buried in. It isn't a necessary step, but it helps prevent the sand from shifting and ruining the pattern as the foam melts. With any lost foam casting, you must pour fast and continuous once you begin. Slacking off will usually ruin the casting. Be prepared for smoke, fire, and nasty smells. Always stand upwind or have a fan blowing the fumes away.

    For a slurry, I use drywall mud thinned 50/50 with water. I dip the parts, making sure they're thoroughly coated about 2-3" up the sprue, then hang them to drip-dry. Generally, my patterns get 3-4 dips to build up the coat, waiting for the coating to dry between dips. On parts with internal cavities, be sure to rotate the pattern around to ensure the internal areas are covered thoroughly. Hard-to-reach areas can be done by hand with a brush. With attention to detail and some skill, holes can be cast in patterns provided you allow for the shrinkage factor.

    When burying the pattern, be sure to get sand into any crevices so the slurry shell is completely supported. It will crack as you're pouring, and the sand simply provides support. With luck, the cracks won't be visible in the finished casting, and if they are, they're easily cleaned up with sand paper.

    A "fluidized" sand bed can be made by blowing air into the *bottom* of the container. The air disturbs the sand, and you can simply push the pattern down into the sand, then turn off the air and it will settle around the pattern. I don't recommend going through the trouble of this unless you're casting a *LOT* of patterns.

    As always, your sand must be clean and *DRY*. Damp or wet sand is a bad thing, as the water will flash to steam and fling blobs of molten metal all over. I use a popcorn tin with a tight fitting lid (for storage). Don't use plastic buckets! In a pinch I've used cheap metal trash cans, large coffee cans, and even large soup cans for small castings.
    • CommentAuthorsundog
    • CommentTimeMay 14th 2009
     
    Once the pattern is cast, either pour your other patterns, or pour the remaining aluminum into ingot molds. If you're done, set the crucible back in the furnace and let everything cool down. If not, move on to your next melt. It helps to have all your patterns ready to go, as you waste less fuel re-heating a hot furnace than a cold one.

    After everything cools off (give it an hour), you can grab the sprue with *PLIERS* and pull the casting from the sand. I hit mine with the garden hose, *FAR* away from the furnace setup. Usually the drywall mud comes right off, with some steaming from the parts. Inspect the casting. If it's good, set it aside for later. If it's bad, toss it back into your "to be melted" bucket, mindful of it's origin, cast or extruded. Don't mix the two for best results. And just because you melted extruded aluminum and cast the part, that doesn't make it "cast" aluminum in chemical makeup.

    Now you've got a stack of hopefully good castings, with few or no rejects. You can cut the sprues off (I use a hacksaw or Sawzall). Toss the sprues back in the "to be melted" buckets, and have fun machining your casting!
    • CommentAuthorsundog
    • CommentTimeMay 14th 2009
     
    Some advanced tips -

    Coring.

    With a wooden pattern, sometimes it's necessary to use a core to create a purposeful void in the casting. Either to reduce weight and metal usage, or for a subassembly, shaft, etc to exist in.

    When casting in sand with a wooden pattern, cores are typically made of sand treated with sodium silicate, or "Water Glass". You make a female mold of the core, then mix the sodium silicate with sand and pack the mold. Once it hardens, you turn it out. The pattern is rammed up in the flask (box that holds the sand), and the core is put in place when the pattern is removed.

    With foam, you follow a different procedure to obtain the same effect. If it is a hole, simply cut the hole a bit undersized in the foam pattern, and dip it in thinned drywall mud (I'm calling it slurry from here on out). The slurry coats the hole, and excludes the aluminum from filling it.

    For something more complex, like a cylinder bore, it's the same procedure. The water hopper/cylinder I have to cast has an internal void where the water goes, and a "tube" of aluminum that a steel sleeve will be pressed into.

