Attempting to cast a 2" high, 5" long aluminum tunnel ram for a model engine I've been working on. This is a first time evolution for lost foam casting. Let's get started....
The prototype was fabricated to get a feel for the proportion to the engine, and start learning how to use the hot wire cutter and fence. Also improving the techniques such as sanding and gluing. First intake is closest and took 12 hours. Next two took half that time. I have a high degree of confidence this won't yield acceptable results on the first pour, so I'm making several.
In order to learn what gating to use, I made some simple shapes and cast some scraps of extruded aluminum conduit. I took deliberate short cuts such as no flux, minimal sanding, no pour cup and no dip coating. All pours used #100 sieved Florida sand left over from previous failed green sand experiments using ground kitty litter. I usually just spread it on plywood when I do sand casting as fire/spill protection so I sifted out the coke and wood particles. Used a Sawzall held to the cope to pack the dry sand. I even tried two parts in one flask to get a feel for what happens when the sand gets hot. Curious to see if it collapsed the second part's sprue. The intended use if these samples worked was a shop ashtray with lid, wood burning makers mark, and a separate tunnel ram plenum. We figured we would objectively criticize them in the third person. This was the primary reason that I joined the forum. Me and "Johnny" felt kind of foolish talking to ourselves. The best result had used a single white foam shape for the sprue. It was cast first in the same flask as the one to the right labeled "ran short". Here are the results... Please reply with your ideas
May have an issue with this three way sprue based on these trial pours. We are thinking this will be a sacrifice part anyway to test the drywall mud coating and newly made pouring basin. Watched Kelly's video on rammable refractory and foil tape basins. All I had was an old piece of calcium silicate high temperature pipe insulation. It's softer than fire brick and has an upper limit of 1200 F, so may not work but it's what I have on hand
You're off to a great start Blue. For the intake manifold, I'd just gate into the carb pads. Your trial pours don't look like they had a pouring cup. The one marked "too much glue" looks like an interrupted pour. When the pour is interrupted, the mold collapses where the sprue was because there is no metal pressure to hold the mold media in place. When you pour a lost foam casting, there is a classic "pause" that occurs after you first introduce metal. This almost always fools first time casters into think the pour is complete. It is not. The mold will start taking metal again so you need to be ready to fight through any fire or smoke to complete the pour. In very small pour like yours this is less noticeable, but for small parts, the sprue and gating are often larger than the part itself. For a pouring cup, even a soup can placed around the sprue will do, then add some more sand to cover the depth of the can. Pouring cups provide a buffer volume of metal so if you are a little slow on the draw to add metal, it doesn't uncover the sprue and interrupt the pour. Round cans can tend to aspirate air. An offset pour cup is an improvement. I suspect aluminum will adhere to calcium silicate. Here is a link to the moldable ceramic fiber I use. If you just smear it on the surface of the pouring basin you fashioned, let it dry, sand it smooth, aluminum will not wet or stick to it and you'll likely get a number of reuses. I'd suggest you make future cups a little deeper with more draft. Here’s “Ceramic Fiberboard Moldable Mix- CAULKING TUBE” https://www.ebay.com/itm/254519449811?hash=item3b428a98d3:g:np4AAOSwlHJeUDSY Here’s a “Ceramic Fiberboard Moldable Mix- GALLON” https://www.ebay.com/itm/254519450959?hash=item3b428a9d4f:g:np4AAOSwlHJeUDSY Since those links will probably die, for posterity’ sake, here’s the sellers eBay store link. https://www.ebay.com/str/hightemperaturematerials?_trkparms=folent%3Ahightemperaturematerials%7Cfolenttp%3A1&_trksid=p3542580.m47492.l74602 You'll want to ditch the extruded stuff and use a scrap casting as stock for your actual go. Extruded stock does not flow/cast nearly as well as casting alloys. After you outgrow the hot wire, if you are a woodworker, you can make pattern guided router templates and take a shot at casting the runners and carb plenum cavities for a near net shape part. Happy casting. Best, Kelly
Thank you for the instructive tips and advice. We are blessed to have a local refractory wholesaler nearby that is willing to sell to me. The owner gave me a tour, and I will be buying some raw materials for a future electric heat treat oven. I'll add a pail of moldable to the quote. Here is a picture of the finished pour cup and handle.
An inquisitive neighbor stopped by during the casting session and photographed the pour. While the pouring cup material did survive the melt, the damn thing leaked or floated upward during the pour. You might see the molten puddle to the left of the basin. This ruined the cast. I have plans to add steel to the cradle and pin the light cup to the frame with some finish nails and try again.
This piece was too tall anyway, and my best pattern was next up. I used one homogenous sprue to eliminate the hot glue joints, and gated it simpler per advice given. Pretty fragile piece as shown during dipping. The plan was to use my best scrap material for the real pour. Unsure of the actual material composition, but It's fairly difficult to cut up. I've used it before for important parts using greensand casting. Not as gummy as T-6061. I think it was a hydrogen cooled generator collector end seal approximately 4 foot diameter.
