Metal Casting Pattern Question

I'm in the middle of creating a pretty complex pattern that I intend to
green sand (Petro Bond) cast in aluminum. I chose basswood for the pattern
because there is a lot of carving to do to create the organic pattern I am
making, and this is my first significant woodcarving project. Basswood seems
to be a dream to shape because it turns, carves, and sands so easily; and
there is very little grain in the wood for an excellent surface finish. Now
that I'm some 20 hours into the job it occurs to me that it might be too
soft to withstand the ramming process without being damaged, and I would
like to get at least 5 or 6 good castings from it. Now I'm wondering if I
chose the wrong material. Has anyone else any experience with basswood in
this application? I was planning to spray it with polyurethane before using
it but I'm not sure that will add enough hardness. Would an epoxy paint make
any significant difference? Any thoughts out there before I put another 20
hours into it?
Reply to
Terry Mayhugh
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Are you using green sand, or are you using petrobond? They are different. Green sand is sand, clay, and water. Petrobond is sand and a petroleum binder.
Are you doing the castings yourself or farming them out to a foundry? Fragility may be an issue if you are handing your pattern to a foundry, but likely will not if you are the one ramming up the molds. As long as you have the pattern well supported while ramming up, it will endure more than you will be willing to put to it. On the other hand, I have seen what can be done to profesionally built patterns in a foundry, and it was pretty brutal.
Petrobond will be easier to get fine detail without having to deal with issues relating to drying of the mold sand. That may or may not be an issue for you.
I have seen guys ramming up patterns for fine detail using only hand pressure to put in the facing layer of sand. Once the later layers are started then the rammer can be applied a bit more vigorously.
For your own use, boxwood should be fine. You will know where the potentially fragile bits are, and you will treat it accordingly. As you only want to get 5 or 6 good castings from it, it may even be overdoing it a bit.
Paint it with whatever you have that will leave a smooth finish to allow easy release from the sand.
Cheers Trevor Jones 222 79799 body Terry Mayhugh wrote:
Are you using green sand, or are you using petrobond? They are different. Green sand is sand, clay, and water. Petrobond is sand and a petroleum binder.
Are you doing the castings yourself or farming them out to a foundry? Fragility may be an issue if you are handing your pattern to a foundry, but likely will not if you are the one ramming up the molds. As long as you have the pattern well supported while ramming up, it will endure more than you will be willing to put to it. On the other hand, I have seen what can be done to profesionally built patterns in a foundry, and it was pretty brutal.
Petrobond will be easier to get fine detail without having to deal with issues relating to drying of the mold sand. That may or may not be an issue for you.
I have seen guys ramming up patterns for fine detail using only hand pressure to put in the facing layer of sand. Once the later layers are started then the rammer can be applied a bit more vigorously.
For your own use, boxwood should be fine. You will know where the potentially fragile bits are, and you will treat it accordingly. As you only want to get 5 or 6 good castings from it, it may even be overdoing it a bit.
Paint it with whatever you have that will leave a smooth finish to allow easy release from the sand.
Cheers Trevor Jones
Reply to
Trevor Jones
It should hold up perfectly fine under whjat its going to endure durjing raming. If your after a lot of detail go with petrobond.
Reply to
Roy
Coat your project with silicon rubber and let it dry... Peel the mold off and use it to fill with epoxy mix... Let it dry and you got a tough mold pattern...
Terry Mayhugh wrote:
Reply to
kbeitz
Coat your project with silicon rubber and let it dry... Peel the mold off and use it to fill with epoxy mix... Let it dry and you got a tough mold pattern...
Terry Mayhugh wrote:
Reply to
kbeitz
This would be expensive, depending upon the size of the pattern. I don't even have any silicon rubber 'cause I know that I would never be able to justify using it, given its cost. As to epoxy, when I built my stripper canoe 11 years ago, it was $120 a gallon. It's not any cheaper now.
Bob
Reply to
Bob Engelhardt
Sugar Pine was once said to be the most widely used lumber in the pattern industry. It is a very soft wood; it might even be softer than your basswood. So for your limited use I would think the basswood should do fine. Damaged is more likely to be caused by tool banging or other abuse, which would damage hardwoods and soft metals as well.
Reply to
Billy Hiebert

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