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Thread: Novice Casting Questions

  1. #31
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    I went ahead and machined my cracked and shrunk sheave. To my surprise almost all the crack machined out. I think it is good enough for me to use.

    IMG_1042.jpg

    The new one is on the right and the crack is upper right in the photograph.

    IMG_1043.jpg

    One more attempt at a sheave. The first attempt was better than the second, so I just hollowed out the flat side in the cope a little to give it shrink material, not liquid to fill the shrinking cavity. If I get internal cracks this is a bad plan, but I've seen no internal cracks in my other attempts.

    IMG_1044.jpg

    Made a shallow gate with a little rise in it to make a choke.

    IMG_1045.jpg

    Failure! It only took a little metal. I went ahead and melted some more cans while waiting for it to cool.

    IMG_1046.jpg

    When I cracked it open I was able to figure out what was wrong. Dummy left the pattern in.

    IMG_1047.jpg

    I'm pretty sure I'm not the first to do that, but I also be tit will help me remember to remove it. It was late and I went ahead and salvaged the drag.

    IMG_1048.jpg

    Casting turned out OK. A few shrinkage cracks around the hub but I think that's because I have too tight of a radius on the pattern.

    IMG_1050.jpg

    I had put a vent in the middle of the flat side and the metal ran right up the vent. I guess that means it was plenty hot and fluid for being can-o-lite.

    Please post your comments and observations. I'm here to learn.

  2. #32
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    I've never left a pattern in the mould but I have put the cope down 180 degrees out! I cast a nice sprue that day and nothing else.

  3. #33
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    You are off to a great start. Given that there is a name for a casting with the pattern left in (I don't have C.Ammens book handy to look it up) you certainly arent the first to do that.

    That is a pretty thick casting, so you want to pour it at the lowest temp you can get away with. From the surface finish you are pouring pretty hot. at less than five bucks a pop, getting a thermocouple or two is well worthwhile.
    http://www.alloyavenue.com/vb/showth...ight=pyrometer

    Adding a core to bore it out that pattern would also cut down the mass a lot and should help reduce the srinkage issues.
    Mark

  4. #34
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    Quote Originally Posted by oldironfarmer View Post

    Thanks for your comments. I hope you can elaborate my questions above.
    Oh yes, this is indeed a casting forum, but I would own fewer woodworking tools and none of my metal working machine tools if it weren't for my metal casting. So it all fits here, as do any fabrication projects. We try to keep things in the appropriate subforums, so just about anything goes (within reason), and we all have the added benefit of learning and sharing things with folks with a huge amount of knowledge and experience.
    I've never left the pattern in but I've forgotten to cut the gate more than once. Not a happy day!
    Ordinarily with all things being equal, the metal will start to solidify farthest from the sprue. The last metal in will solidify last. Adding thicker sections to the pattern complicates matters so you want the thinner sections to fill first. Because your hub is in the center and is facing down it fills first and starts cooling faster than you want it to. Because of its mass it doesn't solidify as fast as the most remote part of the casting but it is still solidifying before the area between it and the sprue. Since your pattern is designed to be a one piece mold, meaning the draft is all in the same direction perhaps you could try to ram your drag solid and flip the pattern so you do all of your business in the cope. Maybe even cut your gate into the drag. That way it would fill from the bottom and your hub would fill last. That might be enough to eliminate the need for a riser. Otherwise you could then add more height to the hub giving it more mass.
    I hope that makes sense. That's how I'd try it anyway.


    Pete

  5. #35
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    Keep at it, you'll get there. I've never left the pattern in but have forgotten to cut the gate.
    Large solid objects like that, I pull the pot from the furnace thirty seconds after last piece melts in the crucible. I've run it up to three minutes for a long thin pattern.
    That's not can-o-lite, that's Candemonium... rhymes with pandemonium. :-)
    The sooner you run out and move to wheelium the better the casting will be.
    Bones

  6. #36
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    Oh that sucks... Any chance you can save the pattern? Guessing not, probably too charred. I haven't done that (other than lost foam where it is supposed to work that way and burn up the pattern), but once I had to remake the cope of a sand mold after I had cut some gates in the drag, and almost tried to pour the mold without realizing the new cope had closed off the gating... I would have ended up with a nice casting of a sprue... Not sure why but something made me open the mold back up to have a look, so I was able to carve the inverted gating off the cope and wound up with a great casting after all... But it was a close thing.

