Patent Application
20100050845
This present invention relates to a locking mechanism for a positionable power tool, and in particular, a magnetic lock for a miter saw.
Positionable power tools are well known. In the context of miter saws, such tools generally have a workpiece support table, as well as a saw carriage and blade, which can be rotated through a range of angles relative to a tool base. Typically, a mechanical locking mechanism is provided to lock the position of the workpiece support table at a desired angle. For example, one type of locking mechanism consists of a locking pin connected to the workpiece support table that is engagable in one of a series of corresponding detents or slots located on the tool base. However, with this type of locking mechanism, the angles at which the workpiece support table is capable of locking are limited to the fixed locations of the detents or slots.
In an alternative type of locking mechanism, once a desired angle is obtained, the position of the workpiece support table may be locked relative to the tool base by a cam or threaded device that pushes against and frictionally engages the tool base, thereby preventing further rotation. However, this type of locking mechanism is disadvantageous in that the cam or threaded device necessarily requires large loading forces applied against the workpiece support table to generate sufficient friction to lock the position of the workpiece support table. Such loading forces can cause deflection of the workpiece support table, resulting in inaccurate cuts.
A magnetic lock for a positionable power tool of the type comprising a workpiece support table moveable relative to a tool base. The magnetic lock comprises a braking surface configured to contact an outer edge of the tool base, and a magnetic device mountable to the workpiece support table adjacent an outer edge of the tool base. The magnetic device is configured to provide a selectively variable force to push the braking surface against the outer edge of the tool base. When the braking surface is pushed against the outer edge of the tool base, the workpiece support table is substantially prevent from moving relative to the tool base.
a is a side view of the internal magnets housed in the switchable magnet mechanism of
b is a side view of the internal magnets housed in the switchable magnet mechanism of
c is a phantom side view of the magnetic lock of
d is a cutaway side view of the magnetic lock of
The present invention relates to a magnetic lock for a positionable power tool. Although the description of the magnetic lock is explained below in the context of a miter saw, it should be appreciated that the invention is not limited to miter saws. Rather, the invention may be useful in any positionable power tool, and in particular, those where accuracy is desired.
In a first embodiment, a magnetic lock 226 having a switchable magnet mechanism 228 is provided.
The switchable magnet mechanism 228 may comprise any commercially available switchable magnet mechanism, such as the Mag-Jig or the MagSqaure, sold under the name MAGSWITCH, available from Magswitch Technology, Inc., of Littletown, Colo., 80120 USA. Descriptions of suitable switchable magnet mechanisms may be found in U.S. Pat. Nos. 6,707,360 and 7,012,495, the entireties of which are hereby incorporated by reference herein. Although the switchable magnet mechanism 228 may be of any size, shape, or strength, a mechanism having cylindrical magnets 20 millimeters in diameter and a holding force of at least 20 pounds is preferable.
Briefly, switchable magnet mechanisms are commercially available devices that allow a magnetic field to essentially be mechanically turned on and off, similar to an electromagnet, but without the need for an electric power supply. Switchable magnet mechanisms generally comprise a pair of magnets contained within a housing. Such magnets are typically of the rare-earth type, such as Neodymium. Typically, one of the magnets is fixed to the housing while the other magnet is rotatable with respect to the housing. A rotatable knob operatively attached to the rotatable magnet may extend from the housing of the switchable magnet mechanism to provide a means of rotating the magnet. Rotation of the knob rotates the rotatable magnet.
A side view of the internal magnets housed within the switchable magnet mechanism is shown in
The switchable magnet mechanism 228 shown in
When the switchable magnet mechanism 228 is turned off, the switchable magnet mechanism 228 may be disengaged from the tool base 212. The disengaged switchable magnet mechanism 228 may remain within millimeters of the tool base 212, yet avoid contact with the tool base 212, to allow a user to easily position the workpiece support table 214. Alternatively, although the switchable magnet mechanism 228 is turned off, the switchable magnet mechanism 228 may remain in sliding contact with the tool base 212. The sliding contact may result in friction between the tool base 212 and the switchable magnet mechanism 228, but such friction is low and can easily be overcome by the user in adjusting the position of the workpiece support table 214. Regardless of the orientation of the switchable magnet mechanism 228 when turned off, the magnetic lock 226 is unlocked and the workpiece support table 214 is permitted to move.
In contrast, when the switchable magnet mechanism 228 is turned on, a portion of the switchable magnet mechanism 228 firmly engages the tool base 212 under the force of magnetic attraction. This portion may be considered a braking surface 227, which could be part of the housing of the switchable magnet mechanism 228, or alternatively, a separate layer of material connected thereto. The magnetic force operates to greatly increase the frictional resistance between the switchable magnet mechanism 228, or the braking surface 227, and the tool base 212. When the switchable magnet mechanism 228 is turned on, the magnetic lock 226 is locked, and the workpiece support table 214 is substantially prevented from moving relative to the tool base 212. With the position of the workpiece support table 214 locked relative to the tool base 212, a user may proceed with making a cut.
