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Here are several tips to help you flatten a cupped board. You can try stacking the boards tightly and then use plywood to weigh down the top board. Planing from the opposite direction can also help you achieve the desired result. As moisture changes the wood, it will eventually flatten out. To prevent this from happening, try using a straightedge or thickness planer. Afterward, you can use a straightedge to check the final product.
Planing from the opposite direction
If your board is cupped, you may need to plane it from the opposite direction. Planing a cupped board may not be necessary for every defect. However, it is necessary to determine the high points and work your way around them. Plane the board in two directions: with the grain and the straightedge. You should eventually end up with a flat board. To avoid tearing out the board, don’t spend too much time on trouble areas, and gently feather them out.
Using a planer is a good solution for boards that are too wide to fit through a jointer. You can use this tool to flatten the board’s surface by balancing the removal of material on both sides. When milling lumber, balance the amount removed from each side. You can also use a jointer to plane thicker stock. You can then use the thickness planer to flatten the edges.
Before you start milling the wood, identify the shape of the cupping. If your board is cupped or bowed, look underneath with the straightedge to see if the light comes through it. If it is flat, mark the high spots with chalk. Aim for a square surface at the first end, and a flat surface on the second. Once you’ve done this a few times, the process becomes faster and easier.
If the board is not flat when finished, clamp it with cauls to prevent it from twisting too much. Leave it there for a couple of days until it is ready for use. After that, you can use it to sharpen hand planes and use it as a bench for finishing your project. Then, you can start planing the other side of the board. It should be flat by now.
Using edge-joined cups
If you have a cupped board, one way to flatten it is by ripping out the center of the board. This will produce two edge-joined cups that look more like a shallow W. Because these are shaped like an edge, they require less wood to flatten compared to a traditional cup. You can then run this board through your planer to flatten it.
The first thing you should do is identify whether the board is cupped or bowed. You will need a straightedge to find the high spots, such as the dreaded “bowing out.” Similarly, you can use chalk to mark high spots. This way, you will know exactly where to clamp the board for flattening it. If the board has a cupped or bowed appearance, use a scrap piece of wood to fill the gap.
If you’re working with a wide board, ripping it will almost eliminate the curve. It will create a board with a much thinner thickness, but you’ll lose some width in the process. Depending on the width of the board, you may need more width than you originally planned. To avoid warping, use a finish that will stabilize the surface. Remember, you should leave your panel in a controlled environment, not the sun, so that it doesn’t dry out too quickly.
When you’re ready to flatten a cupped board, make sure to secure it properly to your bench. You can use bench dogs or tail vises to secure the board in place. Just be careful not to apply too much pressure, because it will cause the board to bow. Also, too much pressure can cause the board to break, which won’t help it flatten.
Using a thickness planer
If you’ve ever used a jointer to flatten a board, you probably have noticed that the concave side is thinner than the convex one. This happens when moisture in the wood causes it to expand and contract, leaving you with a cupped board. To flatten the board, you must restore the moisture balance in the board to ease the tension and flatten it. Thicker wood needs more water to flatten properly, while thicker wood needs less. To further ease the process, place some weight on top of the board.
Before you use a thickness planer, prepare the board and prepare it for the planing process. Start by attaching a strip of scrap wood to one end of the board. You can then use glue or double-sided tape to secure the strip. The strip will act as a shim between the board and the feed rollers. Once the top face of the board is flat, remove the shim and continue to plan the board.
The blade of the thickness planer is adjustable, and it shaves the surface in successive passes. It is not necessary for fine woodworking, but it’s helpful for making 2 faces parallel. A thickness planer can’t help you with wood that is twisted, however; you’ll end up with a board that has parallel faces. It’s a good idea to carefully measure the thickness of the wood before starting the process.
When using a thickness planer, be sure to set the feed rate to a slower speed for final passes. You’ll want to reduce the chip-out and snipe by removing 1/32 inch of material per pass. You may need to use shims for boards that are cupped. If you don’t have a thickness planer, you can still use a scrubbing plane or a jack plane. But do note that a jack plane won’t be as effective at flattening a cupped board.
Using a straightedge
If you’ve noticed that your wood isn’t flat, you might have a cupped or bowed board. To identify a cupped board, start by checking the surface with a straightedge. If it isn’t flat, try to see if there is light underneath. If the surface is high, mark it with chalk. This will help you avoid making any mistake while flattening the board.
First, secure the board on a bench or work surface. You can use a tail vise or bench dogs to secure the board. Be sure to apply just enough pressure to keep the board from moving, or you’ll risk bowing it and causing it to be less flat than you’d like. Use a marking gauge (a 2-in.-thick block with a 5/8-in. dowel set in the hole).
After that, wet the wood with a damp cloth or spray bottle. Do not leave any standing water on the wood. The amount of water needed will depend on the thickness of the wood and its warping condition. Thicker wood requires more water than thin, and vice versa. It’s best to use sparingly and prevent the wood from becoming damaged. This step is necessary to achieve flattening a cupped board.
To use a straightedge to flatten a curved board, start with a square. You should hold it with the blade of the square against the board edge and sight it toward a light source. You should see light at every six to eight inches. If the edge of the square is not parallel to the edge of the board, then it is not flat. If the board has high spots, remove them using a power hand planer.
Using a card scraper
Using a card scraper to flaten a cupped board involves adjusting the presentation angle of the tool and changing the trajectory of the board. This method is ideal for smaller boards, where a single thumb scrape can easily flatten the cupped side. The scraper should be angled downwards by 1/16 inch from the board’s bottom. The heel of the hand method is best for boards that have small troughs, but it will not be as effective if you try to use two hands to flatten the board.
A card scraper is a tool that you can buy or make yourself. You’ll need a power tool to cut the scraper. You can also use a scraper to remove tool marks from wood. For a small board, you can use an old table saw blade. Once you have the scraper made, you can use it to flatten the cupped board.
If you’re using a rectangular scraper, you should prepare all of the edges with the scraper. Curved scrapers, on the other hand, should be prepared by holding it up to the board. You’ll need to move it around a few times to find the right curve. A curved scraper has a curved burr, and a square file won’t work well. To avoid wasting time, use a half-round file instead.
Using a card scraper to flaten a cupped board is another useful tool for reshaping a board. You can purchase one from a woodworking catalog. There are various types of scrapers available in different thicknesses, but the most common is the #80. The basic method of edge preparation is the same as the method for using a rectangular hand scraper, with a slight variation in the method of flattening the board.
