Hello again, I'm pretty hooked on using lost foam after using this process on my 1/6 scale Demon V-8 tunnel ram and bellhousing. I have started the next project and intend to cast some more parts out of aluminum. This project is a steam engine, but uses an unique valve mechanism that appears challenging and appealing when running. Most steam engines of this type and purpose are single cylinder and use an eccentric to time the slide valve. This engine has two cylinders, phased 90 degrees and uses an adjustable cam so the user could adjust the timing lead for torque and speed, but also reverse the direction of the drive wheel (over/under). The plans were featured in an old model engineering magazine in 1905. A good place to start a project like this is the base. I scaled it down to 0.6 scale of the original so it fit my collection, and equipment capabilities of my forge and lathe. Started by cutting sides and cross webs using my shop-made hot wire table. I used hot glue and some slower setting craft glue with pins for trim and top parts. Let that set overnight with painters tape, and the next day sanded flat, and added raised features for mounting the cylinders, slide rails, main bearings and mounting bosses. I used a lathe to turn the bosses to size (1/2") and counterbored them to print using a two flute endmill on my mill. I had read about using candle wax for fillets and used that to fill some seams, tear-outs and inside corners. Last project I used toilet bowl wax and a disassembled inspection mirror for the ball on a stick. the candle made my shop smell nice, and I liked how the wax wicked into the fillets once I practiced a bit. I had to use the curved end of an engineers scale to tidy up an area where I applied too much. I then coated gated and coated with thinned drywall mud. This is the largest and thinnest piece I have ever attempted to cast. I don't think I have a big enough crucible (4KG) or bucket (5 gal). I ordered a 6 KG crucible, and can build a wood crate easy enough. I also plan on weighting the sand down so it doesn't float.
The position of the pattern in the flask inferred by the sprue looks good. For aluminum, I dont think float is much of a threat as long as it's burried deep enough and based your sprue and likely added cup height, that looks pretty good also. Don't underestimate how heavy that mold will be. It will take some fairly powerful vibration to insure good packing. Vibing in stages as you fill will help as the mold mass will be lower. Once you get to the sprue, it will become less critical. I cant see the features where the sprue is attached, nor amI sure about the dimensions of the pattern, but if I was gating that for a one and done, I'd probably place runners along most of the length of the base. The runners can be more generous cross section than the pattern and assure hot feed metal is available everywhere. It's a little more work to degate (usually rip on table saw with carbide blade) but has very high success rate. Here's an example. http://forums.thehomefoundry.org/index.php?threads/automotive-oval-air-filter.894/#post-20757 Pour at 1400-1450F. Candle wax can very greatly in melt temp. If it's workable and not melting your foam, probably OK, but if you're going to do much LF casting, I highly recommend you purchase the freeman wax fillet stock formulated especially for lost foam casting (same melt point). Nice work so far. Good luck on the pour. Best, Kelly
Hey Kelley, Well it didn't work out as I had planned today. I didn't have enough melt for the base even with the "bigger" crucible. Then my wooden flywheel patterns kept pulling the inner spoke sand out when attempting to remove them (twice). I did have success with some small bearing caps, and standards I doubled down on these luckily. One standard didn't completely form at the top. The foam flywheel came out complete also (I need two). I measured the bigger 6KG crucible by filling my smaller 4 KG crucible with sand. Not much more melt (volume). I also weighed the casted base, flywheel, small parts, and some ingots. They weigh 1.1-1.2 kg and I'm supposed to yield 1.8 kg aluminum. Back to Amazon and ordered a 8KG crucible. I don't think my forge will support the combustion with the bigger diameter though, and may have to fabricate a thinner wall steel pipe crucible if I can't get the flame to stay lit. I included a picture of the heat treat oven that I built which I used to preheat the 6KGcrucible before use. I relieved the hard edges on the wooden flywheel spokes and coated again with shellac.
