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Thread: Casting thin shell bronze blocks

  1. #36
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by lupussonic View Post
    Jim, I have zero casting experience, but couldn't you heat the sand / mould In an oven to help keep the metal fluid? Might help with the thin sections...?
    That is done with lost wax investment casting. The ceramic shell formed by dipping the wax in a thin clay and drying multiple times. The mold is heated to melt and drain the wax, then the clay is fired to harden it. The ceramic is fairly strong and very heat resistant. I worked on a large thin wall investment casting where the mold was heated to 1800įF to get the thin sections to fill. (I was on the finding a foundry and making sure they were on top of things side.) Anyway, sand can take some heat if the binder is a phenolic or linseed oil that has been baked, but only about 400F.

    Sand castings tend to have better mechanical properties because the metal cools faster. Investment can be a lot more complex with finer detail. The lame joke is that it is called investment because it costs so much. The whole solidification rate, grain growth, segregation, heat treatment side gets complicated if you are going for high performance aerospace parts and alloys. You could make a BeCu block that was three times as strong and cost as much as the rest of the boat. It wouldn't be any better though.

    Seriously, though, at this backyard casting level the methods are so crude, the necessary experience so lacking and the conditions so variable that plain luck is the biggest variable.
    You are either very lucky or have more experience than you let on. If you're really that inexperienced, you have done your homework.
    Looks like there is a bit of shrinkage at the center. Would a fatter riser help?

    EDIT: https://books.google.com/books?id=BX...page&q&f=false sand
    Last edited by MN Dave; 01-10-2018 at 12:59 PM. Reason: typos
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  2. #37
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by MN Dave View Post
    Anyway, sand can take some heat if the binder is a phenolic or linseed oil that has been baked, but only about 400F.


    You are either very lucky or have more experience than you let on. If you're really that inexperienced, you have done your homework.


    EDIT: https://books.google.com/books?id=BX...page&q&f=false sand


    Dave, sand using the linseed oil binder is commonly used for baked cores, something I hope to be experimenting with later in this thread. There are various recipes, usually combining with small amounts of cereal with the mix. I recently purchased a pound of dextrose for that very purpose. The cores get baked in an oven to attain their strength. The cereal binder burns off at about five hundred degrees during the pour, but by that time the mold has already filled. This burning-off weakens the sand core just enough to make the core partially disintegrate as the metal cools and contracts. If the core retained it's full strength it might tear the cooling casting.

    It's possible to make a baked mold, or a sodium silicate mold if needed, however, either are more work than a sand mold.



    Regarding experience, I've been casting on-and-off for probably five years. Most of my efforts have been chronicled here, starting with the building of the crucible furnace...

    http://forum.woodenboat.com/showthre...nze&highlight=


    Casting rudder hardware...

    http://forum.woodenboat.com/showthre...are&highlight=


    Making the sheaves seen in these pictures...

    http://forum.woodenboat.com/showthre...ave&highlight=


    Casting the boom gooseneck...more on that to come...

    http://forum.woodenboat.com/showthre...ing&highlight=


    saving the best for last, the quadrant...

    http://forum.woodenboat.com/showthre...ant&highlight=


    Enthusiastic amateur is the label that fits best...lucky enthusiastic amateur.

    Jim

  3. #38
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Canoeyawl View Post
    For boat parts I prefer the patina of Manganese bronze, a lovely and stable blue/green. Silicon bronze (Everdur) seems to go to a brown/red color and leaves bits of itself in flakes all over the deck. Unfortunately I was gifted several hundred pounds of silicon bronze, so I will just put up with it...

    Knowing that you are going to be polishing and oiling this stuff daily, it shouldn't be a problem Jim.

    (I have some "White bronze" ingots also (maybe 200 lbs), now what on earth am I to do with that?
    Might make a good anchor...

    Yup, you just know you're having a bad day when someone gives you a couple of hundredweight of bronze and it's the wrong alloy. "Brown? I wanted green." Ingots, was it, or scrap?

    What is the "White bronze" of which you speak?

  4. #39
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Thad View Post
    You're just having too much fun there, Jim. Fun to watch too.

    Hiya, Thad! I'm glad you're enjoying this!

