I’m building a 10′ X 5′ eliptical table top out of hard wood flooring ( Brazilian teak ) boards of random lengths – with the tongues & grooves cut off. After gluing the boards up, parallel, in a rectangle, I plan to cut the elipse, a bit wide, with a jig saw. Then, using a template & a bearing bit, I plan to hand route the final shape. Then I’ll use a roundover bit for the edge.
Most of this is new to me. I’m concerned about tear out, since the boards may be running different directions & I’ll also be routing in end grain. I’d appreciate any ideas or suggestions.
Thanks,
Morty
Edited 10/31/2009 9:09 pm ET by morty
Replies
When sizing up the top, it's best if you don't have much to cut with the router. To avoid tear out, you have to cut with the grain. When you do circular work, this often requires you to make "climb" cuts. A climb cut is running the router with the rotation of the bit, instead of against the rotation.
Climb cutting can be dangerous, the router wants to pull out of your hands and you are helping it. When I need to do it, I work differently than when going against the rotation. Going against the rotation, you start at one point and go to the other in a full motion. When climb cutting, I take little bites and move back towards what has already been cut, basically starting at the end and nibbling your way to the start.
When you are going with the rotation, the bit grabs the uncut material. By nibbling, there isn't uncut material, "ahead" for the bit to grab, if this makes sense. On an elliptical top, imagine looking down and just routing the left half. On the side away from you, you would work going with the rotation of the bit until you reached the "tip" of the ellipse. To finish routing the side closest to you, you would start at the tip, plunge in a little and then pull the router towards the "tip". Repeat a 1/2" at a time. It's better to take small bites, incrementally increasing the bit depth after each time you go around. The router has to move in a smooth flow. Stopping or baubling for a split second will cause a burn.
Work like this in larger shops might be done on a shaper since the cutters can be flipped and the shaper run in the opposite direction, "reverse". You can't do that with a router. The old timers would have cut the shape with a bow saw, spot on, and smoothed up the cut with abrasives or a hand plane. The edging could be done with left and right planes or a scratch stock. It would be a good idea to identify the grain direction on the boards that will be the long sides. Then you can position them to your advantage.
Some tearout management therapy.
Clean and sharp are your friend, as are high precision and high quality cutters. Make the final cut very light. Also, Freud has a new bit technology called "Quadra-cut" that's designed to reduce tearout...if they have a bit with the profile you want, that technology is a consideration.
Take several light cuts. The end grain will cut differently than edge grain and tend to be more "grabby" I'd avoid starting on the ends. Climb cutting may work for you if you do some practice cuts first but if you're really a beginner I'd be hesitant of that procedure until you feel more confident.
Given that it is a table top I imagine that matching a pattern exactly is not exactly critical. In this case cutting with a jig saw to the outside of your pencil line and then smoothing with a power sander or plane would probably be the fastest.
Assuming you really want to use a pattern then you can avoid tearout without having to climb cut by using a double bearing flush cutting bit: http://www.leevalley.com/wood/page.aspx?c=1&p=51851&cat=1,46168,46171&ap=1.
With that bit you join the pattern and table top together (double sided tape or screwed to the underside of the top). Cut the portions of the top that are with the grain. Flip the stock and pattern upside down, readjust the bit height and cut the remaining material. The attached diagram shows how this would work assuming straight grain lumber.
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