WIDE BELT SANDER

Info

Publication number: 20120052777
Type: Application
Filed: Aug 31, 2010
Publication Date: Mar 1, 2012
Inventor: Wen-Chi CHANG (Shengang Hsiang)
Application Number: 12/872,233

Abstract

A wide belt sander has a base, a driving axle, a driven axle bracket, a driven axle, a belt and an automatic adjustment device. The driving axle has a central axis. The driven axle bracket is pivotally mounted on the base along a longitudinal axis perpendicular to the central axis of the driving axle. The driven axle is rotatably mounted on the driven axle bracket along a rotating axis parallel with the central axis of the driving axle. The automatic adjustment device drives the driven axle bracket to swing relative to the base along the longitudinal axis in a simple harmonic motion and has two pushed elements and a cam. The pushed elements are mounted separately on the driven axle bracket. The cam is mounted between and alternatively pushing the pushed elements to swing the driven axle bracket relative to the base.

Description

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sander, and more particularly to a wide belt sander having adjustment devices to make a belt moving smoothly and keep deviations from occurring.

2. Description of Related Art

To polish surfaces of an article, a sander is always used and substantially comprises a base, two axles and a belt. The axles are rotatably mounted on the base and are arranged in parallel, and the belt is endlessly mounted around the axles and is driven to polish an article. To keep the belt from deviating during the polishing process, an adjustment device is always arranged on the conventional sander. For example, Taiwan Patent No. 1279285, entitled to “Wide Belt Sander With A Reciprocal Adjustment Device” discloses an adjustment device having two cams mounted respectively at two sides of a pushed element that is secured on a driven axle bracket. When the rotation of the cams, the pushed element is alternatively pushed by the cams to make the driven axle bracket to swing in a simple harmonic motion. Accordingly, the travel track of the running belt can be automatically and actively adjusted to prevent deviation of the belt from occurring.

However, the conventional adjustment device has the following drawbacks.

1. The cams have to be rotated simultaneously but in reverse, a specific gear box is necessary. The gear box of the conventional adjustment device has to be designed or manufactured specifically, so the cost for manufacturing is high.

2. The belt of the conventional sander still deviates due to uneven force applied to the running belt during the polishing process even when the conventional adjustment device is arranged.

To overcome the shortcomings, the present invention tends to provide a wide belt sander to mitigate or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

The main objective of the invention is to provide a wide belt sander having an adjustment device to make a belt moving smoothly and keep deviations from occurring.

The wide belt sander in accordance with the present invention has a base, a driving axle, a driven axle bracket, a driven axle, a belt and an automatic adjustment device. The driving axle is rotatably mounted on the base and has a central axis. The driven axle bracket is pivotally mounted on the base along a longitudinal axis perpendicular to the central axis of the driving axle. The driven axle is rotatably mounted on the driven axle bracket along a rotating axis parallel with the central axis of the driving axle. The belt is endlessly mounted around the driving and driven axles. The automatic adjustment device is mounted between the base and the driven axle bracket to drive the driven axle bracket to swing relative to the base along the longitudinal axis in a simple harmonic motion and has two pushed elements and a cam. The pushed elements are mounted separately on the driven axle bracket. The cam is rotatably mounted on the base and is mounted between and alternatively pushing the pushed elements to swing the driven axle bracket relative to the base.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a wide belt sander in accordance with the present invention;

FIG. 2 is a partially exploded perspective view of the wide belt sander in

FIG. 1;

FIG. 3 is an enlarged perspective view of a contacting switch of the wide belt sander in FIG. 1;

FIG. 4 is an enlarged front view of the wide belt sander in FIG. 1;

FIG. 5 is an enlarged top view in partial section of the gear box of the wide belt sander in FIG. 1;

FIG. 6 is an enlarged operational side view in partial section of the gear box in FIG. 5;

FIG. 7 is an enlarged operational top view of the automatic adjustment device of the wide belt sander in FIG. 1 showing that the cam is at the 0° position;

FIG. 8 is an enlarged operational top view of the automatic adjustment device in FIG. 7 showing that the cam is at the 90° position;

FIG. 9 is an enlarged operational top view of the automatic adjustment device in FIG. 7 showing that the cam is at the 180° position;

FIG. 10 is an enlarged operational top view of the automatic adjustment device in FIG. 7 showing that the cam is at the 270° position;

FIG. 11 is an enlarged perspective view of the electrical adjustment device of the wide belt sander in FIG. 1; and

FIG. 12 is an enlarged operational end view in partial section of the wide belt sander in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

With reference to FIGS. 1, 2 and 4, a wide belt sander in accordance with the present invention comprises a base 10, a driving axle 20, a driven axle bracket 30, a driven axle 40, a belt 50, an automatic adjustment device and an electrical adjustment device.

