Friday, March 16, 2007

Talking Travishers


Travishers are one of the tools that make me want to make chairs. They are as fun to use as they are effective. There are some simple misunderstandings about travishers that I've come across and the problem isn't just the users, it's the manufacturers.
I make my own travishers. My first one was with a blade from the bargain bin at Garrett Wade and later ones with blades that I make myself (much easier than it sounds). I have three observations that are common to most manufactured travishers. The first is that the handles are wrong, unless you are a barrell or bowl maker. I like the handles to reverse the bend of the bottom. This is a small gripe, but the control gained by having the handles in a comfortable position makes a difference.
My second observation is with the extreme sweep that I see on most travishers. The seat of a windsor chair looks incredibly shapely, but in reality, the curves are relatively flat. The steepest curve on my chairs is at the back of the seat and can be carved out to a final shape by running my travisher at the angle shown in the photo. I know to stop when the travishers profile is imparted to the curve. Most travishers have such a tight radius that it is like trying to achieve a finished surface with a scrub plane. It is important to getting a scraper ready surface to be able to take thin, wide shavings.
My final observation is about the shape of the sole on a travisher. The sole, the wood in front of the blade, should have a gentle radius, curving away from the blade. Unlike modern spokeshaves with flat soles and depth adjusters, the depth of cut on a travisher is dictated by the soles point of contact with the workpiece (old wooden spokeshaves often work this way as well). I used to wonder how I was supposed to adjust the blade on these old tanged tools, I'm not! By tilting the tool in use, I am able to take a deep cut or a fine shaving, it's fantastic.
The one thing about cutting this way is that it is not intuitive. Our natural tendency is to pull out of a cut, or attempt to take a lighter cut by leaning the tool back. The problem with this is that it brings the contact point closer to the blade and actually deepens the cut! Look at the result and you often see tearout at the end of the cut, where the cut gets deep and the shaving is ripped from the seat. It also results in a shaving that is thickest at the end and doesn't like to clear the throat.
I teach folks to use the travisher by stressing "Not cutting". Try running the travisher on the sole without contacting the blade. Go ahead and scrub away, it may seem silly, but this is how it works. As you are scrubbing away, the tool is bound to catch a small shaving. When it does, lean forward onto the sole and you'll notice two things. The blade will dissengage and the shaving will get thinner at the end and spill out the throat! Keep doing this until your instinct changes to tilting the tool forward at the end of each stroke. It is tough to retrain the instinct to pull out of the cut by tilting back, so practice. One thing that might help is to lighten the pressure that you are applying with your thumbs at the back of the tool. You'll notice that the tool will automatically want to roll forward as you do, coming cleanly out of the cut. Just remember, coming out of the cut requires rolling away from the blade on the sole! Control in cutting is as much about the wood that you leave behind as the shaving you take.

1 comment:

Unknown said...

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