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What Chazza does in his spare time

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  • Chazza
    replied
    Nothing like learning details from a tradesman, or artisan, instead of a novice like me. Go for it – I wish I had a foundryman to talk to!

    Cheers Charlie

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  • cliffrod
    replied
    I've got to get down to the nearby aluminum foundry at some point. Maybe the owner Steve can shed some light on sand details that I can share. They do gravity casting, no pressure casting iirc.

    Before I knew the, Steve rode the flat track race bikes that my best friend Dennis tuned. (Including HD XR750, Ducati bevel/Roundcase 750 Desmo) so,with the family foundry at home they cast some unique parts for their bikes that were otherwise unavailable. I've got the last unused XR750 triple tree they made hanging in my shop as a souvenir. Steve's father (who started and ran the foundry until recently) died over Christmas and I wasn't able to go to services. Dennis said we could cast new intakes for my Guzzi project down there but still need to get time to get there.

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  • Chazza
    replied
    Originally posted by cliffrod View Post
    Is the sodium silicate sand a one time use item, with only tthe residual that washed away with water being lost or is it reusable? What about the resin sand- can it be broken up and reused at least as a larger aggregate to conserve loose sand or is that not a viable method?
    Not sure about the sodium silicate sand being re-usable; I suspect that it might be.

    The resin sand could probably be recycled; mine is so coarse that I dump it on the foundry floor. What I would really like to find out, is how to treat new sand with a resin binder, but Google has yielded nothing useful so far.

    The boys on my foundry forum are getting great results with sodium-silicate core sand. Once I have got rid of the bugs in my system I will have another go,

    Cheers Charlie

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  • cliffrod
    replied
    Man, you're killing me Charlie. I don't need to start doing something else completely different, but I sure do want to do some foundry projects like yours here in the studio. I really like seeing this here.

    Is the sodium silicate sand a one time use item, with only tthe residual that washed away with water being lost or is it reusable? What about the resin sand- can it be broken up and reused at least as a larger aggregate to conserve loose sand or is that not a viable method?

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  • Chazza
    replied
    40 degrees C today, so I got down to the shed early; finished some moulding and decided to fire the furnace.

    I poured 5 boxes and managed to make mistakes on most of them; just shows what a lack of practice does; I don't think I have done any casting since Sep '19.

    Anyway the thermostat housing I showed you earlier during the moulding process appears to have turned out well.

    Photo below; The mushroom shaped thing is where the bush was, the cone below it is where the cone was placed in the cope; and the in-gate, which I cut in the drag with a trowel, can be seen as a rough piece of aluminium. Note the original part number has been reproduced by the sand; the sand is very, very fine.

    The aluminium caps on the end of the sand-core are created when the metal finds any gaps – it flows like water.

    Click image for larger version

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    Clean-up involves sawing, or knocking off the sprue and the flashing. Thin flashing gets sanded off on a disc; heavier flashing gets returned to the crucible along with the sprue, etc.

    The core can be drilled out with a masonry bit; small rotary wire brush; compressed air and a pick. Resin-sand stays quite strong when it has been cooked and can be tricky to remove from hard-to-reach places. if I ever get the sodium-silicate sand to work for me, it can apparently be washed out with water.

    Hope all this wasn't too boring; feel free to ask questions,

    Cheers Charlie

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  • Chazza
    replied
    Your wisdom triumphs again Cliffy!

    I shall give this a go today hopefully. Could you email me your worksheet please? It might be a bit easier for me to read – I hate screens!

    Cheers Charlie

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  • cliffrod
    replied
    Just in case anyone thinks a sliding divider or proportional caliper is as professionally viable as the proper traditional use of compasses/calipers as I describe above, let's not go there.... There's a reason that none of my masters use those amatuer toys while all of them are fluent with compass and triangle.

    TIA.

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  • cliffrod
    replied
    As a small thank you for all you're posting, maybe I can contribute something worthwhile here. This is how I would figure such contraction calculations for almost free.

    In my business, sculptors make the original shape. These are traditionally then given to a carver- professional or apprentice- to measure and copy into stone. The bulk of the stone is removed by lower paid person(s). The project may ship as done by the carver or a master sculptor may finish the job. A carver is generally not as experienced/skilled as the sculptor, so mechanical means are utilized to help them duplicate models very accurately. A Carver may also not be as educated, so handing one a pencil & paper to make endless accurate mathematical calculations or to expect a fluency of geometry and trigonometry are non-starters. So this is how we do it do dirt cheap with almost no calculations-

    For 1:1 duplication, an exact model is duplicated in 1:1 scale with a pointing machine as shown in my previous stone carving thread. It can be done with compasses as I will discuss, but unless the job is being carved in reverse, a pointing machine is usually faster.

    for other dimensional manipulations, a compass (or caliper- not "proper" terminology, but think of calling a motorcycle vs enginecycle...) is employed. Technically, a compass measures a radius and a caliper measures a thickness. Each measure accurately and quickly without difficulty.

