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Hot Rods Aluminum casting Guys

Discussion in 'The Hokey Ass Message Board' started by Bonehead II, Apr 30, 2020.

  1. Bonehead II
    Joined: Apr 18, 2005
    Posts: 417

    Bonehead II
    Member

    Hi Guys, I would like to try to do some casting of aluminum, can anyone tell me how much aluminum shrinks during the cooling stage, I will try to compensate during the mold building stage. or is it worth it ?....Thanks...Mike
     
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 15,699

    alchemy
    ALLIANCE MEMBER

    I build patterns to 102% of final part size.
     
  3. 19Fordy
    Joined: May 17, 2003
    Posts: 6,872

    19Fordy
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  4. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 684

    fourspd2quad
    ALLIANCE MEMBER

    I agree with Alchemy 102% :)
     
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  5. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,497

    Rand Man
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    My grandpa was a pattern maker and had special rulers and calipers scaled on the shrinkage of different metals. Took the math out of every pattern measurement, but you had better not mix them up or use them for some other purpose.
     
    Pat Thompson likes this.
  6. Pat Thompson
    Joined: Apr 29, 2012
    Posts: 198

    Pat Thompson
    Member

    Rulers are called Shrink rules. I have several that I no longer use. I worked in a pattern shop for 35 years. Most of our work went by 1/8" shrink per foot.
     
  7. CNC-Dude
    Joined: Nov 23, 2007
    Posts: 889

    CNC-Dude
    Member

    Don't forget that all the surfaces need draft angle on them all to help release from the core box.
     
  8. alchemy
    Joined: Sep 27, 2002
    Posts: 15,699

    alchemy
    ALLIANCE MEMBER

    Make your own scales. Set a nice ruler on the copier, and bump up the percentage to 102%. Then have it laminated. Cost under a dollar. But make sure to write on it very clearly that it's 102%!
     
  9. pirate
    Joined: Jun 29, 2006
    Posts: 505

    pirate
    Member
    from Alabama

    The “Aluminum Association” has a book named “Standards for Aluminum Sand and Permanent Mold Castings” that has a lot of information about castings including draft angles, shrinkage, alloys, standards, etc. that would be very helpful information. Not sure if it is online or only available as the paperback shown below. Might try doing a Google search or contact the Aluminum Association to see if it is still available.

    [​IMG]

    \
     
    CNC-Dude, pitman and Desoto291Hemi like this.
  10. Bonehead II
    Joined: Apr 18, 2005
    Posts: 417

    Bonehead II
    Member

  11. There was a good series of books years ago by David Gingerly. “The Charcoal Foundry” has lots of good info.
     
  12. '51 Norm
    Joined: Dec 6, 2010
    Posts: 697

    '51 Norm
    Member
    from colorado

    Make a rod for a pattern a foot (or other known length) long.
    Use the rod to make the sand mold.
    Make a casting using the metal that you are planning to use.
    Measure the casting and figure the amount of shrink.
    Takes all of the guesswork out of it.
     
  13. X-cpe
    Joined: Mar 9, 2018
    Posts: 975

    X-cpe

    First copy the ruler at 100% to make sure the copier is accurate. Years ago when I was teaching wood shop I had to teach them how to read a ruler. The copier would distort the line lengths I had drawn on the work sheets for the students to measure. I had to copy the ruler too so the worksheet lines and the copied ruler had the same distortion.

    Now a couple of questions. If you cast aluminum around an iron object, does it shrink away from the object or shrink tighter against it? Would chilling the object help the casting to fit tight to the object?
     
    Last edited: May 1, 2020
  14. pirate
    Joined: Jun 29, 2006
    Posts: 505

    pirate
    Member
    from Alabama

    Casting iron/steel insets into aluminum castings is quite common however rarely is a metallurgical bond achieved. Typically a mechanical bond is achieved and usually with the aid of the iron/steel being prepared with grooves, splines irregular surfaces or heavy grit blasting. When the aluminum is poured into the mold it fills the grooves, splines, etc. to lock the insert into the cast aluminum. This is a mechanical bond and if the casting is sectioned/cut up the aluminum can be separated from the iron/steel fairy easy. The shrinking of the aluminum enhances the mechanical bond.

    A metallurgical bond can be achieved between aluminum and iron/steel but it is more involved. Pistons often have a cast iron ring land cast into them that is a metallurgical bond.This is achieved using the Al-Fin process in which the iron insert is dipped in pure aluminum just prior to being cast with the aluminum. There are some other processes using aluminum enhanced with other chemical elements to form a soluble alloys which will metallurgically bond to iron/steel.

    Usually if iron/steel is chilled it has the opposite effect and the molten aluminum will form a solidified skin next to the iron/steel insert resulting in the aluminum not flowing around the insert and no mechanical bond will be achieved.
     
    Last edited: May 1, 2020
    X-cpe and fourspd2quad like this.
  15. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 684

    fourspd2quad
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    Can you share with us what you are trying to cast? It would be more helpful in understanding what the complexity/potential issues you may have with your design.
     
  16. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,589

    Kan Kustom
    Member

    Man that was was quick and to the point. This place amazes me.
     
  17. Bonehead II
    Joined: Apr 18, 2005
    Posts: 417

    Bonehead II
    Member

    I want to build an intake to fit on top of a 671 blower with 4/6 Rochester 2bbl carbs
     
  18. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 684

    fourspd2quad
    ALLIANCE MEMBER

    Now THAT is ambitious.
     
    JUSTIN PERSINGER likes this.
  19. tjm73
    Joined: Feb 17, 2006
    Posts: 3,373

    tjm73
    Member

    Years ago a HAMB'r did a very detailed writ eup on home casting some aluminum valve covers. He made a wood buck and then made the sand casting box and then cast them. He talked about shrinkage. It was a pretty amazing thread.

    EDIT: holy cow I found it. if the pics don't show up, hit reply and you will be able to see them in the reply.

    https://www.jalopyjournal.com/forum...lhead-valve-covers.142941/page-2#post-1593073
     
    Last edited: May 1, 2020
    JUSTIN PERSINGER likes this.
  20. SEAAIRE354
    Joined: Sep 7, 2015
    Posts: 183

    SEAAIRE354
    Member

    @bonehead thank you for starting this thread. I’ve had casting on my bucket list of things I want to learn and try but haven’t had the time to sit down and start the research. This has definitely inspired me. And thank you to all the brilliant member’s replying. Keep it coming.


    Sent from my iPad using The H.A.M.B. mobile app
     

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