The base 10 comprises a bottom frame, a column 12, a slider 13, a motor 14, a holding bracket 15 and an axle frame 150. A second belt 11 may be endlessly mounted on the bottom frame in a horizontal direction to provide a further polishing effect. The column 12 is upwardly mounted on the bottom frame. The slider 13 is slidably mounted on the column 12 with a threaded rod that is mounted rotatably on the column 12. A dove-tail engagement is mounted between the slider 13 and the column 12 to allow the slider 13 slidable relative to the column 12 smoothly. The motor 14 is mounted on the slider 13. The holding bracket 15 is securely mounted on the slider 13 above over the bottom frame and has a top, an axle hole 151, a channel 152 and two threaded holes. The axle hole 151 is defined in the top at the middle of the holding bracket 151. The channel 152 is defined in the top near one end of the holding bracket 15. The threaded holes are defined in the top of the holding bracket 15 near the channel 152. The axle frame 150 is securely attached to the holding bracket 15 at one end opposite to the slider 13.

The driving axle 20 is rotatably mounted between the slider 13 and the axle frame 150 below the holding bracket 15 and has a central axis. The driving axle 20 is connected to and driven by the motor 14. In addition, the channel 152 in the top of the holding bracket 15 is defined along a direction perpendicular to the central axis of the driving axle 20.

The driven axle bracket 30 is pivotally mounted on the base 10 along a longitudinal axis perpendicular to the central axis of the driving axle 20. The driven axle bracket 30 has a central shaft 31 formed on and protruding downward from the bottom of the driven axle bracket 30 and rotatably and slidably extending into the axle hole 151 in the holding bracket 15.

In addition, a pneumatic cylinder 60 is mounted between the holding bracket 15 and the driven axle bracket 30. The pneumatic cylinder 60 has a first end connected to the driven axle bracket 30 and a second end connected to the holding bracket 15 with a universal jointer. The cylinder 60 can provide a supporting effect to the driven axle bracket 30 to keep the driven axle bracket 30 away from the driving axle 20 at a desired distance.

The driven axle 40 is rotatably mounted on the driven axle bracket 30 along a rotating axis parallel with the central axis of the driving axle 20. The belt 50 is endlessly mounted around the driving and driven axles 20,40.

Additionally, an axle adjusting device is mounted between the base 10 and the driven axle bracket 30 to change a distance between the driving and driven axles 20,40. The axle adjusting device comprises a handlebar 61 and a pushing plate 64. The handlebar 61 is pivotally mounted on the holding bracket 15 with a pivot 62 and has a guiding channel defined through the handlebar 61 at one end of the handlebar 61. The pushing plate 64 is pivotally mounted on the holding bracket 15, is pivotally and slidably connected to the guiding channel in the handlebar 61 with a sliding pivot 63 and is connected to the central shaft 31. When the handlebar 61 is pulled upward, the driven axle bracket 30 is moved toward the driving axle 20 with the transmission of the pushing plate 64 and compresses the cylinder 60. Accordingly, the distance between the driving and driven axles 20,40 can be shortened, and to replace a worn belt 50 with a new one is convenient.

When the handlebar 61 is released, the driven axle bracket 30 can be pushed upward to the original position where the belt 50 is at a tightened condition for polishing with the recoil force provided by the pneumatic cylinder 60.

With reference to FIGS. 1, 2 and 4 to 6, the automatic adjustment device is mounted between the base 10 and the driven axle bracket 30 to drive the driven axle bracket 30 to swing relative to the base 10 along the longitudinal axis in a simple harmonic motion. The automatic adjustment device comprises a gear box 70, a cam 71, two pushed elements 72,73 and a driving assembly. The gear box 70 is adjustably mounted on the holding bracket 15 of the base 10. The gear box 70 has a bottom and two ribs 701 formed on the bottom of the gear box 70 and slidably held in the channel 152 in the holding bracket 15. A wing 702 is mounted on and laterally extends from the bottom of the gear box 70 and has two elongated holes 703 defined through the wing 702 and aligning respectively with the threaded holes in the holding bracket 15. With two bolts 704 extending through the elongated holes 703 in the wing 702 and screwed into the corresponding threaded holes in the holding bracket 15, the gear box 70 is securely mounted on the holding bracket 15. With releasing the bolts 704, the gear box 70 can be moved along the channel 152 in the holding bracket 15 to adjust the position of the gear box 70 relative to the holding bracket 15.

