So I have my furnace set up in the shop at work right now, so my boss keeps coming up with stuff for me to cast. 1st project is to cast a simple grate for this old floor drain. The old one has been missing for years, and the plumbing shop couldn't seem to find one. Figure it will be a good 1st part for lost foam aluminum. About 6 inch sqaure.
So what purpose does coating the pattern in drywall mud serve. Is it a barrier between the sand and the metal ?
Yes as to barrier. The coating is what determines the surface finish of the casting. Whether the stippled finish of direct loose sand texture or the as finished surface finish of the foam pattern. It replicates the detail and may slightly aid the fill if there is any variation in the packing of the loose sand, although it will not block runouts if there are any pockets. Sometimes I just embed the foam when I do not care about surface finish, but have found that I get better results with even a single coat of thinned mud that is fully dried. Orientation of the pattern is important so there are no voids in the sand.
So what does the pattern look like, what tools do you have for working foam, and how do you intend to make the foam pattern? Best, Kelly
That's the project for tomorrow . I bought a sheet of 2 inch foam today. We have a mill and other stuff at work that might be useful. I have woodworking tools that might be of use. There is always a pocket knife and a dremel. Pattern should be fairly basic, essentially just need a sqaure plate with some holes in it. I'll make something up as I go.
The sight of an open floor drain always reminds me of the time I got my walkbehind forklift stuck in an one. The cast iron cover had already been smashed by running it over previously. The rear steer/drive wheel is 5”wide and I think the hole was 6”. I had to run a tow chain out the shop door and pull it out with a truck. My caster side says go for it. It will certainly be a great exercise. Pete
Keep in mind that there will be shrink in the casting, approx 1.3% or .078" on 6" (corrected by Kelly downthread) One idea would be to make the foam in pieces: one sheet for the upper grate and then make whatever bars you need underneath to support it and hot melt glue them together before coating. Those 8 little shelves in the concrete are both nice to have and a nuisance to work around for patternmaking...
Thanks for the shrink number. I knew it was something around there but wasnt sure exactly how much to add in. I haven't quite decided how to do the under structure yet. Building it up out of cut pieces would be easiest. I don't have the tools, materials, or knowledge to do any wax fillet work yet. May see if I can use a ball end cutter to cut most of it directly so I don't have to worry about that. Thinking about running two tapered bars across the bottom the width of the plate. Act as stiffeners/understructure as well as part of the gate/runner system. Luckily this grate is in a bathroom so I don't have to worry about forklift or dolly traffic.
Shrinkage for aluminum is 1.3%........or .013/1 unit. A 6" dimension must be made at 6.078" on the pattern. Best, Kelly
If you plan on doing any lost foam casting, the first thing you need to do is build yourself a hot wire cutter. The are simple, cut quickly, cleanly and accurately, without dust or noise (some minor odor). Though I primarily use mine for resizing stock, you might be surprised at the complexity of patterns they can make. In a few minutes you could rip planks and pieces that could be assembled into the grate. Hot Wire Build | The Home Foundry https://forums.thehomefoundry.org/index.php?threads/sand-cast-or-lost-foam.2663/page-2#post-51524 https://forums.thehomefoundry.org/index.php?threads/sand-cast-or-lost-foam.2663/page-3#post-51574 I did this spider web with a utility knife in about 15 minutes. -Not far from a grate or trivet. ....And Along Came a Spider - Halloween Casting Contest 2017 | The Home Foundry The fastest and most simple grid pattern would probably be holes like Tops posted. A Forstener bit with all the speed your drill press can muster will make the cleanest cut. If you prefered a slotted pattern, router bits work well but again need router speeds (20krpm+) to work well. I use spiral flute upcuts. Milling cutters typically don't have the rake or clearance to be good foam cutters and a metal milling machine won't have the speed capability. For parallel milled/routered webs, I'd recommend cutting the grid into thicker stock then hot wire the stock to the grate thickness. That way the foam webs are supported and attached at the bottom while being machined and wont rattle under the cutter load. How you gate will become very important with an array of grid webbing in order to get all the divergent streams of metal to fully fill the part. Best, Kelly
Thanks for keeping me on the straight and narrow and saving @Mburtis from having to sand off .110"...