    Jim

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by lupussonic View Post
    Jim, I have zero casting experience, but couldn't you heat the sand / mould In an oven to help keep the metal fluid? Might help with the thin sections...?
    Raising the pouring temperature 50 F helps.
    '' You ain't gonna learn what you don't want to know. ''
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  6. #41
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by PeterSibley View Post
    Raising the pouring temperature 50 F helps.

    Pouring at a too cool temperature is the chief culprit of my casting failures. These thin castings need a high pouring temperature. I've had two flasks lined up, the first poured successfully, while the second, poured only seconds later failed due to low temps. The cooling happens that fast. As a result I'm only going to pour one flask at a time, putting the crucible back into the furnace for a reheat before pouring the second.

    I finally bit the bullet and sprang for an immersion pyrometer, which will allow me to finally test the temperature of the melt before pouring. Putting things on a more scientific basis, y'know.


    Here's the result of the pour I mentioned. One was almost perfect, easily repaired by welding using silicon bronze rod. The ducks foot thing froze too early as a result of the metal being too cool.

    If you look at the sprue on the right you can see a depression in the top. This is called piping and is caused by the cooling mass below drawing off the molten metal above. The metal next to the sand freezes first leaving a core of molten metal, which then gets drawn down to feed that lump on the bottom of the sprue.

    The semi-polished piece is one of the first pair of castings.

    One more thing...I tried to simplify the gating on this pour, doing away with the circular runner. One almost worked, but for reliability I think I'll go back to the original feeding arrangement.



  7. #42
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    Default Re: Casting thin shell bronze blocks

    A pyrometer is magic !

    How will you deal with the shrinkage that caused that hole Jim ? Do you think a riser on the face side would help?
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  8. #43
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    Yup, you just know you're having a bad day when someone gives you a couple of hundredweight of bronze and it's the wrong alloy. "Brown? I wanted green." Ingots, was it, or scrap?

    What is the "White bronze" of which you speak?
    20lb ingots... maybe 30 of them.

    "White bronze" is copper, tin, zinc in variable amounts.
    The more tin, the more expensive. It can be used as a substitute for "silver" on decorative work with the obvious cost advantage and the fact that it does not tarnish.
    The thing is, on boat parts it is easy mistaken for that hateful stainless steel. It looks a lot like nickel if you are familiar with that color.

    *A note about investment casting. It is unforgiving, the ceramic shell is strong enough to tear the solidifying metal if this is not anticipated. It is an easy mistake to "trap" some part of the casting between larger dimensions and ruin it. Tricky that bit, almost like the parts have to have "draft" built into the shape. For example - oarlocks with tapered or straight shanks. It seems like a simple project to investment cast these and use the shank as a sprue, but no... That button on the sprue will tear the shank right off.
    Sand or petrobond is much more forgiving in that regard.

  9. #44
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by PeterSibley View Post
    A pyrometer is magic !

    How will you deal with the shrinkage that caused that hole Jim ? Do you think a riser on the face side would help?
    I'm not sure if that was a shrinkage defect or the metal freezing too soon. If it needs a small riser on the outside that would be an easy fix, easy to mold, easy to grind off. I took the opportunity on several of the failed castings to do weld repairs and I'm pleased with the result. The repairs match perfectly in color while the strength should equal that of a perfect casting.

  10. #45
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    Default Re: Casting thin shell bronze blocks

    This might be a good time to introduce some foundry terms to those interested.
    Jim, you're AWESOME. That's an *excellent* post. Just what the thread --and the Forum!-- needs.

    Port Townsend Foundry blocks , illustrating Alex's description.
    That's very funny: Those are from a pattern I built about ten years ago, an almost direct copy of the blocks on my grandmother's catboat. I've seen them listed elsewhere (Bristol Bronze? Can't recall...) as an 1893 pattern, which fits with my grandmother's boat. Anyway, I built the pattern on spec and traded it to Pete for some other castings (can't remember what). He turned around and made a match plate out of it, and has been whacking them out fairly regularly for the last ten years. But yes, that photo illustrates the principle I was trying to explain.

