Discussion in 'Metal casting projects' started by Ironsides, Jan 12, 2020.
It has been a while since I have made a machining video of my castings, so here it is warts and all.
I love the video. Nice little anvils! My guess is the sanded one. It had less damage to the horn and more damage to the backside.
You are correct.
OK, as your video invited comments from the "peanut section," I will hazard a guess as to why the shrink defect occured:
I think the shrink defect occurred because your riser and its gate are less massive than the top,of the anvil. The top was still molten and shrinking after the riser gate froze. It looks like your risers do not show collapse and therefore did not feed the casting---as best I can see from the video. That left no choice but for the shrinkage to defect to occur. In the one case it happened visibly at the riser gate and in the other anvil did it happen inside the body of the anvil perhaps? Might have.
How to get around that? Well, if the anvil could be cast vertically with it filling from the bottom and a broad (full width of anvil top) 2" high flat-topped riser cut right into the top of the anvil with no necking down, then that area of the combined anvil and gate would be the last area to freeze and donor metal could come from the riser. At least I would try that. Not too long ago I cast an unusually beefy special-purpose face plate for a friend using a similar technique as I was concerned about voids forming. In that case I saw good collapse of the top of the riser and no voids were found in the face plate.
My best guess, offered for the sake of discussion. Why do you think it happened?
Maybe the same general strategy could be used with the anvil on its side. Just fill from the bottom side and cut a flat top (collapses better than a dome) broad full-width riser on the top with no gate---just a bulge on the top. It might be possible to conserve local heat (molten condition) and avoid the full-width attachment of the riser if a person used a very short gate that was 1/4 to 3/8" length and an inch wide, say, between a broad riser and the top,of the anvil. That would allow cutting off the riser later without so much machining needed. Stream of thought...
I’m curious what you filled it with? And process?
Most of the time I fill cast iron cracks or imperfections with a nickel alloy. The nickel does not show up in your Video, this is why I question your fill material.
Denis, I was puzzled as to why it only happened on the last casting and not the second. Both had the same gating and sized risers. Yes this alloy tends to form a skin on top of the riser and prevents feeding. It could be that the metal was too cold to feed the last casting. If I was to cast these anvils again I would use a bigger riser.
Matt, I made a plug from cast iron so it would be hard to see the repair. Drilled and tapped a hole in the anvil and cut a thread on the cast iron plug and screwed it in very tight so it will never come out or move.
Very neat. I guess like mined... I also use JB Weld. It’s a lubricant going in and a two-part Apoxy. These are just cast-iron plugs you buy off-the-shelf at the hardware store.
AHHH!!! So THAT'S how I get rid of extra threaded holes in my column on the mill. I can do that! And I was just going to fill them with bondo.
You just neatly paint the words "Oil Here" below each hole.
It would look like the Valdez was parked in my garage! Actually I think my mill escaped the drill pretty good through the years. I only have 5 or 6 that need attention. I can live with that.
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