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Thread: Casting catboat rudder hardware

  1. #1
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    Default Casting catboat rudder hardware

    I'm taking steps down a road that, hopefully, will result in a complete set of rudder hardware for the Brewer catboat. The furnace is made and operational, most of the materials required are now on hand. I'm going to post some pictures and make some comments about the patternmaking and ,soon, the casting. Anyone who's done this before may feel free to make any suggestions, because I'm feeling my way along here.

    This is the beginning of the pattern for the lower gudgeon, which attaches to the aft end of the keel. It will be a split pattern with two cores. The turning has been glued up with a piece of newspaper in the joint, which will allow the piece to be split lengthwise. A simple diagram has been drawn on plywood to provide a guide and help with the visualization of the piece. The turned piece in the foreground will become part of the lower pintle.



    Here the pieces have been split and some brass alignment pins installed in drilled holes.

    It doesn't look like much yet, but I can't tell you how many hours I've spent mentally going over and over this process in recent months.


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    Default Re: Casting catboat rudder hardware

    Quote Originally Posted by boylesboats View Post
    Nice start there Jim...
    Now you got lotta old brass and copper radiators to collect yet.. melt both alloys together you'll get a nice bronze castings..
    Are you goin' to sand cast them?
    Hey, Larry. These pieces are too critical to use scrap metal of unknown content. For the effort needed to make the pattern and do the casting, the cost of a bronze ingot is only a small portion of the equation.

    And, yes, as soon as they're made, I'll attempt casting them in sand.

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    Default Re: Casting catboat rudder hardware

    A nice pattern Jim ,did you say above that the pin will be an extension of the casting ? Not a core print ? Don't forget to feed that big lump .!...at the risk of mentioning something you know well already , the flat section and the cylindrical extension will cool and solidify well before the main cylinder ....it will need a reservoir of molten metal to draw on as it cools .Said reservoir will need to be of greater volume than the casting ....so it cools more slowly ....unfortunate but true .Otherwise the thing will be hollow ...ask me how I know !

    Do you have any draft on that strap ? You will need a little , even with petro sand ...well maybe you could get it out with a bit of rapping , but make it slippery ! ( That's a good place to use acrylic sheet .)

    If you need any advice about this type of thing ,look up Foseco ( foundry supplies ) in the phone book and pay their salesman a visit .He's usually a tradesman moulder and helpful as can be ! He will have forgotten more than you and I will ever know .
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Hey Jim,
    Since you say you're going to have two cores in the pattern shown in progress there, and seeing how you've split the turned piece, your parting line will be down the verticle, longitudinal plane of the gudgeon, yes? If so, your second core will be the interior of the part; or 'between the straps'. This is the best way to go to produce strap-type pintles and gudgeons, since it allows parallel faces between the straps. For those budding patternmaker/founders out there, the downside of this technique is simply time. I rarely take this path as the time required to make the core master and core box is commercially co$t prohibitive. Silicon bronze would be the superior alloy to use, as it's the most noble of the common casting alloys. Manganese bronze is a sure "don't", as it's really a high strength yellow brass. Over one third pure zinc. I've seen lots of below-the-waterline parts cast from manganese brz. - bad choice. Your part will be best gated and risered into the fat end where the round core is. Silicon bronze's solidification range means you don't need an insulated riser sleeve, but do make the riser large enough. Also remember to vent well off the strap ends. Nothing more satisfying than hanging hardware you made yourself. Nice job.

    Chuck

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    Default Re: Casting catboat rudder hardware

    Peter, the pins on the patterns are core prints. I'm going to use sodium silicate mixed with fine sand to make the cores. Have you got any thoughts about runners and gates for a shape like this? Could a large sprue serve as a reservoir for the heel section?

    Goldrock, thanks for the helpful comments. I appreciate the advice.

    Meanwhile, I've pushed things along some and the final form is becoming apparent. Now it's shaping, fillets and sanding.


