Jan Bianchi
11-16-2010, 1:59 PM
I have been trying to use The Shrinkulator http://www.woodbin.com/calcs/shrinkulator.htm to calculate the length of each slotted screw hole I need to attach my madrone table top to its base and to keep it flat. (Thanks Kent Bathurst)
My problem with using the calculator is how do I know what either the initial or final moisture content will be? I don't know what the initial moisture content after air drying was, but I know it is 10% now according to my moisture content meter. How would I know that the final will be?
If I use the relative humidity values instead of moisture content, then do I use lowest possible humidity and highest possible humidity in my Seattle home (I don't have a humidifier in my house). My humidity monitor reads 63% right now in a house that is currently heated to 63.4--sunny outside today--surprise. But my monitor reads a low of 54 and a high of 89 degree humidity and 50 and 73 temperature. (this is in a heated basement which isn't heated in the summer,)
I tried reading the Hoadley book on wood movement, but it doesn't really explain, at least not to me, what values you use to calculate this.
In case a description of the table would be helpful: the table top is 42 inches wide and 72 inches long with the grain running along the length. It is an extension table so the top is cut into two leaves. The middle end of each leaf will be attached to three runners, one on each side and one in the middle, that slide open lengthwise inside a structure between the aprons. (The structure will also hold an extension leaf that folds underneath the table top in a butterfly fashion). The leaf will be attached to each runner with at least three screws. A cleat three inches from the other end of each leaf is a concession to madrone's tendancy to move and intended to keep the end of the table flat. It is not connected to the base. The cleat will have a minimum of five screws in it. Thus I understand the slots will be a different size on the cleat than on the runners.
My problem with using the calculator is how do I know what either the initial or final moisture content will be? I don't know what the initial moisture content after air drying was, but I know it is 10% now according to my moisture content meter. How would I know that the final will be?
If I use the relative humidity values instead of moisture content, then do I use lowest possible humidity and highest possible humidity in my Seattle home (I don't have a humidifier in my house). My humidity monitor reads 63% right now in a house that is currently heated to 63.4--sunny outside today--surprise. But my monitor reads a low of 54 and a high of 89 degree humidity and 50 and 73 temperature. (this is in a heated basement which isn't heated in the summer,)
I tried reading the Hoadley book on wood movement, but it doesn't really explain, at least not to me, what values you use to calculate this.
In case a description of the table would be helpful: the table top is 42 inches wide and 72 inches long with the grain running along the length. It is an extension table so the top is cut into two leaves. The middle end of each leaf will be attached to three runners, one on each side and one in the middle, that slide open lengthwise inside a structure between the aprons. (The structure will also hold an extension leaf that folds underneath the table top in a butterfly fashion). The leaf will be attached to each runner with at least three screws. A cleat three inches from the other end of each leaf is a concession to madrone's tendancy to move and intended to keep the end of the table flat. It is not connected to the base. The cleat will have a minimum of five screws in it. Thus I understand the slots will be a different size on the cleat than on the runners.