Hi everyone, What a great Forum. I do Tesla conversions on the side and had designed a new setup for running the motor with out the differential by splitting the Model S unit in half. In doing so I needed a custom casting. So of course Youtube became my best friend for a few weeks as I built my furnace, my tongs my sand box with attach old hand sander for the shaker etc. Then watched way to many lost foam casting videos. Then I found Kelly's videos. Studied his channel until I was confident to let loose. Here's my results and pictures of my setup. In one area it seems I gone a little mixture of aluminum and sand in a bearing hole, it will be machined away but wonder what happened. Any thoughts? I also needed a radius and looked at the Freemans wax radius but from what I found out here, is you get a lifetime supply if you need 6 inches. So after watching the vegoilguy (gotta love Youtube) I thought I'd give brushing a radius a try with candle wax. Low and behold it worked great. I almost said and Bob's your uncle but I live in California so that's just not right. I put the pictures as thumbnails so I hope they get big when clicked on. First post so I'm not sure. I want to thank Kelly personally for the great Youtube videos.
Hi Jack, Great job and glad you found the videos helpful. The sand inclusion defect is what we call leakers. I believe it was actually THF member FishbonzWV that coined that phrase but it stuck. This occurs in overhangs in the mold that require the sand to flow the opposite direction of gravity. Inadequate vibration in either amplitude or direction is the cause. When molds get large and heavy it's more difficult to excite the mass to where the entire mold is near fluidized. There are things that help and work arounds in (my) descending order of preference: Positioning the pattern in the mold to eliminate or minimize the overhung cavity Higher amplitude/direction vibration and placing the flask on an unstable platform like springs to help excite the mold mass. Pack problematic cavities with bound sand. If you provide a little more information on how the pattern was oriented in the mold we can give you some practical options. If you used a pattern coating like PoP, you may find you can strike the defect with a cold chisel and it will release from the part. Sand is hell on machine tools. Best, Kelly
Hi Kelly, I used drywall mud for the coating. I had the pattern standing up like in picture #4 with sprue on top. I'll try the chisel method, if that does not work I'll grind it out before trying to cut the bore. Packing the holes with bound sand would have been the ticket for sure. The sand was packed really hard but like you said I had a leaker. My box was not wide enough to do a tipped lay down which also would have fixed it. Next time I'll be sure to use a 5 gallon bucket for that type of part and lay it back a bit to make sure there is no overhung cavity. Cast and learn.
Jack, There is a simple improvement and potential solution. If the pattern is oriented like this, the top of the circular cavity is no longer an overhang and is more receptive to better vibratory packing. If your flask can't accommodate it........another flask is due. Give it a try....you'll like it. I always position top gated patterns at an angle, even if they don't have overhangs. Best, Kelly
Thanks Kelly, your picture was in mind almost exactly after our first conversation. Now it can be in everyone else's too, that's great. I ground down the leaker and it is pretty much all aluminum, the top was coated with embedded drywall mud and very little sand. So all in all I'm pretty jazzed and can't wait to machine and fit. The only thing I can add is that if anyone tries using candle wax for fillets and uses drywall mud is to have the mud thick enough so it does not fish eye or run away from the wax. I thickened mine up a bit for the first coat then a couple thin coats afterward. Worked great.
The reason it's mostly aluminum is because that area of the sand was not sufficiently packed/stable and dislodged under the molten metal pressure. When that happens the thin, weak, plaster coating is breached by the pressurized molten metal which compresses and fills the uncompacted sand. Sometimes the plaster breach is local and the thin plaster layer remains in place acting as a barrier. That's why a strike can (sometimes) release the leaked area. The reason the wax fish eyes is because it's very hydrophobic. A surfactant can be very helpful. So is the foam but not as bad a wax. Propylene glycol is good surfactant. It's used as an anti-spotting agent in dishwasher detergent. Dawn dish washing soap is also rich in propylene glycol. I dip my foam patterns in a 5 gal bucket of soapy (a couple tablespoons of Dawn) water before I dip them in slurry. Spritzing from a spray bottle also works well. If you are brushing your coating, adding a little Dawn to your thinned drywall mud will do the same, but better if you also wet the pattern in soapy water (shake or blow off the excess) before doing so. Best, Kelly
It might be a little hard to find in California especially this time of year but propylene glycol is cheap and sold by the gallon at hardware stores as plumbing antifreeze, it's used for things like winterizing the plumbing system in an rv.
