Wood?s Lack of Stability Raising Hell? Help!
Short Version
I?ve turned a lidded box that HAD a very tight lid to base fit when it first came off the lathe - finished (wax). An hour later, the tight fit had become a loose fit. Piece is from a 10? diameter heartwood cherry blank that is at least 7 years old that I know of - probably more like 8 or 9 years old. The piece was turned within a day of bandsawing three 3
1/2? square blanks from the original blank, the latter containing no pith. The walls of the lidded vessel lid are a little over 1/16th inch at the lip and a tad over for the sides of the lid, maybe 1/8th at the top of the lid. The bottom was maybe twice those thicknesses.. The shape is a squat cylinder with almost hemispeherical top and bottom.Question: Why did the fit of the lid go from very snug to loose in a few hours?
Long Version
I think it was Dan Bollinger who mentioned the Super Egg in a thread on creativity. It?s a 3-D shape that?s very tipsy but will always return to upright. Take and two eggs, cut each in half and join the two bottom halves and you have an approximation of a Super Egg. Since I was playing with the idea of tipsy turned lidded boxes I had a go at making a turned Super Egg lidded box.
A friend had given me two cherry roughly sawn to round blanks, each about 10? in diameter and about a foot tall. He?d had them for four or five years and they?ve sat under my assembly bench for another three or four years. Both are all heart wood with the grain running vertically. From looking at the end grain, it appears as though the pith was three or four inches away from the nearest edge of each blank.
Though the ends had been sealed, there was some cracking in both blanks, With some careful bandsawing I was able to get three 3 1/2? square by10? long blanks out of one, though two of the three did require some CN glue to stabilize some small checks.
I used the best blank to turn my version of a Super Egg box. I roughed the blank to round and cut in a lip for the lid to fit onto, then shaped the ends to their close to final curves, leaving a spigot on each end for chucking later.
Chucked up the lid and hollowed it, being carefull to maintain a very tight fit with the lip on the base. This would make finishing the top of the lid easire later by using the base as a jam chuck. If necessary later, I could lightly sand either the lip or the inside of the lid to fine tune the fit.
Once both parts had been hollowed and the insides finished, I finished off the top of the lid. It took a bit of care end force to get the lid off the base, the fit being pretty tight. I set the finished lid aside while I hollowed and finished the bottom part of the box. I then set both parts aside while I turned a finial for the piece. Only when I put all three parts together did I realize that the lid fit was now quite loose. If I held the box by the finial, the bottom would fall off.
What happened? The wood was pretty dry, the walls fairly thin, the grain running basically parallel to the sides of the box and the humidity in the shop hadn?t changed much over the last week. I could understand this happening if I?d started with green wood, or mixed sapwood and heartwood, or had the grain been oriented ?acrossed? the piece. This thing shouldn?t change shape as much as it has, as quickly as it did - but it did. If this is inherent to woods like cherry, as opposed to denser woods like ebony or rosewood, I?ll quit trying for tight fitting lids.
Help!
charlie b