Good second attempt at the pour! A few defects from the pattern, but it cast very well. I used toilet wax and part of a telescopic magnet as the fillet tool for the radius'. Minimized the amount of hot glue and did not hollow out the runners or carb mounting pads. That may have something to do with the previous pour failing. Trapped air may have burped and caused the basin to lift and leak out the bottom? Hard for me to keep very precise alignment using foam. Does anybody use jigs or alignment pins/locators as they glue up fiddly parts? Even though I made a gluing jig, the actual angle of the intake flanges is off 3-4 degrees, but it cleaned up during machining. Biggest lesson learned is to be more generous on material surfaces to be machined. The estimated shrinkage used during pattern making was 1% and it appears to be closer to 2% on the cast part. I imagine I sanded some material away though. It barely covers the backing mounting holes in the heads, but with some rough machining done I think it may be a keeper. No way that I would have been able to make this part using a manual mill and my skill set.
Congrats on a successful casting. -Now you've done it.....and so it begins......the onset of casting addiction. You need to fill the sand mold up to/near the top of the cup. Even one inch of metal head pressure will be enough to float a light cup. The additional height/weight of sand will prevent that. That's also why a little deeper cup can be beneficial......burry it deeper and don't fill it completely full of metal. It's handy stuff to have around. It's a little fragile for structures that will be handled or see tool contact. That's why I have sheet metal lifting cradles for handling but if you heat the used pouring basin to say 1500F, it will return to a pristine white state and can be patched or repaired indefinitely if needed. I have a number of them and have well over a hundred pours. There's a whole thread on them here: http://forums.thehomefoundry.org/in...le-offset-pouring-basin.688/page-3#post-39356 I think you did very well. Not sure how much LF casting you intend to do but a set of fillet tools would be a good investment. They are cheap on Amazon. Also, Freeman Manufacturing Supply sells fillet wax strips specially formulated for LF casting. Very easy to apply, behaves like foam when melting/evaporating, and $40 gets you a lifetime supply.....also very handy to have around. Did the first one have hollow runners? Oh yes, all the time on more complex parts. Hot melt is great for instant stick, but some times you need a little longer working time. Ordinary PolyVinyl Acetate white glue works well. Apply it very thin. I like Arlene's Fast Grab Tacky glue because it's virtually self fixturing. Also inexpensive on Amazon. Tip: You can use small strips of tape to hold PVA joints in place then just remove them after the joint is cured. Apologies if I already posted this but this thread is good read for LF casters. http://forums.thehomefoundry.org/in...ssions-of-a-lost-foam-caster-5-years-on.1650/ One last thing, on gating......the rules for gates and runner sizing typically used in conventional open cavity casting don't really apply because the progression of metal is controlled by the evaporation rate of foam, not the velocity created by gravity and cross sectional area of the feed system. Typically I like to top feed a part. I would never do that in an open cavity mold. It's good to be able to gate into the most massive area of the part and better if that is higher(est) in the mold. I dip coat my patterns so the feed system needs to be strong enough to support the weight of the slurry covered part. Ease of degating and casting cosmetics is also a consideration. I use a .75-1" Sprue for almost everything <10lbs. The orientation of the part in the mold can be a little bit more involve discussion, but in general, a tilted angle that minimizes horizontal overhangs of features is best. Happy New Year Best, Kelly
Great advice Kelly. Thank you again for compiling the 5 year compilation of tips and tricks. I have read and reread several times. I seem to learn best by reading/listening and then doing it. Make mistakes of course, but the visual experience seems to stick better inside the gray matter. As far as the casting addiction: When I release a cast part from the sand, I feel like a five year old again unwrapping a gift under the tree. Could be oranges and walnuts, or might be that wood burning kit you really wanted.... The first pattern did have crudely hollowed runners. I was making sure that I could connect the intake ports to the plenums using the jobber length drills I have too many of. I covered the "ports" back up with the white sprue material which morphed into using three gates. My reasoning for not casting the ports into the pour is two fold. I had little hope it would work due to inexperience and small scale Wanted to control the port diameters to help ensure the engine would start/run and have some decent throttle response. The plans call for 3/16" ports and a 1/4" x 1/2" plenum cavity for a single carburetor. As a younger man, I learned the hard way that bigger is not better when it came to carburation and intakes. It is critical that this engine runs. I wouldn't be able to settle for a static display, no matter how many times I remake the parts. On the topic of hollow ports: I used some brand new "carbide" burr bits of reasonable quality to hog out the plenum. Worked great for the first minute, but they dulled rapidly. I cleaned the flutes, but they seem to be ruined. Do you think I overheated them, or where they just junk? I suspect that plunging them melted the foam which then abraded the flutes. An ex tool and die maker at work once related the abrasiveness of PVC to me. I also attempted to use a homemade hardened tool steel plug cutter that had worked really well on my distributor cap towers, and it worked for two times before also dulling and tearing the foam. Guessing the cutting edges need more clearance than what I'm accustomed to? Happy New Year