    For simple whole factor manipulation like 2x, 4x, the desired measurement from the model is captured with a compass and walked along a straight line (proper terminology is a Ray, but...) from a dedicated origin point. The end point is lmarked gently. A new compass is used to capture the measurement between the origin and this end point. This compass is used to transfer the new calculated measurement to the job.

    for all calculations between 0 (model measurement 100%, job measurement 0%) and 200% (model measurement is exactly 1/2 of job measurement), the function of the apex angle of a triangle is employed. For this discussion, I'll use the more simple isosceles triangle method. It's a lot harder to write this down than it is to do it. Enlargement of a scale model also enlarges discrepancies so is best done in several smaller steps instead of one large jump in size.

    I've mentioned this before on AMS and have presented at Redneck Roundup. I've been trying to do a concise video of this as well, but have not been happy with multiple attempts. This information is somewhat obscure, so I also have reservations about who knows this & what is done with it. The last USA workshop presenting this info as "lost art" was $700+ per person and completely misrepresented that many of us whom the organizer knows regularly use this technology.

    For this example, imagine I have a plaster model that is 3'-0" tall and I want to carve a statue that is 5'-2 1/2" tall. To figure out several hundred accurately factored new dimensions with pencil and paper would be untenable. For Charley's pattern, capture an easily measured dimension from either the model or the job and multiply/divide as needed it by the contraction factor if you like or do as described later producing a generic specific ratio function triangle template. At this point, Using a value that is easily divided by two speeds this process.

    See attached. Hope,you can see this ok. If not I'll rework it. I usually do this by using a durable item such as a nail with a small divot struck or drilled into the head to use as the apex point. Fine lines and sharp points are your friends. When using such a triangle I draw it on a sheet of nice plywood for big jobs or even paper for small projects like scaling up pieces fro my Guzzi. I'll post some compass & caliper images after I get back into studio.

    A desired job or target measurement is chosen or calculated.

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    1. Draw a centerline through the apex point.

    2. Construct a pair of long parallel lines each equidistant from the apex point, hence the easily divided by two advice. The distance between these parallel lines should be the job measurement. This could be checked with another caliper if desired.

    3. Using a compass, capture the corresponding dimension of the same detail on the model. Place one point of the compass into the apex point, swing the other point across each parallel line to strike an intersection.

    4. Draw three lines to connect the apex point to the two strikes (model dimension) and the two strikes to each other (job dimension). If the job dimension on triangle is not the largest dimension on the job, draw the two model sides as rays (continuing past base). All you need is the apex angle and these two lines.

    Now, take a measurement from the model with compass. Place one point in apex point. Swing and strike across each model leg. Use another compass to capture the distance between those two strikes. Apply this to the job. Repeat until finished.

    As mathematical proof of this process, see sidebar of drawing. It's a long time since college, so bear with me-

    If model dimension is 100% and job dimension is 0%, this will produce a triangle with superimposed sides but no width. This is a proof.

    If the triangle is acute with model dimension greater than job dimension (greater than 0% but less than 100%) the job will be be a reduction of the model.

    If model dimension is equal to job dimension, the triangle will be an equilateral. This is a proof.

    If job is larger than model but less than twice as large (greater than 100% but less than 200%). The triangle will be obtuse and will allow a model to be enlarged.

    If the job is exactly twice as large as the model, the base will be twice as long as each side with apex point located at the midpoint of the segment. This will construct as a flat line with sides superimposed upon the base. This is a proof.

    The master who taught me how to use the compasses and triangle was barely literate and hardly fluent in math. That is the brilliance of this method. The proofs and such come from my advanced math instruction in college, which was brought into practical life application by my stone training.

    We will then use specific agreement of groupings of three radii, captured from the model & enlarged or reduced with the triangle, to accurately produce and even reverse a job that is replica of a model. That's an entirely other process.... So is using a right triangle instead of an isoceles triangle .

    For the purpose of contraction rates, you could simply construct a triangle with a base & sides that are exactly 1:3 to 1 for that specific metal or alloy and use it forever. The specific job & model measurements are irrelevant. Make it easy math because the factor doesn't change. The apex angle will provide the function of 1:3 to 1. I would make one triangle template for each contraction factor, Mark them, hang them on the wall and use as needed.

