wood movement calculator and some food for thought

[CarvedTones]

There is a nice calculator here:
http://www.woodworkerssource.com/movement.php

One of the reasons I thought to post this today was because of a couple of postings I did recently about getting pretty accurate on the cheap. Here are a few salient points mentioned in the notes below the calculator:

Shrinkage green to ovendry: laboratory tests have been conducted for most commercial woods to measure how much the wood shrinks from the green to the ovendry condition. In this context, "green" refers to wood at or above the fiber saturation point. Shrinkage is greatest in the tangential direction (along the growth rings), ranging from about 6% to 12% with an average of 8%. Shrinkage in the radial direction (perpendicular to the growth rings) ranges from about 3% to 5% with an average of 4%. Shrinkage in the longitudinal direction is minimal, only about 0.1 %, and can generally be ignored for most furniture applications.
Keep in mind that the green to ovendry shrinkage values are maximum shrinkage values; kiln-dried wood that is stored indoors will only shrink perhaps one-fourth to one-half of the maximum amount.

Lets take the absolute low limits from the above - longitudinal shrinkage for KD lumber stored inside and say it is 1/4 of 0.1%. What does that mean in plain English? At a length of greater than 4", it is virtually impossible to have accuracy of a thousandth of an inch except for right at the instant you cut it. At over 5', claiming accuracy of a hundredth is iffy at best.

This is not an excuse for sloppy work. But it does make it difficult to justify the expense of some of the high tech measuring devices.

 

[mlzettl]

Andy,

I couldn't agree more. Measuring things to the .001 inch, or even to .01 inch doesn't make much sense to me, and it never has. It's not like I'm building parts for a jet engine. Our forefathers, who built some of the finest furniture ever made in the 18th and 19th centuries, seemed to do quite well with what would be considered crude measuring tools today.

Thanks for posting this.

Matt

 

[mkepke]

AFAIK, there is no furniture that requires a high degree of accuracy - although the advent of mass production systems such as the 34mm system has made accuracy more important than it was. However, there is a lot of furniture that requires a fairly high degree of precision (e.g. inlays).

Accuracy is one mean to achieving precision - but there are at least a couple other (cheap !) ways to achieve precision.

-Mark

 

[Gofor]

As to accuracy, there are places where it matters. Mostly it has to do with mating surfaces at joints. And then, it usually has more to do with the mating surfaces being parallel. These are also the areas that are usually hand refined with a chisel, plane, kerfing in with a fine saw,etc, more so than being exact right off the power equipment. 1/100th of an inch usually doesn't matter in the overall dimensions, but it sure is visible in a dovetail, or on a surface of edge-glued boards.

This is not in disagreement with anything stated above: in fact it is in agreement. When it gets to the point of working to thousandths, it is usually a custom fitting, and not something you use a measuring tool for.

JMTCW

Go

 

[Dragon]

Only work I've done where the measuring was in the 1000's range was gunsmithing and reloading. You'd best measure twice in those fields or you're almost guaranteed to get more bang for your buck.

Working in wood, I can see where some things need to be very precise as has been mentioned already. Most of you guys and girls do flat work with dimensional lumber and lathe turned projects. I do mostly odd sized and fairly large work with my stumps and logs. I am about ready to try my hand at some spinny stuff pretty soon if all goes well and we'll see if I'm any good at it. Wood movement is always a consideration, especially if you're working with stuff you harvested, dimensioned, and dried yourself. Thanks for posting that.

 

[Gofor]

Dragon:

Enjoy your posts and am inspired by your work to try some basic stuff of the like. That said, my first thought when I saw you had posted to this thread was the old GI maxim concerning over-attention to detail: "Measure with a micrometer and cut with a chainsaw", which I think kinda captures the nature of this discussion. :gar-Bi:gar-Bi

Go

 

[CarvedTones]

Dragon:

Enjoy your posts and am inspired by your work to try some basic stuff of the like. That said, my first thought when I saw you had posted to this thread was the old GI maxim concerning over-attention to detail: "Measure with a micrometer and cut with a chainsaw", which I think kinda captures the nature of this discussion. :gar-Bi:gar-Bi

Go

Especially when you add the carpenter's credo as steps 3 and 4 - "Beat it to fit, paint it to match"...

 

[Stick&String]

My dad made a four post bed and matching dressers from cherry for my wife and I when we got married. The dressers had dovetails on the fronts and the drawers. The dovetails on the fronts have “popped” about a 32nd to a 16th of an inch. I thought it was because we overloaded the drawers and stressed the joints but my dad said it was just the wood moving and shrinking with the dryness of our house (forced hot air).
I’ll post a pic when I get home.

I like the quote about measuring with a micrometer and cutting with a chainsaw :gar-La;

 

[RayH]

Dragon:

Enjoy your posts and am inspired by your work to try some basic stuff of the like. That said, my first thought when I saw you had posted to this thread was the old GI maxim concerning over-attention to detail: "Measure with a micrometer and cut with a chainsaw", which I think kinda captures the nature of this discussion. :gar-Bi:gar-Bi

Go

Don't forget the step where you, "mark it with a grease pencil" ccasion1

 

[Stick&String]

you can see where it shrunk on the short grain and popped out

you can PM me if you have a sugestion. I dont want to hijack this thread

 

[CarvedTones]

I don't think you are hijacking, but this thread had just about run its course. I suggest you start a new one in general woodworking so you get additional people reading it, especially more flat workers. A lot of us reading this thread are log wrasslers...