    Here are a couple of the originals, that I have in my "chandlery", together with a shell block similar to Jim's project:



    Unfortunately I was gifted several hundred pounds of silicon bronze, so I will just put up with it...
    That seems to be an unfair burden for you to bear, Canoeyawl; send it up here and I'll take care of it for you.

    Alex

  11. #46
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    Default Re: Casting thin shell bronze blocks

    Jim, my comment was intended to be complimentary.

    The comment about baked sand molds was intended to indicate that preheating the sand wasn't an option. I have a terrible memory for names, and while I remember yours (when I see it) as someone who is pretty capable, I forget capable of what. So when it comes to sand, I should have remembered this: Simple casting patterns. Oh well.

    The shrinkage in the center looks to me more like that spot is still molten when the riser above it has solidified. That is why I suggested a fatter center riser. The reason I found the link to the book at the end of my last post was that I was looking for some information on chills. The book looks good. I know enough about chills to be dangerous but not how to make one. The chill that I don't know enough about would somehow magically appear right in the center of the mold below the central riser. Some types of sand can be used as chills. The book talks about using a different type of sand as a chill.


    More ignorance: I thought white bronze was German silver. Apparently Nickel is bad ju-ju these days and white bronze is "White bronze is not actually bronze. It is an alloy consisting of a combination of copper, tin and zinc. Tri-metal alloys are white in color, similar to bright nickel, silver or rhodium and are extremely resistant to tarnish and corrosion. The alloy range is centered around 55% copper, 30% tin and 15% zinc."
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  12. #47
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    Default Re: Casting thin shell bronze blocks

    White bronze is not actually bronze...
    Forgive my ignorance in turn, but I thought that bronze was, by definition, copper and tin, often plus other metals and occasionally non-metals --thus wouldn't an "alloy range ... centered around 55% copper, 30% tin..." still be bronze, despite the 15% zinc? Or does the zinc definitively make it a beast of an entirely different nature?

    The Wiki article lists a few alloys that seem to have a lot of zinc: https://en.wikipedia.org/wiki/Bronze...ion_and_alloys

    And if that's too much thread drift, just ignore me.

    Alex

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    Default Re: Casting thin shell bronze blocks

    Manganese bronze is high zinc.
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Pitsligo View Post
    Forgive my ignorance in turn, but I thought that bronze was, by definition, copper and tin, often plus other metals and occasionally non-metals --thus wouldn't an "alloy range ... centered around 55% copper, 30% tin..." still be bronze, despite the 15% zinc? Or does the zinc definitively make it a beast of an entirely different nature?

    The Wiki article lists a few alloys that seem to have a lot of zinc: https://en.wikipedia.org/wiki/Bronze...ion_and_alloys

    And if that's too much thread drift, just ignore me.

    Alex
    Can I just say that whether white bronze is a bronze is a grey area? I never heard of the stuff before. I just grabbed a quote out of the article I linked because it gave a composition. I think brass or bronze normally refers to the reddish/brownish/yellowish stuff that isn't gold. Brass and bronze are traditional terms that predate all of the fancy things with Mn, Ni, Si, Al and foo foo dust. You are right, and I would have to look up too much stuff to give a sharp definition of the fuzzy line between brass and bronze. Click this link for the best definition of tradition.

    The article gave the composition of an electroplated deposit. If the color is right, the composition must be close, unless it isn't. The bulk alloy appears to be a proprietary alloy made by Belmont metals and this link is as close as any to giving the casting alloy composition. The SDS was inspired by CPES; a long list of maybe and no real information.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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    Default Re: Casting thin shell bronze blocks

    Jim, you've probably seen this but seeing you use silicon bronze I thought I'd put it up just in case you haven't.

    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting thin shell bronze blocks

    Dave, forgive me, I never took your comments to be anything other than amicable. I regret if my reply seemed otherwise. For my part I thought that linking other casting threads to this one would make it simpler for anyone interested to find further material. Your comments are very interesting, for someone who claims little knowledge of the subject you seem to have some insight into casting processes far beyond the scope this experiment Thanks for the input.

    To throw more confusion into the fire, Stephen Chastain, author of the excellent book "A Sand Casting Manual for the Small Foundry", describe manganese bronze as a high-strength yellow brass.


