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  1. #21
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    This is a big issue today and I personally believe these internal stresses that cause warping are caused by rapid cooling after casting. I further believe that once there, they can never be removed completely and the casting should be considered scrap only. The real issue is to let these casting cool very slowly, but production demands and profit maximization force the casting to be cooled way too quickly at the foundry.

  2. #22
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    'Cast iron" in all names, types, recipes and whatever, at room temperature, is a solid mixture of elements, compounds of elements, frozen in place. The atoms of each element and compound have a favored position relative to its surrounding atoms and elements. Some members are trapped in a position they are not liking and want to move. When the atoms have enough energy or time, realignment and positioning, takes place. Different compounds may be formed, lattice positions may change. Just as in the hardening process in carbon steel.
    The machining process gives the cast iron the energy to allow restructuring of the elements, and may change dimensions of the machined part. The posts recommending machining in steps with the final machining of light cuts and light clamping appears to be the option of choice.

  3. #23
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    Heat treat regimens can also generate realignments such as the proprietary Meehanite or ductile iron varieties. It's still probably to the point to cool down slowly rather than toss them from the furnace into wet sand so you don't reintroduce changes or stresses.

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  5. #24
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    Quote Originally Posted by Trueturning View Post
    It seems like one of those parts

    Often the user does not care except for when things on the print are so tight for most shops they can demand a much lower price for the parts ran than originally bid. This is negotiation to them as they know they can live with less yet they never change the print to reflect this because they know as is it makes them money. This does happen frequently.
    Now I herd it all.This seems like a pretty cheezy way to make a buck.Bid out a job and plan on making your profit by chisleing the vender"Let the vender beware".Edwin Dirnbeck

  6. #25
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    Cadillac use to age the old cast blocks outside here in Michigan for 1 year. Big piles of stock.
    Chevy and Buick tried for 1-3 months. Better of not who is to say.
    Making brake drums and rotors less than 2 or 3 weeks old was a real problem.
    We called this "green" iron, it ate tooling like mad along with size control when you had to machine 1-2 day old castings.
    When just in time became a fad this became a nightmare.
    It needs to sit some time, how much may depend on the complexity of the casting.
    Bob

  7. #26
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    I remember seeing a picture of Powermatic Table Saw castings in a large pile outside at their production facility. That's how they used to do it.

  8. #27
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    Quote Originally Posted by edwin dirnbeck View Post
    Now I herd it all.This seems like a pretty cheezy way to make a buck.Bid out a job and plan on making your profit by chisleing the vender"Let the vender beware".Edwin Dirnbeck
    Haven't you heard Edwin ;- It's a pretty cheesy world!

  9. #28
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    I've always thought Monarch did the best job.

    Monarch Cajun Seasoning Granulated 22 oz.

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  11. #29
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    rons mentioning Powermatic table saws. I remember seeing a NOS Powermatic 66 table saw at an auction, it had a tag stating the cast iron table was tested to be better then .010" flat. I think most are better then that, but unlike metal working machines, there seems to be no standards at all for woodworking machines.

    I had a warped fence on my Powermatic jointer, it was concave about 1/8" giving a bad bearing surface for the board at the cutterhead.

    This is what I did.

    Blocked up the fence at the ends on the floor, set up a dial indicator, then stood on the back side of the fence.

    Watching the indicator, I could deflect the narrow cast iron fence in the right direction with my weight, but it would return when I stepped off.

    To move the iron, "Set, and relieve".

    Set, with my weight on the iron, I took an 8oz steel hammer, stuck the iron hard enough to feel the shock through my feet, that was also where I wanted it to bend.

    Ok, now the indicator will show the metal is moving in the right direction, but it will not stay, it will drift back toward where it was.

    Relieve, take the hammer and strike the iron without weight on it, the iron will drift back toward the error, but not all the way.

    With those motions, the cast iron can be walked back true, as it was when machined, but internal stresses, and some you probably just caused can cause future warping. And, its possible to break what you want to straighten.

    The cast iron Stanley hand planes, are a great study of many problems with cast iron, they were made for so long, and have a difficult shape to stay true.

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  13. #30
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    Quote Originally Posted by Limy Sami View Post
    Haven't you heard Edwin ;- It's a pretty cheesy world!
    Wallace can verify that, along with support from the faithful Grommit.

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  15. #31
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    Quote Originally Posted by TGTool View Post
    Wallace can verify that, along with support from the faithful Grommit.
    Hmmm.......Stilton or Wensleydale?

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    Quote Originally Posted by muckalee View Post
    The posts recommending machining in steps with the final machining of light cuts and light clamping appears to be the option of choice.
    Endorse that. It’s the Practical Machinist Forum and your point is precisely what we can do. Everything else is castors or managers’ business. My experience with stress relief is based on the turning of thin-walled bronze bushes out of centrifugal cast tube sections. Tolerances of 0,01 mm (± 0,005 mm) for a very lively material. We put the roughed green bodies aside for a couple days but the best method is to allow stress to diminish by removing material in deliberate steps. Mind you all that an intermediary honing operation by which a surface is broken up into a multitude of irregular forms helped a lot.

    Wise clamping of parts is the other half of the story.

