Abrasive Belt-type Lumber Planing Machine

Abstract

An abrasive belt-type lumber planing and dressing machine in which the workpiece is fed horizontally through the machine by the top stretch of an endless conveyor belt, to have its upwardly facing surface acted upon by a contact drum-supported endless abrasive belt traveling at high speed, and in which a downwardly biased infeed pressure shoe holds the workpiece down on the conveyor belt along a transversely extending area just ahead of the zone of contact between the workpiece and the abrasive belt, the pressure shoe being mounted in the machine by a parallelogram linkage which maintains the toe of the pressure shoe at substantially the same distance from the zone of contact between the workpiece and the abrasive belt despite changes in the elevation of the pressure shoe caused by variations in workpiece thickness.

Description

This invention relates generally to abrasive belt type sanding machines, and refers more particularly to machines of this kind that are especially designed for the planing and sizing of rough lumber.

These machines have a sanding or abrading head which comprises an endless abrasive belt trained over vertically spaced parallel rolls, the lower one being usually referred to as a contact drum since it supports the abrasive belt against the thrust of the workpiece as the workpiece moves through the machine. Usually it is the contact drum that is driven to impart high speed orbital motion to the abrasive belt.

The workpieces are carried horizontally through the machine with their top surface in contact with the drum-supported abrasive belt, by a conveyor unit vertically adjustably mounted in the machine below its sanding or abrading head. The conveyor unit has an endless power driven conveyor belt, the top stretch of which slides across and is supported -- especially directly below the contact drum -- by a smooth surfaced horizontally disposed platen. By adjusting the elevation of the conveyor unit, the machine is adapted to workpieces of different thicknesses.

A downwardly biased infeed shoe holds the workpiece down on the conveyor belt as it enters the abrading zone and comes into contact with the drum-supported abrasive belt, and an outfeed shoe holds the workpiece down as it leaves the abrading zone.

It has long been known that to meet close tolerances in the sizing of workpieces it is necessary that the toe of the infeed pressure shoe press down on the workpiece just as close as possible to the zone of action, or in other words very close to the bottom of the drum-supported abrasive belt. If that close juxtaposition is not maintained, the leading edge or end of a workpiece approaching the abrasive belt could be lifted off the platen supported conveyor belt by strains and stresses in the workpiece caused by warpage, and when that occurs the cut taken by the abrasive belt is greater than it should be to maintain uniform flatness of the abraded surface and the desired thickness dimension.

For finish sanding the conventional manner of mounting the infeed pressure shoe is entirely adequate because workpiece thicknesses are practically invariably uniform, but in planing and sizing rough lumber the conventional way of mounting the infeed pressure shoe creates intolerable consequences.

An example of the conventional way of mounting the infeed shoe may be found in the copending application Ser. No. 249,175, filed May 1, 1972 now U.S. Pat. No. 3,782,044. As illustrated in that application of Paul H. Olin, the conventional way of mounting the pressure shoe constrained it to pivotal or rocking movement about a fixed axis. With a view to applying downward pressure onto the workpiece as close as possible to the zone of action, the axis about which the shoe pivoted was so located that upon any appreciable elevation of the pressure shoe by an increase in work thickness, the toe of the shoe would collide with the abrasive belt. The sparks resulting from such contact created a serious fire hazard.

To eliminate that hazard, the shoe location was moved farther upstream, at the expense of losing the hold-down pressure where it was most needed. Such shifting of the pressure shoe location also created a gap between the shoe and the surface of the sanding belt, large enough to allow relatively big pieces or chunks of wood, knots and so forth that broke loose from the rough lumber, to collect between the shoe and the belt surface. When that happened, the sudden elevation of the toe of the shoe by an incoming over-thick piece of lumber often drove the knot or loose piece of wood against the belt with such force that the belt would be torn or cut, or at least severely damaged.

With a view to overcoming the objectionable consequences of the conventional way of mounting the infeed hold-down shoe of belt-type sanding and abrading machines, this invention has as its object to so mount the infeed shoe that its toe at all times remains at substantially the same short distance from the zone of contact between the workpiece and the abrasive belt regardless of changes in the elevation of the toe of the shoe resulting from variations in the thickness of the workpieces.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of the embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a more or less diagramatic side view of an abrasive belt-type lumber planing machine embodying this invention;

FIG. 2 is a detail sectional view through the portion of the machine at which the abrasive planing action takes place;

FIG. 3 is a cross-sectional view through FIG. 6 on the planes of the line 3--3, illustrating the relationship between the infeed hold-down shoe and the contact drum-supported abrasive belt, and the mounting structure for the shoe;

FIG. 4 is a diagrammatic view illustrating in an exaggerated way, the retention of substantially constant positional relationship between the toe of the infeed shoe and the surface of the abrasive belt despite changes in elevation of the shoe;

FIG. 5 is a perspective view of one end portion of the shoe and the adjacent shoe mounting structure; and

FIG. 6 is a top view of the structure shown in FIG. 5.

