Hey Stefan, look at this link, lot's of variable's to drive us insane
http://www.scribd.com/doc/51971976/1...TIES-HOT-TEARS
Can you post picture's of the defect's? The wax isn't your problem. How the part is oriented, how it's gated-the hole for pouring and the venting hole. Multiple gate's or hole's with smaller runner's will help with the tempurature differential's of the mass cooling. A bad example would be trying to cast a hotdog with butterfly wing's, the mass of the hotdog will cause the thin wing's to fail, while cooling from casting. Everything need's to cool at the same rate. I would try the other foundry, and explain to them what happened last time. Sometime's it's better to leave a cavity out and machine it in after casting, to keep the cross section of the part more consistent.
http://en.wikipedia.org/wiki/Casting_defect
Now the disclaimer, my experience was with aluminum and not near the quality of your stuff. Still learning! I tried brass once, that stuff is realy hot! when pouring it.
Not enough help today, hope you gained a few idea's!
The stuff that I cast, looked like a porcupine when it came out of the sand, lot's of small vent hole's, to let the gases out of the mold. I'll have to find the offending part for picture's.
http://www.iron-foundry.com/casting-...-pictures.html
Cheer's, Neil.