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Thread: Casting thin shell bronze blocks

  1. #106
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    Default Re: Casting thin shell bronze blocks

    The depth of the piece is controlled by the distance between the shells. Establishing the location of the core hole suggests the two end cuts. Measuring up an arbitrary distance to the center of the shackle hole gives a limit to the length of the piece. Tracing the shackle directly where it will bear gives a logical radius to the top end. A few connecting lines drawn and the piece starts to appear out of the fog. It absolutely has to look like this. Mostly what's left is refinement, but the shape itself has to be some variation of this.

    It occurs to me that I should have reversed the orientation of the piece on the glued up board. The top end could have been machined and carved out while still attached and the two forty-five cuts could have then parted it free. It seems such a compelling idea that I think I'll make another rather than continue with this one.

    The next one will take half the time.



  2. #107
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    Default Re: Casting thin shell bronze blocks

    Jim,
    In post #88, you alluded to a tweak to the gating. Can you elaborate?
    Thanks.

    Sweet castings BTW.

  3. #108
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by DoctorB View Post
    Jim,
    In post #88, you alluded to a tweak to the gating. Can you elaborate?
    Thanks.

    Sweet castings BTW.

    Sure, Doc, with pleasure. The problem was the casing would have voids in the thin sections and cold shuts.

    Part of the solution was pouring hot, about 2050 or 2100 degrees, but I still had too many failures.

    Pictured here is a successful casting. It's using essentially the same gating as I'd been using all along. The oval runner that surrounds the casting was molded from a pattern that was placed in the drag along with the casting pattern. The sprue was pressed into the cope after ramming up but before opening the mold to remove the pattern. The gate between the sprue was cut by hand, in the cope, as was the four ingates between the runner and pattern.

    In practice, the runner filled up completely and then the metal entered the mold cavity through the ingates in four simultaneous streams, meeting in the middle.

    The problem lay in the connection between the four ingates and the mold cavity. There's not much room there due to the thinness of the cavity and any carelessness in cutting the ingates resulted in a restricted flow. The solution was to increase the size of the ingates and to pay particular attention when cutting up to the cavity to get an unrestricted opening.

    Another thing that happened with this pattern is that, because of the shape and lightness of the pattern, it would always stick in the cope when the mold was opened up. With most patterns this would have ruined the mold, but it turned out to not be a problem here. It always came away cleanly.

    A match plate of this pattern and channels would turn out a cleaner and more consistent casting and be much faster to mold, that is, if you needed to make enough to warrant the work of making the plate.

    Jim



  4. #109
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    Default Re: Casting thin shell bronze blocks

    Here's the toggle pattern being shaped while still attached.





  5. #110
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    Sure, Doc, with pleasure. The problem was the casing would have voids in the thin sections and cold shuts.

    Part of the solution was pouring hot, about 2050 or 2100 degrees, but I still had too many failures.

    Pictured here is a successful casting. It's using essentially the same gating as I'd been using all along. The oval runner that surrounds the casting was molded from a pattern that was placed in the drag along with the casting pattern. The sprue was pressed into the cope after ramming up but before opening the mold to remove the pattern. The gate between the sprue was cut by hand, in the cope, as was the four ingates between the runner and pattern.

    In practice, the runner filled up completely and then the metal entered the mold cavity through the ingates in four simultaneous streams, meeting in the middle.

    The problem lay in the connection between the four ingates and the mold cavity. There's not much room there due to the thinness of the cavity and any carelessness in cutting the ingates resulted in a restricted flow. The solution was to increase the size of the ingates and to pay particular attention when cutting up to the cavity to get an unrestricted opening.

    Another thing that happened with this pattern is that, because of the shape and lightness of the pattern, it would always stick in the cope when the mold was opened up. With most patterns this would have ruined the mold, but it turned out to not be a problem here. It always came away cleanly.

    A match plate of this pattern and channels would turn out a cleaner and more consistent casting and be much faster to mold, that is, if you needed to make enough to warrant the work of making the plate.

    Jim


    Thanks for the explanation. Perhaps clocking the gates 45 degrees to align with the thicker webbing would help with filling. Also, venting would be easier by flipping the pattern so it's only in the cope, and this would also increase the cross sectional area at the gate/part intersection. Filling from the bottom and all that. No need to chase ghosts as you're getting good parts - just some thoughts. Thanks for sharing all this really awesome work.

  6. #111
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by DoctorB View Post
    Thanks for the explanation. Perhaps clocking the gates 45 degrees to align with the thicker webbing would help with filling. Also, venting would be easier by flipping the pattern so it's only in the cope, and this would also increase the cross sectional area at the gate/part intersection. Filling from the bottom and all that. No need to chase ghosts as you're getting good parts - just some thoughts. Thanks for sharing all this really awesome work.

