Quick 'N Dirty Lost Foam

All right then, here goes nothing... I was tempted to just post a link to the muller build thread, but then I thought, who doesn't like more pictures... even if they are all just screen grabs from the video?

This is the way I sometimes do lost foam casting. Which I normally only do when I want to get from idea to casting in a short amount of time, when it's not something I can see wanting to cast in large numbers, and where exact precision and a very smooth finish is not required. Goofy "artistic" stuff, halloween skulls, muller clamps. That sort of thing. If you want to make precision engine parts using lost foam casting, this is not the thread for you, go see Kelly's threads.

But if you're just getting into casting and don't have a lot of equipment for patternmaking, or you want to cast something where a quick and dirty approach is good enough, or heck maybe you're like me and are just a little impatient (I can't stand sitting around watching mud dry), then read on and maybe this will give you some ideas. I've got a bunch of pictures of how I cast the muller clamps to post here as an illustration of how I set these up to cast, but there are many ways to skin a cat.

First you need a foam pattern, which means you need a template to cut it out. This is where high tech CAD comes in: Cerealbox Aided Design. I traced the end of the pipe on the cardboard wth a marker, then I drew out the outeside edge of the clamp, just by eyeballing it. I probably used a straight edge to draw the bottom edge, I'm not sure. Then I cut it out with scissors.



Then I traced it out on a piece of blue extruded polytyrene foam, the styrofoam they use to insulate new houses, sometimes it's pink but I got one 2" thick sheet and one 1" thick sheet of this blue stuff back in 2013 that I'm still working my way through, this is the 1" thick stuff. If you have a hot wire foam cutter, there's no need to trace the template, you can just stick it to the foam temporarily with a kid's school glue stick from their pencil case or something and use the cardboard as a guide for the hot wire. I have a hot wire table but it's a little broken right now. They are very easy to make though...



With no hot wire foam cutter, I used my little benchtop bandsaw to cut out the patterns. It's almost useless for cutting wood as it was designed for, but it works really great for cutting this foam, you can spin the foam in place without it tearing apart or use it almost like a really skinny belt sander. If I ever rebuild my hot wire cutter, it'll be a horizontal wire type instead of vertical, then I could cut slabs of foam to thickness and cut out shapes from the slabs with this bandsaw. Maybe I could have stacked up the blocks of foam and cut out a few patterns at a time, and if they all (I made 8 of them) had to be exactly identical, I probably would have tried that. Instead, I traced the template on each piece of foam and cut them out one by one.



Then I sanded out the hole a little bigger so it would be sure to fit over the pipe these clamps were designed to clamp onto. I sanded the holes a little oversized, hoping the shrink in the casting would leave a nice snug fit. Yeah, right... First I used a rolled up piece of sandpaper to enlarge the hole to the traced line, then a piece of sandpaper taped to the pipe to make it more round and a little bigger than the pipe itself. Then I cleaned up the outside surfaces a little to break the sharp corners and smooth it out just a bit.









Of course, they did not come out all identical. Remember, this is the quick and dirty version of lost foam!



But the foamies I had designated as matched pairs did come out a little closer to each other. I sanded the bottoms of them with each pair pushed up together in order than the holes would line up about right. They don't have to be exactly right, just pretty close.



Time to sprue them up. There are a lot of ways to get this done. I hot glued the foamies directly to the bottom of the sprue so the trees would fit in my sand buckets. I often make the whole sprue out of expanded polystyrene foam, the white and beady kind of styrofoam, because who really cares if the sprue looks like Styrofoam? I save the nice foam for the patterns themselves. So I don't always use toilet paper rolls for sprues, they were just handy in this case. I don't always hollow out the styrofoam sprues either, but I like to do so just to ensure the metal gets into the patterns themselves as quickly as possible. That's completely optional. It's at this point that you need to know whether you want to invest the pattern or not. I don't usually bother because I mainly do lost foam when I feel a quick an dirty approach will suffice, but I'd recommend it for precision parts or parts that need to be machined - Kelly has pointed out that sand gets into the surface of unmudded castings, ruining tooling, and that makes a lot of sense to me. I usually am able to brush the sand off my castings well enough for my purrposes, but I've never tried machining any of them. Very fine sand can leave very little texture on the casting, especially if you disregard the upcoming advice about pouring hot...



when I bury the foamies in the sand (I'm actually using abrasive glass bead blasting medium, but I would not recommend that if you can get nice fine sand as it will be cheaper and work at least as well, but I'll just call it sand to avoid confusion), I fill up the bottom of the bucket with rocks and pieces of bricks etc. to fill up the space down there, then fill it up with sand until the pattern can sit on the sand with the top of the sprue not too far below the rim of the bucket (this makes it easier to hit the sprue when pouring). I usually shake the bucket around a bit to settle the sand, then I press the pattern down into it so it is fairly solidly bedded.



