Well after 2 attempts I decided I better make a page for this
thing. The first set is my first attempt. read on down for
more attempts :) What's the saying "third time's the
charm ?" something like that.
After it cooled (remember its
up-scaled about 2 times) looked good at first. Check the pics on
the right for the shrink and voids. If the feet were good I might
use it. Need to vent the feet better and fix the pattern so it
doesn't break the sand. Its real ZA3 and pistonium to make it flow
better. Think I will add some more pistonium next time and make
sure I have enough to hot top the spru to prevent the shrink. ZA3
gives it a lot of weight.
The day started with good intentions. I fixed the pattern.
Had a convex area on the bottom of the left hand side. Kept
breaking the sand as I pulled the pattern. Rammed it up, looked
good." :) WooHoo" Forgot the pics :( Started to
get a nasty headache. I should have known. Put the mold
together and got ready to poor. I was using my new cast iron bean
pot to practice for the bed. Started to poor. Hmm something
not quite right. Then I saw it. AL started running out
between the cope and drag !! Kept poring and it stopped (glad I
had 7.5 qt half full pot :) ) Had to go somewhere with it. I
figured it was a total loss. Not sure if the mold wasn't closed or
pressure separated it?
Except for the shrink (again) its not all that bad ??
Moved the spru directly on the casting this time. I'm gonna try it
1 more time. Never did get the carriage done, headache made me
quite. Open for suggestions on how to get rid of that shrink!!
Three strikes your out :( - Well after posting for some help and getting
several suggestions, I tried 1 more time. I ran short on AL so I
blame that for the results. I will try #4 soon and use the best
one. The shrink is not as bad as before. This one is all AL
with no zinc. Don't know if that makes a difference.
Some pics of the mold setup. Top
left -The pattern sitting on a false cope. Mid left - Drag all rammed
up. Top right - Pattern removed from drag. Notice the vent holes around
the pattern as well as in the pattern. Also have a gate cut from
the bottom of the spru, could be better. Mid right - Rammed
up cope after splitting the flask. There are 3 vent holes in each
foot. These are required for this mold or the feet wont fill
correctly. I use a false cope to embed the feet. Have had
trouble getting a clean parting line. The false cope I use is
about 1.5" thick. I ram it softer than a mold. Bottom -
closed up after cleaning loose sand and ready to go. Spru is
on the left, that's a BIG riser over the shrink area I have been
getting. After I pored I put sand over the spru and riser to hold
in the heat. You can see how the AL sucks in from both on the
- FINALLY !!!. Still needs some finishing but it came out with no
shrink. I believe part of the problem was the ZA3 I was trying to
use. I knew it would be hard to get it to fill with no shrink, so
I added some pistonium and a little copper to get it closer to
ZA12. I did not do a test to see how close I was but
suspected I needed more AL. I added more AL and copper for this last
piece . I decided to put the spru directly on the thinner end
instead of off to the side. I also used a 2" riser directly
over the big end. I made room in the mold to "hot top"
the casting. Basically providing a large pool of still hot AL to
draw from as the casting cools. No chill but I did consider it ;)
So what did we learn? First make the parts of a pattern as
close in size as possible. Second ZA3 does not like to be cast in
thick sections. A big riser "might" help fix a bad
pattern. If I were to do this again a completely different
headstock design would be considered.
I have heard that some people do have problems with this
casting. I would start with a riser and spru directly on the
casting instead of the way gingery recommends. That only works if
you can melt more than 1 quart at a time. Yes it is a pain to cut
them off but no one will see the evidence once its assembled.
A note on ZA3. You probably wont run into much of it in the
wild. It is not normally sand cast like I was attempting. I
happened to find a few pounds of real ingot at a price worth trying.