As Min mentioned, both clay bodies are cone 5, so it will not be as bad as mixing earthenware and stoneware. it will be more like adjusting shrinkage by adding grog. The changes in shrinkage comes from the added grog content. I hope.
Yes, I use a shrinkage ruler. I measure the % shrinkage from wet (fresh out of the extruder) to bisqued as well as from bisqued to vitrified. Knowing the amount shrinkage at each step makes it easier to predict hole placement.
I want to clay with a little tooth in it for strength, but more importantly I want to get as close to 10% shrinkage as possible. I make Native American flutes. The diameter and length determine the fundamental pitch, key and hole placement. Just a mm difference can drastically alter the sound. I tune the flutes after the bisque firing and tune then flat by the amount shrinkage will occur in the final firing. Tuning at this point is much harder
My issue is that since I just got a new extruder, I need to make new tube dies. My old dies don't work in the new extruder. So, since I have to make new dies, why not try to simplify my calculations. I want the final tube diameters to be 1" and 3/4" after firing. Everything would be easier. For example, if the shrinkage were 10%, the linear length would be .90 of original and the area would be .81 smaller (almost 0.8). I can calculate these in my head. It makes it much easy for hole placement and tuning. But first, I have to make new tube dies. Is everything as clear as mud?
I have about 100 lbs to play with so the "test, test, test"-ing will start tomorrow.
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