the preheating is with a heat gun,,just go over the parts to be bent put some heat just to give the heat time to soak in to the center of wood to make sure it is heated through,,and by laying the heat to it,, it just means to heat it very well,,I use the back of my fingers to test heat as the underside of fingers and hands are not as soft,,it needs to be very hot to the touch,,but not scorching the wood,,,, sorry if my wording confused you,,instead of a spell check on my computer I need a hillbilly check,,because I live here deep in the tn mountians,, I will add some more this eve,, time to work now,,, thanks mike