Congratulations on your results so far. Between your existing skill set and experience and Kelly’s advise you’re sure to be successful in this project. I’ve done a couple of lost foam castings which turned out ok, but nothing of this nature so I have nothing to add specific to lost foam. I do mostly all of my casting in greensand or petrobond with either wooden or rigid PVC patterns and although casting to net shape and size are ideal, considerations for things like shrinkage, directional cooling, final fit, and work holding come into play in designing the pattern or in the molding process. There’s often the potential for casting warpage and pattern deflection when packing the mold as well. That little bit of extra thickness (I believe it’s referred to as padding) here and there as needed can really save the day. I’ve gone way overboard at times and created a lot of unnecessary work in milling, filing, etc, but when it’s a one-off casting I’d rather err on the side of caution and go oversize in certain areas and deal with it afterwords. Sometimes I regret the decision (like during hour 2 of milling or filing) but sometimes there’s no way around it. Machining capabilities are helpful in making those decisions. I’m interested in the fixture in your last picture above with your part mounted at an angle. Is that shop-made. Is it aluminum or steel? I’ll be following with interest. Pete
Welcome to the club pal..... Don't ever put hollow cavities into a lost foam pattern or hollow out a sprue.......very bad. I'm not talking cored features I mean closed off hollows......very bad. It causes air pockets and localized mold collapse. That's probably the source of the bubbling you saw. You want the molten metal to just homogenously progress through the foam in a continuous uninterrupted front if possible.....like plugged flow. Those are small and will/would be challenging to keep sand in them stable. You can have a look at the link below as an example of the water jacket in a mock engine block. It was an exercise in the art of the possible. http://forums.thehomefoundry.org/in...ed-loose-sand-coring-in-lost-foam.12/#post-55 The positive aspect is you can get the sand to flow through the runners as opposed to blind passages. That means they stand a better chance of packing well. If you wanted to try to cast those ports, I would position the intake carb pads up in the mold and then pour a very fine sand in the plenum, vibrate it, then fill the remainder of the mold with your normal sand. The other possibility is use a very small amount of epoxy resin (it needs to be some thing that chemically cures and doesn't attack the foam, = epoxy) as binder, and pack the runners so it becomes a solid core, then use normal lost foam process on the rest of the mold. It's starting to approach the limits of lost foam method. It's probably better suited to be 3D printed in PLA and then investment cast.....but if you aren't set up to do that, well....I'm set up for LF so when your only tool is a hammer, everything looks like a nail! Honestly, for the size and precision you're looking for, I would cast it solid with the exterior features you want and machine both the runners and the plenum, even if you had to make a bolt on plenum lid to do so. From you're engine pictures, the adjacent intake runners have already been combined in the heads in what appears to be a round port, so I'd just do the same with the runner and make a it a straight shot into the plenum. -Just a practical compromise. Metal grinding burrs do not work well in foam. Wrong cutting and relief angle. Using a round nose wood working router bit with all the rpm you've got. The wide gullets in wood working bits clear the foam chips and the cutting and relief angles are much better suited for foam. Best, Kelly
Looking great. HT1 steered me to the Dremel 562 tile cutting bit. I don't remember cutting much foam with it but it was great on my wood patterns.
Thank you, it's shop made based on a gentleman's video on Youtube called Pragmatic Lee. Wonderful set of video's. I had a need to mill on it rather than just drill, so I made extra support and adjustment using a rear leg. It aligns itself fairly accurately in the table's teeslots, but I typically dial it in with a parallel bolted to it. I use either a digital angle reader, or do the Trigonometry (like a Sine Plate) depending on accuracy required. It was built when I needed to do all the machining on the cylinder heads for this engine. Very handy, but I still need to make a wooden storage case and dedicated clamping hardware. It also merits knurled knobs instead of hex nuts on the adjustment.
Angle Table pictures. A few items worth noting if you build one. Its important to mill the 2 inch cylinder so the table comes in at a tangent, but yet a few thousands proud in case material overhangs. The angle bracket holes should have a sliding fit on the cylinder center bolts and also have several thousands clearance so they secure the cylinder into the tee slot. The fit on the pivot bar to the table should be snug also. I used 1/4 drill rod and threaded it thinking that the remaining shoulder would help stiffen the assembly, but ended up threading almost all of it. 1/4-20 all-thread would be simpler. For quick jobs, one could just clamp it in the vice and use it as a fixture pallet also... Nice project and comparable quality to the Import angle tables for sale
Looking good. When I saw the post title first thing that came to mind was David Freiberger and him saying "Tunnel Ram!" Maybe I watch too much Roadkill/Engine Masters, lol. I do love the scale engines and would love to make one some day, just don't have the time now with so many other projects. Keep up the good work.
Machining completed. I cross-drilled the front plenum to the rear and have a setscrew plugging the rear hole. I might make a cast a piece of round, thread it and file smooth so it disappears. Haven't finished the distributor yet so I held off on drilling that. I cast a mounting pad on the valley for it just below the set screw. The T-stat and carb bolts are #0-80. Eyeglass size tap. Would have been a bad day to break those off.