    I concur, Doctor, your ideas have merit. Flipping the pattern over has even more advantages than the ones you mention. At some point in the series I started putting a riser in the drag, under the boss. This was to prevent shrinkage in the heavy center of the shell. Were the pattern to be flipped over the riser would be in the cope and could go all the way through and act as a vent. If I were to do a second run, this is the way I would go. What would need to be done to make this possible is to carve a recess into the bottom board, the same kind of recess that I use for the drilling jig. That would allow the pattern to sit flush in the drag. The movement of the liquid metal in the mold cavity would also be improved. Instead of flowing down in four separate streams the metal would fill up the cavity evenly from the bottom with better mixing and much less turbulence.

    Thanks for your ideas, they make a lot of sense.


    Here are a few of the patterns for the little bits that will, hopefully, make this all work. In the vise is a toggle for a single block. The pattern tor the double block toggle is in the upper left. The projecting pieces are the core prints which will make the cavity in which to place a sand core of the same cross section. The bicycle-chain looking piece is a becket for a single block. The next one I need to carve is a double block becket, and that should suffice.

    Jim



  7. #112
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    My apologies, Wainair, but I didn't see your post until now when I reopened this old thread. I'm impressed with your efforts, including the gas burner, which will open up a new range of casting possibilities. That's a nice cleat pattern and I would like to see the finished product. To answer you question, the sand I'm using is Petrobond, which starts out an orange color but turns black with use. Every so often I retemper the sand by adding a few tablespoons of thirty weight, non-detergent motor oil.
    Thanks for the info on your sand! Your work is excellent!

    The cleat buffed up nicely but I think I will cast another one to use on my boat. This one will make a nice desk ornament!
    97504D17-F5AA-406E-9B32-A5CDB6436964.jpg

  8. #113
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by wainair View Post
    Thanks for the info on your sand! Your work is excellent!

    The cleat buffed up nicely but I think I will cast another one to use on my boat. This one will make a nice desk ornament!

    That's gotta be the prettiest pattern and cleat I've ever seen, Wainair. You should be doing a casting thread so's we can all learn something. Keep 'em coming!



    Finally, after months of evenings, the four wee patterns are done, the last of the parts needed to assemble the set of blocks. The morning sun coming through the window caught them nicely, as the last coat of paint was drying.





    I made four molds, each mold holding one example of each pattern. They might look rough here, but they're all useable.

    Good things coming up...stay tuned!



  9. #114
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    Default Re: Casting thin shell bronze blocks

    sweet!

  10. #115
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by DoctorB View Post
    sweet!

    Thanks, Doc.

    Here's a single block toggle casting after some grinding and scrubbing.

    There's some fitting to be done between toggle and shell. Luckily, a loose fit is what I'm going for here. The grinding is accomplished with an old Foredom rotary Mchine, the kind that hangs up and powers a flex shaft and handpiece. I'm using a little set of carbide burrs. There's some filing been done afterwards to kinda polish and even things up.

    Boring the hole for the shackle went okay, got it near center. Finding the center on a sorta round casting like this can be helped by finding a suitably sized washer to approximate where the center should be. Center punched, and then drilled on the press an eighth inch pilot hole, followed by the seven sixteenth bit. A small wooden handscrew worked well as a quick and dirty jig holding the piece while boring.

    So, the question is...how smooth is smooth enough?


    Jim



  11. #116
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    Default Re: Casting thin shell bronze blocks

    ^The higher off the deck, the rougher the blocks can be...
    If any of your crew tells you the blocks aren't smooth enough, toss them overboard ( the crew, not the blocks!).
    Of course, on the Great South Bay they can pretty much walk home...
    That's the beauty of a catboat on the shallow waters of the Great South Bay.
    I was born on a wooden boat that I built myself.

  12. #117
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Rich Jones View Post

    toss them overboard

    Of course, on the Great South Bay they can pretty much walk home...
    That's the beauty of a catboat on the shallow waters of the Great South Bay.

    Sure you can walk home, Rich...if you live on the beach. But let's not forget the wind, it's always windy there.

    Imagine that!

    Jim

  13. #118
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    Default Re: Casting thin shell bronze blocks

    Post #115 should titled 'Art expressed in Bronze' - Great work, Jim !

  14. #119
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    Sure you can walk home, Rich...if you live on the beach. But let's not forget the wind, it's always windy there.

    Imagine that!

    Jim
    I lived on Long Island for over 30 years and never once went boating on the Great South Bay. 30 years of sailing on Long Island's north shore on the Sound. Very often we'd get a flat calm. Is there always a breeze on the Bay?
    I was born on a wooden boat that I built myself.

  15. #120

    Default Re: Casting thin shell bronze blocks

    Jim,
    This is such great work!
    Those little molds are BEAUTIFUL.
    I am a little confused through, are you using a core for the triangular opening? How about a shot of the mold ready to pour? I know, You do beautiful work and I just want more, more. more. Any pictures of your core boxes? You just could not post enough pictures.
    I was going to post a thread to show the struggles I went through to make a set of Gaff Jaws, but I seem to have lost the pictures and talking about it just doesn't do it.
    Please keep the pictures coming.
    ShorelineJohn

  16. #121
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by hawkeye54 View Post
    Post #115 should titled 'Art expressed in Bronze' - Great work, Jim !