    Here are a couple of decent half shells and a failed attempt. The pattern has been thinned down from its original dimensions, both inside and out. Traces of the original primer remain but the new finish is sprayed-on shellac. The shellac fumes, being alcohol, are much easier on the central nervous system than regular spray paint, especially if you're in a closed-up shop in the winter. As it dries quickly and cuts into itself you can get multiple coats on in a day.

    The inside of the shell is being cleaned up with a carbide burr. Entire sets of these burrs are available on Ebay for immediate purchase for twelve dollars, Wear glasses and gloves, use a light touch and keep your fingers clear.



  17. #52
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    Default Re: Casting thin shell bronze blocks

    Another pattern in the pipeline is this aluminum cleat. It's a Merriman cleat found on Ebay. It's a more complex casting than the blocks, involving a core to hollow out the inside. The plan is to split it in half lengthwise, as the original pattern was. I'll be needing four of these cleats for the boat.

    i'm going to attempt making a baked sand core for this casting. i'll be using a recipe based on linseed oil along with a few other ingredients. To this end my wife has found me a convection oven in the local thrift store which should be capable of cooking the core at 400 degrees for the required time...outside the house.

    The mast bands are most likely manganese bronze, cast from an old propeller shaft, which probably accounts for the gold color.



  18. #53
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    Default Re: Casting thin shell bronze blocks

    This is fascinating stuff Jim.

    My old man had a small furnace and he used to cast silver, brass and nickel. Im now wishing Id paid more attention....all thats left is a pair of gauntlets which Im sure are loaded with asbestos and a couple pair of crazy tongs for fetching the crucibles.

    Im going back and rereading the sheave thread now....did I mention fascinating?

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    Default Re: Casting thin shell bronze blocks

    Jim, the pattern in post # 51 is so elegant, it could serve as a candy dish after your casting run

    Looking good

    Rick

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by willin woodworks View Post
    This is fascinating stuff Jim.

    My old man had a small furnace and he used to cast silver, brass and nickel. Im now wishing Id paid more attention....all thats left is a pair of gauntlets which Im sure are loaded with asbestos and a couple pair of crazy tongs for fetching the crucibles.

    Im going back and rereading the sheave thread now....did I mention fascinating?
    I'm glad you're enjoying this, Willin, I find it kinda fascinating myself.


    Things are at a bit of a standstill in the casting shed while I wait on a part for the welder. I need the welder to finish up a set of lift-out/pouring tongs for a smaller crucible than the one I've been using. I want to use a smaller pot because it's easier to lift and pour than the larger one. As the pours are only a few pounds and the metal needs to be piping hot a small crucible makes sense because it can get the metal out of the furnace and down the hole with very few motions.

    Meanwhile, let's catch up on the cleat pattern project. Here the bottom of the cleat is being filed flat, for what's to come. The hollow interior of the cleat shows up well here.




    Here I've sawn the cleat in half lengthwise to make the two-part pattern...




    Filling the interior space with Bondo produces a male mold that will be used to make a mold for the core...




    The two core halves get lightly glued together in order to sand them fair...


  21. #56
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    Default Re: Casting thin shell bronze blocks

    It occurs to me Jim that the sawn halves of that aluminium cleat are the perfect molds for your baked linseed oil cores .They won't mind the heat of the oven.
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting thin shell bronze blocks

    Jim

    Is there a technical advantage to pouring hollow cleats or are you just challenging yourself?

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by willin woodworks View Post
    Jim

    Is there a technical advantage to pouring hollow cleats or are you just challenging yourself?

    Larger cleats are cast hollow to save weight and use less metal.

    To to answer your other question, I'm not challenging myself. Given the choice I'd just as soon carve them out of locust. It's the cleat itself, you see...just sitting there on the shelf all smug..."ooh, look at me. So hollow so thin, so damn good looking, l'm a Merriman, you know, l know you know, you putz, you'll never be able to cast the likes of me." This has been going on for some time now. Is it me? Does this sort of thing happen to you?

  24. #59
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    Default Re: Casting thin shell bronze blocks

    Theres a chunk of gorgeous ebony in my scrap rack that has an irritating tendency to remind me of its presence...psst, hey, still here....those cabinet pulls came out nice.....whats next...hey, dont ignore me...