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    Default Re: Casting catboat rudder hardware

    Jim ,regarding the cores ...I'd drop by a foundry supply and buy a couple .The commercial ones are much stronger , especially with the overhang in one of those castings .If you can't do that include a length of 3/8 or 1/2 steel rod in the core .You don't want it to droop !
    The feeding is a problem .I work with manganese bronze mostly and it shrinks a LOT .Probably the worst of them ,but anything will shrink and the fat sections will feed the thin .

    A large sprue could serve but if there is any constriction between it and the casting it will freeze first and stop the flow .It may just be a case of cutting a large reservoir off afterwards .If you have to do that make sure you can get a 9" grinder or your steel cutting 14" drop saw to the cut .

    You may end up doing this twice if you don't feed it enough .....better to melt a pound of extra metal and cut it off afterwards than do it again .

    Sorry I can't give a definitive answer ,perhaps Chuck will chip in ?
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Something else Jim, seeing we are amateurs and don't need to worry too much about the time it takes !
    If you end up having trouble getting the shape out of the sand ,think about a big core (sodium silicate ) between the blades .It would remove the problem of cleanup in there as you can get a nice smooth surface with no flash on the parting line .
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Quote Originally Posted by PeterSibley View Post
    If you end up having trouble getting the shape out of the sand ,think about a big core (sodium silicate ) between the blades .
    The pintle is going to have a core print between the blades, a core pattern and a sodium silicate sand core. I was going to do something similar with the gudgeon, but now I'm thinking along the lines of coping down the drag pattern, putting the two pattern halves together, and then molding a core in place for inside of the piece, using the sodium silicate, then ramming up the cope.

    Does that sound feasible to you?

    Also, if I knew of a foundry supply where I could get 1 1/4" round cores, I'd buy some.

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    Default Re: Casting catboat rudder hardware

    Do you think the sodium silicate will handle the ramming above it ,if I've understood you ? I find it strong but brittle . Perhaps petrosand with a generous coating of parting dust ?
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Hey Jim,
    Been away for a couple of days. You can do that pin core in green sand. Just make up a simple core box, open on both ends. Ram it up and drop it in. On such a short core, you shouldn't need a reinforcing rod, though it won't hurt if you want to put one in. You can buy commercially made sand cores, but most suppliers will have minimums. Gate right into the fat end. Riser the gate. The riser volume should be at least twice the volume of the part, preferably more. Cut the riser right up through the cope. If you want to go blind, dome the top of the riser well, and vent heavily up through the cope. Remember also to cut some of the riser down into the drag. You want to concentrate the greatest and most insulated mass of the riser right behind the gate. The gate should be no more than, say, 3/8" from the riser to the part. The sprue doesn't play any part in risering unless it is very near the gate, and this is usually unwise as it encourages dross to enter the part. The ideal gating system for this part is to feed the cavity with a short runner connecting the sprue to the riser, allowing the runner to continue past the riser for a couple of inches. This allows any dross or slag to collect in the end of the runner, and gives the metal a chance to stablize a bit before the pressure wave backs up and starts feeding the part. Use the opening of the sprue into the runner as the choke. If for instance, from the pictures, your pin diameter is 1", and the wall thickness of the straps is 1/4" to 5/16", try a choke opening of .25 in. sq. to .30 in. sq. Manganese should be choked more than silicon, (though I strongly dissuade the use of manganese for rudder fittings). Try a cross sectional area at the gate of about four times the choke, or, for our example, about one inch or slightly more. Lastly, if I percieve that last picture correctly and you're boxing in that one pintle, make sure the core box produces a core which will yield proper fillets at those jonts. You'll get shrink tears like mad without. Rule of thumb on fillets at joints of equal cross sectional thickness is a spandrel 'diameter' equal to the wall thickness. That is, if your strap thickness at the joints is 5/16", a proper fillet would be created with a filleting ball of 5/16" diameter. Nice looking job so far. Let's see those finished castings. Good luck.