    So, you're saying you like it, Rick?


    Quote Originally Posted by Rich Jones View Post
    I lived on Long Island for over 30 years and never once went boating on the Great South Bay. 30 years of sailing on Long Island's north shore on the Sound. Very often we'd get a flat calm. Is there always a breeze on the Bay?

    If there's no breeze, Rich, there will be one shortly. The Great South Bay is separated from the Atlantic Ocean by a thin sand bar, Fire Island; any ocean breeze from the South blows over the bay almost unhindered. The northern side of the bay is a flat plain that extends a dozen miles before there's any hint of a hill.


    Quote Originally Posted by ShorelineJohn View Post
    Jim,
    This is such great work!
    Those little molds are BEAUTIFUL.
    I am a little confused through, are you using a core for the triangular opening? How about a shot of the mold ready to pour? I know, You do beautiful work and I just want more, more. more. Any pictures of your core boxes? You just could not post enough pictures.
    I was going to post a thread to show the struggles I went through to make a set of Gaff Jaws, but I seem to have lost the pictures and talking about it just doesn't do it.
    Please keep the pictures coming.
    ShorelineJohn

    So...more pictures then. Okay. Thanks for the kind words about the patterns, I like the way they turned out myself.

    I am using a sand core for the triangular openings. The projecting arms you can see on two of the patterns are what's called core prints; core prints form the recess in the mold into which the sand core is placed. Once the metal is poured and cooled the sand core is knocked out, leaving the hole through the casting.

    I didn't take any pictures of the molds because I've done so many times before. However, in the face of your most welcome interest, I will do so the next time I have a chance.

    To shed some light on the core making process I submit the following picture. The first step was to make a wooden strip planed to the cross-section of the intended hole, seen here painted red and another in gray primer. The red piece was used to make the core mold; the core mold is the odd shaped piece in the photo, painted red with the core pattern casually placed on top. This mold is used to make the sand core itself, the core that gets put into the casting mold.

    A word, if you will, about the core mold. Core molds are often made of plaster. This one is made from Durhams Rock Hard Water Putty, which is great stuff to have around. I use it to fill nail holes and fix dents that will be painted. It's a fine powder that you mix with water to the consistency required. When mixing a fairly large batch like this it's important to add the powder to the water, not the other way 'round. Spoon it in slowly until it stops dissolving on it's own, then mix in more to achieve the desired thickness. Here it needs to flow, but not be too runny. The pattern and bottom board are coated with Vaseline as a release agent, and the mixture poured over. Wait a day and pop the pattern out. Any holes or defects can be repaired with more water putty. For a small mold such as this it's better than plaster, as it dries completely quicker and is stronger.

    The gray painted stick is left over, in case I need another pattern. You can see how the stick was incorporated into the patterns. One thing, though, because the patterns are split, the core print stick needs to be able to be split lengthwise as well. Before shaping the stick was glued up lengthwise with a piece of newspaper in the joint. You can see the newspaper where the pattern is split.

    I hope some of this answered your question, John, and you find it helpful in your own endeavors.

    Jim


    Last edited by Jim Ledger; 09-03-2020 at 06:38 AM.

  17. #122
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    Default Re: Casting thin shell bronze blocks

    I came on this late but it looks like you have it all well under control!
    Very nice work!
    Jay

  18. #123

    Default Re: Casting thin shell bronze blocks

    Thanks Jim.
    I guess my confusion comes from not knowing how all these pieces go together, but I can just watch, don't let me disturb you.
    John

  19. #124
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    Default Re: Casting thin shell bronze blocks

    I could take one of my old Merriman Bros. Blocks apart and check the separator ring they used if it will be of any use to you?
    Cheers,
    Jay

  20. #125
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by ShorelineJohn View Post
    Thanks Jim.
    I guess my confusion comes from not knowing how all these pieces go together, but I can just watch, don't let me disturb you.
    John
    Your questions are very welcome, John, thanks. It's not always clear to me just how much detail to go into, whether anybody reads it or not. Details can get tedious to both read and write but there's no other way to describe the small but important points about the process. If I think there's interest out there I don't mind writing.

    Jim

  21. #126
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jay Greer View Post
    I came on this late but it looks like you have it all well under control!
    Very nice work!
    Jay

    Thanks, Jay, the important thing is that you're here now. There were a few times I almost called you, but things worked out on their own. Glad you're here.


    Quote Originally Posted by Jay Greer View Post
    I could take one of my old Merriman Bros. Blocks apart and check the separator ring they used if it will be of any use to you?
    Cheers,
    Jay

    That's a kind offer, Jay. I took apart a Merriman sheave to see how they work before I made my own. I ended up making my own separator rings to fit and have a few left over for spares. I will keep your offer in mind, though, should I run out of those.



    Jim

  22. #127
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    Default Re: Casting thin shell bronze blocks

    Nice to see this in the latest email from the WoodenBoat Store:

    F0E75574-4B31-47D7-AB4D-7BA90665F5A0.jpg

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