Hey Blue, a lot going on in that post above. On the base if it was a short pour, not much to say as far as the fail, but I never really got a very good look at the gating. The failed casting doesn't seem to look much like the features on the pattern......perhaps due to mold collapse due to the short pour. If you interested in trying again with another foam pattern, I can try to expand on my previous post regardng gating approach. Best, Kelly
Hey Kelley, Here is a closeup of the dipped base upside down. The part closest was on the bottom of the flask and it completely formed. The sprue between the second bulkhead and the topmost was not filled as the crucible contents expired. I'll try foam again with a larger melt volume and I am interested in any gating tips you offer. I used the pin router approach you suggested on the flywheel and have two more foam patterns on the spoked centers, just need shape and laminate more rims. Thank you
Here's what I'd suggest. Similar to the previous link I posted to the air filter, attach a runner (or gate? The lines blur a bit with lost foam) the entire length of each side, each connected to the sprue via a Y branch. I don't know the dimensions of the part but I'm guessing 15"l x 5"w. I use a cove or ball nose bit to reduce the width of the contact surface of the runner with the pattern for a couple reasons. This makes for a massive amount of contact area to feed the pattern and allows for a more massive runner to supply hot metal to the entire part without having to travel long distances through thin and tortuous paths within the pattern. This also makes degating easier since you can cut through the thinner runner section. I use a carbide blade on a table saw. You'd probably need to make a crude wooden sled to hold the casting parallel to the rip fence to do a good job. I remove as much of the gate as I dare without cutting into the casting then remove the rest with my mill or belt sander. The runner height is greater near the sprue than the end of the of the casting. This is just because the bottom section of the part does not require the full cross section of the runner to be fed and also to reduce the total metal volume of the gating system. The gating volume will be non-trivial. Since you are close on crucible capacity, you may want to calculate/estimate it. If you don't taper the runner, you may be able to use it directly against the rip fence without a sled. It needs to be positioned leaning in the flask with the box shaped cavities exposed upward, as it appears you did. I might flip the pattern around so the open section was near the sprue, but only if I thought there was more metal mass in that third of the part than the opposing end. Looking at your pattern construction picture, it looks like the wall thickness is greater in the open section. Placing that at the top of the mold means it will always be fed by the hottest metal and freeze last........in an ideal world directionally from the bottom up. If there isnt a significant difference in metal mass on either end it probably doesn't matter. An interupted pour is the kiss of death for a lost foam casting. The molten metal pressure is what holds the undbound sand in place. When there is a gap in metal flow the foam is evaporated and the resulting cavity usually causes localized mold collapse. Use a good sized pouring cup. It provides a buffer so you have more time to see through flame/smoke and respond to that classic lost foam pause and gulp in feed rate. Best, Kelly
Hello, Here in not so sunny Florida following hurricane Denise, we had a good day casting. I gated the part following Kelly's advice and got acceptable results with the larger 8KG crucible. I only got 1.9 KG of aluminum when I should have yielded 2.5 KG using a ratio of 2.7/8.5 AL/Br. Got a flaw on the top that looks like I didn't vibrate the sand long enough or it was too damp, or both. Still it was good enough, and I went on to cast the two flywheels while the forge was hot. These parts have a lot of flashing and poor surface finish due to the sand sticking while pulling the patterns. I was very low on baby powder, so hopefully they clean up. Instead of buying baby powder is the real parting powder worth it? I can get 5lbs for $30 bucks on Amazon. My daughter videoed the pour, and will review it and perhaps post it on youtube and provide the link later.
I don't understand what ratio you are referring to. You're casting aluminum.....correct? We LF guys call that flaw a "leaker". It is caused by insufficient packing; either poor vibration (not dry) sand condition. Vibing as you fill the flask, before it gets full and heavy, can help. If the sand isn't packed well, the molten metal will leak through the refractory coating on the pattern, mix with and displace, the loose sand. If you had a decent amount of refractory coating on the pattern, it's likely that most of it is still there between your original pattern surface and the flaw. Sometimes you can get those to pop right off if you can get the edge of a sharp chisel under it and give it a sharp rap. Just be advised, if you try to machine it off, there will be sand mixed in the metal so don't use a cutting tool that you very are fond of. Best, Kelly
Hi Kelly, Yes this was poured using a large salvaged aluminum machinery casting cut up and melted. It is definitely aluminum. Because of running short on the last attempt, I carefully measured and calculated the volume of the foam pattern and sprue/gating. I compared this to a best guess of the larger crucible which is advertised as a #8 size, 10 KG which I believe to be the capacity in brass. To estimate the aluminum weight I used a ratio of density (actually specific weights to avoid the pesky gravity constant). I weighed the as cast part and it weighed less than 2 KG or 4-1/4 lbs. Just sharing the experience of the import crucibles being on the small size. The OD was less than listed also 5" vs 5.6"
Ahhh, I understand. I can't say with certainty as far as actual crucible volume, but they are usually all rate at brim-ful so unless it's spilling over the top full, you won't realize rated volume. I use Morgan crucibles and the A series are brimful aluminum weights. They often list liter volume too. You are correct that kg rated crucibles are most often bronze, but not sure the entire world observes such. I have seen a number that use precious metals as their standard as well. Best, Kelly
Somewhere along the line I had gotten the impression "#8 10kg" meant 8 pounds of aluminum or 10kg of brass. But some quick internetting tells me that a lump of brass the same size as 8 pounds of aluminum would actually weigh a little over 11kg. Not TOO too far off though. Jeff
Last weekend I machined the sand casted flywheels. There was a fair bit of filing required to clean up the spokes, but the rest of the machining was straight up lathe work using a faceplate to bore the shaft, taper the hub, and cleanup a few spots where the pattern didn't pull cleanly on the inner rim. Then I fastened each one to an 7/16" arbor and trued up the outer diameter. I had to use the boring bar upside down and run the lathe in reverse to get this to work on my 7X14 mini-lathe but got a very good finish using auto feed at 500 RPM with copious spraying of WD-40. The aluminum that was remelted to cast these is giving a very nice surface finish so far, unlike other extruded melts that I have done which were gummy and smeared. Then I broached the keyways, primed the centers and set aside to dry. I will polish up right before final assembly as the aluminum seems to scratch easily unlike cast iron.
