GB1566547A

GB1566547A - Dressing apparatus and methods

Info

Publication number: GB1566547A
Application number: GB2713775A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-09-27
Filing date: 1976-09-27
Publication date: 1980-05-08

Description

(54) DRESSING APPARATUS AND METHODS (71) I, JAMES FRANCIS THOMAS, a British subject of 29 Colwyn Crescent, Colwyn Bay, Clwyd LL28 4RH North Wales, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to dressing apparatus and methods, particularly to apparatus and methods for dressing the blades of squeegees, such as are used in screen printing and in the production of printed circuits. Hereinafter, such dressing apparatus will be referred to as a "squeegee dresser".

In the process of screen printing a squeegee is used to apply ink, paint or dye through a stencil onto the surface of the work. Many screen printing applications require the reproduction of fine detail and thus sharp definition. A number of factors contribute to the sharpness of definition, but the primary controlling factor is the condition of the edges of the squeegee blade. A rounded or ill-defined edge to the squeegee blade will produce a heavy deposit of ink or like material on the workpiece, resulting in both poor definition and an excessive use of ink. On the other hand, a sharp edge which is regularly maintained will produce a well-defined and clean reproduction of the stencil. This is particularly important in the manufacture of printed circuits for the electronic industry and also in the production of multi-colour pictorial prints.

Conventional squeegee dressing machines normally use a belt-sander for sharpening the squeegee blade edges. However, this arrangement is unsatisfactory for precision work because of the difficulty of maintaining controlled contact between the blade and the moving belt. This problem is inherent in the use of a long moving belt whose main support and drive is provided by rotating pulleys which may be of the order of 12 inches apart.

It is an object of the present invention to provide a squeegee dresser which will resharpen a squeegee blade to produce a sharp defined working edge and thus to overcome the aforementioned disadvantages of conventional dressing machines.

In accordance with one aspect of the present invention there is provided dressing apparatus comprising a base upon which a squeegee is arranged to be placed, cutting means mounted on the base, and a guide which is pivotably mounted on the base to be movable towards and away from the cuting means, the guide defining a rectilinear surface which is arranged to abut the squeegee and to exert pressure thereon in a direction to urge the blade of the squeegee against the cutting means, a space between the cutting means and said surface defining a path which is substantially at right angles to said direction and along which the squeegee is caused to travel.

In accordance with a further aspect of the invention there is provided a method of dressing the blade of a squeegee comprising the steps of placing the squeegee on a base between a fixed cutting means and a pivotably movable guide, advancing the guide until a rectilinear surface thereof abuts the squeegee with the blade thereof in engagement with the cutting means, removing the squeegee, further advancing the guide through a predetermined distance towards the cutting means, and passing the squeegee along the path between the guide and the cutting means thereby to dress the blade.

Preferably, the guide includes stepping means by which the rectilinear surface thereof can be moved a predetermined distance towards the cutting means after a squeegee has been placed in position on the base for an initial setting and has thereafter been removed.

The guide may include clamping means to clamp it to the base after the initial positioning of the squeegee between the cutting means and the guide, the stepping means then being operable after the squeegee has been removed to move the guide the predetrmined distance towards the cutting means to provide a controlled depth of cut on the squeegee blade when the squeegee is caused to travel along the path between the cutting means and the guide surface.

The stepping means may comprise an adjustment screw, or alternatively a solenoidcontrolled mechanism, or alternatively a stepping cam, for example a rectangular cam. For example, the guide may comprise a housing, one face of which constitutes said rectilinear surface, locking means engageable with the base to hold part of the guide in a fixed position, and a stepping cam within the housing and which upon rotation thereof causes the guide housing to move through said predetermined distance towards the cutting means relative to the locked portion of the guide.

In order that the invention may be fully understood, a number of embodiments in accordance therewith will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a general perspective view of squeegee dressing apparatus in accordance with the present invention to illustrate the relationship of the parts; Fig. 2 shows a first form of guide stepping means; Fig. 3 shows a second form of guide stepping means; Fig. 4 is a top plan view of a modified form of guide, with the internal stepping mechanism omitted; and, Fig. 5 is a sectional view taken along the line V-V of Fig. 4 and showing details of the stepping cam mechanism.

Referring first to Fig. 1 this shows the squeegee dressing apparatus indicated generally at 1. The apparatus comprises a base 2 upon which is mounted a high speed grinding wheel fuot shown) housed in a control box 3. A knob 4 controlling an on/off switch is used to control the speed of rotation of the grinding wheel. The type of grinding wheel that is used will depend upon the product to be dressed; a burr-type grinding wheel may be used.