Referring to the accompanying drawings the numeral 7 indicates generally a lumber planing machine of the type to which this invention appertains. As is customary such machines have a conveyor bed 8 by which the workpieces are carried or fed horizontally through the machine with their top surface in engagement with the endless abrasive belt 9 of a sanding head 10. The sanding head is fixedly mounted in the frame of the machine and comprises an abrasive belt 9 trained about a contact drum 12 and an idler roll 13, the former being power driven to impart highspeed orbital motion to the belt.

Although not necessary for an understanding of this invention, it should be noted that the abrasive belt 9 is maintained under tension by an upward biasing force acting upon the idler roll 13 and that the manner in which the idler roll and the contact drum are mounted enables removal and replacement of the abrasive belt. For a disclosure of that sanding head structure reference may be had to the copending Bernu application Ser. No. 240,683 now U.S. Pat. No. 3,777,442, which is assigned to the assignee of the present invention. As explained in that application, in the operative condition of the sanding head its contact drum is solidly held against any displacement from a predetermined position with its axis accurately horizontal and the bottom-most part of the abrasive belt directly above a platen 14 which forms a part of the work feed conveyor bed 8.

The conveyor bed comprises a rigid horizontally disposed frame designated generally by the numeral 15 with driven and idler rolls 16 and 17 respectively journaled in its opposite ends and a conveyor belt 8 trained over these rolls. The top stretch of the conveyor belt is supported by the platen 14 and a plurality of idler rolls 19 which collectively maintain the top stretch of the belt accurately horizontal. The drive for the conveyor belt, indicated generally by the numeral 20, is conventional and comprises a motor and a suitable speed reducer.

To enable the machine to handle workpieces of different thicknesses, the conveyor bed is vertically adjustable in the conventional manner which involves imparting simultaneous actuation of a plurality of nut and jack screw supports (not shown) by which the conveyor bed is mounted in the frame of the machine. A hand wheel 21 at the side of the machine and appropriately connected with the nuts on the jack screws provides the means for adjusting the elevation of the conveyor bed.

Since the distance between the underside of the contact drum-supported abrasive belt and the platen determines the amount of stock removed from the top side of the workpieces, it is important that the workpieces be firmly held down on the platen supported conveyor belt not only at the zone of action but also as the workpieces approach that zone. For that purpose an infeed hold-down shoe 22 is provided. There is also an outfeed hold-down shoe 23 which holds the workpieces down on the platen-supported conveyor belt as they leave the zone of action, and both upstream and down stream of the zone of action there are pinch rolls 24 that coact with the idler rolls 19 of the conveyor bed to hold the workpieces in contact with the conveyor belt and assure their advance through the machine.

As explained hereinbefore, the planing and sizing of rough lumber with an abrasive belt-type machine poses a problem that is not encountered in finish sanding. This stems from the fact that rough lumber is often warped by internal stresses and its surfaces are anything but uniformly flat. Accordingly, unless the infeed shoe holds the workpiece down directly adjacent to the zone of action, the leading edge or end of the advancing workpiece may be lifted off the platen-supported conveyor belt as it approaches initial contact with the abrasive belt. If that occurs, more than the desired amount of stock will be removed making it impossible to meet close thickness tolerances.

The need for having the infeed shoe exert its hold-down pressure as close as possible to the zone of action, has always been appreciated, but with the conventional way of mounting the shoes, which simply provided for rocking movement of the shoe about a fixed axis, the greater variations in thickness and the uneveness of the surfaces of rough lumber, often lifted the toe of the shoe into contact with the abrasive belt. This was inevitable since the mounting of the shoe constrained it to pivotal movement about a fixed axis so located that the toe of the shoe traveled in an arc that intersected the circumference of the contact drum.