    Chuck

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    Default Re: Casting catboat rudder hardware

    Nice to have someone who knows what they're talking about eh Jim !

    and I don't mean me !
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Sorry Jim, just had my second up of coffee and re-read some of the earlier posts more closely. Both of the cores of these parts are very simple and will suffer to be made in plain green sand very easily. There's no need to go to any kind of bonded sand unless it purely suits you. Now, I'm presuming some things here. What kind of sand mix are you using? I work exclusively with a clay and water bonded sand. Oil bonded types I'm not particularly familiar with, but either type will yield suitable green sand cores for shapes like these. You can get down-and-dirty with your core box making, however. Take the strap type gudgeon, for example. The core print that will create the space between the straps is bilaterally symetrical. That is, each half (separated at the parting line) is identical to the other. What's more, the shape required, excepting the point at which the straps join the mass with the pin hole, is just a flat sided "box". The bits of material you shape to make this core print that you will incorporate into the pattern is called a ''core master". Excepting the areas of the core master that will form a surface of the casting, you can make this bit any shape you like that will reasonably pull out of the sand. So you make the core print uniformly flat sided in shape such that you can build the core box right on the core master. Imagine you had a perfect cube, say six inches on a side. You could cut pieces of plywood that you could perfectly enclose, or 'box in' that cube, right? Same thing with a simple core master like this. The differences are that the sides of the 'box' will be drafted slightly. No problem there. A few judicious bevels at the joints takes care of that. And that area where the straps meet the 'head'? Make the core master a uniform shape. Then as you test fit it into the pattern, mark this area's boundaries with a pencil. Hog off more stock than is needed to clear things. Then lather the pattern in this area with paste wax, and liberally daub the corresponding area of the core master with Bondo (or any other cheap, fast curing polymer), press the two together, sip some java while it cures, trim off the excess and you have the perfect core master in no time. Build the corebox around this cheap and simple form. Use the same Bondo technique to recreate the 'strap/head interface area' shape from the core master to the core box for each half of the core master, and fillet the interior joints of the core box. Remember to drill for and insert indexing pins in the core box. Now just saw off the end of the completed core box opposite the 'strap/head' side and you're in business.
    Regarding the gating setup, consider some of Peter's astute remarks. Don't be at all shy in gating and risering. Big risers and correctly sized and shaped gates are critical. It is presumed as standard at our shop that the weight of a broken out casting will be at least fifty percent gates and risers. Be generous. On a casting the size of the pintle in the photo, I can see a riser at the gate of three or more inches in diameter at least. Don't be shy venting, either. Bigger is usually better. In your case, definately. Tally ho.

    Chuck

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    Default Re: Casting catboat rudder hardware

    Just want you guys to know that I'm sitting here LMAO at the fact that I do not understand a single word of what you all are saying . I know it's real English and everything, but you might as well be speaking Swahili.

    Not complaining, mind you - in fact I'm loving every bit of this.

    It was Jim's comment about "ramming up the cope" that really got me!

    - Norm

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    Default Re: Casting catboat rudder hardware

    If you're on top you can Cope , being down is a Drag .
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Quote Originally Posted by outofthenorm View Post

    It was Jim's comment about "ramming up the cope" that really got me!

    - Norm
    Norman, would you like to get up here in front of the class and explain to all of us what you find funny about 'ramming up the cope"?

    Goldrock, thanks for the instructions. I had to read your posts a few times to get it all and found it very helpful, especially the riser info, and the core patterns.. The sand is going to be Petrobond, BTW.

    Here's the rudder pintle, almost finished. The block of wood between the arms of the pintle is called the core print. When the pattern is molded in the sand, the core print leaves an impression. The block of wood in front of the pattern is what Goldrock refers to as the core master. It's the same shape as the core print. The idea is to make a sand plug the same shape as the core master, then place it in the cavity left by the core print. doing this will define the interior shape of the casting, i.e. the space between the arms.

    The cylindrical extensions projecting from the pattern are also core prints. A cylindrical shaped core of sand will lay in the impressions made in the sand, producing a hole in the finished casting.

    Last edited by Jim Ledger; 11-15-2008 at 07:23 PM.