So carved out a rough pattern... ok very rough compared to some of the work you guys put out. Mostly free handed it with the dremel for the first one. Not a well designed casting I'm sure. Used a scrap spray can as a pouring cup. Went ahead and buried it in a bucket of play sand. The sprue into the top face was definitely not ideal for many reasons. I think it would be better on the bottom so no finishing would have to be done to the top. I didn't coat this one as I was curious what an uncoated surface finish would look like. Its honestly better than what I thought it would be. Vibrated the bucket with a air needle gun. Seemed to work pretty well actually. I think the pattern beng the other way up in the sand would be better now. The pour went well, the part didn't come out but I wasn't really expecting it to on the first one. It failed to fill and has what I assume are shrinkage defects caused by the thick ribs on the bottom stealing metal from the top face. All the defects are perfectly obvious based on where I put the sprue. Of course the thin sections between the slots froze before filling since they were the farthest away from the feed. I'll make a new pattern and try it again. Ill make the slots a lot smaller and neater this time. I may try to build it up out of blocks instead of carving it out this time, we will see. Ill think about redesigning the ribs too since i know an X is generally poor casting design. I'll spend a little more time on this next one and coat it just to see the difference. I'll also have to think about how to better gate and runner this part to get it to fill. I may not have accomplished anything but that doesn't mean I wasted the day.
Doing it similar to that was actually the first idea I had. I went with the other way just because it was the easiest and simplest way. Thanks for the input and the models.
You are welcome. I am missing a grate in the basement at home, once you figure it out I will be all over it
Your pattern looked very good, especially for a free hander. -Good job. Sanding the pattern with 220g can greatly improve surface finish. If you increase the width of the webs between the openings they will fill more easily. Also increasing the thickness of the grate may help. In general, I try to shoot for ~>1/4" wall thickness unless the part really needs otherwise. Gate it like Tops showed only tilt the pattern about 20 degrees so it is not straight up and down. The sprue can still be vertical. In general, gate into the more massive areas of the part that minimize the distance the molten metal must flow from the feed system. Gating into your support ribs actually will act like a more massive runner to feed the rest of the part. How are you determining your pour temperature? A contact pyrometer should be high on your priority list. If you don't know your pour temp it's just a shot in the dark. -Best to eliminate that variable.....you only get one shot as a lost foam caster. Best, Kelly
@Al2O3 thanks for the input. I used 120 grit paper to smooth the pattern somewhat. I wasn't being very careful so kept catching the edge of the paper and tearing the foam, especially in the corners. I'll use a smaller bit to cut the slots next time so the webs are bigger between the slots. Need to rig up better way to cut them, maybe I'll clamp the dremel to the side of the mill or something. Or maybe I'll stop being lazy and just cut them with an exacto knife. I really thought about gating it like you describe based on some of your work I've seen on here. I was sorta hoping running the sprue into the center of the part would allow the ribs to act like runners to feed the webs. Maybe if I would have flipped the part over and ran it in the bottom it would have worked better. I'll try feeding it more vertical and see how it works. Think I will make the top plate thicker. I can always machine it off later. As far as pour temp, I just wait till it gets real liquidy like then dump it. A real temp reading would be a good step to take.
I'm resisting getting sucked back into the 3d model world. I did it professionally as a mechanical engineer for a few years after college. Now I do electrical maintenance and controls programming in my day job. Try to keep computers out of my hobbies as much as possible. I'm more of a pen and ink sketch kinda guy now. Looking at the models though, I'm going to think about making the ribs thicker to serve as runners better. They were around 1/4 inch. Maybe I'll bump them to 3/8 or 1/2 inch. Or maybe I'll think about a different way to lay them out. From my understanding from the navy foundry manual, the thick junction of the X is not a great design. Maybe it doesn't matter on such a small piece out of aluminum. Maybe I'll try a couple of different designs and see what works best.