    To make this, I'll cut the sides, front, back, and top of the hopper from foam. The bottom will be cut in curved sections. Next, I cut rings of foam, and glue them into a tube. I cut a matching hole in the front and back, then assemble the whole mess. This yields a tank with a front, back, top, and bottom, hollow in the middle except for the tube, which passes through the front and back sides. When dipping this mess in the slurry, I make sure I get plenty of slurry *in* the hopper, and roll it around to coat the inside. When burying the pattern in the sand, I take care to fill the hopper with sand, to support the slurry shell. When I pour, the foam melts and the aluminum fills everywhere the foam was, leaving me a nice empty hopper with a tube running front to back. Pictures will help, and I'll be sure to document my construction of the above mentioned item.

    Cores can also be made using wooden forms placed in the pattern. It'll burn a bit during the pour, so make sure it's undersized from what it's supposed to be, and that it protrudes from the pattern so the sand can keep it in place. When the part is to be machined, you can drill out the wooden core and then machine the bore. Steel rod can also be used for cores, but I dislike doing that, as it must be very clean, have a very good surface finish, and usually must be hammered or pressed out of the casting in a hydraulic press. It does leave a very accurately sized bore, though.

    More to come later.
  1.  
    Sandog,

    Thanks for taking the time for the new thread. LOTS of great information.

    Could you cover some furnace making and so on. Or just the principals around it. and heating fuel, regulaters ect.

    I found a metal container today at the dump which I thing will be good for my first furnace attempt.

    Jan
    • CommentAuthorsundog
    • CommentTimeMay 14th 2009
     
    I'll start another thread on furnace and burners, fuels, etc. In this thread I'm dealing primarily with making and using lost foam patterns. I'm breaking the information into separate posts to keep it organized by idea. Hence, some long & short posts.
  2.  
    Good Idea.

    Jan
    • CommentAuthorsundog
    • CommentTimeMay 15th 2009
     
    Foams to use -

    There are several types of foam that work properly for lost foam casting, and several that do not.

    What you want is expanded polystyrene foam. It's called EPS foam, and there's a couple of breeds.

    The most common is the white packing foam, made of small white beads. While it is usable for casting, it's not ideal. It doesn't cut cleanly with a knife or hot wire saw, is nearly impossible to carve or sand, and makes an unholy mess as it sheds little white beads all over the place.

    Blue or pink EPS foam is excellent for casting. It's a dense, close-celled foam and is produced by an extrusion process. The only downsides to it is the stresses inherent in extruded materials. If you remove a great deal of the surface on one side, either with a knife, hot wire saw, or engraving, it tends to warp. I've had better luck against warping by peeling off the plastic film on both sides, but that isn't a necessity.

    DO NOT USE POLYURETHANE BASED FOAMS!!!
    That expanding insulation stuff, green floral foam, and generally orange or yellow foam is often polyurethane foam. This stuff produces nasty, toxic gasses that will make you sick as hell and is *FATAL* to birds!!! Don't use it!!! If in doubt, don't use it!

    For the rest of the posts, I'll assume the reader is using good EPS foam, either blue or pink.


    Cutting foam -

    Foam cuts like a dream with a hotwire saw. I use a box cutter with a new, sharp blade to cut my foam into manageable chunks. Long pieces I score, then cleanly snap the foam and cut the remaining plastic film with the box cutter. Small pieces I cut in two passes, careful not to lop off a finger.

    There's plenty of information on the 'net about hotwire saws. I use an old 12v transformer from a battery backup unit I scrapped, and a Variac to control the voltage. the wire I use is annealed steel wire, though I need to replace that with better wire for cutting with.

    I use hot glue sparingly to join pieces together with, sometimes using plain sewing pins or bits of toothpick to do a mock assembly before gluing everything together. 240 grit sandpaper works well for smoothing surfaces, and I remove excess glue with an Xacto knife if it oozes from a joint. Fillets can be made by sparingly using wax obtained from toilet wax rings. I just use nitrile gloves and my fingers to manipulate the wax. It's inexpensive, widely available, and works well. Just don't overdo it, because it tends to boil and flame when the metal hits it.
  3.  
    Sandog,

    Sorry for the silly question but what is "toilet wax rings" ? ? ? ?
    what other type of wax is good to use.... Bees wax OK?
    I think we use a different system here in norway for our toilets.
    Is this the ring that seals it to the floor pipe??
    Probably other on US guys out there wondering about the same thing.

