Post by iau461 on Aug 19, 2023 16:35:21 GMT -8
Hello all,
After unsuccessfully trying to find a US supplier of vacuum-formed ceramic fiber risers, I broke down and decided to try casting one. I was afraid to do it for various reasons, but it wasn't that hard. Hopefully it works.
WARNING: it hasn't seen heat yet, so I can't speak to either function or durability, but given the material I'm hopeful.
Pictures are at photos.app.goo.gl/VqjiHKNUafJUYqvXA
The most difficult thing was making the two forms. One for the two bottom pieces, one for the two top pieces. I spent maybe 2-3 hours designing the forms, and maybe 3-4 hours making them out of plywood I had laying around, with some cheap sheet aluminum (roof flashing) from the big box hardware store.
I cut the wood pieces with a portable table saw. The aluminum was cut with scissors. After assembling everything, I took it back apart and put several coats of gloss spray paint on all wood surfaces that would come in contact with the castable. Then I coated all surfaces (wood and metal) that would touch castable with a thin layer of axle grease, spread by fingers, to ensure the form would release easily after curing.
I bought 50 pounds of Loucast 3000 castable from Sheffield Pottery in Massachusetts. With shipping it came to $106. Turns out 27# was enough to make a riser for an 8" system, approximately 9.25" ID, 3/4" thick. So if I bust a piece somehow I can replace it.
The Loucast mixed easily in about 30 seconds, using a paddle mixer and strong drill. Working time was supposed to be on the order of 20-30 minutes. I cast my 4 pieces one at a time, and was able to pack a form in about 10 minutes, without the material stiffening. I loaded 2-3" of mix at a time into the form, and then packed it down using a 3/4" square stick. If I had it to do over again, I would use a heavier sheet metal, the aluminum had a tendency to bulge out of shape if I tamped too hard. After 24 hours of curing I took the forms apart, and the shapes released fairly easily with a little tapping.
If you look closely you can see that I wasn't able to get all the air out by tamping. Lots of small voids. Hopefully that won't be a problem. I plan to coat it all with zirconia, both to reflect heat and minimize fluxing, I hope that will fill in/cover the voids.
The castable manufacturer recommends firing gradually to 1000F over about 30 hours, and then up to operating temperature, to drive out the excess water. I don't have a kiln. I'm planning to put the pieces in the kitchen oven, gradually raise to 500F (max) over 8 hours, and hold there for another 16 hours. Hopefully that will be enough to drive most of the water out of these relatively small/thin pieces. First firings of the core will be kept small, maybe smoky but I'd rather nothing explodes. :-)
That's pretty much it. Hope this helps someone. Questions and comments welcome, and thanks to all who answered my earlier questions and encouraged me to try castable.
After unsuccessfully trying to find a US supplier of vacuum-formed ceramic fiber risers, I broke down and decided to try casting one. I was afraid to do it for various reasons, but it wasn't that hard. Hopefully it works.
WARNING: it hasn't seen heat yet, so I can't speak to either function or durability, but given the material I'm hopeful.
Pictures are at photos.app.goo.gl/VqjiHKNUafJUYqvXA
The most difficult thing was making the two forms. One for the two bottom pieces, one for the two top pieces. I spent maybe 2-3 hours designing the forms, and maybe 3-4 hours making them out of plywood I had laying around, with some cheap sheet aluminum (roof flashing) from the big box hardware store.
I cut the wood pieces with a portable table saw. The aluminum was cut with scissors. After assembling everything, I took it back apart and put several coats of gloss spray paint on all wood surfaces that would come in contact with the castable. Then I coated all surfaces (wood and metal) that would touch castable with a thin layer of axle grease, spread by fingers, to ensure the form would release easily after curing.
I bought 50 pounds of Loucast 3000 castable from Sheffield Pottery in Massachusetts. With shipping it came to $106. Turns out 27# was enough to make a riser for an 8" system, approximately 9.25" ID, 3/4" thick. So if I bust a piece somehow I can replace it.
The Loucast mixed easily in about 30 seconds, using a paddle mixer and strong drill. Working time was supposed to be on the order of 20-30 minutes. I cast my 4 pieces one at a time, and was able to pack a form in about 10 minutes, without the material stiffening. I loaded 2-3" of mix at a time into the form, and then packed it down using a 3/4" square stick. If I had it to do over again, I would use a heavier sheet metal, the aluminum had a tendency to bulge out of shape if I tamped too hard. After 24 hours of curing I took the forms apart, and the shapes released fairly easily with a little tapping.
If you look closely you can see that I wasn't able to get all the air out by tamping. Lots of small voids. Hopefully that won't be a problem. I plan to coat it all with zirconia, both to reflect heat and minimize fluxing, I hope that will fill in/cover the voids.
The castable manufacturer recommends firing gradually to 1000F over about 30 hours, and then up to operating temperature, to drive out the excess water. I don't have a kiln. I'm planning to put the pieces in the kitchen oven, gradually raise to 500F (max) over 8 hours, and hold there for another 16 hours. Hopefully that will be enough to drive most of the water out of these relatively small/thin pieces. First firings of the core will be kept small, maybe smoky but I'd rather nothing explodes. :-)
That's pretty much it. Hope this helps someone. Questions and comments welcome, and thanks to all who answered my earlier questions and encouraged me to try castable.
