This thread is a condensed version of an AA post at the link below where the unabridged version and contributions of others can be found. http://www.alloyavenue.com/vb/showthread.php?13288-More-Fun-With-Lost-Foam-Part-2 OK, so we’ve had intersecting tubular plumbing, small unsupported loose sand cores, how about deep aspect ratio features? So I thought I'd start another thread for this subject. Sing along please: It’s 2” bore. The fin thickness and spacing are about 0.1” and cylinder itself about 3/16” wall. The fins are 9/16” deep so between a 5:1 and 6:1 aspect ratio, no draft of course. Ah heck, it needs a cylinder head too. Same fin dimensions. I just drilled a shallow hole with a forstener bit, ripped the fins on the table saw while the block was square, then sanded it round and rabbited the bottom with a router bit. -It was quick. Are ya still with me? I made a router jig so finned cylinder foamies are easy to come by now. It is further discussed here http://forums.thehomefoundry.org/index.php?threads/machining-xps-foam-patterns.14/#post-61 Here are the resulting patterns. I applied a very thin coat of mud on the jig machined pattern. I just slathered it on and brushed with a small paint brush while it dripped off. This thin, it a couple coats. I poured them all together. Here they are sprued up. I think I could have just as easily gated into the side of the head and cast it at an angle like the rest of the parts but decided to use a horn gate on the head to see how well it worked running in blind under the head. When I was machining the first larger pattern before I made the jig, I gouged a few of the fins. So I thought it would be a good test part to see if the thin spots filled. So I cast it first. It filled well and was a good part. You can see where the pattern fin was thin and it seem to cast just as the pattern appeared. This one was not coated; just bare foam in coarse sand. Seeing how well the sample part poured I just decided to cast the remaining foamies together in the same session. Here they are in my lost foam rig before I slipped the pouring cup on them. …and here they are as cast. They all filled well. The larger cylinder and head were bare foam in sand and the smaller cylinder I cut on the router jig was coated with dry wall mud. Here they are with the sprue and gates removed. I really didn’t make much effort to improve the foamie’s finish on the smaller cylinder but I did take the time to coat it with several thin layers of drywall mud and must say, it makes for a nice part and think it may modestly help with mold stability. Success came quickly with finned cylinders. Wow, I’m very impressed with the lost foam process. Here's a thread of a similar part for a chainsaw cylinder head. http://forums.thehomefoundry.org/index.php?threads/chainsaw-cylinder-head.268/#post-4714 Best, Kelly
Thanks Pat, much appreciated. Me too! -Still learning the art of the possible and re-learning some things I thought weren't possible. Best, Kelly