The gear box 70 comprises a driving shaft 705, a driven shaft 708 and a gear device. The driving shaft 705 is rotatably mounted on and extends into a side of the gear box 70. The driven shaft 708 is rotatably mounted on and extends out from the top of the gear box 82. The gear device is mounted in the gear box 70 and is mounted between the driving shaft 705 and the driven shafts 708. The gear device comprises a worm rod 709 and a worm gear 709′. The worm rod 709 is co-axially mounted on the driving shaft 705. The worm gear 709′ is securely mounted on the driven shaft 708 and engages the worm rod 709. Accordingly, the driven shaft 708 can be rotated with the driving shaft 705 at a reduced speed.

The cam 71 is mounted securely on and driven by the driven shaft 708. Preferably, the cam 71 is mounted on a middle position of the top of the gear box 70.

The pushed elements 72,73 are mounted on the bottom of the driven axle bracket 30 at an interval. The pushed elements 72,73 have a center line defined between centers of the pushed elements 72,73. The cam 71 is mounted between the pushed elements 72,73 and alternatively pushes the pushed elements 72,73 to swing the driven axle bracket 30 relative to the base 10 as shown in FIGS. 7 to 10. The cam 71 has a rotating center where is mounted around the driven shaft 708 and located at a middle point of the center line between the pushed elements 72,73. Thus, the cam 71 has an equal distance to each pushed element 72,73. Preferably, each pushed element 72,73 is a bearing having a central hole 720,730 defined through the pushed element 72,73. Two securing bolts 721,731 are mounted respectively through the central holes 720,730 of the pushed elements 72,73 and mounted securely to the bottom of the driven axle bracket 30 to mount the pushed elements 72,73 on the driven axle bracket 30.

The driving assembly is mounted on the base 10 to drive the cam 71 to rotate and comprises a driving pulley, a driven pulley 706 and a driving belt 707. The driving pulley is co-axially connected to and rotated with the driving axle 20. The driven pulley 706 is co-axially connected to the driving shaft 705. The driving belt 707 is mounted around the driving pulley and the driven pulley 706. When the driving axle 20 is rotated by the motor 14, the cam 71 will also rotate with the transmission of the driving assembly, the driving shaft 705, the gear device in the gear box 70 and the driven shaft 708.

Additionally, an indicating board 80 is securely mounted between the holding bracket 15 and the driven axle bracket 30 and has multiple mounting holes 801, an upper indication channel 81 and a lower indication channel 82. The mounting holes 801 are defined through the indicating board 80. Multiple bolts 802 are mounted respectively through the mounting holes 801 and screwed into the threaded holes 803 defined in the holding bracket 15 and the driven axle bracket 30 to secure the indicating board 80 on the holding bracket 15 and the driven axle bracket 30. The upper indication channel 81 and the lower indication channel 82 are laterally defined through the indicating board 80 and are parallel with each other. Each indication channel 81,82 has an index mark 83 formed on an edge of the channel 81,82. An upper pointer 84 is mounted on the driven axle bracket 30 at the middle point of the center line between the pushed elements 72,73 and extends into the upper indication channel 81 in the indicating board 80. A lower pointer 85 is securely mounted on the gear box 70 at a position aligning with the cam 71 and extends into the lower indication channel 82 in the indicating board 80. With the arrangement of the pointers 84,85 and the indication channels 81,82, the positions of the driven axle bracket 30 and the gear box 70 are identified. When the driving and driven axles 20,40 are completely parallel with each other, the pointers 84,85 correspond respectively to zero points of the index marks 83.

