Bevel angle

The flank angle determines how well you get into the root. If it's too small, you can't reach the flanks properly and risk lack of fusion. If it's too large, you melt unnecessary material, the part gets hotter and tends to shrink more. For normal steel work, a typical value is an angle that lets you get cleanly to the root. For thicker plates, better use a U-groove, saving filler metal and heat. The bevel must be clean and free of burrs. If the weld gets too wide, use more passes. If you can't get into the root, rework the joint.