I did a search for the propylene glycol and California does not like it. At the ranch in Oklahoma I buy gallons every year to do freeze protection over the winter. I'll try Dawn dish washing soap on my next one. Here are some pics after machining the bearing holder/cover. I do have some porosity in the casting which is probably my own mistake. I should have stirred the caldron a bit as I only pulled the dross off. I realized after the pour I never stirred it at all as I read that stirring excessively causes other issues. So any thoughts would be helpful on this. I also did not use flux or degas because I read too many conflicting as what to use. Salt, diet salt, baking soda etc. So I figured on a straight pour to get a base line. On to the next pattern. Motor side cover with cooling fins, this should be fun. Climb milling fins is the only way, thank you Kelly for that thought, works great. I tried use a heat gun to clean up the little hairs that seem to be left behind and it worked great once I got the distance and time right.
Well I can't say about California but Propylene Glycol is in all kinds of common consumers products, including Dawn and most dishwashing detergents. Dawn should suit you fine. It doesn't take much. Your casting is fairly chunky, as opposed to being a more uniform wall thickness and that in itself can aggravate some porosity and shrinkage issues. However, if the added material cost and weight isn't objectionable, there's are lot to be said for simplicity of the pattern and the flaw/fault tolerance that comes with added material and strength. -Just a practicality thing. When it comes to aluminum, degassing and fluxing aren't the same thing. I used the eutectic of KCl and NaCl (table salt and light salt) for a while when I started but haven't in years. Melt fluxes are typically just to help gather oxides and frankly I've never found that to be much of a problem. Degassing is trying to liberate dissolved H2 for molten Aluminum. I still degas occasionally but not much since I started using virgin ingot. Here's my degassing lance build. http://forums.thehomefoundry.org/index.php?threads/degassing-lance.204/page-3#post-3911 I you don't recall you mentioning what are using for casting stock. Scrap? Known material? Best, Kelly
I have no idea what aluminum I used since I got the ingots off Ebay weeks ago before I found your videos and THF. I would actually like to use virgin ingot myself now since I know my furnace works and I believe I can do better now. I would imagine 356 aluminum would be best but I'm open for suggestions for sure and where to buy.
How many of these are you looking to make Jack? Getting commercial metal sources to deal with you on small quantities is difficult and for small buys shipping often inflates cost 30-40%. I buy about 750lbs at a time and that's peanuts. The only reason they sell to me is past relationships. You also wouldn't want to truck it across the country if avoidable. You might be better off approaching a foundry for small purchase. Foundries might be more scarce than Propylene Glycol in CA. 356 is a decent all-round casting alloy but really needs post treatment for strength and machinability. A T5ish treatment is easy and gains a lot of strength and machinability. There are other alloys that have better as-cast properties. Best, Kelly
Jack, one thing I should have mentioned, when it comes to casting aluminum, be sure you maintain a lean burner tune. The added hydrocarbons from a rich flame can be a big aggravation to hydrogen porosity. I use a resistive electric furnace so cant get much leaner without inert gas. Best, Kelly
Jack, For fillets in foam, you can make a simple extruder and use bee's wax to make strings of varied diameters. 1. Make a brass cylinder 3/4 od, 1/2 id, 4 to 6" long, closed on one end. 2. Drill the closed end the size rod you desire. Or tap it for changeable "dies." 3. Make a piston 1/2 diameter at least 1" longer than the cylinder bore. 4. Fill the cylinder with shavings of bee's wax half to 3/4 full. 5. Put the piston in and warm the exit end of the cylinder. 6. Press to extrude the wax rod. Bee's wax is a bit sticky and you can put the rod into the corners of your foam pattern. Make a ball end stylus (I use 1/4" rod) and warm it slightly to form the wax into a fillet. In my lost foam experience, I find these other things disappear ahead of melted aluminum; wax, hot melt glue, masking tape, Elmer's glue. I always fill from the bottom using a cardboard tube from paper towels for the sprue. This may eliminate the drops. Another wetting agent is Kodak Photoflow 200. Regards, Ray