An elongate guide 5 is pivotally mounted on the base 2 for rotation about a pivot pin 6. The base 2 has an arcuate slot 7 through it, the slot 7 being on an arc of a circle described about the pivot 6. The outer end portion of the guide 5 traverses this slot by pivotal movement of the guide. The guide 5 comprises a base portion 8 and an upturned flange 9 along its leading edge defining a rectilinear surface. Adjacent to the end of the guide remote from the pivot 6 is a stepping mechanism comprising a clamping means in the form of a screw-threaded locking knob 10 and a solenoid stepping mechanism 11. The stepping means is shown in more detail in Fig. 2 which is slightly modified in that the locking knob 10 is here replaced by a course locking knob 12 which acts by drawing up a locking plate beneath the base 2. Two guide pins 13 extend downwardly through the slot 7 into the bottom locking plate from an upper locking plate 14 which projects out beyond and behind the base portion 8 of the guide 5. A solenoid 11 is carried by the upper locking plate 14 on arms extending up through a hole in the guide base 8, and a bracket 15 is secured to the base portion 8 adjacent to the solenoid armature. when the locking knob 10 or 12 is tightened to clamp the locking plate 14 to the base 2 and when the solenoid 11 is actuated, the guide 5 will be moved a predetermined distance a towards the grinding wheel due to the attraction of the bracket 15 by the solenoid.

An alternative form of stepping means is shown in Figure 3 and comprises a locking knob 16, which performs the same function as knob 10 of Fig. 1 and knob 12 of Fig. 2, and a micro meter-adjuster screw 17 for providing the movement of the guide 5 through a predetermined distance towards the grinding wheel.

Fig. 1 also shows a squeegee 18 lying on the base 2 between the guide surface 9 and the grinding wheel, the squeegee including a blade portion 19 which has its surface to be dresed facing the grinding wheel.

Before the description of the preferred form of stepping means illustrated in Figs. 4 and 5 a description will be given of the method of use of the dressing apparatus described above.

The squeegee 18 is placed on the base 2 generally as shown in Fig. 1 The guide 5, with the locking knob 10 released, is then rotated about the pivot 6 until the straight edge 9 abuts the squeegee and the squeegee blade 19 is in contact with the grinding wheel. When this initial position has been set up the coarse locking knob 10 is tightened. The squeegee is then temporarily removed and the solenoid 11 or the adjusting screw 17 is actuated or turned as the case may be to move the guide 5 through the predetermined distance towards the grinding wheel. Then, the squeegee is re-placed on the base 2 so that its handle is abutting the straight edge 9, whereupon the squeegee can be pushed manually or automatically past the grinding wheel to dress and sharpen the blade 19. It will be appreciated that the direction of travel of the squeegee past the grinding wheel is substantially at right angles to the direction of the force exerted by the guide against the squeegee as it is pushed past the grinding wheel. The amount of material removed from the blade 19 corresponds to the required depth of cut determined by the predetermined distance to which the guide has been moved. The depth of cut is usually of the order of between 0.02 and 0.05 inches. This depth of cut ensures that regularly sharpened squeegee blades do not have an excessive amount removed, in contrast to what is often the case with manually set squeegee dressers.

Figs. 4 and 5 show an alternative form of guide and stepping mechanism. In this arrangement the guide is in the form of a box housing 20 having a bottom wall 21, peripheral walls 22, and a cover plate 23. In Fig. 4 the cover plate 23 is omitted. A bracket 24 is welded within the housing to provide support for the guide pivot assembly (not shown) by which the guide is mounted on the base board 25 of the machine. The bottom wall 21 of the housing is provided with a circular hole 26 and an elongated hole 27 for purposes which will become apparent later. Nylon bushes 28 are provided in the bottom wall 21 of the housing to aid movement of the guide over the base board 25.

The stepping mechanism is here mounted within the guide housing 20. A square crosssection hollow tube 30 is supported adjacent to the bottom wall 21 of the housing and a screw-threaded bolt 31 is threaded through the tube 30, down through the recess 27, and into a threaded receiving hole in a locking plate 32 beneath the base board 25. The bolt 31 thus extends down through the arcuate slot which, as in Fig. 1, is provided in the base board 25. The locking plate 32 has a hank-bush 33 welded to its underside and a bolt 34 having a knob 35 at its upper end extends down through the tube 30 and the circular recess 26 in the bottom wall 21 of the housing to be received in the bush 33. A second knob 36 is provided on the top of the guide and this carries a spindle 37 which extends down through the tube 30 and through the hole 27 in the bottom wall 21 of the housing, and then down through the locking plate 32 where it is fitted with a nut. At this end of the tube 30 the two side walls of the tube are cut back to form side recesses in order that a rectangular cam 38 can be mounted on the spindle 37 between the upper and lower webs of the tube. The cam 38 is pinned to the spindle 37 with washers 39 above and below it. The cam 38 is rectangular with one dimension differing from the other by for example 0.02 inches.

