I was doing a very similar project so decided to give this one a go. http://forums.thehomefoundry.org/index.php?threads/wheel-center-cap-needed.2077/ Fired up the CNC Router and did a test cut today. Looks good to go. The extensions on the backside bosses are the gates. It’s 7” in diameter and only .125” wall. I'll make a small fixture and machine the counterbores into the face. On the original the wall thickness was only .035" on the counterbore cylindrical walls! Apparently they have a tendency to break. I'll thicken those boss walls up a little. -Let the games begin! This is never going to work Best, Kelly
Now I see why I hired you, way beyond my capability. Looks great and I'm enjoying seeing the process!
Today was about as good as a weather gap as I was going to get so I got after it. I didn’t do anything special, just an ordinary gravity fed pour. Here it is dipped and ready for the sand. …..as it came out of the sand. Kind of interesting, you can see the nit lines by the carbon signature in almost perfect pie segments. That was some really crappy foam I used for the gate. I pitched the rest of that. ….degated and cleaned up …..and finally next to the original. I’ll make a fixture to machine the counterbores and cast a couple more. Best, Kelly
Wow, I'm very impressed how good it came out for as thin as the foam was. You really have proven that there is no real limit to using foam for casting.
Those came out great Kelly. I use some of the lighter packing foam for my sprues, but I may need to rethink that. It looks like it almost aspirated in one of the gates.
The white foam is ok depending upon density. That stuff was crazy low density. I didn't weigh it but I'm guessing ~<0.3lb/ft3 so much so there were gaps between the expanded beads. That let the coating penetrated those gaps. I didn't like that and it was flimsy. I think most of the white/EPS I have is about 1 lb/ft3 which works fine and can be sanded smooth like XPS. You can tell the difference by denting with you finger. I could also just use the pink stuff which is 1.5lb/ft3. It's definitely stronger which is a benefit when you dip and hang the wet heavy pattern......I've broke the gating and/or sprue a couple times when doing so . I use the white EPS primarily because I seem to have an inexhaustible supply that I'd otherwise throw away. It does give a good visual contrast between gating and pattern for posting to threads and videos, and in my head, I think using the lower density stuff gets the gating and feed system full before the part, which would be beneficial if true, but that may just be imagined. Best, Kelly
Kelly, Besides an amazingly good outcome, something that, to me, seems surprising is the nearly perfect seven-piece pie pattern seen in your casting before it was cleaned up. Sure, there are seven gates. But, those gates are at all different levels and one would expect they filled at different times. But that pattern suggests seven liquid fronts converging uniformly and simultaneously to near perfection. Splain that, please. Denis
Here's my guess. That sprue/runner was such low density foam, and given it's shape and orientation, filled almost immediately. I'll call the gates the seven little 3/8" diameter cylinders that connect the sprue/runner to the pattern. They attach to the part at the boss locations on the wheel center that were left solid. I think that further contributes to the pie segments because those bosses are both comparatively massive (5/8"D) and denser foam. So I'd imagine they take a little more time for the feed system to penetrate and consume them. This gives the feed system further time to catch up if it wasn't already full. The rest of the 1/8' thick pattern is attached to the bottom of those bosses so the bosses must be completely consumed before the rest of the part can be fed. I suspect the metal front again slows as it enters the thin regions. But when those bosses are full, you have seven nice, hot, and comparatively massive, 7 x 5/8"x Pi x 1/8" cross sectional area sections feeding seven centrally spaced locations to feed the remaining thin sections of the pattern. I'd imagine you'd just have seven circular metal fronts growing in diameter, and they meet in the manner of the carbon signature. Like I said, this may all just be the product of my imagination. I've been tempted to buy an infrared camera or iPhone add-on and film the metal front through the flask wall but at $300-$400 it's sort of like whether the light really goes out when the refrigerator door shuts.........and until then, there's still my imagination. Originally, I had drawn up a circular gate that contacted the rim around the perimeter and had the counter bores machined in the pattern. ....but I suspected the counter bores would have been problematic areas to fill without flaws and the bosses looked like ideal locations to feed and for ease of gate removal.......so that's the way I went. Best, Kelly
Decided to bring them into the world two at a time. Dipped and ready to go Indoor melt today, but wheeled the flask outside to pour. ……..and two more were born. Degated and cleaned them up.... The deal was just for raw castings but I couldn’t resist and polished them up a little with a scotch bright disc and some Tripoli on an old ratty buff. Not finished but most of the way there and what I could do quickly. Rodney can polish them to whatever standard he wants. Made an MDF machine fixture that indexed off the mounting tab, cleaned up the backside bosses, and machined the counterbores into the face. This one is a wrap. Best, Kelly
I am very impressed with K. results! Very excellent results and he went beyond original agreement. Thank you very much K.
