Thread: Machining big slabs

I've been machining slabs for bench-tops and eventually came up with this simple device: I clamped two straight edges together and made a carriage for my router that slides between the straight edges. The straight edges slide on beams set horizontal at each end of the slab. The set up pictured below machines a 2.4m slab 1.2m wide - any size is possible as long as the straight edges can handle the span between beams. I use a Carb-I-Tool 35mm dia straight bit and cut about 5mm depth each pass. One pass takes me about 30min - it's slow but the slab ends up flat (plus or minus 1mm). Dry lube on the carriage and straight edges reduces the friction. There is some marking as the straight edges flex but I finnish with an electric planer that has blades sharpened with rounded corners, then sanding and cabinet scraping. When I turn the slab over I pack it up till it's equal depth below the straight edge at each corner - so ensuring parallel faces. I've found it best to work from one (long) side cutting across to half way and moving to the left - the forward cut is the best but I cut back and forward for the first rough cuts.