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Thread: Novice Casting Questions

  1. #21
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    I cast my sheave (pulley) pattern today. There were some shrinkage cracks.

    IMG_1023.jpg

    IMG_1024.jpg

    Is the gate too small, sprue too far away, both? Should I have fed the gate to the center of the pattern? A core would help too, I assume.

    IMG_1025.jpg

    It is machining well

    IMG_1027.jpg

    Comments appreciated. Yes, this is still can-o-lite metal.

  2. #22
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    Pretty clunky is right. That can turn into a lot of turning. All the more reason to use a good castable and machinable alloy. Like any other job the end use of your casting will determine the materials and procedures needed to best produce it. Does it need to be strong, pretty, machinable, dimensionally stable, etc, or some combination? Alloy and casting methods and pattern design will all come into play. Sometimes you need a Howizer, sometimes you need a cork gun.
    If you're going to bore that casting out anyway the crack near the center may just get cut away, but you could have internal problems as well which remains to be seen.
    Check out this link
    http://archive.hnsa.org/doc/foundry/index.htm#pg1
    The first couple chapters talk about solidification and its characteristics in some detail but is written in such a way that it's fairly easy on the brain. It will help in understanding about the need for risers, proper gating, and other techniques for minimizing shrinkage defects among other things. There happens to be an active thread on the same topic now. http://www.alloyavenue.com/vb/showth...Grinder-Sander

    Pete

  3. #23
    Just a couple of thoughts (from a guy that's furnace is still just components in the garage) ... what if you would have placed a riser right on the center of the form? I think it may have helped by giving the cooling ali a place to pull from. But the other thing it would have made it easier to chuck up in the lathe.

  4. #24
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    Quote Originally Posted by Petee716 View Post
    Pretty clunky is right. That can turn into a lot of turning. All the more reason to use a good castable and machinable alloy. Like any other job the end use of your casting will determine the materials and procedures needed to best produce it. Does it need to be strong, pretty, machinable, dimensionally stable, etc, or some combination? Alloy and casting methods and pattern design will all come into play. Sometimes you need a Howizer, sometimes you need a cork gun.
    If you're going to bore that casting out anyway the crack near the center may just get cut away, but you could have internal problems as well which remains to be seen.
    Check out this link
    http://archive.hnsa.org/doc/foundry/index.htm#pg1
    The first couple chapters talk about solidification and its characteristics in some detail but is written in such a way that it's fairly easy on the brain. It will help in understanding about the need for risers, proper gating, and other techniques for minimizing shrinkage defects among other things. There happens to be an active thread on the same topic now. http://www.alloyavenue.com/vb/showth...Grinder-Sander

    Pete
    Thanks for the link to the Navy foundry book. That is going to be good reading.

    - - - Updated - - -

    Quote Originally Posted by Mister ED View Post
    Just a couple of thoughts (from a guy that's furnace is still just components in the garage) ... what if you would have placed a riser right on the center of the form? I think it may have helped by giving the cooling ali a place to pull from. But the other thing it would have made it easier to chuck up in the lathe.
    I had thought the same thing. It didn't work that way.

  5. #25
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    Quote Originally Posted by Mister ED View Post
    Just a couple of thoughts (from a guy that's furnace is still just components in the garage) ... what if you would have placed a riser right on the center of the form? I think it may have helped by giving the cooling ali a place to pull from. But the other thing it would have made it easier to chuck up in the lathe.
    I had thought the same thing. It didn't work that way.

  6. #26
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    While I'm trying to read the Navy foundry manual I tried another sheave casting. But first I machined out the first sheave. The can material will stick to my cutting edge when it gets hot and makes a rough cut. If I clean it off and take a light finish cut I'm getting good results. I relieved the face and got all the cracks out.

    IMG_1031.jpg

    Haven't finished the bore or cut the keyway yet.

    IMG_1032.jpg

    I left the hub rough cast.

    So I tried putting on a blind riser, and made the gate bigger. I learned a lot. The face of the sheave shrunk and cracked between the riser and the gate.

    IMG_1035.jpg

    I was the only one surprised. A large pool of metal in the center of the casting and a large pool in the gate let the rim of the sheave cool first and then get distorted by both sides drawing.

