MDF can be used as the framing and for the skins of flush doors constructed with paper honeycomb or other lightweight cores for interior use.
The frame has three main functions,
1. To hold the skins apart
2. To provide bending and torsional stiffness
3. To provide secure fixing points for handles, hinges and locks.
The homogeneous nature of MDF and the absence of knots or other grain defects eliminates the need for selection of raw material and allows almost 100% conversion from boards. Kiln drying is not required as MDF is normally supplied in the moisture content range 8 ± 3%.
In the preferred method of construction, strips of MDF are used "on edge" so that the door skins are laminated to the board edges whilst the face of the board becomes the edge of the door. This orientation of the MDF using a "rip and twist" method ensures high stiffness in the plane of the door and good screwholding for the hinges fitted to the door edges. Boards in the thickness range 19 to 25 mm are commonly used for flush door framing.
Thin MDF in the thickness range 1.8 to 6 mm can be used for the door skins. Where wood veneer or printed paper foil finishes are required, the surfacing material is bonded to the MDF skins before laminating the door panels. The absence of grain features in MDF
eliminates the surface checking problems which can occur when decorative wood veneers are bonded to plywood faced doors for use in heated buildings. Alternatively, the laminated doors can be painted.
Flush doors requiring a high degree of fire resistance would need to be manufactured with a solid core, particleboard for instance, instead of a paper honeycomb core. Alternatively, they could be manufactured entirely from solid panels cut from flame retardant MDF.
More decorative doors for internal use can be manufactured from solid MDF sheets with the faces router cut to create a three dimensional frame and centre panel effect. Alternatively, a raised panel effect can be created by fixing MDF mouldings to a standard MDF skin flush door.
Glass panel doors can be manufactured from MDF using tongued or dowelled rails following the constructional procedures used for solid wood doors. A more cost effective construction however, makes use of a single MDF sheet with the apertures for the glass panel cut directly in the sheet, thereby eliminating the need for joints.
The smooth surfaces of MDF and its good machining characteristics will ensure a high quality paint finish.