    If the little bump on the top of your casting in the last 2 pix of post #26 is your blind riser, it is way too small. Needs to be wider than the thick section of the part that you are worried about, and also tall enough to contain enough metal to do the feeding. IMO it is better if it is a little too big than too small; why not use an open riser? That way, for one thing, since it comes right up off the pattern, you'd have been able to see that you forgot to remove it before it was too late... I think blind risers are only needed when an open one would cool too fast to feed the part properly, but I am not 100% sure about that, maybe there are other good reasons to use blind "shrink bobs".

    Here's a pic of a casting where the 2 open risers were big enough to feed the part so the casting had no shrinkage defects, just to give you an idea. Note the "piping" on top where the shrink occurred as the risers fed the thick sections of the casting on either side of the core:



    Pretty sure it's the right pic; photobucket is blocked from here so I have copied this IMG tag from another post based on the caption I gave it there. The navy manual linked upthread probably has guidelines for how to size your risers more effectively; it is a really great resource.

    Kinda funny, but the pic is the same casting I described above, which I almost tried to pour with the gating all filled in.

    Good luck,

    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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  7. #37
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    Quote Originally Posted by Peedee View Post
    I've never left a pattern in the mould but I have put the cope down 180 degrees out! I cast a nice sprue that day and nothing else.
    I was afraid of doing that so I painted one end of my flask red and the other end green. As long as I keep green to the starboard I'm OK.

  8. #38
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    Quote Originally Posted by rotarysmp View Post
    You are off to a great start. Given that there is a name for a casting with the pattern left in (I don't have C.Ammens book handy to look it up) you certainly arent the first to do that.

    That is a pretty thick casting, so you want to pour it at the lowest temp you can get away with. From the surface finish you are pouring pretty hot. at less than five bucks a pop, getting a thermocouple or two is well worthwhile.
    http://www.alloyavenue.com/vb/showth...ight=pyrometer

    Adding a core to bore it out that pattern would also cut down the mass a lot and should help reduce the srinkage issues.
    Mark
    Thanks for the link, and comments!

    Sadly, I have a thermocouple and the instrument to read it. I kind of backed into casting, I was just going to make muffins and one thing led to another. I also didn't know how to insert one. Interesting in the link you provided one poster said his sheath melted off but the thermocouple continued to work, and has for a few years. As cheap as they are I can't see trying to protect the junction. Especially outside the furnace.

    I probably need to be controlling my furnace temperature, I'm pretty sure it is over 1,600F, maybe 1.800F, trying to judge from color. Also need to build a larger furnace. Right now I have flame impingement on my crucible. I'm not seeing any deterioration but I'm thinking the crucible is getting hot enough that I'm overheating the aluminum liquid as I'm still trying to melt more.

    I am working on a core.

    Thanks again for all the information!

    - - - Updated - - -

    Quote Originally Posted by Petee716 View Post
    Oh yes, this is indeed a casting forum, but I would own fewer woodworking tools and none of my metal working machine tools if it weren't for my metal casting. So it all fits here, as do any fabrication projects. We try to keep things in the appropriate subforums, so just about anything goes (within reason), and we all have the added benefit of learning and sharing things with folks with a huge amount of knowledge and experience.
    I've never left the pattern in but I've forgotten to cut the gate more than once. Not a happy day!
    Ordinarily with all things being equal, the metal will start to solidify farthest from the sprue. The last metal in will solidify last. Adding thicker sections to the pattern complicates matters so you want the thinner sections to fill first. Because your hub is in the center and is facing down it fills first and starts cooling faster than you want it to. Because of its mass it doesn't solidify as fast as the most remote part of the casting but it is still solidifying before the area between it and the sprue. Since your pattern is designed to be a one piece mold, meaning the draft is all in the same direction perhaps you could try to ram your drag solid and flip the pattern so you do all of your business in the cope. Maybe even cut your gate into the drag. That way it would fill from the bottom and your hub would fill last. That might be enough to eliminate the need for a riser. Otherwise you could then add more height to the hub giving it more mass.
    I hope that makes sense. That's how I'd try it anyway.