The obvious solution to that problem, namely moving the pivot axis of the infeed shoe farther upstream, not only objectionably withdrew the location of the hold-down pressure from its desired close proximity to the zone of action, but also created a space between the toe of the shoe and the surface of the contact-drum-supported abrasive belt that was large enough to allow knots and chunks of wood to accumulate therein, with the devasting potentiality of having the same forcefully driven against the abrasive belt by elevation of the toe of the shoe.

With the improved manner of mounting the infeed shoe which this invention provides, the desired location of the hold-down pressure is maintained despite the inevitable less-than-ideal conditions presented by rough lumber. This improved mounting features a parallelogram linkage indicated generally by the numeral 25 by which the shoe is connected with the frame of the machine. As depicted in diagrammatic FIG. 4, the linkage makes it possible for the toe 26 of the shoe to travel in an arcuate path delineated by the broken line AP which is substantially concentric with the cylindrical surface of the contact drum delineated by the arc CS. As a result throughout the complete excursion of the toe of the shoe as the shoe is lifted and descends with variations in the elevation of the top surface of the workpiece, the hold-down pressure is exerted at a location directly contiguous to the zone of action. For clarity, FIG. 4 illustrates the hold-down shoe traveling through a much greater distance than it does in practice.

The parallelogram linkage 25, which is duplicated at opposite ends of the infeed hold-down shoe, comprises a pair of links 27 and 28 mounted to swing about speed parallel horizontal axes fixed with respect to the frame of the machine and lying in a horizontal plane. The links project downwardly from the fixed axes about which they swing, and have their lower end positions pivotally connected with the shoe, the pivot axes of those connections being parallel and horizontally spaced apart the same distance as the aforesaid fixed axes.

Bearing in mind that the structure now being described is duplicated at the end of the shoe not shown in the drawings, the fixed axes about which the links 27 and 28 swing are defined by bearings 29 in a bracket 30 that is suitably fixed to the main frame of the machine. One of those bearings 29 has a stub shaft 31 journalled therein, the other rotatably mounts one end of a shaft 32 that extends across the machine to have its other end similarly supported. The links 27 and 28 which are of the same length have their upper ends respectively keyed and fixed to the stub shaft 31 and the cross shaft 32, and as best seen in FIG. 6, are laterally spaced from one another so as not to collide during movement thereof as the pressure shoe rises and falls.

The axes of the pivotal connections between the lower ends of the links and the shoe, are defined by bearings 33 in an arm 34 fixed to the shoe and projecting rearwardly from its heel. The rearmost of these bearings 33 has one end portion of a stub shaft 35 journalled therein, the other end portion of which is keyed and fixed to the lower end of the link 27; and the other of the two bearings in the arm 34 freely rotatably receives a cross shaft 36 which, like the shaft 32 extends across the width of the machine. The ends of the shaft 36 are keyed to and fixed in the lower ends of the links 28.

A spring 37, one at each end of the pressure shoe, yieldingly urges the shoe towards the contact drum and by virtue of the downward component of the arcute travel of the pivotal connections of the links 27 and 28 to the shoe which results from the approach of the links towards vertical dispositions, the spring force exerts far greater downward pressure on the shoe than would the case if the same spring acted directly downwardly on the shoe.

The spring 37 reacts between an arm 38 fixed to and projecting from the end of the shoe, and a nut 39 on a bolt 40 that passes slidably through a hole in the arm 38 and is threaded in and fixed with respect to a laterally projecting flange 41 on the bracket 30. The spring surrounds the bolt and the head 42 of the bolt limits the spring-produced motion of the shoe and thus defines the lowermost limit of the up and down movement of the toe of the shoe.

Elevation of the shoe produced in any way in opposition to the spring force is limited by an adjustable stop 43 in the form of a bolt threaded into the flange 41 with its head positioned to be engaged by the arm 38.

The shoe 23 at the downstream side of the zone of action, is mounted in the conventional way by a cross shaft 44, since it does not encounter changes in elevation of the top surface of the workpiece passing through the machine.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

Claims

The invention is defined by the following claims:

1. In an abrasive belt-type lumber planing machine wherein workpieces to be sized are fed horizontally through the machine by the platen-supported top stretch of a conveyor belt mounted in the frame of the machine, with the top surface of the workpiece in contact with the underside of a contact drum-supported abrasive belt, and wherein a downwardly biased pressure shoe has a toe portion that engages the workpiece and holds it down on the platen-supported stretch of the conveyor belt along a zone that extends transversely across the workpiece closely adjacent to the zone of contact between the workpiece and the abrasive belt, the improvement whereby upon up and down movement of the pressure shoe resulting from variations in workpiece thickness, the toe of the pressure shoe moves in an arc substantially concentric to the contact drum, so that the pressure shoe exerts downward pressure upon the workpiece at substantially the same distance from said zone of contact regardless of variations in workpiece thickness, and which improvement comprises

a parallelogram linkage mounting and connecting the pressure shoe with the frame of the machine, two of the four axes of said linkage being fixed with respect to the machine frame and the other two being fixed with respect to the pressure shoe, and all of said axes being parallel with the contact drum axis.