The switchable magnet mechanism 228 may be mounted to the workpiece support table 214 by any suitable means which permits the switchable magnet mechanism 228 to firmly engage the tool base 212 when the magnetic lock 226 is locked, and disengage the tool base 212 when the magnetic lock 226 is unlocked. Importantly, the switchable magnet mechanism 228 should be mounted to the workpiece support table 214 such that, when the magnetic lock 226 is locked, the switchable magnet mechanism 228 does not transfer any significant loading forces to the workpiece support table 214. For example, the switchable magnet mechanism 228 and/or the mounting block may be movably attached to the workpiece support table 214 by means of a hinge, a track, a slot, etc., to freely permit the switchable magnet mechanism 228 to move radially, both toward and away from the tool base 212, while substantially preventing lateral movement relative to the workpiece support table 214.
As seen in the phantom view shown in
Referring again to
The tool base 212 may also be fitted with a steel plate 242 on which the switchable magnet mechanism 228 may be affixed when the magnetic lock 226 is locked. As shown in the context of a miter saw 210, the steel plate 242 is contoured according to the radius of the tool base 212. However, in the context of other positionable tools, the steel plate 242 may be planer. The switchable magnet mechanism 228, and any additional surfaces extending therefrom, is also precisely contoured according to the contour of the tool base 212 or the steel plate 242, thereby increasing the surface area of frictional engagement with the tool base 212, and providing a larger braking surface 227. Alternatively, the switchable magnet mechanism 228 may be planar.
Furthermore, one or more of the tool base 212, the steel plate 242, or the switchable magnet mechanism 228 may be coated with a highly durable, weather resistant coating, such as Titanium Nitride, to prevent wear. In addition to improving the durability of the coated components, the coating serves to increase the coefficient of friction, and therefore the frictional resistance, between the switchable magnet mechanism 228 and the tool base 212. Additionally one or more strips or pads of a frictional material, such as rubber or Silicon, may be provided on the braking surface 227 of the switchable magnet mechanism 228 to improve the frictional resistance between the switchable magnet mechanism 228 and the tool base 212. In order to keep the frictional material level with the surface of the switchable magnet mechanism 228, one or more depressions may be machined in the switchable magnet mechanism 228 for retaining the frictional material.
The tool base 212 includes a series of detents 243 to provide the user with an index of cutting angles, or alternatively, as shown in
To use the magnetic lock 226, a user may begin with the switchable magnet mechanism 228 turned off. Advantageously, the user is capable of selecting arbitrary positions at which the workpiece support table 214 is lockable. After rotating the workpiece support table 214 to the desired position, the user could then use a micro adjustment lever (not shown), if provided, to make any precise adjustments. Once the workpiece support table 214 has been moved to the desired position, the user may lock the position of the workpiece support table 214 by rotating the knob 232 one-half a revolution, thereby also rotating the rotatable magnet in the switchable magnet mechanism 228. With rotation of the rotatable magnet, the switchable magnet mechanism 228 turns on and provides a magnetic attraction directly toward the tool base 212. If the switchable magnet mechanism 228 is fully disengaged with the tool base 212 in the unlocked state, depending on the means by which it is attached to the workpiece support table 214, the switchable magnet mechanism 228 will either move into engagement with the tool base 212 under the force of magnetic attraction, or the user will move the switchable magnet mechanism 228 into engagement.
As shown in
The magnetic force provided by the switchable magnet mechanism 228 operates to increase the normal force the tool base 212 applies against an engaged switchable magnet mechanism 228, thus increasing the frictional resistance between the tool base 212 and the breaking surface 227 of the switchable magnet mechanism 228. The increased friction between the tool base 212 and the switchable magnet mechanism 228 operates to resist movement of the switchable magnet mechanism 228 relative to the tool base 212. In turn, movement of the workpiece support table 214 is resisted because the switchable magnet mechanism 228 is mounted to the workpiece support table 214 by a means that substantially prevents lateral movement of the switchable magnet mechanism 228 relative to the workpiece support table 214. Furthermore, because the magnetic force acts to pull the switchable magnet mechanism 228 directly toward the adjacent tool base 212 without transferring any significant forces to the workpiece support table 214, deflection of the workpiece support table 214 is substantially avoided. Once the switchable magnet mechanism 228 is frictionally engaged under the force of the magnetic attraction, the user can perform the various cutting and other operations provided by the tool. A user may unlock the locking mechanism 226 by rotating the knob 232 one-half of a revolution to also rotate the rotatable magnet within the switchable magnet mechanism 228.