    Jan
    • CommentAuthorsundog
    • CommentTimeMay 15th 2009
     
    Yup, it's the wax ring that seals the bowl to the drainpipe. Here in the US, the common brand is "Johnny Ring". It's basically a thick, greasy wax that deforms under pressure to ensure the water and contents of the bowl don't spill out on the floor under the commode when you flush. Most home improvement stores carry them in the plumbing or bathroom section. For obvious reasons, don't use a "used" ring. I wear gloves to keep the mess off my hands, but it's safe to handle.
    • CommentAuthorjay rich
    • CommentTimeMay 15th 2009 edited
     
    hi sundog jay here i was wondering to have you tried the paper trick as i did in my j 8 casting i did not dip my form in to the 50/50 mix of water and drywall compound i should hae but did not but i did leave the paper on my form and what i noticed is the paper stayed to a point and the flat finish under it was real close and flat you can see this in the pic of the head of the j 8 i only had to machine down 0.005 now the under side of the casting well it was a mess and not level try it out its fun to see burned out blue print on a fresh casting ....jay
    • CommentAuthordavid
    • CommentTimeMay 16th 2009
     
    I started a page of Backyard foundry advice from the two threads to make it more of a How to. Click on Tips and Links in the left menu then Backyard Foundry and pattern making
    The descriptions are wonderful but light on pictures.
    If you want to post to this page you can send me a e-mail and embed photos in the text. The foundry threads are also available.
    As different people try casting at home, please share your experience with the rest of us. It takes one little extra idea that changes a armchair engine builder to a real builder and I suspect that same idea may be al that’s needed to get some of us making castings in the near future.

    I want to thank Sundog especially for all the time he has taken documenting his process.

    Sundog,
    Can you write me off thread. david@floridame.org
    • CommentAuthordavid
    • CommentTimeMay 23rd 2009
     
    Oops, Wrong email david@floridaame.org
    • CommentAuthorrobert6951
    • CommentTimeMay 25th 2009
     
    Hello Sundog
    I am new to casting and still learning terms. What is a sprue and how is it used. I am working on a couple ideas and need to cast some parts to be machined to fit a small motor.
    From Riverview
    Thanks Robert
  4.  
    Because of the chatter here!

    I was invited to a casting party last weekend. I had to go to see what you guys were talking about. There were 3 pours made of things like flywheels and fictional engine blocks. All were done as lost foam. It was a great day and alot was learned.

    Of course almost a week later, I have gathered almost everything needed to build a small furnace. I think i want to go the way of sand casting using cope and drag. I realize the green sand can be a pain when not used for a while. It seems that with sand, one mold can be reused many times where as foam, only once.

    Maybe by mid-summer i will be able to contribute photos of do's and dont's and cool looking parts of wood and foam molds.

    Should be picking up refractory to pour the furnace lining a week from tomorrow!!

    Steve
  5.  
    Steve,

    You are a few steps ahead of me, summer time here in norway is spent doing everthing we cann't do in the long winters we have. Shop time is nill unless I have to repair something. I hope to do some pours this fall winter.
    I am looking forward to seeing your casting work. By the way... GREAT job on the PeeWee. Very sharp work! Would be nice to see it run on YouTube when all is ready.

    Jan
    Norway
    • CommentAuthorsundog
    • CommentTimeJun 1st 2009
     
    Ah, Steve, You got bit bit the bug didn't you?

    Visions of castings dancing in your head, wonder at how a crucible full of silvery aluminum, bright orange iron or curiously dull brass can become an intricate work of art.

    It's addictive as hell.

    For your green sand, order the Bentonite sand from Axner, on the East coast. It's inexpensive, and mixes very well. Don't bother buying green sand unless you get it dirt cheap (no pun intended) and it's workable from the get-go.

