IPAust 18 MAy 20, AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT ABOVE-TABLE ROUTER LIFT The following statement is a full description of this invention including the best method of performing it known to me: ABOVE-TABLE ROUTER LIFT The field of this invention relates to commercial plunge routers produced for the 5 woodworking and carpentry industries and more particularly to a router lift mechanism that applies a centre weighted movement to the plunge router to facilitate incremental height adjustment of the router bit when the router is mounted upside down underneath a router table. 10 Plunge routers feature two columns fitted with springs to provide the up and down plunge function that adjusts the distance between the router bit and the work piece. In addition plunge routers are often fitted with screw-wind adjustment mechanisms operated by turning a knob clockwise or anti-clockwise to facilitate fine router bit height adjustment. When the router is fitted underneath a router 15 bench the manner in which height adjustment is achieved is difficult and cumbersome and access to the control mechanisms is inhibited by their position. The screw-wind mechanisms are usually placed on or near either of the two plunge columns, and when moved apply uneven pressure favouring one side over the other and causing the columns to jam or the router bit to lock off-centre. 20 Problems of access to adjustment controls, jamming of the plunge action and cumbersome operating actions when the plunge router is mounted underneath a router table need to be addressed, particularly as the tool in the inverted position broadens the range of its application. Several commercial adjustment mechanisms are available but they are cumbersome, expensive and do not 25 attend to all difficulties presented above. The above-table router lift mechanism in accordance with this invention comprises a lift arm, a steel threaded drive shaft, a router lift base plate attached to the plunge router table and an adjustment handle, the said mechanism 30 designed to adjust the router bit height by applying a centre weighted movement to the head of the plunge router motor housing. This invention has been specifically devised to provide a simple, inexpensive, compact and improved router bit adjustment mechanism for plunge routers mounted upside-down underneath a router table or workbench and can be retrofitted to most plunge routers available in the market. The above-table router lift is preferably made from steel components however other materials such as aluminium can also be 5 used but may increase manufacturing costs. The invention may be better understood with reference to the illustration of embodiments shown in the line drawings of a plunge router incorporating the above-table router lift. The features of the above-table router lift in accordance 10 with this invention are herein described as if the plunge router is fitted upside down underneath a router table or workbench. Figure 1 shows the above-table router lift fitted to a plunge router in side view. Figure 2 shows the above-table router lift fitted to a plunge router in rear view. In both Figures 1 and 2 the embodiments of the invention include the following components: a drive shaft 1; 15 drive shaft retention blocks 2; the drive shaft housing 3; the lift arm 4; steel lift arm blocks 5; a 1/4" adjustment handle drive socket 6; adjustment handle 7; lift arm receptor bar 8; plunge router motor housing 9; plunge router base 10; plunge router table 11; above-table router lift base plate 12; split pin and nylon bearing 13. 20 The operation of the present invention will now be described with reference to the preferred embodiment. The accompanying diagrams illustrate but do not limit the use and operation of this invention. Figure 1 shows a plunge router and an above-table router lift mechanism in side view. Figure 2 shows a plunge router 25 and an above-table router lift mechanism in front view. In Figures 1 and 2 a length of steel tubing has been cut to form a section of steel channel referred to as the drive shaft housing 3. This drive shaft housing 3 is welded upright front and centre to a steel plate facing the front of the plunge router referred to as the above-table router lift base plate 12. The above-table router lift base plate 12 30 features four location holes for fixing to the router bench with recessed head screws and lock nuts and one hole positioned in the centre of the drive shaft housing 3 to provide access to the drive shaft 1 from above the plunge router bench using the adjustment handle 7. The drive shaft I fabricated from a length of galvanised steel threaded rod has a section of thread removed top and bottom to accommodate two cube shaped steel blocks cut from solid steel bar, the drive 5 shaft retention blocks 2 and drilled vertically to the diameter of the blanked section. To provide up and down movement for the router plunge mechanism the drive shaft I features two cube shaped steel blocks fabricated from solid steel bar and drilled and internally threaded to match the drive shaft 1 thread, referred to as the lift arm blocks 5. A one-piece L-shaped lift arm 4 has been drilled 10 laterally and fitted to the lift arm blocks 5 with cap screws. The top of the drive shaft 1 has been fitted with a 1/4" adjustment handle drive socket 6. The adjustment handle 7 has been fitted with a male end to engage the drive shaft socket 6 through the plunge router table 11. As shown in Figures 1 and 2 the drive shaft mechanism incorporates the drive shaft 1, drive shaft retention blocks 15 2, split pin and nylon bearing 13 to act as bearing surfaces, the lift arm blocks 5, and the 1/4" adjustment handle drive socket 6 that has been fitted to the drive shaft housing 3 with screws through the housing into the blocks. Both the drive shaft retention blocks 2 and the lift arm blocks 5 have been polished to a fine tolerance to provide smooth movement of the lift arm blocks 5 within the drive 20 shaft housing 3 to prevent lateral movement. Figure 3 illustrates a plunge router motor housing in front view. To avoid any interference with the design of a plunge router or function of the air cooling system, a lift arm receptor bar 8 made from hardened steel and featuring slotted ends is fitted to the plunge router motor housing 9 using plastic tube spacers 8a to avoid contact with the plunge 25 router motor housing 9. To accommodate the thickness of the lift arm receptor bar 8 and the plastic tube spacers 8a, extended screws 8b attach the lift arm receptor bar 8 to the router motor housing 9 using the existing motor housing cover screw receptors 8c. 30