    IMG_1036.jpg

    I kept seeing the word choke in the gate structure but it didn't make sense until I saw the pictures in the Navy manual. I will put a choke in but I don't yet know why. It seems wrong to just pour through the center of the hub but I'm going to try that next. I am also going to try one gate with a small riser centered on the hub.

    Any comments are appreciated.

  7. #27
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    The ingate from the sprue should be much smaller. In this case it has the singular function of filling the mold. The feeding of the cooling casting is done by the riser which should be somewhat larger in volume than the section you're trying to feed. You want that hub to be the last to freeze so the riser should be attached directly to it. Having the hub in contact with the sand is causing it to cool faster.
    Your sheave turned out pretty nice. Do you have an application for it or just testing/accumulating?
    Ill be interest to see how you cut the keyway.
    Machine tools and woodworking stuff is all very welcome here. Are you holding out on us ? Lol

    Pete

  8. #28
    Petee - Thanks for posting that link to the Navy manual. I had seen it referenced before, but never found a link or PDF.

    Quote Originally Posted by Petee716 View Post
    Ill be interest to see how you cut the keyway.
    That keyway is the easy part, the rest of this is head scratching!! :-) I think when I get my furnace built (after the weather warms a bit) ... my first project will be a set of wheels for it, that won't catch fire. Between this thread and the other on the belt sander wheel, this is good stuff.

  9. #29
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    Quote Originally Posted by Petee716 View Post
    The ingate from the sprue should be much smaller. In this case it has the singular function of filling the mold.

    I understand this and see what the large gate did to shrinkage.

    The feeding of the cooling casting is done by the riser which should be somewhat larger in volume than the section you're trying to feed. You want that hub to be the last to freeze so the riser should be attached directly to it. Having the hub in contact with the sand is causing it to cool faster.

    I don't understand this. I don't know how to attach a riser to the hub without running it along the side of the wheel. Is that what you mean? Or should I be casting it upside down to what I have been doing and have a riser come up out of the center?

    Your sheave turned out pretty nice. Do you have an application for it or just testing/accumulating?

    Thank you. I do not have an immediate application but motor sheaves always come in handy. It was an easy pattern to make and seemed like a good next step after the cylinders I cast. My ultimate goal is to be able to make parts I need and can't otherwise easily fabricate. I have made sheaves out of plate with a hub welded on. The first time was to replace a worn out cable sheave on the bar lift on a NH sickle mower. It took me three hours to make it. They were available in Tulsa for $65 and it takes me an hour to drive there, half hour minimum to get the part, and an hour to drive back. So it was a practical fabrication. Not everything I do is practical from an economic standpoint and it doesn't need to be.

    Ill be interest to see how you cut the keyway.

    I just use a broach, but I need to ream the holes to 5/8" first. They are drilled 1/2" now and I'll wait until I have a need to finish but since I've got two now I might just finish one.


    Machine tools and woodworking stuff is all very welcome here. Are you holding out on us ? Lol

    I thought this was a casting forum? I have a few tools, I tell my wife just the bare minimum. I've got a minimal machine shop and a fair wood shop so I think I can make patterns. Working with draft is new to me, however. I need to make a 1 degree reamer for through holes, I guess. The cylinder and sheaves are the first time I've machined rough castings. You really just have to pick where to get started the see if everything else will come out right. I can't imagine trying to finish castings without a mill and lathe. One conundrum I have is I don't want to do wood work on my metal lathe but I think I have to to get good tolerances. I hand turned the sheave pattern on a wood lathe.


    Pete

    Thanks for your comments. I hope you can elaborate my questions above.

  10. #30
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    Quote Originally Posted by Mister ED View Post
    Petee - Thanks for posting that link to the Navy manual. I had seen it referenced before, but never found a link or PDF.


    That keyway is the easy part, the rest of this is head scratching!! :-) I think when I get my furnace built (after the weather warms a bit) ... my first project will be a set of wheels for it, that won't catch fire. Between this thread and the other on the belt sander wheel, this is good stuff.
    My furnace is outside under a detached shed roof. It was a stiff breeze and 34F today. The fire sure felt good. What I need is a lot of practice so I'm using the fuel to keep making stuff until I get comfortable. I'm really loving playing in the green sand. It is great stuff and a blast to ram the mold up.

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