This difference in the two dimensions of the rectangle will be equal to the depth of cut and to the incremental distance through which the guide is advanced during operation of the machine. It is essential that the spindle hole through the cam is exactly central so that the feed distance is identical whichever way thec am is set into operation.

It would alternatively be possible to use a cam specially shaped so that rotation of the cam through successive angles of 90" would result in successively greater depths of cut. However, for the majority of applications, it will be sufficient to use a rectangular cam as aforementioned.

The cam 38 is adapted to act against a cam block 40 which is welded to the inside face of the leading edge of the guide hous ing 20. The other end of the tube 30 is cut away to form a pair of tongues which act as retaining seats for one end of a helical spring 42 which at its other end abuts against the internal face of the housing wall.

This spring 42 acts to urge the tube 30 and thus the cam 38 towards the cam block 40.

From the foregoing description of the method of use of the apparatus shown in Fig. 1 the manner of use of the modified guide shown in Figs. 4 and 5 will be evident. First of all, the machine is first set by rotating the knob 35 to lock the plate 32 against the base board 25. This is carried out with the housing 22 lightly pushing the squeegee blade against the abrasive wheel, and with the position of the cam 38 such that its two longer sides lie parallel to the face of the cam block 40. The squeegee blade is then removed from the machine and the cam operating knob 36 is turned through 90 , thereby rotating the cam 38 through 90" and displacing the cam block 40 and the guide housing 20 to the right as viewed in Fig. 5 through a distance equal to the predetermined depth of cut. The motor for the grinding wheel is then switched on and the squeegee is passed along the leading edge of the guide past the grinding wheel.

Although the squeegee is normally moved manually past the grinding wheel, means may be provided for moving the squeegee automatically, preferably mechanically, past the abrasive wheel.

WHAT I CLAIM IS: 1. Dressing apparatus comprising a base upon which a squeegee is arranged to be placed, cutting means mounted on the base, and a guide which is pivotably mounted on the base to be movable towards and away from the cutting means the guide defining a rectilinear surface which is arranged to abut the squeegee and to exert a pressure thereon in a direction to urge the blade of the squeegee against the cutting means, a space between the cutting means and said surface defining a path which is substantially at right angles to said direction and along which the squeegee is caused to travel.