With reference to FIGS. 1 to 3, 7 and 11, the electrical adjustment device is mounted on the holding bracket 15 of the base 10 to pivot the driven axle bracket 30 relative to the base 10 so as to adjust a period of the simple harmonic motion of the automatic adjustment device. The electrical adjustment device comprises two contacting switches 91,92, two electromagnetic switches 94,95, a holding frame 93, a connecting frame 96 and two springs 941,951. The contacting switches 91,92 are mounted on the top of the holding bracket 15 of the base 10 respectively at two sides of the belt 50. Each contacting switch 91,92 has a contacting arm 911 protruding from the contacting switch 91,92, selectively abutting with an edge of the belt 50 and having a ceramic sleeve 912 mounted around the contacting arm 911. The ceramic sleeve 912 can keep the contacting arms 911 from being damaged or worn off by the running belt 50.

The holding frame 93 is mounted securely on the top at one end of the holding bracket 15. The electromagnetic switches 94,95 are electrically connected respectively to the contacting switches 91,92 and are mounted on two ends of the holding frame 93 respectively at two sides of the driven axle bracket 30. The electromagnetic switches 94,95 have a timing function to switch the electromagnetic switches 94,95 off automatically after a predetermined time, for example 5 seconds.

The connecting frame 96 is mounted securely on one end of the driven axle bracket 30 and has a bottom having two sides and two ends and two connecting ears 962. The connecting ears 962 are respectively formed on and protrude from the two ends and the two sides of the bottom of the connecting frame 96.

The springs 941,951 are connected respectively to the electromagnetic switches 94,95 and the driven axle bracket 30. Each spring 941,951 has two ends connected respectively a corresponding one of the electromagnetic switches 94,95 and one of the connecting ears 962 on the connecting frame 96. Accordingly, the springs 941,951 are connected respectively to the two sides of the driven axle bracket 30 via the connecting frame 96 to provide pulling forces in opposite directions to the driven axle bracket 30.

Before the wide belt sander is in used, the positions of the driven axle bracket 30 and the cam 71 of the automatic adjustment device must be zeroized. With reference to FIGS. 9 and 10, to zeroize the position of the driven axle bracket 30, the driving belt 707 is detached from the driving and driving pulleys 706 and the motor 14 is switched on to rotate the driving axle 20. At this time, the cam 71 is kept at a 0° or 180° position as shown in FIGS. 7 and 9. With the rotation of the driving axle 20, the driven axle 40 will be rotated with the transmission of the belt 50 but the cam 71 keeps stationary. Because the driven axle bracket 30 is pivotally mounted on the holding bracket 15 with the central shaft 31, the angular position of the driven axle bracket 30 is adjusted manually relative to the holding bracket 15 to make the belt 50 running in a desired travel track. After moving the indicating board 80 to make the zero point of the index mark 83 on the upper indication channel 81 aligning with the upper pointer 84, the bolts 802 are screwed completely into the threaded holes 803 in the holding bracket 15 and the driven axle bracket 30 to securely the indicating board 80 on the driven axle bracket 30 at the zeroized point.

Then, the bolts 704 for securing the gear box 70 are released, and the position of the gear box 70 is adjusted along the channel 152 to make the lower pointer 85 aligning with the zero point of the index mark 83 on the lower indication channel 82. At this position, the cam 71 is at the middle of the center line of the pushed elements 72,73. Accordingly, the driven axle bracket 30 and the cam 71 are zeroized, and the driving belt 707 is mounted around the driving and driven pulleys 706.

Consequently, the cam 71 can be rotated with the transmission of the driving assembly, the driving shaft 705, the gear device and the driven shaft 708 while the driving axle 20 is rotating. Accordingly, with reference to FIGS. 6 to 8, the pushed element 72,73 will be alternatively pushed by the cam 71 to make the driven axle bracket 30 to swing relative to the central shaft 31 in a simple harmonic motion. With the swinging of the driven axle bracket 30, the travel track of the running belt 50 can be automatically and actively adjusted, such that the movement of the running belt 50 is stable and smooth. Within one rotation of the cam 71, the driven axle bracket 30 can be adjusted twice and this means that two adjustment frequencies are provided. The movement travel of the running belt 50 is smooth, and the belt 50 can be kept from being worn off at a single edge. The useful life of the belt 50 can be prolonged and the belt 50 is durable.

