Remove the cracked frame from the bed and place it on a plain surface. Bend the frame in order to open the cracked area. Now squeeze the glue into the cracked part. If you find multiple cracks, make sure your put the glue in each part.
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Take wood clamps and place them around the cracks. You must place one clamp at the middle of the frame and other clamps around six inches along the cracks. After you place the clamps to tighten the cracked areas, some amount of glue will come out of them. Use a damp rag to clean up the glue. Wait one hour before you remove the clamps from the side rail.
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Sometimes, you will not be able to see complete damage caused by the crack. In such case, yellow wood glue is used, which bonds the wood so well that the joint becomes stronger than ever. To reinforce the patch that you applied, take 1/4-inch plywood, which should be 8 inches longer that the crack and ½ inch less in width compared to the width of the side rail.
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Now clamp the plywood over the cracked area. Make sure you evenly distribute the surface of the clamp on both sides of the crack.
Using a drilling machine, make four rows of countersunk pilot holes. Make sure you make three holes in each row and they should be equally distanced from each other. The holes must also run from top to the bottom of the patch should be equally distributed across the width of the patch.
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Now join the plywood with the wooden frame, by screwing them using a Philips screwdriver. Make sure you do not use drill machine to screw, as the drill can over drive the screws into the wood, which can cause huge damage to the frame.
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If you still find any portion of the crack visible, you can use wax crayon to fill it. Then you can colour the repaired area, according to the overall colour of the wooden frame.