Magic Numbers

When I first read about working with green wood, I recall being overwhelmed by all the talk of equilibrium moisture content,  tangential to radial shrinkage ratios and wet dry hygrometers. Clearly, you need an advanced degree to sidestep the lumberyard and work with green wood!

 

Of course, in time, I came to understand what all of those things mean, but most importantly, I came to recognize that there are a few common sense pieces of information that can replace them. 

The basic notion has two parts, 

Part 1. Wood has moisture in it and shrinks as the moisture exits and swells when it comes in.

Part 2. Wood shrinks more along the growth rings than it does across them. This is why  becomes oval when turned green.

I used to split all my turning stock green and immediately turn my chair parts, leaving the tenon ends oversized. Then I'd dry the tenon ends and re-turn the final tenons once the wood stopped shrinking. Now I prefer to rough out all my stock green, then air dry it in my shop for anywhere from a few weeks to, well, forever.

This gives me less warping and distortion after turning, a slightly better surface quality and less waiting time for the tenons to be superdried once they are rough sized. After the rough sized tenons are superdried, I chuck the turnings back in the lathe and take them down to the final size, removing just a few thousandths of an inch to get there.

So what are these magic numbers!? These numbers are the amount that I oversize a tenon based on the moisture in the wood. I know to expect a certain amount of shrinkage once the tenon goes in the kiln, and if I don't leave enough extra material, I won't have enough wood left to turn to the final size.

So let's say that I'm using a 5/8" mortise, which translates to .625". If the stock is green, I assume that the tenon will shrink along the growth rings (tangetial plane) about 60 thousandths of an inch, so I oversize the tenons by turning them to .695" or .700"(notice that I've added a little extra). The beauty in doing this green, is that you can estimate the shrinkage accurately. Because it hasn't even begun to shrink, it will be the same every time.

When using air dried stock, I oversize the tenons from 25 to 35 thousandth. So depending on how long the stock has been sitting around drying, I turn the tenons to .660" or .650". In the image above, I am measuring the tenon along the growth rings (tangentially), which I drew in pencil. This is the plane that shrinks the most. This tenon was turned at .655" and you can see that it has shrunk to .635". To me, this is close to ideal.

Here is the radial plane, and as you can see, it shrank much less, only 5 thousandths of an inch or so, which is to be expected. I am showing you this to knock home the idea that it matters a great deal which way you measure your tenons. Once you've done it a couple times, you'll get and get used to measuring them in the two orientations, then you can accurately tell when they've stopped shrinking and are ready to be final sized and assembled.

At first, it's reasonable to oversize the rough tenons too much, but with time, you'll get the rhythm and get closer to the final size. By the way, I have a special drill bit that I ground for those "special" tenons that shrink more than expected. Good luck!

Moment by Moment

I've had a lot of quiet time to myself in the shop lately, which has been a real luxury. Sometimes it can take a while to get to that calm place where fun and creative things can flow. I know that this is even harder for folks who only have a few rushed hours on the weekend to fit in their "relaxation shop time". Sue has seen me in the mad dash to enjoy my free time, we call it gulping.

It's usually a sort of of tragic comedy that ends up with stupid mistakes, poor decision making and a general sense of defeat. It's like I left the window open and all the junk that I'm trying to ignore comes rushing in to wreak havoc.

I've found that these times are best suited to small stuff that can be picked up and put down easily. I think that carving spoons fits the bill perfectly. I know that I've said it before, but spoon carving is one of the great teaching activities as well as being portable, cheap and rewarding, perfect when you don't have the time or inspiration to tackle that highboy you've been meaning to build.



In the past weeks, with no students around and my caliper safely in the hands of the retailers, I've set out to remember what it is that I'm supposed to do after my coffee. So while I'm having my coffee, I've been carving spoons. And sure enough, not only has it helped ease me back into full time shop life, but the lessons learned have found their way into my chairs.



These spoons came from the same hunk of applewood that I harvested a few weeks back. I can only imagine why they have such a marked color difference. The goals and tools in spoon carving are very similar to chairmaking. A fine spoon can be useful, delicate looking, strong and beautiful, all at once.



Generally, I've left the knife cut finish just about everywhere on the spoon, but with this batch, I tried to accentuate the gentle rounding of the handle by smoothing the surface and letting the grain tell the story.
But as you can see, the surfaces of the bowl portion are knife faceted. As I worked on them and lived with them, I've come to really like the transition and juxtaposition.



Beside working on a new rod back armchair, I've been designing and building a fan back that I'll be teaching next year at Kelly Mehlers in Berea. I've always wanted to make a fan back with a crest like this, and I figured this would be the opportunity.



As I was shaping it and thinking of the surface finish, the lessons from the spoons came to mind and I decided to have the shape be smooth and fluid on the front of the "ears" and faceted on the back. I'm pleased with the results.



Like most folks, I try to make the most of my time in the shop, but sometimes there's more to it than that. The shop isn't just a place to get away, but a space to work out all influences of the world that we bring with us, and sometimes all we can manage is a foot in the door, or maybe just a spoon, and that's more than enough.

Turning Practice

I recently wrote guest blog entry and made a video for Highland Woodworkings blog and I wanted to make sure that I posted the link. You can click here to view the post and video.
I've finally figure out my new editing software and should have more videos coming soon!


And for all our old friends, here is the Chairnotes covergirl last week on our brief vacation to the Fingerlakes in upstate New York. We were visiting a local goat farm when we came across this pooch who happened to be the spitting image of our beloved Daisy dog. Someone once described heaven as seeing all the dogs you've ever loved running up to greet you. I think the look on her face says it all.