An alternative embodiment of a magnetic lock 326 is shown in
To use the magnetic lock 326, a user would begin with the switchable magnet mechanism 328 tuned off. When the switchable magnet mechanism 328 is turned off, the switchable magnet mechanism 328 and the hinged mounting block 330 are freely rotatable about the pin 334. By lifting upward on the lever 331 and/or the grip 335, a user may fully disengage the switchable magnet mechanism 328 from the tool base 312 as it rotates about the pin 334, away from the tool base 312. A releasable means for retaining the lever 331 in an upward position may also be provided. Alternatively, when turned off, the switchable magnet mechanism 328 may remain engaged in sliding contact with the tool base 312. At this point, a user can move the workpiece support table 314 to the desired position. To lock the position of the workpiece support table 314, a user would first rotate the switchable magnet mechanism 328 back into engagement with the tool base 312, if previously disengaged. The user would then turn on the switchable magnet mechanism 328 by rotating the shaft 333 using the grip 335. As the switchable magnet mechanism 328 is turned on, the switchable magnet mechanism 328 is attracted directly toward and firmly engages the tool base 312, thereby locking the position of the workpiece support table 314, without transferring to the workpiece support table 314 any significant loading forces. To unlock the magnetic lock 326, the user would use the grip 335 to rotate the shaft 333, and therefore the rotatable magnet within the switchable magnet mechanism 328, one-half of a revolution.
In a third embodiment, a magnetic lock 426 having an electromagnet 428 is provided.
Briefly, electromagnets are devices that that allow a magnetic force to be generated and controlled by delivery of an electric current. Electromagnets generally comprise a segment of wire in the shape of a coil wrapped around a core of ferromagnetic or paramagnetic material. When an electric current flows through the wire, a magnetic field is generated around the wire and a magnetic force concentrates in the core. The strength of the magnetic force is dependent on the amount of current flowing through the wire and the number of turns in the coil. The magnetic force generated by the electromagnet permits the electromagnet to be affixed to a surface. The electromagnet 428 shown in
The primary difference between the structure, operation, and use of the magnetic lock 426 shown in
Like the switchable magnet mechanism 228, the electromagnet 428 is mounted to the workpiece support table 414 by any means which permit the electromagnet 428 to firmly engage the tool base 412 when the magnetic lock 426 is locked, and disengaged the tool base 412 when the magnetic lock 426 is unlocked. The electromagnet 428 should also be mounted to the workpiece support table 414 such that, when the magnetic lock 426 is locked, the electromagnet 428 does not transfer any significant loading forces to the workpiece support table 414. Accordingly, the electromagnet 428 may be mounted to the workpiece support table 414 by the same or similar means as those described above with respect to the switchable magnet mechanism 228. The electromagnet 428 may also be mounted to the workpiece support table 414 in any location that permits the electromagnet 428 to engage the outer edge of the tool base 412, including the vertical surface 438, as shown in
To position a power tool using the magnetic lock 426, a user may begin with the electromagnet 428 turned off. As with the switchable magnet mechanism 228, the electromagnet 428 permits the user to select an arbitrary position at which the workpiece support table 414 may be locked. Once the user has moved the workpiece support table 414 to the desired location, the user may lock the position of the workpiece support table 414 with respect to the tool base 412 by activating the electric switch 432 and turning on the electromagnet 428. As the electromagnet 428 is turned on, the electromagnet 428 is attracted toward the tool base 412 under the force of magnetic attraction, the breaking surface of the electromagnet 428 firmly engages the tool base 412, and the frictional resistance between the electromagnet 428 and the tool base 412 is substantially increased. The magnetic lock 426 also avoids deflection because the electromagnet 428 is attracted directly toward and firmly engages the tool base 412 without transferring to the workpiece support table 414 any significant loading forces.
In a fourth embodiment, a magnetic lock 526 having a permanent magnet 528 is provided.
The magnetic lock 526 differs from the embodiments shown in
The permanent magnet 528 is attached to the workpiece support table 514 by any suitable means which permit the permanent magnet 528 to firmly engage the tool base 512 when the magnetic lock 526 is locked, and fully disengage the tool base 512 when the magnetic lock 526 is unlocked. In order for the magnetic lock 526 to remain selectively lockable, a user must be able to overcome the magnetic attraction between the permanent magnet 528 and the tool base 512. Accordingly, as shown in
It should be appreciated that the permanent magnet 528, like the switchable magnet mechanism 228 and the electromagnet 428, may be mounted to the workpiece support table 514 such that the permanent magnet 528 engages the outer edge of the tool base 512 on the vertical surface 538, as shown in
To position a power tool using the magnetic lock 526, a user begins with the permanent magnet 528 engaged with the tool base 512. The user may unlock the magnetic lock 526 by pulling upward on the grip 535 and/or the lever 532 to overcome the magnetic attraction between the tool base 512 and the permanent magnet 528. As the user pulls the lever 532 upward, the mounting block 530 and the permanent magnet 528 rotate about the pin 534, the permanent magnet 528 disengages the tool base 512, and the workpiece support table 514 is permitted to move with respect to the tool base 512. A releasable means of retaining the lever 532 in an upward position may also be provided. Once the workpiece support table 514 is moved to the desired position, a user may lower the lever 532 until the permanent magnet 528 is firmly engaged with the tool base 512 under the force of magnetic attraction. Like the switchable magnet mechanism 228 and the electromagnet 428, the permanent magnet 528 substantially avoids deflection during the locking of the workpiece support table 514 because the permanent magnet 528 is attracted directly toward and firmly engages the tool base 512 without transferring to the workpiece support table 514 any significant loading forces.
Thus, the present invention provides a positionable power tool having an improved magnetic lock. The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the present invention is susceptible of many variations and modifications coming within the scope of the following claims.