2. In an abrasive belt-type lumber planing machine, the improvement defined in claim 1 wherein said parallelogram linkage by which the pressure shoe is mounted comprises:

A. a first cross shaft extending transversely across the machine;

B. coaxial bearings fixed with respect to the frame of the machine and having the end portions of said first cross shaft journalled therein;

C. a first pair of spaced apart parallel links fixed to said first cross shaft and projecting radially therefrom in the same direction, to have their free ends swing in an arc about the axis of said first cross shaft;

D. a second cross shaft extending transversely across the machine in parallel spaced relation to said first cross shaft,

said second cross shaft having its end portions connected to the free ends of said pair of links;

E. bearing means on the pressure shoe having said second cross shaft journalled therein;

F. a second pair of parallel links;

G. first coaxial pivot means rockably connecting the same end of each of said second pair of links with the machine frame; and

H. second coaxial pivot means rockably connecting the other end of each of said second pair of links with the pressure shoe.

3. In an abrasive belt-type lumber planing machine, the improvement set forth in claim 2, further characterized in that

1. the axes of said first cross shaft and of said first coaxial pivot means lie in a substantially horizontal plane spaced upwardly of the pressure shoe, and

2. the axes of said second cross shaft and of said second coaxial pivot means lie in a substantially horizontal plane spaced downwardly from said other substantially horizontal plane.

4. The abrasive belt-type lumber planing machine of claim 3, wherein the toe of the pressure shoe lies in a plane spaced a short distance below said plane containing the axes of the second cross shaft and the second coaxial pivot means.

5. The abrasive belt-type lumber planing machine of claim 4, wherein all of said links are at all times substantially parallel to one another and project downwardly from the axes of their connections with the machine frame at an inclination away from the toe of the pressure shoe and at an angle to the vertical that is less than 45.degree., so that the pivotal connections of the links with the pressure shoe move along arcuate paths having both a vertical and a horizontal component as the elevation of the pressure shoe changes, and

wherein the means by which the pressure shoe is biased downward comprises a compression spring reacting between the machine frame and the pressure shoe and arranged to urge the pressure shoe horizontally towards the contact zone between the contact drum-supported abrasive belt and the workpiece.

6. In an abrasive belt-type lumber planing machine, the improvement set forth in claim 5, further characterized by stop means to limit the spring produced movement of the pressure shoe.

7. In an abrasive belt-type lumber planing machine, the improvement set forth in claim 6, further characterized by other stop means to adjustably limit spring opposed movement of the pressure shoe.

8. In an abrasive belt-type lumber planing machine, the improvement set forth in claim 5, wherein near each end of the pressure shoe there is a substantially vertical wall fixed with respect to the machine frame,

wherein the pressure shoe has an endwise projecting rigid arm on each end thereof located between said vertical wall and the contact zone,

wherein two compression springs reacting through the parallelogram linkage hold the toe of the pressure shoe down on the workpiece, and

wherein said compression springs react between said substantially vertical wall and the endwise projecting rigid arm at each end of the pressure shoe.

9. In an endless belt-type sanding machine having a sanding head with an endless power driven sanding belt and conveyor means to carry workpieces horizontally through the machine with the top surface thereof in engagement with the sanding belt of the sanding head, and a pressure shoe to hold workpieces down on the conveyor means, the improvement which comprises:

A. linkage means pivotally connected with the pressure shoe and with the frame of the machine, the latter connection being at an elevation above the pressure shoe,

said linkage means mounting the pressure shoe in the machine and constraining the shoe to movement in an arcuate path having both a horizontal and a vertical component, the former being greater than the latter; and

B. spring means reacting along a substantially horizontal line between the pressure shoe and the frame of the machine and applying a force on the pressure shoe urging the workpiece engaging portion thereof horizontally towards the zone of engagement between the workpiece and the sanding belt,

whereby the resultant downward component of the arcuate movement to which the pressure shoe is constrained presses the toe of the pressure shoe solidly against a workpiece on the conveyor means.