Thanks, Jim; for the founding process. I've been on a tour of a foundry (not a piano plate) and am somewhat familiar with the process. My impression is that after a wooden model of the item to be cast is made, they cut it in half and mount each half onto a follow board. * It would be interesting to know how they slice a plate pattern lengthwise *. I would like to interject a related piece of info passed on by a plate foundryman(?). Knowing that the top side of the plate is in one half (cope?) and the bottom in the other (drag?), if they are not mated perfectly together for pouring, the v-bar to duplex ridge distance will be off; since the duplex ridge is formed in the top half and the v-bar in the bottom half of the mold. Which would account for those troublesome string segments . Jon Page Cape Cod. Mass jpage@capecod.net ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ At 07:41 AM 11/28/96 -0700, you wrote: >Joel and Priscilla: > >I tho't I'd jump in and answer this one. > >When a plate has been designed, a wooden pattern (often solid mahogony) is >prepared using a shrink rule (1/8 inch per foot larger than normal). >This pattern is mounted to a follow board (heavy platform). A rectangular >flask (like a heavy formed steel band) is placed on top of the board. This >flask is about 12 inches high all the way around. There is a steel >reinforcing grid across the top of the flask which holds the sides rigidly. >A powdery releasing compound is lightly dusted over the entire follow >board and the pattern. > >Sand is poured down thru the grid to completely cover the pattern. Workers >standing on top of the grid begin ramming the sand tightly around the pattern >and solid upon the follow board. Jack hammers and ramming rods are used. > >This sand is a special mixture of sand, bentonite, molasses and perhaps other >ingredients which make the sand stick together when compacted. > >There a flask which holds the molded sand for the shape of the top side of >the plate pattern and then another flask which holds the molded sand for the >shape of the bottom side of the plate pattern (like the horn, bosses, etc.). > >These two flasks are called the cope and the drag. When they are lifted >off of the pattern, the draft angle is important to avoid any sand being >accidently dislodged and falling down from the flask which holds >the reverse shape of the pattern. The cope side has little sprue holes >carved into the sand to allow pouring in the white hot metal mix when >the cope and drag are mated together. When they are mated together, there >is a piano plate shaped space between the cope and the drag. The >sprue hole are placed so that all parts of the cavity between the cope >and drag are completely filled and running over. After the metal cools >sufficiently, the flasks are removed, or the sand is shaken out. The sand >usually goes onto conveyor belts which takes it up to be renewed and >processed for use in some future casting. The plate is then shot peened, >sent for curing, then ground down at rough edges, and then drilled. If any >sand had fallen into the cavity before pouring, it would have ruined the >plate. Hence, the need for good draft angle. the foundry would >really like 4 to 7 degrees draft angle to help avoid cave-ins. > >Jim Coleman, Sr. > > >On Wed, 27 Nov 1996, Joel Rappaport wrote: > >> Danny, >> You are the perfect one to ask a question that occurred to me while >> reading the various responses in this thread. How many times is a sand >> mold used to cast a plate? Is the draft angle necessary for a clean >> release so as not to disturb the sand of the molding so it can be used >> again, or for a clean casting? >> >> ----Joel >> >> Danny Dover, RPT >> Dartmouth College, Hanover, NH wrote: >> >> > Patternmaking has its own set of rules, just as we have, to design >> > pieces that will release cleanly from the sand mold. One of those rules is, >> > the deeper the impression in the sand (that is, the higher the vertical wall of >> > the piece coming out of the sand), the more draft angle required to get a clean >> > release. So if the height of the flange changes, you can expect the >> > patternmaker to have changed the angle as well, to make sure they pour a clean >> > plate every time. >> > > >
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