    I have been working to simplify a method of using the most powerful triangle- acute, between 0% (nothing) and 100% (everything)- to facilitate producing work from archive images such as profile photographs and mechanical drawings that lack dimensional information. By reversing the side where a dimension is applied (I.e.- model at base) the calculated dimension can be any factor desired. For example, a profile image of a vehicle with a known wheelbase, wheel diameter, etc could be used to construct triangle which in turn could help produce all visible dimensions. The chance for error is greater, but likely not any worse than a highly pixelated blown up photograph. And it would cost nearly nothing. For these little dimensions described by Charley, I would use a magnifier to see what I was doing, super sharp points on your tools and very fine lines on my triangle.

    CAD and such may suit some people better. This is where all of that came from. The calculations done within a computer program are all based upon the mathematical function of the apex angle of a triangle constructed using such corresponding dimensions as described.

    Hope this helps. Ask questions if you like and and I'll try to clarify things. This is all second nature to me so I may not be as good as explaining/writing as I am at doing it. Sure takes a lot longer to write it down than to just do it.... Once you do it, it's really fast and easy with no math once you construct the triangle. Drawing two parallel lines equidistant from your apex point is the hardest part..
    Last edited by cliffrod; 12-21-2019, 08:52 PM. Reason: seemingly endless spellcheck typo problems and some regular mistakes by me...

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  • Chazza
    replied
    I have never had to make a core-box from scratch, but I have made this pattern from scratch, which involves much the same skills and some of the techniques.
    A friend asked me to make an exhaust valve side-cover for a 1948 Land-Rover and he lent me one to copy.

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    Photo 1. The outside shape made in jelutong, because it is easy to sand out marks.

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    Photo 2. The inside shape. While this pattern does not require a core, the hollow I created here with gouges and a mallet, is a similar technique used to make some core boxes. Curves were copied with a comb-gauge and templates made out of card – same as we do when copying panels. Plastic filler has been used to correct imperfections and to make concave radii

    To begin with, an accurate sketch had to be made of the original part and the dimensions measured with vernier calipers and steel rules. But now comes the risk, which can ruin a good project, if not understood by the person making it.

    Metal, as I am sure we all know, expands when it gets hot and contracts when it cools. Aluminium contracts by 1.3% (“The Foseco Foundryman’s Handbook”; 9th Edition; pp49); therefore when making a pattern it should be 1.3% bigger than the drawing, or the original part. Pattern makers use a contraction-rule to make production quicker but as they are rather expensive, I write the contraction-allowance sizes in red ink, next to the dimensions on my sketch.

    Before I take merrily to the sketch with my red pen there are some other things to consider first. Because I took my measurements from a casting, not a drawing, it means that the casting has already shrunk by 1.3 % when it was first made back in ’48. Therefore the original pattern was 1.3 % bigger than the casting in front of me.

    But how do I know if this casting is an original, or one that has been made using a casting as a pattern? If that was the case the casting is 2.6% smaller than the original pattern. The answer is that I do not know, so it is wise to measure the component that the casting is to be fitted to, to check that the pattern and casting will fit.

    Plus, I also need to consider machining: How will it be held? Would a spigot or two, be useful for clamping, etc.?

    Now 1.3% of 6.35mm is 0.08mm; this is such a small size that I can’t reproduce it with hand tools so I can either ignore it, or make the pattern 6.5mm thick to compensate. On long parts such as the side-cover, which is about 420mm long, if I ignored the contraction-allowance, it would come out of the mould about 5.5mm too short! 5.5mm is an easy dimension to correct by making the pattern longer. Similarly all dimensions, which can be measured with a rule, can be enlarged.

    Feel free to check my maths; I am notorious for getting it wrong,

    Cheers Charlie

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  • Chazza
    replied
    CORE BOXES:
    One of the hardest things for people to get their head around in the pattern making process, is what shape should the core be and how to go about making one. Earlier pages showed a core in the green-sand mould, but no information about making one.

    Imagine you are standing in the foundry in 1854 and a customer wants a bronze pipe made, 12" long and 1" in diameter. So the pattern is turned on the lathe and split down the middle – see Fig.1 below. Having established the shape and diameter of the outside of the pipe, you now need to physically make the shape of the inside of the pipe, on a separate pattern called a core-box. Let us say that the pipe was just a straight-forward hollow cylinder. So the wooden blank could be held in a chuck and a drill bit, or boring-bar, passed all the way through the length to make a hollow cylinder and then the core box is split in half, as in the sequence shown below.