Then I pour sand over the pattern until it is covered and gently compress the sand a little with my hands to ensure it is secure and won't move around too easily.



Then I fill up the bucket to a little below the top of the sprue, stopping periodically to slap and kick the sides of the bucket (a vibration tool of some kind would work a lot better) to keep settling the sand tightly around the pattern and sprue. It's not shown here, but then I take a soup can with both ends cut off and push it down into the sand around the sprue. Ths way when I can just pour until the soup can is full and the extra metal will add more head pressue instead of just spreading out to cover the surface of the sand. But I'm getting ahead of myself here...



Once the molds are ready, it's time to melt some metal! With lost foam, it's important to heat it up more than you would if it was a sand casting being made. My "poor man's pyrometer", a preheated steel rod, isn't super accurate but when it shows I'm at a normal pouring tempeature (ie. the rod pulls out of the melt clean), I give it another minute or two. This is the quick and dirty way, so we're not worried about avoiding a little bit of porosity from an overheated melt so much here, we just want to be sure it's hot enough not to freeze off leaving half a mold of half melted styrofoam buried in our bucket. So I try to err on the side of waiting a little longer rather than a little shorter.



Pour until the soup can is full. You won't be able to see when it's full because of the smoke and fire shooting up out of the sprue. You'll know you're there when it overflows, or maybe you'll catch a glimpse of the soup can changing colours as the level of molten metal rises up above the sand. With small parts like these clamps that is enough; bigger castings can trick you sometimes, the sprue is full and you stop pouring, then suddenly it starts draining into the mold again! Be ready to resume pouring and hope for the best, I think the extra heat may help avoid this delayed sprue drainage issue but I can't be sure as it's been a while since I tried to do a larger lost foam casting. Aim for the toilet paper tube in the middle if you used it...



After that it's just a matter of waiting for the casting to freeze, shaking it out, removing sprues, and any other finishing work that may be needed. I'll include those details of the muller clamps in the next post for the sake of completeness.

Jeff

 

Here are the muller clamps just shaken out of the sand:





Bolt holes were drilled through the 3 protrusions: 2 to attach the clamps to the muller's crossbar, one to tighten the clamps on the lengths of pipe. A slot was cut to give the clamps room to close up when the third bolt is tightened. I used a drill press and a portable bandsaw for these jobs but a regular hand drill and hacksaw should work fine with a little care.



My clamps shrunk little more than would have been absolutely perfect, so I had to file them out some to make the holes a little bigger. Much easier than having to try and make the holes smaller, am I right?



Now that the pipe fits snug in the clamps, I tested them out by tightening up the clamps then trying to make them move. They seem quite secure, I'm very hopeful that two of them will be enough to prevent the pipe from swiveling or moving at all once they are holding the scrapers onto the crossbar with sand dragging on them when the muller is running. I haven't tested them in actual use yet, but those details will be posted in the muller thread whenever I get to that point.





That's all for now.

This is not the good way to do lost foam, just the good enough way... But sometimes that's all you need.

Already posted in my muller build thread, but here is a video covering all the making of these clamps:



Jeff

 

Glad to hear it seems that way!

But nah, the video took way longer to edit, it takes ages to get rid of all the boring parts and awkward pauses, decide what to speed up as opposed to cutting, and then each time I watch what I think is the finished video after waiting half an hour for it to export, I realize there's so much more I should have cut. (Goodbye long and poorly lit tour of my old charcoal furnace...) This was really just watching it again, pausing it 21 times to grab screenshots, then hammering out some BS to go between the pix.

Jeff

 

Better quit worrying and get it done; you don't want to blow the deadline on your maker movement documentary!

Jeff

 

Thanks Mark. It's supposed to rain here all weekend, not sure if I'll feel like going out in it to figure out where to attach that pipe and make some kind of cereal box cardboard scraper templates for it. We'll see...

Jeff

 

Ha! I enjoy his videos, his casting skills have improved a lot in a short time.

Jeff

 

He's also been getting a lot of advice from olfoundryman... I thought some of his failed attempts at that center finder might have worked out if he had filled up his crucible a bit more so it would not lose so much heat by the time he got to pouring. Or maybe he just didn't have it quite hot enough for that thin part to begin with...

Jeff