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    Default Re: Casting catboat rudder hardware

    Nice lookin' Jim. What are the dimensions of the cat you're building? I made a pattern for a mastband a couple of years ago for a mast 11" in diameter. Came to find out, it was for a 28' catboat! Thought it was for a big schooner!
    Norm, the amount of arcana involved with sand casting is indeed bizarre. Then again, it's an awfully ancient aspect of human endeavor. As old as ship building, and look what a linguistic circus that is! I've collected a number of books on foundry work and pattern making over the years, but, for the most part, the only ones that are relevant to the way I do things are generations out of print. There are exceptions, however. There's a fellow named Steve Chastain who's put together a two volume set of books on all things small foundry, as it were. They're pretty cheap, as I recall, and have lots of good stuff in them. I've made a few of the matchplate vibrators described therein (another one for you Norm) and they work great. Google his name and you'll doubtless find links. It's an awfully fun thing to do, casting is.

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    Default Re: Casting catboat rudder hardware

    Oh, and here's a bit of explaination on my reference to a core master Jim. You have created two essentially identical pieces of wood to produce 1) the coreprint on your pattern, and 2) the core box (or so it appears, correct me if I'm wrong). My description assumed using the same shaped piece to do both things. Use the 'core master' to produce the core box, then incorporate it into the pattern. That might help explain my rambling a bit. A wonderful thing about pattermaking, of course, it that there are frequently any number of divergent paths that all lead to the same successful conclusion!

    Chuck

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    Default Re: Casting catboat rudder hardware

    Quote Originally Posted by Jim Ledger View Post
    Norman, would you like to get up here in front of the class and explain to all of us what you find funny about 'ramming up the cope"?
    Been a long time, but it's not the first time I've heard something like that.

    Goldrock. Thanks for the tip. I'll look for the Chastain books. Even if I never do the actual casting, I'd like to learn about pattern-making. The man who built my boat was a pattern-maker by trade, and his workmanship was superb.

    Sorry for the interruption. Carry on!

    - Norm

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    Default Re: Casting catboat rudder hardware

    I've looked at the Chastian books ,I'd like to build a very small cupola but coke is nearly impossible to get here these days .I wonder if you could use charcoal ? Chuck ...any idea ?
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    Default Re: Casting catboat rudder hardware

    Sugsestion, I have made patterns for castings according to the foundrys specs.taken them in and had them cast,simple. Enjoy the woodworking leave the rest to the metal makers. The cost is resonable.
    Last edited by Vinny&Shawn; 11-16-2008 at 09:58 PM.

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    Default Re: Casting catboat rudder hardware

    Hey Pete,
    Charcoal can be used, but it doesn't generate the kind of heat other fuels do. A well made charcoal furnace can probably attain temps. in the 1400-1500 deg. F range, which is good for aluminum and some brasses. Check out the website for Lindsay publications. www.lindsaybks.com These guys are great. One of their specialties are reprinting technical texts that have entered the public domain (no longer protected by copyright). Ask them to send you their free catalog. It's full of intersting stuff. A guy named Dave Gingery has a book called The Charcoal Furnace. He shows how to throw a small one together out of virutal scraps. Neat stuff.

    Chuck

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    Default Re: Casting catboat rudder hardware

    Sorry Chuck ,a misunderstanding .I have a furnace now , gas fired and quite OK for 1300 C or so.The idea is a cupola , fired with charcoal instead of coke ? Any ideas ?
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Great thread!! Another pointer for when I get around to my wee catboat/flatiron.
    Jarndyce and Jarndyce

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    Default Re: Casting catboat rudder hardware

    No, Pete. What experience I have with cupola furnaces is what I've glanced at in books. However, charcoal still has a fairly low energy yield when burned as compared to, say, coal. So I defer on the grounds of being clueless.

    Chuck

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    Default Re: Casting catboat rudder hardware

    OK ...thanks anyway .I'll keep asking around but unfortunately Steve Chastain doesn't reply to email enquiries on the subject.
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    Default Re: Casting catboat rudder hardware

    Chuck ,
    by way of introducing myself to you ..this is a project of mine .All the patternmaking and all the casting except the casing which required too much metal for my little setup .

