[Public-List] Rudder Shoe Casting Shrinkage Issues

[George Dinwiddie]

Peter,

On 7/17/12 12:43 AM, Peter McEvoy wrote:
> Thanks Gordon and George for chiming in about the rudder shoe casting and
> whether or not shrinkage will be an issue for us.
>
> To keep it short, I really don't think it will be an issue. Shrinkage of 2%
> would indeed matter for an auto part, as Gordon cautioned. But for this
> situation, it really just needs to fit snugly on the butt of the keel. From
> my reading, I understand that the shoe is placed on the keel with an
> intermediary layer of epoxy or adhesive, and then drilled into the keel-
> this sounds to me like there is some wiggle-room. Even with maximum
> shrinkage, we'd only lose 3/32" in length and 3/64" in width. I would call
> that negligible.
>
> Then again, I don't know how picky people are. Anybody whose replaced a
> shoe- do you think these numbers will make a difference?

I've had the shoe off several times. It's not a close fit to the fiberglass.

> We could make the mold bigger if this is necessary, it's just more work
> (and mold-material cost).  I wish it were as simple as Kris suggested-  to
> heat the piece to increase it's size before taking the mold- but alas, the
> mold material (urethane rubber) is heat sensitive and also cures over a
> span of 24 hours or so, which would not make the method practical. We could
> do it if we need to, but let's see what hands-on-experienced folks think
> first.

If you were so inclined, you could coat the plug with wax first, both to 
make it larger and to make it easier to remove from the mold.

  - George

-- 
  ----------------------------------------------------------------------
   When I remember bygone days                         George Dinwiddie
   I think how evening follows morn;            gdinwiddie at alberg30.org
   So many I loved were not yet dead,           http://www.Alberg30.org
   So many I love were not yet born.                          also see:
                'The Middle' by Ogden Nash     http://idiacomputing.com
  ----------------------------------------------------------------------






 1342520052.0