    This of course is an incredibly inefficient way to make a pipe – although better than machining one from solid bar – which is why no one does it anymore. However, it is essential in casting to know how to make cores, as they are needed to make hollow shapes and to reduce the thickness of castings, where too much metal would be detrimental, or wasteful and expensive.

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    Fig. 1 Method used to turn identical halves in timber on a lathe.

    The method shown in Fig. 1 is very useful, whether or not, the object to be made is cylindrical. When I reverse-engineer a casting, the first thing I look for are lines of symmetry, or lines where a pattern, or part-pattern can be split. Note, that if the piece is to be turned, the wood-to-wood on the ends makes it less lightly to split down the paper line, when the tailstock is tightened.

    The second thing I ask myself; is whether the pattern could then be withdrawn from the sand, or not, i.e. does the pattern have a draught, or does draught need to be put onto it? On a new pattern draught can be turned, planed, sanded, or sawn to give the 3° draught required. On existing patterns – e.g. a sawn-in-half metal part – draught can be added with plastic filler.

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    ​​​​​​Fig. 2 Finishing the core-box.

    In Fig.2, are some simple core boxes and two suggestions for the type of sand to use. When using either, sand is poured into the core-box and then screeded with a strickle, before hardening. The sheet metal ends can be loosened after the core has hardened, to facilitate removal of the core. Glue the two halves together with PVA wood and paper glue.

    Sodium-silicate, also known as water-glass, when mixed in damp sand, can be hardened with carbon dioxide in a matter of seconds. As long as the wooden core-box is smooth and well varnished and a release-agent such as talc, or silicone spray, has been applied to it, then by inverting the box and rapping it on the bench, a core of this shape, will fall out easily. For awkward shaped cores, ejector pins need to be fitted to the core-box to help get the core out. Advantages; cheap sand mix; no hot work; fast; fine sand can be used; strong core. Disadvantage; have to buy CO2 and regulator.

    Resin sand requires a metal core-box; the core-box is heated over a gas flame and the resin hardens and so the core is formed. Advantage; makes a strong core. Disadvantages are; expensive sand, if you can get it; time-consuming to make core-box twice; my resin sand is coarse and gives a rough finish on the casting; hot work is tiresome and presents safety hazards.


    When I made my first thermostat housing, pictured below, I devised a plan where I would cut the corroded original in half and make some timber ends which were glued to the aluminium. The ends had a hole bored in them, which was the same size as the core prints on the pattern. To bore half a hole, use the cartridge paper method, or even easier, is to clamp the two pieces in a machine vice and then drill them.

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    ​​​​​​Photo 1 above; the old thermostat housing has been cut in half along a line of symmetry; ends have been made to support the core-box, they have draught so that a mould can be taken, to reproduce it in aluminium. Note the use of plastic filler on both halves to repair corrosion damage and to create draught on the base. Note also, the half-holes on the ends; these will form a cylinder, which rests in the core prints on the mould. Top left is the cast part, still needing some finishing where the hose goes on.

    Although this part has a line of symmetry in it, the two parts of the core and of course the pattern, will not be identical i.e. they will be left and right-handed. This time both sides of the core-box will be needed, unlike the simple core-box in Fig 2. (1).

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    ​​​​​​Photo 2 above; here is an asymmetrical core for a Land Rover thermostat housing. I cut the old housing in half, to eventually end up with two aluminium core boxes. The sand is resin-sand and as can be seen, it is coarse sand and leaves a rough finish on the aluminium. This is one reason why I am experimenting with sodium-silicate cores, so that I can have smoother castings for the customers.

    If I had to make the core box from scratch – perhaps from a drawing – then it becomes much more difficult. In the past pattern makers were experts at making patterns in wood, which is what I wish to be; much like the objectives off this forum to learn traditional shaping methods. Anyway, back to making a core-box from scratch; nowadays we can use plastics, wood, metal or a 3D printer to make patterns. Some of this core could be made on a wood lathe and perhaps parts of it by hand with good chisels.

    Soft hardwoods such as Jelutong were used in the past but there isn't enough rainforest left, to countenance that anymore. I use recycled timber from old furniture and a local hardwood called jarrah. Any timber pattern needs to painted, or varnished and kept out of the sun, as this is one disadvantage of using timber; warp and shrinkage.
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    ​​​​​​Photo 3 above; two core-boxes cast in aluminium; the top one is for one-half of the core in photo 2, the heads of the two screws are the ejector-pins. The bottom one is an aluminium box made from the pattern in photo 1, the ejector pins are raised because it is sitting on the bench. When I cook the cores I have to be careful that the pins drop though holes in the mesh, which sits on top of the burner.