    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    Very nice. You have, then, experienced the awareness, as you develop the ability to design and manufacture your own hardware, that nothing on your boat is any longer adequate. Redesign, add, modify. Frankly, it's more of an affliction... Guess we manage to suffer with it, eh?

    Chuck

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    Default Re: Casting catboat rudder hardware

    Indeed .Hell ,I even designed the boat .
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    Default Re: Casting catboat rudder hardware

    There is a small foundry, just outside St. John's, that casts small bronze sculpture etc. using charcoal as their fuel.Apparently make their own, I haven't seen the shop, but I know the operators and if I get the chance , I'll collect some information on the process and post it.

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    Default Re: Casting catboat rudder hardware

    One of the tasks left to do before any casting is to make the sand cores that will form the holes in the casting.

    The first thing to do is to make the core box. A core box is a mold that will produce the desired shape of core for the purpose. They can get quite complicated, but this one is a simple cylinder with a diameter of one and a quarter inches.

    The picture's showing two attempts to produce a satisfactory core box. The two halves in the lower right were the first attempt. the halves were glued with paper in between, then turned on the lathe. The hole through the center was bored on the lathe, but the bit wasn't long enough to reach all the way through. Boring from the other end produced a mis-aligned hole that would have produced a badly shaped sand core. In addition, the surface was rough from the boring

    The piece in the clamps has been routed with a five eights inch radius cove bit. Gluing the pieces together produces a smoother, more accurate mold that can be made in any reasonable length.

    Last edited by Jim Ledger; 11-24-2008 at 07:38 PM.

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    Default Re: Casting catboat rudder hardware

    This is the set-up. The core box, from the previous post, clamped together. a handful of fine sand blast sand, to be mixed with about a tablespoonful of sodium silicate, the liquid in the can. When the sand mixture is exposed to carbon dioxide, it sets up solid, right away. It's the coolest thing. The carbon dioxide is applied with this high tech apparatus, consisting of a bicycle tire inflator, plastic tubing and a funnel.

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    Default Re: Casting catboat rudder hardware

    The sand mixture is packed in the core box. The wire will be removed, leaving a hole for the gas to permeate the core. The funnel gets placed over the top and a shot of gas applied.



    Here's the result. The first one wasn't packed hard enough at the bottom, but the remaining sand made a core with a fine finish. Very encouraging.

    I might add that this technique was taught to me by Sam Johnson in his bronze casting class and is explained in his book "Bronze Casting for Boatbuilders", an excellent introduction to the art. The book is available from Sam for anyone who is interested.


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    Default Re: Casting catboat rudder hardware

    Very nice Jim ,the only improvement I would make would be to align the 2 halves of your core box then drill for some alignment pins .1/8" diameter nails would be fine .I tend to ram up my cores then push a bike spoke in afterward .....I find it easier to do and easier to get a consistence ram up .
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Casting catboat rudder hardware

    I'm sitting in the moaning chair.

    I measured the gudgeon and calculated the weight and it's too heavy, way too heavy, for me cast.

    So, there's got to be some major backtracking and reconfiguring to get a marginally workable solution.
    Last edited by Jim Ledger; 11-26-2008 at 08:16 AM.

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    Default Re: Casting catboat rudder hardware

    Quote Originally Posted by Jim Ledger View Post
    I'm sitting in the moaning chair.

    I measured the gudgeon and calculated the weight and it's too heavy, way too heavy, for me cast.

    So, there's got to be some major backtracking and reconfiguring to get a marginally workable solution.
    I have shared your pain Jim ,it's the problem with shrinkage allowances .Off to the local foundry ...there will be other jobs you can do .

    If you ever want to build a bigger furnace I'll send you a few close ups of one .The trouble with more metal is that you have to lift and pour it !
    Last edited by PeterSibley; 11-26-2008 at 02:51 PM.
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