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    Quote Originally Posted by edwin dirnbeck View Post
    Now I herd it all.This seems like a pretty cheezy way to make a buck.Bid out a job and plan on making your profit by chisleing the vender"Let the vender beware".Edwin Dirnbeck
    Bottom line they bid the job based on that print and for a price. If the shop is not able to make the part to print then it is the shops fault not the customer. Most of the time a shop will struggle through and get it done or learn how. Saving money lowering the price per part I s not how they make money at all it is simply extra profit.


    What they need is the part and that is how they make money not the small amount they save bailing you out on material. You can always tell the customer you are having trouble and see what they say. Too you can also apologize to the customer and professionally in some way or another to back out. Always be calm and helpful they may not even know there is a problem even.

  18. #34
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    Default cast iron

    kind of basic apprentice learning of part stability
    .
    cast iron castings are often annealed after casting at a extra charge. if not annealed they can vary more in metal properties that is the metal is not 100% consistent material depending on cooling rates at varies parts. same as if cold rolled steel is not annealed it warps more at machining unclamp than if steel is annealed 1st. cold rolled steel has a harder "skin" than the softer center of thick section. many castings have similar properties on section thickness
    .
    machining its normal to rechuck after rough machining at lower clamping torque so clamping does not distort part
    .
    larger parts are supported to minimize gravity deflection and fixture clamping delection
    .
    most parts on rechuck or when unclamped need time to think about relaxed position. from 5 minutes to many days.
    .
    when a casting varies in thickness the thinner sections tend to be harder and at a higher tensile strength. cause casting metal is not perfectly 100% consistent when material removed unevenly on it often will curl or warp. many castings warp later in a certain range or amount. not a question of if only how much warpage for a particular casting
    .
    sometimes warpage also varies depending on temperature. bimetalic bending is common. that is casting metal if inconsistent may change bending amount depending on its temperature.
    .
    obviously if during machining, an end of a part gets hotter or colder than the rest of the part it will change when the whole part returns to the same temperature. very common for a larger part to get bigger or smaller over .0005" during machining and after temperature stabilizes you can measure the change. obviously with bad coolant temperature control part can easily vary more than .001" later at 70F room and part temp

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  20. #35
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    I worked in a machine shop for five years where everyone but me was German or some other European descent. I don't know if this technique is practiced here but I have not heard of anyone else doing it. What they did was take cast iron stock and put it in a strong magnetic field. I think it was just the stator out of a large scrapped motor. They would apply AC to the field and they claimed that the rapid reversal of the molecules would "season" the cast iron. They would leave it in the field for a couple of days. It seemed to work for them. There was pretty much zero scrap due to warping. There was some scrap but I always attributed that to the fact that they kept beer up on the machines to keep it warm and drank it all day long. I must say they were damn good machinist however.

  21. #36
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    I think my former employer when casting transmission cases just let them shakeout green sand then cool for a week or two. After that some smaller castings went to a wheelabrator tumblast for a while. Larger ones were shotblast too but not sure how. Maybe a Rosler or something? The cases usually came to me cleaned and painted on the inside so I saw a little of the preprocess but not much. I don't believe any cast iron went through heat treat, That was all for the transmission gears and shafts.

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    Many years back, we used to get gray iron castings from the old Alamo Iron Works in San Antonio Texas. We hardly had any issues with castings until the foundry was moved to it's new location. The old location is where the Alamo Dome is located today. There was something about the ground, sand, etc. that made good castings that couldn't be reproduced effectively at the new location. Still kick my a$$ for not buying a REAL frying pan from the foundry. They never come up for sale, ever! They always cast "The Alamo" in every castiong that left that foundry until it's end. Ken

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    Quote Originally Posted by BoxcarPete View Post
    I came here for the wrong kind of information. You see, my morning eggs are starting to stick to my pan...
    Scrub pan, let dry, put in 1/2 inch of cooking oil, put in oven at 200 degrees F for several hours, shut off, let cool over night, pour out oil. wipe clean with paper towel, cook per usual. Do not wash, wipe out with oil.

    Paul

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  25. #39
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    Quote Originally Posted by paul39 View Post
    Scrub pan, let dry, put in 1/2 inch of cooking oil, put in oven at 200 degrees F for several hours, shut off, let cool over night, pour out oil. wipe clean with paper towel, cook per usual. Do not wash, wipe out with oil.

    Paul
    Did both my pans this weekend. Everyone has their own opinion on the best way, but I can say that what worked for me was shortening applied with a paper towel to the pans (uncomfortably hot to the touch), then a clean paper towel to leave only a thin layer. 350°F upside down in the oven for one hour, then let cool for 15-20 minutes, repeat. I went three times total, until the oil was weeping out of the pores in the oven. I'll probably have to do it all again in a few months since I refuse to dirty an extra dish every morning scrambling the eggs before dropping them in the pan. If I did that, the daily application of bacon grease would probably go indefinitely.

    But for now, nothing stuck whatsoever, so I'm happy for the time being. Best part about it is that I rescued both pans, one from a thrift shop for under 5 bucks, the other mere hours from the landfill itself. A scotchbrite and a little elbow grease can bring a decent cast iron back from the brink into tip-top shape.

  26. #40
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    I know alot of material moves whilst machining , I have sent 2 woodworking machines back because of warped castings.
    Now is it from green castings, poor fixturing ? Maybe both.


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