    On the top core-box, part of a handle can be seen, so that I don't get burnt. For the bottom one I use vice grips, but it is fiddly, hot and not the best way to do things. When I perfect sodium-silicate core sand, I can still use these core-boxes.

    More to follow.
    Last edited by Chazza; 01-24-2020, 03:41 AM.

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  • cliffrod
    commented on 's reply
    Looking forward to pics of your English wheel someday and maybe some history about its past life, if you happen to have it.

  • Peter Tommasini
    replied
    I might have a job for you as well,....... keep posting
    Cheers
    Peter T.

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  • Chazza
    replied
    Originally posted by cliffrod View Post
    ... (umm, spellcheck changed "interesting" to "erecting", but that's not the kind of exciting I was talking about....) ...
    Ha ha!

    Cooler change on Friday; with a bit of luck I will be here still and can do a pour early in the morning on Saturday.

    Just a piffling 38C today.

    Glad you like the articles Cliffy.

    Better go now, English Wheel arriving in 20 minutes!

    Cheers C

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  • cliffrod
    replied
    Hot damn, Charley- this is fantastic! Maybe someone will post something more interesting (umm, spellcheck changed "interesting" to "erecting", but that's not the kind of exciting I was talking about....) someday. until that happens, you're alone at the end of the ruler. Lots of questions to ask, but want to get them organized. Thank you very much.

    Please be carfeful at work. They're talking about the AU fires on the news here in the states.

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  • Chazza
    replied
    SAFETY:
    I usually put the safety rules first in articles I write, but I didn't want to scare anyone off what is a very useful set of skills, in a very safe trade, if the safety rules are obeyed without question, or exception.

    I have been pouring aluminium since 1978 and have had only one near-miss and that was early on, following some very poor instruction and involved water as a binder.

    In 1985 I was most fortunate to have had some very useful instruction from a pattern-maker whose father had been a moulder. What that man didn't know about both trades, wasn't worth knowing I suspect.

    If you have an interest in casting, then ignore 99% of what you will find on Youtube. Most of the posts there show a complete lack of safe-working practice and in some cases, an appalling ignorance of potential dangers. In any case some of the techniques and practices are not the best ones to use.

    I am also a member of a casting forum, where I have been ridiculed for pointing out unsafe practice. One man even suggested it was a point-of-honour, to carry the scars on your arms caused by spalling concrete. If he is more of a man than me, then I am happy to be called something inferior to him!

    Before the rules let us consider the potential hazards, which are easily minimised to nothing.
    • Hot flying metal and concrete.
    • Losing your life.
    • Suffering permanent disfigurement and disability.
    • Losing your income permanently.
    • Losing your house or shed.
    • Injuring or killing another person.

    All of these consequences are avoidable and when we think about them, are no different to some of the hazards many metal work tasks have.

    Hazards in capitals. Safe working practice listed below.

    FIRE.
    • Melt metal only on a sand floor to prevent spills from contacting flammables.
    • No water or dampness EVER in the foundry.
    • Remove all flammable materials well away from the pouring area.
    • Guard flammables such as gas hoses, with steel screens.
    • Have appropriate fire-fighting equipment nearby and ready to use.
    • Use only approved and licenced gas equipment.
    • If using solid fuel, use spark arrestors.
    • Make sure that inside and outside the foundry has all fuel removed.
    • Do not use the foundry on dangerous-fire-condition days.
    • Only melt inside a dry foundry, never outside.

    HAZARDOUS FUMES
    • Clean scrap only.
    • Teflon coatings are hazardous!
    • Wear a respirator capable of dealing with gas and dust.

    BURNS
    • Wear full PPC; boots; leather spats; leather trousers or chaps; leather boiler-maker's jacket over a leather apron; leather cap with neck protection; goggles or safety spectacles; full face-shield; long leather welding gloves; cotton or woollen clothing under above.
    • Treat all metal as hot.
    • Use tongs and other suitable tools instead of hands.
    • Secure the foundry from people and animals during and after a pour.
    • Do not allow others to watch a pour; show them a video instead.
    • In the unlikely event of a burn, know where the nearest cold running water is, to begin first aid.

    There may be hazards I can't think of but if you work on the principle of;
    1. Removing the hazard first.
    2. Engineering to minimise the hazard
    3. Isolating the hazard
    4. And last of all wearing PPC to protect from accidental contact,
    it is highly unlikely that anyone will get hurt.

    Cheers Charlie

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