Keeping in mind that as a cuemaker i am a neophyte. I do have over 40 yrs pro woodwhacking experience.
I was thinking that in the beginning it would have a greater impact and to let it relax from the stresses of material removal in the beginning instead of the end processes. it has been many years since I turned any wood. How much time would you allow between removing most to taking the last few cuts?
You might be sorry you asked my opinion.
Stress in wooden parts comes primarily from internal factors relating to how the wood grew, and how it was dried. Internal stresses set up when the tree was growing include reaction wood in hardwoods that interest a cuemaker, and tension wood, primarily but not exclusively in softwoods. This (reaction/tension) wood is built in the tree to counteract gravity - if the tree leans much it will build it on one side; and branches are full of it. This type of wood can be recognized partly by the grain, and it is the stuff that a cuemaker eventually uses for tomato stakes or kindling because it just won't stay straight, moves every time it is machined.
A problem in the supply chain is how was the wood dried? If somewhere in the origins the wood spent time in a kiln that was forced to expedite the drying schedule, it gets case hardened. The wood dries too fast on the outside and shrinks, adding compression. Wood takes "compression set" when constrained against MC and stresses are set up. This is the kind of board that when faced on one side, it curves the other direction, then joint the bow off, and it curves back. If you resaw it, both pieces spring apart bowed in length and width with a cup in the middle. It may settle down over time, or if straight grain & dried for (I tend to think 7 years) in a dry space with temperature and some moderate MC variation over the seasons.
A lot of "cut a little and hang a lot" is not really doing too much for the wood, but it allows discovery of this kind of bad stuff before a customer does. It also allows a gradual approach to finding moisture equilibrium even in "good" wood.
I think any wood benefits from "years" of drying in the blank form, especially if laid up flat in a place where the temperature varies widely, and the MC is within a moderate range.
Let's move on to "good" wood from huge old straight slow grown trees, where the blank has rested for "a long time". Wood is a great material because it has been constantly stressed in the tree & evolved to accommodate that, to resist stress. Since wood is not uniform, it will move a bit as it is machined, but if properly dried, not very much.
Does material removal cause stress in wood?
Wood is a little like metal in the sense that processes that heat it locally, can put stress back in. Dull tools that burn or burnish it. Heat wood locally to something above maybe 300F and it will put stress in, again by causing localized heating, expansion, and compression set. If you see burn marks, it was heated to closer to 450-500F at least on the skin. It is the differential stress that will cause issues. Gradual removal of the stressed surface with sharp tools and no burnishing will generally relieve this, like a cuemaker machining over time. (These burn marks on the skin won't much affect a 2 x 2 turning square, they will affect a near size cone)
Small amounts of mechanical "stress" such as vibration, i tend to think relieves internal stress so long as things are not bending (magnitude) to where the fibers start to slip or separate.
That long winded answer to the time question boils down to "know your wood, understand & recognize where stress comes from (growth factors, drying factors storage factors, and mc)." If sharp cutters and reasonable machining methods are used, machining's primary function is to release the stress. A highly stressed piece of poorly grown lumber might take years, or never be stable with any small change in MC. A better piece might well be stable if processed complete in a few weeks.
Most of the timeline after initial machining allows us to find & discard the worst offenders, equalize the "pretty good" blanks over a range of MC's and discover the ones that seem not to move at all for our better shafts. Like most, i have noticed that if i process a shaft too fast, it is going to curve a little in use, so patience is a good plan at the near finished stage.
The straighter the grain, generally the less movement with changes in MC. Within normal temperatures, temperature does not affect wood much except as it affects MC. I think a shaft needs to "experience" a small range of humidity/MC variation while being built, to settle down. But the trick is deciding where in the range to machine it again. I really want to know (& control) my shop's humidity; but can only guess about where it is ideal to do machining based on where a cue might end up. A cue going to Louisiana is going to equal out at a different MC than one that goes to Nevada or NM. Locally/upstate NY i want the wood to be about 8 - 9%MC. I don't poke the parts being made with a tester, but do check other wood around the shop. I might modify that number with experience, too.
Roughing down to dowels or to oversize cones fast with sharp tools is not going to affect things by causing any stress if the blanks are old enough and dry enough. We're trying to release what is already there.
smt