If the sander is applied with an uneven force to cause the deviation of the belt 50, the belt 50 will abut against the contacting arm 911 of one of the contacting switches 91,92. Thus, the pushed contacting switch 91,92 will send a signal to activate the corresponding electromagnetic switch 94,95 to pull the corresponding spring 941,951 with a pulling force of 0.8 to 1.5 Kg. Consequently, the pulled spring 941,951 will pull the driven axle bracket 30 to swing via the connecting frame 96, and the period of the simple harmonic motion of the automatic adjustment device can be changed. Accordingly, the belt 50 can move backward the desired travel track. After the predetermined time set up in the electromagnetic switch 94,95, for example 5 seconds, the electromagnetic switch 94,95 is switched off and the driven axle bracket 30 can be pivoted to an original position with the recoil forces provided by the springs 941,951. Therefore, another adjustment effect is provided, such that double adjustment functions can be provided by the automatic adjustment device and the electrical adjustment device.

With reference to FIGS. 2 and 12, a limiting device is mounted between the driven axle bracket 30 and the holding bracket 15 to limit the swinging range of the driven axle bracket 30. The limiting device comprises a limiting bracket 97, two limiting bolts 972 and a base bracket 974. The limiting bracket 97 is mounted on the bottom of the driven axel bracket 30, is inversed U-shaped and has two ears respectively formed on and protruding from two ends of the limiting bracket 97. The limiting bolts 972 are mounted respectively on the ears of the limiting bracket 97 and protrude toward each other. The base bracket 974 is mounted securely on the top of the bolding bracket 15 and has a top extending into the limiting bracket 97 to a position between the limiting bolts 972.

Accordingly, when the driven axle bracket 30 is swung by the automatic adjustment device or the electrical adjustment device, the swinging range of the driven axle bracket 30 can be limited by the abutment of the base bracket 974 with one of the limiting bolts 972.

With the aforementioned description, the wide belt sander has the following advantages.

1. With a single cam 71 arrangement, the gear device in the gear box 70 has not to be specifically designed and manufactured. The gear box 70 can be a standardized product, such that the cost for manufacturing the wide belt sander can be reduced.

2. To assemble a single cam 71 onto the gear box 70 is easy and convenient, and the zeroizing process of the cam 71 is also easy.

3. The wide belt sander in accordance with the present invention has two adjustment means, such that the travel of the belt 50 can be well controlled on a desired track. The useful life of the wide belt sander can be prolonged and is durable.

Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A wide belt sander comprising:

a base;

a driving axle rotatably mounted on the base and having a central axis;

a driven axle bracket pivotally mounted on the base along a longitudinal axis perpendicular to the central axis of the driving axle;

a driven axle rotatably mounted on the driven axle bracket along a rotating axis parallel with the central axis of the driving axle;

a belt endlessly mounted around the driving and driven axles; and

an automatic adjustment device mounted between the base and the driven axle bracket to drive the driven axle bracket to swing relative to the base along the longitudinal axis in a simple harmonic motion and comprising two pushed elements mounted separately on the driven axle bracket; and a cam rotatably mounted on the base and mounted between and alternatively pushing the pushed elements to swing the driven axle bracket relative to the base.

2. The wide belt sander as claimed in claim 1 further comprising an electrical adjustment device mounted on the base to pivot the driven axle bracket relative to the base to adjust a period of the simple harmonic motion of the automatic adjustment device.

3. The wide belt sander as claimed in claim 2, wherein the automatic adjustment device comprises

a gear box adjustably mounted on the base 10;

a driving shaft rotatably mounted on and extending into the gear box;

a driven shaft rotatably mounted on and extending out from the gear box and on which the cam is mounted; and

a gear device mounted in the gear box, mounted between the driving shaft and the driven shaft and comprising a worm rod co-axially mounted on the driving shaft; and a worm gear securely mounted on the driven shaft and engaging the worm rod.

4. The wide belt sander as claimed in claim 3, wherein the pushed elements are rotatably mounted on a bottom of the driven axle bracket at an interval and have a center line defined between centers of the pushed elements; and

the cam has a rotating center where is mounted around the driven shaft and located at the center line between the pushed elements.

5. The wide belt sander as claimed in claim 4, wherein each pushed element is a bearing having a central hole defined through the pushed element; and

two securing bolts mounted respectively through the central holes of the pushed elements and mounted securely on the bottom of the driven axle bracket.

6. The wide belt sander as claimed in claim 5, wherein

the base has a channel defined along a direction perpendicular to the central axis of the driving axle; and two threaded holes defined in the base adjacent to the channel; and

the gear box is mounted adjustably in the channel in the base and has a bottom; two ribs formed on the bottom and slidably held in the channel in the base; a wing mounted on and laterally protruding from the bottom of the gear box and having two elongated holes defined through the wing and aligning respectively with the threaded holes in the base; and two bolts mounted respectively through the elongated holes and screwed respectively into the threaded holes in the base.