  25. #60
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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by PeterSibley View Post
    It occurs to me Jim that the sawn halves of that aluminium cleat are the perfect molds for your baked linseed oil cores .They won't mind the heat of the oven.
    That's true, Peter, it would probably work well. However, I'm going to put core prints on the base of the core patters, to hold the cores in position in the mold. I'll be making a couple of plaster molds to mold the cores and prints as one.

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    Larger cleats are cast hollow to save weight and use less metal.

    To to answer your other question, I'm not challenging myself. Given the choice I'd just as soon carve them out of locust. It's the cleat itself, you see...just sitting there on the shelf all smug..."ooh, look at me. So hollow so thin, so damn good looking, l'm a Merriman, you know, l know you know, you putz, you'll never be able to cast the likes of me." This has been going on for some time now. Is it me? Does this sort of thing happen to you?
    There is a pedal car chassis in the garop mocking me as we speak. Darn thing INSISTS I canít build it. Little does it know...

    Peace,
    You Are Not Alone

  27. #62
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    Default Re: Casting thin shell bronze blocks

    Boy Howdy do I feel sorry for you guys that have all these voices in your shops beseeching you. Maybe it's my poor hearing that saves me from hearing them in my shop. Or, more likely, they can't get through the clamor from the voices inside my own head: "Hey, get your lazy self busy and finish that boat!" "Look at that pretty hull... you NEED one." "You putz! Why didn't you put the nail where it won't show!"....... and on and on......


    Jeff

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    Larger cleats are cast hollow to save weight and use less metal.

    To to answer your other question, I'm not challenging myself. Given the choice I'd just as soon carve them out of locust. It's the cleat itself, you see...just sitting there on the shelf all smug..."ooh, look at me. So hollow so thin, so damn good looking, l'm a Merriman, you know, l know you know, you putz, you'll never be able to cast the likes of me." This has been going on for some time now. Is it me? Does this sort of thing happen to you?
    Perhaps I've missed out on the inanimate objects laughing at me from the shelf, perhaps I need to step up my game a bit or perhaps I need to avoid the bottom of the rum bottle.
    "The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails."
    -William A. Ward



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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Canoez View Post
    Perhaps I've missed out on the inanimate objects laughing at me from the shelf, .
    We're mocked relentlessly by artifacts of a distant age, if only you have the ears to hear.


    Here are the finished patterns of the cleat, the outer shells, with the patterns for the sand core placed between. The blocks fastened to the bottoms are the core prints, which will position and support the suspended core in the mold cavity.



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    Default Re: Casting thin shell bronze blocks

    Just wonderful!

    Is that blood from an animal sacrifice for good luck?

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Dave Lesser View Post
    Just wonderful!

    Is that blood from an animal sacrifice for good luck?

    Yup


    Here are the two half shells, pegged together with locust pins for finishing the outside of the block. The pins will be drilled and driven out to separate the halves. This will allow the axle, sheave and end fittings to be put in place, whereupon the halves will be permanently attached with bronze pins...



  32. #67
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    Default Re: Casting thin shell bronze blocks

    So, how are the final pins fastened? Peening or welding/soldering? Curious and learning is all.

    They look great!

    Peace,
    Robert

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by amish rob View Post
    So, how are the final pins fastened? Peening or welding/soldering? Curious and learning is all.

    They look great!

    Peace,
    Robert
    I intend putting a very slight taper on one end of the pins to facilitate driving. Once home the excess will be cut off square, the halves clamped tight and the pins upset to increase their diameter slightly. Then grind and polish the pins flush.

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    Default Re: Casting thin shell bronze blocks

    Quote Originally Posted by Jim Ledger View Post
    I intend putting a very slight taper on one end of the pins to facilitate driving. Once home the excess will be cut off square, the halves clamped tight and the pins upset to increase their diameter slightly. Then grind and polish the pins flush.
    What I thought. Excellent. They should be VERY discrete in the finished product, eh?

    Peace,
    Robert

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    Default Re: Casting thin shell bronze blocks

    Will someone be able to drive the pins out to replace bearings in 100 years if they need it?
    If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours.
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