Those look very nice. Well done. Knowing what alloy you have can make a big difference for parts that will be machined. There are alloys that have good as cast machining properties. I use A356 ingot. It's a good all around casting alloy, but, as cast will be very soft. That can actually be a good thing if you need to straighten a very thin casting. A T5 temper is easily achieved (you can do it at the upper limit of a kitchen oven, though I dont recommend it) and achieves 90% of the property improvement as T6 with much less risk of damaging the casting. An as cast temper casting is gummy and not much fun to machine, even with cutting fluid. T5 makes a big difference in strength hardness, and machinability. You might consider Zamak for some of your sand cast parts. Zinc is quite dense so it would make a very good flywheel (on par with iron) and with the additional aluminum, the as cast strength and machinability of Zamak is quite good. It will also produce great casting detail. However, the melt temp is so much lower it doesnt lend itself as well to lost foam casting. Best, Kelly
Thank you for all the helpful tips and tricks, Yesterday I worked on the large (too me) base. It was pretty scary cutting the gates on the table saw, but had my hands well clear of the blade using C-clamps on a wooden sled and raising the cut half a dial at a time. I machined the bottom, then flipped it and indexed it using the mounting bosses to establish the centerline. After decking the pads, I drilled and tapped the cylinder mounts and then the main bearing journals. This model uses square bronze bearings with a horizontal split to take up wear I suppose. I really like the curvy bearing caps and cast those using foam also. You can see how the flaw from the loose sand cleaned up here to the left of the tap between the valve linkage deck and the cylinder deck. Next I machined out the galleys by plunge cutting and then side milling the perimeter. Finally I side milled the bearing towers using a ball nose end mill and blended the seams. This wasn't really necessary but will allow both bearings and caps to be interchangeable. The difference was about 0.025" on one side due to some leaning of the foam pattern during glue up. I will need to tap the guide blocks and fill the two 1/16 holes I drilled in the wrong spot. Probably sand blast the machined areas and whack the surface with a stiff wire brush to make the surface finish appear uniform. Next I'll work on the bearing caps and valve linkage standards. Very pleased with the results so far. Given my lack of experience, I don't think a wooden pattern would have pulled cleanly and given the detail achieved with this foam pattern.
That looks very good Blue. Congrats on the casting success and results. How did it machine? Raw castings can be a little gummy. For sure. A sharp blade at the shallowest setting, sleds/fixtures where necessary, and hands out of harms way. I find the number of teeth on combo blades seem to work well. For additional reach, I use smaller diameter wood working blades mounted on a slitting saw arbor on my mill. Since you have a mill, that may be more comfortable approach for you too. Getting a perfect match to the as cast surface texture can be difficult, but media blast usually makes for uniform color. Coarse media blast blends better but makes for a high surface area finish that stains easily. Wire wheel on a drill gives a shiny finish but actually does work the surface a bit (especially on soft castings) depending upon how aggressive you get. Try an area that doesn't show to see if you like it. Vibratory media can give some nice finishes too. I like a smooth modeled finish and the right vibratory media makes casting look a dull grey like the oxide layer on die castings that have been anodized. I'm sure it could have been done either way, but for one piece, it's pretty hard to beat lost foam, especially if you dont have an accomodating green sand flask or enough bound sand to handle a larger part. No draft or cores can be a big plus for lost foam too. I'd have a garage full of hard patterns by now if I was a green sand caster. Best, Kelly
Hey Kelly, The castings machined well. I had a few spots on the flywheels that didn't machine out, but it adds to the handmade retro look. It runs happily in FWD and reverse. Build log on HMEM with video of it running
Nice work. It looks every bit the part. Have a link to the build log and video you could post? Best, Kelly
Thank you, The build log is here https://www.homemodelenginemachinist.com/threads/muncaster-joy-valve-steam-engine-1-2-scale.34582/ you tube video is include in above link, but also here
