Abstract: A chamfering device incorporating a power tool for driving a rotary bur or the like provided with an elongated shaft and a cutting head, wherein the shaft is enclosed at a small clearance by a first, mainly tubular member, which, after mounting of the shaft with the said first member fitted thereto in the power tool, is held in position by a second, mainly tubular member, which is fixed to the power tool and is connected to the first member thereby arresting this in position, a third, mainly tubular member being provided over the second member, said third member being displaceable in the axial direction of the second member and lockable in occupied positions, said third member being an adjustable extension of the second member.