So...  I wanted a brass hammer to add to my blacksmith hammer collection...  

 

I got some brass

 

I made some "green sand" for the first time

 

I tried lost foam casting for the first time

 

It worked out... huh... let me say.. HALF way decent!!!

 

 

Fair warning! This is another of my "How I Did It" movies not fully a How To Do it...

 

Learn from what went right and what went wrong...  

 

 

 

I am not as familiar with foam pattern casting defects,  maybe you are right and you did not have enough venting foam does create a lot of gas but you definitely  have shrinks in that casting as well .   For a blocky shape like a hammer you need risers that are  a heavier section than your hammer.  You can cheat on the size by feeding through the riser which superheats the sand in the riser,  and some commercial foundries use insulating sleeves or exothermic sleeves which help keep the riser hot longer.   You want the casting to freeze BEFORE your riser so that the molten metal in the riser feeds the shrinking casting. 

 

 Usually the foundries I deal with design the gating and these day are more and more using computer simulation to prove the gating.  But if I were gating that part for a customer and they asked me to design the gating,  I would do it this way 1/2-3/8" diameter sprue feeding into a well in the drag I would then run a runner bar in the cope then an ingate tangentally feeding a 2" diameter blind riser (vent if it were foam) then an ingate into the casting in the drag.  Ideally you want to feed a casting from as low a point as possible.  If you are using foam that is easier to do as you don't need a core to get you to the bottom of the drag of the mould. 

 

Some foundries prefer runner in the drag and ingate in the cope but using brass that is dirty like yours it will help to trap slag and loose sand in the top of the runner as they float in brass.  Sand does not float in aluminum.

Nice try Chandler. I have done some sand casting, but always into an empty mold. I think part of your problem is that brass cools off pretty fast and because it had to burn through the foam, you got it solidified before it could flow in and fill the whole space and as John Newman says, you need to risers to feed in extra metal as it shrinks.

I think foam only works for high temp metals like iron.  Lost wax would make a pretty hammer - carve anything you want on the master then burn out and cast the metal.  Lots of info on the 'net about it - I have made very complex hardware reproductions using lost wax.

I know foam will work for cast aluminum. One of my Jr high foundry projects was a cast that way.

I have only done lost wax and green sand so will defer to your experience.  Brass is definitely hotter than aluminum at casting temps so that should work with the right gating and vents.

Played with lost foam and aluminum, worked pretty well. Kinda gassy, seemed to get more surface porosity compared to straight green sand, but might have just been lack of technique.

Many of the foundries I do work for dig out most of the foam when they occasionally use foam patterns.  This cuts down on the amount of gas and smoke released when they pour.  This is using airset or sodium silicate sand however so the mould is much more rugged than a green sand mould. 

Thanks for the comments guys...  i was considering hollowing out the foam first and in hindsight I think it most definitely would improve my results.

Nice first attempt. Casting isn't something I have given much thought to previously, other than lead. I have an old lead hammer that I know I'll need to melt down and remake at some point, wasn't sure how I was going to do it, I don't know that foam will work for it due to the low temps.

 

Edit... well not sure if I should thank you or not, but now you have my mind spinning about casting LOL... I did find a pretty good tutorial, foam seems to work even with aluminum. http://www.buildyouridea.com/foundry/lost_foam_howto/lost_foam_howto.html  This guy uses a  coating of thin drywall mix for a smooth finish and a simple head pressure tool  to help eliminate voids. I guess I have something else to try now.