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  1. #1
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
    Age
    56
    Posts
    1,185

    Default Patternmaking failure!

    Vintage engine guys want to do a run of brake drums.

    They spent a while on Sunday trying to cast Ally in the drum to make a pattern, but it didn't work out. Then they come to me yesterday asking for plywood to layer together to make a pattern.

    So, I scrounge for plywood, then find some of Dad's old 8" x 3" pine. (Dad was a patternmaker)

    Cut two squares, lop the corners off, mount onto a faceplate:
    IMG_2689.jpgIMG_2690.jpg


    and start to machine round. Wasn't easy to get the tool far enough out:
    IMG_2691.jpgIMG_2692.jpg

    so in the end I used a cheaper cutter half way out of the holder for roughing down:
    IMG_2693.jpg

    Then clean up with a sharper tool:
    IMG_2694.jpg
    (ground positive rake Aluminium cutting insert, small cuts).


    Now, measuring shows this is a little small for the outside of the drum, because the drum has a lip at the back. So we can use it for the inside mould, right?

    IMG_2695.jpg

    Spend an hour tapering, radiusing the inside corners (fillets), replicating the inside core/negative shape...



    until I realise I am being an idiot!
    The sand mould needs to be that shape, not the pattern to make the mould!!!




    IMG_2696.jpg

    So, here is the brake drum, on top of a much larger bit of old timber (Jelutong), ready to chop the corners off, and bore a CAVITY into.


    Might get lazy, and with a quick trip to a foundry with the drum, cast the cavity in Alloy instead, to machine out into the cavity pattern.

  2. #2
    Join Date
    Dec 2007
    Location
    Sydney
    Posts
    396

    Default

    The jelly won’t work for more than one off, ok if you want a few in Al to remachine and mount on a plate.
    If you want to make a circular shape stay round it’s has to be in segments.
    6 were used just strike the length with the rad.
    Might be best to do it solid with a piston print and corebox.
    For production a matchplate would work. The Foundry usually cast these in Al.from your master.

    Go and talk to the Foundry and find out what they require in the way of pattern equipment.
    Especially if you want to make a few of the brake drums.
    Unless you get a jobbing Foundry they’ll need it tooled for whatever dollar efficient process they use, otherwise they wouldn’t still be in business thanks to the cheap imports.

    This all takes time and if the Foundry boss is busy and they have a lot of paying work on good luck.
    Sorry I should come over and sort this for you but I’m still getting over my skylight trick with my balance.
    Im also over as a patternmaker being the unpaid go-between the customer and Foundry.
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

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