[SEL] Falk piston core box and pattern update.

[Curt]

Tommy,
Consider a piston (or any hollow casting) that is perfectly symmetrical 
on the inside. You make a core box that is essentially 1/2 of the core 
and you ram 2 of these core halves up and glue them together. But in the 
case of Dave's Falk piston or my 3HP Herc piston the inside is not 
symmetric. In Dave's piston there is a bottom that sticks down from the 
top that drips oil on the wrist pin. On the Herc piston there is a web 
across the top that supports the copper tube that oils the wrist pin. 
Because of this you have 2 choices. Make 2 separate core boxes with this 
feature on the right on one half and with this feature on the left on 
the other half.
Or you can make a single core box and make the feature removable and 
swappable (word?) to the other side. You also make a blank. By swapping 
the blank and the feature, you are able to ram right and left core 
halves with the same core box. For small volumes of casting this is the 
most economical method, as making core boxes is labor intensive.

As to the patterns and separating them. I spot glue mine and then split 
with a 2" chisel. The paper method works too, but the spot glue method 
works so well that's all I do now. Maybe 10 little drops spread around 
in a pattern and the drop about 1/8" diameter. When you clamp them to 
dry the spots will grow to about a 1/4" diameter. I also run a thin bead 
at each end. That solid glued section either gets cut away during the 
lathe work or you may have to saw into the end with a hacksaw for a 1/4" 
or so. Then it will split easily. The glued end is to add strength to 
the spreading forces the center tend to impose. Having a pattern fly 
apart in the lathe wouldn't be too fun!
Curt Holland
Gastonia, NC



Judge Tommy Turner wrote:

> Dave or Curt,
>    I have "loosely" followed the pattern making thread but wished I 
> had paid more attention. Here are a couple of questions.  Can you give 
> me some additional info. on the removable insert?  How's it held in, 
> removed, etc.  Second, is it simply paper you put between the two 
> halves before glueing so that you can separate them later?  I had a 
> guy once tell me he glued newspaper between the halves then took a 
> sharp chisel and with a blow of the mallet they would pop apart.  This 
> pattern work is beginning to interest me and I admire the work you've 
> done.  Thanks.
>