Just a quick look at molding and casting the solar mount. Showing why I use a matchplate to get a clean mold. And create all my gating so I don't need to touch the pattern or mold after the cope flask and matchplate have been removed.
It looks like the half cylinder that was supposed to be filled up by a hanging greensand core formed by the cavity on the cope side of the matchplate somehow filled up with metal anyhow. What happened? Or was that just a thin skin of metal that got in between the half round positive and negative?
If you don't mind me picking your brain a bit. When you were working as a pattern maker, what was a typical tolerance required of a final casting? And what was a really hard tolerance to hit consistently that you still could manage?
Typically the required tolerance is on the drawing or defined in a cad model. That said, for small parts .015" - .030" can be achieved for castings under 12" inch in size. I've made a few ship patterns where the tolerance was as much as .25". That was for a propeller strut for a 600 foot tanker. It all depends on engineering requirements. Other things come into play as well, such as type of sand used in the mold, type and hardness of any core used. And experience of the foundry with similar castings. Probably not much help because there are a lot of factors to achieve consistent results on a casting. But in all cases you need a dimensionally accurate pattern.
@@roscoepatternworks3471 indeed! And I appreciate a ballpark answer even though I know it varies from job to job. I'm trying to learn foundry practice and pattern making on the side of my career as a machinist, and simple details like that are surprisingly hard to come by. Engineering handbooks list tolerances that are "possible" for various casting methods, but there's nothing about what a typical, reasonable, and achievable spec looks like.
@DerrangedGadgeteer the problem is there is "no rule of thumb" on casting tolerance. It all comes down to the engineering requirement. So an assumption, you're going to be built patterns for you and friends. Home foundry size? If you design the part or trying to duplicate an existing part, you need to determine what is acceptable. If you build the pattern at net size, you'll get a casting that works. If you're referring to surface quality and accuracy you should be able to polish the part and not lose any dimensional integrity. I'm thinking I may need to do a video along this line.
