A conventional saw blade clamping device 10 is disclosed in U.S. Pat. No. 5,647,133 and FIGS. 1 and 2, wherein the clamping device includes a body 11 having a slot 111 for receiving a blade 20 therein and a passage 112 defined in communication with the slot 111. A tube 14 has a rod 13 received therein and the rod 13 includes a rectangular end 131 which fits an inner periphery of the tube 14. A spring 15 is mounted to the rod 13 and biased between the rectangular end 131 and the inside of the tube 14. The rod 13 threadedly extends through the body 11 and further has a contact end 12 which is able to contact a side of the blade 20. The body 11 includes a serrated surface 113 and the tube 14 is firmly urged by the spring 15 to contact the serrated surface 113. A user has to pull the tube 14 to remove the tube 14 away from the serrated surface 113 and then rotate the tube 14 so as to move the rod 13 to urge the blade 20 or disengage from the blade 20. The user has to use a force that overcomes the force of the spring 15 and simultaneously, rotate the tube 14. This is inconvenient for the user to operate the tube 14 in two different directions. Furthermore, it is difficult to estimate the force that the contact end 12 contacts the blade 20.
FIGS. 3 and 4 show the disclosure of U.S. Pat. No. 6,023,848 illustrating a blade clamping device 30 including a casing 31 and a base member 32 located in the casing 31. A first end of a biasing member 33 is connected to the base member 32. A blade 40 is engaged with the base member 32 and the biasing member 33 includes a protrusion portion 331 which urges against the blade 40. A lever 34 is pivotally connected to the casing 31 and includes an end that may push a free second end of the biasing member 33 to remove the protrusion portion 331 away from the blade 40. Although the biasing member 33 is easy to operate by operating the lever 34, the biasing member 33 quickly looses its biasing force after frequent operation by the lever 34.