    Pete
    I came in at lunch and read your post. I wasn't planning on casting anything today, just working on patterns but your post suddenly made sense so I did reverse my pattern and got great results. Thanks! It is slowly starting to make sense.

    - - - Updated - - -

    Quote Originally Posted by FishbonzWVa View Post
    Keep at it, you'll get there. I've never left the pattern in but have forgotten to cut the gate.
    Large solid objects like that, I pull the pot from the furnace thirty seconds after last piece melts in the crucible. I've run it up to three minutes for a long thin pattern.
    That's not can-o-lite, that's Candemonium... rhymes with pandemonium. :-)
    The sooner you run out and move to wheelium the better the casting will be.
    Candemonium! Makes perfect sense, thanks! I also saw your post at lunch and pulled my crucible out and let it set in 40F wind for about a minute. Got a pretty good pour out of it. Thanks for the advice!

  9. #39
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    Quote Originally Posted by Tobho Mott View Post
    Oh that sucks... Any chance you can save the pattern? Guessing not, probably too charred. I haven't done that (other than lost foam where it is supposed to work that way and burn up the pattern), but once I had to remake the cope of a sand mold after I had cut some gates in the drag, and almost tried to pour the mold without realizing the new cope had closed off the gating... I would have ended up with a nice casting of a sprue... Not sure why but something made me open the mold back up to have a look, so I was able to carve the inverted gating off the cope and wound up with a great casting after all... But it was a close thing.

    If the little bump on the top of your casting in the last 2 pix of post #26 is your blind riser, it is way too small. Needs to be wider than the thick section of the part that you are worried about, and also tall enough to contain enough metal to do the feeding. IMO it is better if it is a little too big than too small; why not use an open riser? That way, for one thing, since it comes right up off the pattern, you'd have been able to see that you forgot to remove it before it was too late... I think blind risers are only needed when an open one would cool too fast to feed the part properly, but I am not 100% sure about that, maybe there are other good reasons to use blind "shrink bobs".

    Here's a pic of a casting where the 2 open risers were big enough to feed the part so the casting had no shrinkage defects, just to give you an idea. Note the "piping" on top where the shrink occurred as the risers fed the thick sections of the casting on either side of the core:



    Pretty sure it's the right pic; photobucket is blocked from here so I have copied this IMG tag from another post based on the caption I gave it there. The navy manual linked upthread probably has guidelines for how to size your risers more effectively; it is a really great resource.

    Kinda funny, but the pic is the same casting I described above, which I almost tried to pour with the gating all filled in.

    Good luck,

    Jeff
    I think the pattern is not too bad. As long as I cut the gate into the burned area. But since it is a two piece pattern all I have to do is make another disk.

    The little bump was my attempt at a blind riser but not knowing that was what it was called. I was just trying to get more metal there and assumed if it shrank it would still be thick enough. It did work that way. I reversed the pattern and poured an open riser and got a pretty good result. Poured colder but probably still too hot. I'm going to use a thermocouple on my next pour.

    Neat axe, I assume that is what it is. Did it have an eye core?

    I'm keeping the Navy manual open on my computer and reading it as I find time. It is easy to read.

    Thank you for your input.

  10. #40
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    I had an outstanding day today. There is a pattern shop next to a machine shop where a buddy used to work. I decided to stop in and meet the guy. He was working on a 60" diameter pattern for a pressure head. I apologized for interrupting but he gave me a half hour tour and answered a lot of questions. Gave me a textbook. Invited me back. A really good contact.

    IMG_1066.jpg

    I had made a 5" wheel for my sheave hub so I cast it today using advice to invert and pour it in the cope. I also added a riser since the hub was now facing up.

    IMG_1060.jpg

    My first open riser and it was a joy to see the metal come up in it. A real confidence builder.

    IMG_1062.jpg

    The bottom of the casting pulled in slightly (less than a 1/16") and the top dished in a bit as well. There are also the same hot tears around the hub. I need to make a new hub pattern with a more generous radius, I think. I don't have a picture of the casting only.

    IMG_1063.jpg

    IMG_1064.jpg

    I'm a little surprised a wheel this big did so well. My plan is to dish both sides and recast it, then drill some lightening holes and cast again.

    Comments?

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