    I mix my own green sand, using 50 lbs of sand to 5 lbs of clay. Mix it up dry first, then add water until it's of a proper consistency. You should be able to make a ball, toss it 3' up and catch it without it breaking apart. When you break it by hand, it should break cleanly, with very, very little crumbling. It should feel barely damp and just a tiny bit sticky. Too sticky means too much water, and excessive crumbliness is too dry. Once you get close on the water content, use a plant mister to add water as you mix.

    A sand muller is a good thing to have, and there's plenty of designs out there. I mixed mine by hand and my shoulders did *NOT* thank me.

    As always, be safe!!!!

    Me... I'm waiting on my darn sand pit to dry out enough so I can cast. Took the cover off it yesterday and the top inch or so of sand is dry, but under that is still damp, with wet sand at the bottom. I "turned" it all over with a shovel, so if it don't rain, maybe I can get some castings poured this weekend or next.
  6.  
    I'm a way's off. First thing i want to do is finish the CNC milling machine. I have an X and Y axis and need to build the spindle. I have all the parts except the ballscrew. Shouldn't be more than a few weeks work.

    After that I need to learn how to use said mill to make wooden patterns. Once i can make patterns, i will need to learn how to cast. Last time i did any casting was in 8th grade shop back in 1978.

    I don't expect to make anything worth keeping. Most of the summer will be testing and learning.

    Here i go again!!
    • CommentAuthorjay rich
    • CommentTimeJun 1st 2009
     
    wow i stared a crazy well if you guys want there are boks on how to make crucibles ive made some and the work great ive made mine from fire clay but stsve you can use your refactory they make great crucibles or i call junk buckets for a alumin pour a stainless steel pot or bucket for these pours i use my flux salt and pool shock i did get luck i found out here in the wild westsome gold crucibles in tombstone az i grabed a cupple for some small pours and the work great have fun and i know i have to rebulid my furnace its shot some of the bricks well they have a nice glass coating on them ....jay
  7.  
    I have made the crucible already. Also have made a propane burner, some molds for ingots (angle iron) and all the stuff to make the furnace and lid.

    I want to make 2 projects and castings are not available for either one. Sooooo. I have to come up with a way to get them done. I also would like to cast sand because if i have a wood pattern, seems easy to make another casting when bad things happen.
    • CommentAuthorsundog
    • CommentTimeJun 2nd 2009
     
    Learning to make good wooden patterns is a not-so-easy task, but pretty darn rewarding.

    Some good sources of information,

    ->link<-


    ->link<-

    Remember that these books were written in the early 1900's, by people who *really* cared about their work. It was their profession, and they wanted to pass on the proper mindset as well as technique. That's something that's really missing in the mass-produced world of today. In technical schools we're taught a skill, or a trade, but without being an apprentice or having an experienced mentor, some of the "intangibles" aren't passed on, and must be re-discovered, lest they perish forever.

    Yeah, the above books are long, but they're pretty darn good reads, and chock full of useful information.

    Hope it helps!

    Shad H.
    • CommentAuthordavid
    • CommentTimeJun 29th 2009
     
    Steve Huck has recently built a furnace for backyard casting and wrote a page about building it.
    ->link<-
  8.  
    Is anyone in the Central Florida area, planning on an aluminum pour after September 1? If so, can I come and observe? I am interested in lost foam casting, for a four cylinder Model A Ford engine. Thanks in advance.
  9.  
    I also want to do a ford model A/B inline 4 cylinder. I have been on the lookout for a doner engine to measure up and generate drawings. Keep us posted if you get started!
  10.  
    I have some pictures and measurements. I am planning on visiting the Henry Ford Museaum this week, to see what else I can gleen. I will share the pics, if you have an interest.
  11.  
    I have a Model "B" inline 4 in the garage. I can get all the external measurments. I just dont want to take it apart to measure the internals. We need to find a disassembled motor and measure the snot out of it.