7. The wide belt sander as claimed in claim 6, wherein

the base further comprises a holding bracket to which the driven axle bracket is pivotally connected and the gear box is adjustably mounted and having an axle hole defined in a top of the holding bracket;

the driven axle bracket has a central shaft formed on and protruding downward from the driven axle bracket and rotatably and slidably extending into the axle hole in the holding bracket; and

a pneumatic cylinder is mounted between the holding bracket and the driven axle bracket and has a first end provided with a universal jointer and connected to the holding bracket with the universal jointer; and a second end connected co-axially to the central shaft on the driven axle bracket to provide a supporting effect to the driven axle bracket.

8. The wide belt sander as claimed in claim 7, wherein the electrical adjustment device comprises

two contacting switches mounted on the base respectively at two sides of the belt;

two electromagnetic switches electrically connected respectively to the contacting switches and mounted on the base respectively at two sides of the driven axle bracket; and

two springs each having two ends connected respectively one of the electromagnetic switches and the driven axle bracket, wherein the springs are connected respectively to the two sides of the driven axle bracket to provide pulling forces in opposite directions to the driven axle bracket.

9. The wide belt sander as claimed in claim 8, wherein each contacting switch has a contacting arm protruding from the contacting switch selectively abutting with the belt and having a ceramic sleeve mounted around the contacting arm.

10. The wide belt sander as claimed in claim 9 further comprising a limiting device mounted between the driven axle bracket and the holding bracket to limit the swinging range of the driven axle bracket and comprising

a limiting bracket mounted on the bottom of the driven axel bracket, being inversed U-shaped and having two ears respectively formed on and protruding from two ends of the limiting bracket;

two limiting bolts mounted respectively on the ears of the limiting bracket and protruding toward each other; and

a base bracket mounted securely on the top of the bolding bracket and having a top extending into the limiting bracket to a position between the limiting bolts.

11. The wide belt sander as claimed in claim 2, wherein the electrical adjustment device comprises

two contacting switches mounted on the base respectively at two sides of the belt;

two electromagnetic switches electrically connected respectively to the contacting switches and mounted on the base respectively at two sides of the driven axle bracket; and

two springs each having two ends connected respectively one of the electromagnetic switches and the driven axle bracket, wherein the springs are connected respectively to the two sides of the driven axle bracket to provide pulling forces in opposite directions to the driven axle bracket.

12. The wide belt sander as claimed in claim 11, wherein each contacting switch has a contacting arm protruding from the contacting switch, selectively abutting with the belt and having a ceramic sleeve mounted around the contacting arm.

13. The wide belt sander as claimed in claim 1, wherein the automatic adjustment device comprises

a gear box adjustably mounted on the base;

a driving shaft rotatably mounted on and extending into the gear box;

a driven shaft rotatably mounted on and extending out from the gear box and to which the cam is attached; and

a gear device mounted in the gear box, mounted between the driving shaft and the driven shaft and comprising a worm rod co-axially mounted on the driving shaft; and a worm gear securely mounted on the driven shaft and engaging the worm rod.

14. The wide belt sander as claimed in claim 13, wherein the pushed elements are rotatably mounted on a bottom of the driven axle bracket at an interval and have a center line defined between centers of the pushed elements; and

the cam has a rotating center where is mounted around the driven shaft and located at the center line between the pushed elements.

15. The wide belt sander as claimed in claim 14, wherein each pushed element is a bearing having a central hole defined through the pushed element; and

two securing bolts mounted respectively through the central holes of the pushed elements and mounted securely to the bottom of the driven axle bracket.

16. The wide belt sander as claimed in claim 13, wherein

the base has a channel defined along a direction perpendicular to the central axis of the driving axle; and two threaded holes defined in the base adjacent to the channel; and

the gear box is mounted adjustably in the channel of the base and has a bottom; two ribs formed on the bottom and slidably held in the channel in the base; a wing mounted on and laterally protruding from the bottom of the gear box and having two elongated holes defined through the wing and aligning respectively with the threaded holes in the base; and two bolts mounted respectively through the elongated holes and screwed respectively into the threaded holes in the base.

17. The wide belt sander as claimed in claim 1, wherein