2. Apparatus as claimed in claim 1, in which the guide comprises an elongate member which is pivoted adjacent to one end

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. past the grinding wheel. The amount of material removed from the blade 19 corresponds to the required depth of cut determined by the predetermined distance to which the guide has been moved. The depth of cut is usually of the order of between 0.02 and 0.05 inches. This depth of cut ensures that regularly sharpened squeegee blades do not have an excessive amount removed, in contrast to what is often the case with manually set squeegee dressers. Figs. 4 and 5 show an alternative form of guide and stepping mechanism. In this arrangement the guide is in the form of a box housing 20 having a bottom wall 21, peripheral walls 22, and a cover plate 23. In Fig. 4 the cover plate 23 is omitted. A bracket 24 is welded within the housing to provide support for the guide pivot assembly (not shown) by which the guide is mounted on the base board 25 of the machine. The bottom wall 21 of the housing is provided with a circular hole 26 and an elongated hole 27 for purposes which will become apparent later. Nylon bushes 28 are provided in the bottom wall 21 of the housing to aid movement of the guide over the base board 25. The stepping mechanism is here mounted within the guide housing 20. A square crosssection hollow tube 30 is supported adjacent to the bottom wall 21 of the housing and a screw-threaded bolt 31 is threaded through the tube 30, down through the recess 27, and into a threaded receiving hole in a locking plate 32 beneath the base board 25. The bolt 31 thus extends down through the arcuate slot which, as in Fig. 1, is provided in the base board 25. The locking plate 32 has a hank-bush 33 welded to its underside and a bolt 34 having a knob 35 at its upper end extends down through the tube 30 and the circular recess 26 in the bottom wall 21 of the housing to be received in the bush 33. A second knob 36 is provided on the top of the guide and this carries a spindle 37 which extends down through the tube 30 and through the hole 27 in the bottom wall 21 of the housing, and then down through the locking plate 32 where it is fitted with a nut. At this end of the tube 30 the two side walls of the tube are cut back to form side recesses in order that a rectangular cam 38 can be mounted on the spindle 37 between the upper and lower webs of the tube. The cam 38 is pinned to the spindle 37 with washers 39 above and below it. The cam 38 is rectangular with one dimension differing from the other by for example 0.02 inches. This difference in the two dimensions of the rectangle will be equal to the depth of cut and to the incremental distance through which the guide is advanced during operation of the machine. It is essential that the spindle hole through the cam is exactly central so that the feed distance is identical whichever way thec am is set into operation. It would alternatively be possible to use a cam specially shaped so that rotation of the cam through successive angles of 90" would result in successively greater depths of cut. However, for the majority of applications, it will be sufficient to use a rectangular cam as aforementioned. The cam 38 is adapted to act against a cam block 40 which is welded to the inside face of the leading edge of the guide hous ing 20. The other end of the tube 30 is cut away to form a pair of tongues which act as retaining seats for one end of a helical spring 42 which at its other end abuts against the internal face of the housing wall. This spring 42 acts to urge the tube 30 and thus the cam 38 towards the cam block 40. From the foregoing description of the method of use of the apparatus shown in Fig. 1 the manner of use of the modified guide shown in Figs. 4 and 5 will be evident. First of all, the machine is first set by rotating the knob 35 to lock the plate 32 against the base board 25. This is carried out with the housing 22 lightly pushing the squeegee blade against the abrasive wheel, and with the position of the cam 38 such that its two longer sides lie parallel to the face of the cam block 40. The squeegee blade is then removed from the machine and the cam operating knob 36 is turned through 90 , thereby rotating the cam 38 through 90" and displacing the cam block 40 and the guide housing 20 to the right as viewed in Fig. 5 through a distance equal to the predetermined depth of cut. The motor for the grinding wheel is then switched on and the squeegee is passed along the leading edge of the guide past the grinding wheel. Although the squeegee is normally moved manually past the grinding wheel, means may be provided for moving the squeegee automatically, preferably mechanically, past the abrasive wheel. WHAT I CLAIM IS:

1. Dressing apparatus comprising a base upon which a squeegee is arranged to be placed, cutting means mounted on the base, and a guide which is pivotably mounted on the base to be movable towards and away from the cutting means the guide defining a rectilinear surface which is arranged to abut the squeegee and to exert a pressure thereon in a direction to urge the blade of the squeegee against the cutting means, a space between the cutting means and said surface defining a path which is substantially at right angles to said direction and along which the squeegee is caused to travel.

and which is provided with stepping means adjacent to the other end thereof by means of which the guide can be advanced by a predetermined amount towards the cutting means.

3. Apparatus as claimed in claim 2, in which the stepping means includes means to lock a part of the guide to the base, and means effective after such locking to advance the rest of the guide including its rectilinear surface towards the cutting means.

4. Apparatus as claimed in claim 2 or 3, in which the stepping means includes a mechanical adjustment screw to set the depth of cut.

5. Apparatus as claimed in 2 or 3, in which the stepping means comprises a solenoid mounted on the guide in such a manner that actuation of the solenoid causes an advancing movement of the guide towards the cutting means through a predetermined distance.

6. Apparatus as claimed in claim 2 or 3, in which the stepping means includes a cam rotatable to effect an advancing movement of the guide through a predetermined distance towards the cutting means.

7. Apparatus as claimed in claim 6, in which the cam is a rectangular cam having its longer dimension of the order of 0.02 to 0.05 inches greater than its shorter dimension.

8. Apparatus as claimed in claim 6 or 7, in which the cam is mounted on a spindle extending centrally through the cam, the cam being positioned within a recessed end of an elongate rectangular cross-section tube held within a box-type guide, the other end of said tube providing a seat for spring means acting to urge the tube and cam towards a cam block secured to the internal face of the guide housing wall which defines said rectilinear surface.

9. A method of dressing the blade of a squeegee comprising the steps of placing the squeegee on a base between a fixed cutting means and a pivotally movable guide, advancing the guide until a rectilinear surface thereof abuts the squeegee with the blade thereof in engagement with the cutting means, removing the squeegee, further advancing the guide through a predetermined distance towards the cutting means, and passing the squeegee along the path between the guide and the cutting means thereby to dress the blade.

10. A method as claimed in claim 9, in which the further advance of the guide through said predetermined distance is effected by the rotation of a control knob fitted to a spindle carrying a cam dimensioned to effect said further advancing movement by rotation of the control knob.

11. Dressing apparatus substantially as hereinbefore described with reference to the accompanying drawings.

12. A method of dressing the blade of a squeegee substantially as hereinbefore des cribbed with reference to the accompanying drawings.