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Thread: Gearing up for sand casting

  1. #201
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    I've got quite a few flat backs too.
    After ramming it and flipping over, I run my finger around the edges and slightly recess the sand. The cope then has a tiny overlap to prevent the flash. Works pretty good.
    Bones

  2. #202
    Senior Member Tobho Mott's Avatar
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    Wow, getting lots of great tips for avoiding flashing here, especially considering it's all based on a casting that only had a little bit of it! Thanks guys, keep'em coming!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

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  3. #203
    Senior Member Tobho Mott's Avatar
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    Latest thing I did was to cast an aluminum blank plaque to use as a pattern. Much inspiration was drawn from fishbonz' plaque pattern posts! Hoping I'll have time to get in another casting session before the foundry is snowed in, after I glue some house numbers on the aluminum pattern so I can cast it as a gift for my sister. The idea of casting it blank is to have a durable pattern that can stand up to repeatedly having stuff glued on and pried off it. Had to build a new 12X16 flask for it, I used bolts as alignment pins (although they are kind of thin, just 1/4" bolts) and made them extend up from the drag in case I ever want to put this pattern on a match plate. Also borrowed a page from Sandrammer's book of tricks and screwed a couple of window sash locks on the flask to keep it clamped shut, since this is a wide casting and I do not want to worry about floating the cope. Not such a worry with aluminum maybe but you never know, I may try casting something in bronze using this pattern one day...

    Came out pretty good, I think... but the ring shaped mark on the back side is strange. Not shrink, I think it will sand off. Anyone got a clue what was happening to the aluminum as it got that far into the mold that would create a mark like that?

    IMG_20171205_103640399-1040x585.jpg

    IMG_20171205_103659496-1040x585.jpg



    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  4. #204
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    Nice pattern work and a great pour Jeff!
    I get discolorations when the metal is too hot. Yours is around the perimeter where the extra thickness is. The center cooled quicker and the temperature gradient is the halo.
    Use 3 vents on the trash gate and use them to find your melt temp. I found if the vents fill to the top, the metal can be poured cooler and that's a good thing on plaques. Each of my plaques has a certain pour temp and I got it from only filling the vents about an inch. Hunting arrows make nice vent cutters.
    You might run a radius at the runner/gate junction, potential for sandwash there.
    Hope you get the real thing made before Xmas.
    Bones

  5. #205
    Senior Member Tobho Mott's Avatar
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    Good tips, thanks Bonz!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  6. #206
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    Nice going Jeff. The plaque pattern turned out great! I enjoyed watching the video too. I really pitied your back when I saw the size of that flask. It doesnt appear to have happened to you, but sometimes not only do you have to be concerned about the whole cope floating, but the sand in the cope can actually rise. I have a fairly thin cope on my large flask (3-1/2" on a 19x19" flask) and if I don't cover the top of the sand with a heavily weighted board the sand will rise. The sheer weight of your cope sand and generous venting probably prevents this.

    Pete

  7. #207
    Senior Member Tobho Mott's Avatar
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    Thanks Petee... Yeah, if I was casting it in bronze or something I think I'd put some weights on the sand just to be safe. Figured the Al would behave though; if it hadn't, I'd have chalked it up as a learning experience...

    It's been pointed out that what looks like a choke in the runner is redundant since the tapered sprue acts as a choke. The one in the runner wasn't meant as a choke, I just wanted to let the well fill up more before the runner began to fill, so the choke was a last minute workaround to make up for poor measurements that had my runner bottoming out too deep on the edge of the well. So, not a feature people should necessarily copy. But it did seem to get me a decent casting.

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  8. #208
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    I could be off base here but my thoughts on sand float...I think it's from the air not being expelled fast enough. It's like a balloon being blown up. I've gone to putting vents on almost all my castings that have a decent amount of metal. It also is a way to flush out any leading edge dross. They are quick and easy to add to the mold and easy to knock off and clean up.
    Bones

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