Method and apparatus for cutting a work piece having a surface coating

Flat multi-layered work pieces, such as panels with a decorative or finish surface coating (5), are prescored and cut through by the same saw blade to avoid damage to the surface coating. For this purpose a circular saw (1) is guided along a guide rail (7) and its saw blade (4) is adjustable to a prescoring depth and to at least one lateral prescoring position to make a first prescoring cut only through the cover layer (5) in a sawing direction in synchronism with the blade rotation direction. If necessary, the blade is adjusted to a second lateral prescoring position to make a second prescoring cut only through the cover layer (5) in a cutting direction in synchronism with the blade rotation. Finally, the saw blade (4) is adjusted to its full cutting depth and to a lateral position between the two prescoring positions and a full cut is made through the entire work piece (6) in a sawing direction counter to the rotation direction of the saw blade. A circular saw for carrying out the foregoing method has a single saw blade, stop elements, and adjustment mechanism for adjusting the single saw blade into the various necessary positions. The prescoring avoids damage to the surface coating even if it is brittle.

FIELD OF THE INVENTION 
The invention relates to a method of cutting a work piece having a surface 
coating, such as a panel work piece, e.g. of plywood or the like, with a 
plastic laminate surface coating. The invention further relates to an 
apparatus for carrying out the method. Such an apparatus is embodied, for 
example in the form of a handheld circular saw. 
BACKGROUND INFORMATION 
Cutting panels, especially panels having a decorative coating layer on one 
side, such as wall paneling, by means of a circular handsaw, involves the 
problem that the cut edge can look frayed on the "good" side of the panel. 
Thus, cutting may have to be done on the backside of the panel, which is 
inconvenient because the lines to be cut must be drawn on the back of the 
panel as a "negative" so that the correct cut appears on the front or 
"good" side of the panel. This problem is especially pronounced where the 
surface coating is hard and brittle. 
To avoid the above problem, German Patent Publication (DE-OS) 3,800,935 
describes a method of cutting panel work pieces made of wood or the like, 
such as plywood or chip-board panels having a cover layer or coating of 
plastic or hard paper, by means of a handheld circular saw which has, in 
addition to the normal saw blade, a special prescoring saw blade for first 
scoring or cutting only the cover layer in a saw moving direction which is 
"synchronous", so to speak, with the rotation direction of the saw blade. 
Then, the regular cutting saw blade is used to completely cut through the 
work piece in a direction opposite to that of the saw blade rotation. In 
this manner it is prevented that the brittle cover layer is torn or 
splintered by the main cutting saw blade during its cutting operation in a 
counter-running direction. As mentioned, the known saw needs a scoring 
blade in addition to the normal cutting blade, whereby the structural 
supporting and drive for the separate scoring blade makes the handheld 
circular saw more troublesome, heavier, and more expensive. 
In order to achieve satisfactory straight saw cuts in a simple manner it is 
generally known in the art to set the handheld circular saw onto a guide 
edge which has been positioned on the work piece, whereby a groove in the 
base plate of the circular saw cooperates with or slidingly engages a rib 
of the guide edge. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide an improved method for cutting coated or layered work pieces 
without damaging the surface cover layers of the work piece to avoid the 
above mentioned fraying; 
to cut a coated or multi-layered work piece by first scoring or cutting the 
surface coating layer in a sawing direction in synchronism with the blade 
rotation direction, and then cutting through the full thickness of the 
work piece in a sawing direction counter to the saw blade rotation 
direction, whereby the same blade is used for both operations; 
to allow a simple adjustment of the saw blade cutting depth in a handheld 
circular saw for selecting an adjustable shallow, scoring depth on the one 
hand, and alternatively to select an adjustable full cutting depth; 
to provide a method as described above, that can be used for right-angle 
cuts and for miter cuts; 
to construct an apparatus for carrying out the described method, especially 
by means of a handheld circular saw which is of relatively low cost and 
durable, simple, lightweight construction; 
to construct such a circular saw to carry out the described method with a 
single saw blade so that separate cutting and scoring blades are not 
required; 
to construct a handheld circular saw to be effectively guided along a guide 
edge for cutting straight line cuts; and 
to provide for a small lateral adjustment of the saw blade perpendicularly 
to the guide edge for easily locating the surface scoring line and the 
full depth cutting line at their respective appropriate locations. 
SUMMARY OF THE INVENTION 
The above objects have been achieved by a method for cutting coated or 
multi-layered pieces according to the invention, wherein the saw blade is 
first adjusted to a shallow scoring depth and the blade position is 
laterally adjusted to make a first scoring cut in a direction in 
synchronism with the blade rotation direction, and then, if necessary to 
obtain two neat cut edges in the surface coating, adjusting the lateral 
position of the blade to a second scoring position laterally next to the 
first scoring cut, and carrying out a second scoring cut in a sawing 
direction in synchronism with the blade rotation direction, and finally 
adjusting the saw blade to a full cutting depth and adjusting the lateral 
blade position to a position between the first and second scoring 
positions and carrying out a full depth cut through the full thickness of 
the work piece in a sawing direction counter to or opposite to the blade 
rotation direction. 
The above objects have further been achieved in an apparatus according to 
the invention, wherein a circular saw, especially a handheld saw, has a 
base plate to which is attached a console to which a guide shoe with its 
guide groove is connected to be relatively slideable in a direction 
perpendicular to the plane of the saw blade. More specifically, the 
console and guide shoe are connected to each other by a threaded bolt 
under constant spring tension urging them apart. 
Thus, when the method of the invention is carried out by the circular saw 
apparatus according to the invention, the scoring and the through cutting 
is made by the same blade, so that an additional prescoring saw blade with 
its own drive and support is not needed. This new operation is achieved 
because the saw blade is moved into the desired scoring positions by means 
of a simple sliding adjustment mechanism, so that after the prescoring cut 
or cuts have been made through the surface coating layer, the final full 
depth cut is made in a counter direction without damaging the brittle 
surface coating layer. 
The adjustment of the prescoring depth is achieved by means of a scoring 
depth stop which assures a reliable operation and which prevents the saw 
blade from contacting the work piece to a full cutting depth during the 
prescoring cut in a direction in synchronism with the saw blade rotation 
direction. In order to carry out a full depth cut, this prescoring depth 
stop must be manually released by the operator, so that the full blade 
cutting depth may be adjusted. It is a further advantage of the scoring 
depth stop, that the scoring depth may be adjusted as necessary to account 
for various thicknesses of cover layers on different work pieces, or for 
exchanging saw blades, or for regrinding saw blades which have become 
worn. 
If a work piece is merely to be trimmed, then the edge trim portion and its 
cover layer are merely scrap. Hence, it is not necessary to carry out a 
prescoring cut on the waste side of the final full depth cut. Such 
trimming or edging is the most common use for the described handheld 
circular saw, so that the operating procedure is usually considerably 
quickened because only a single scoring cut and then a single full depth 
cut need be made. 
When carrying out angular or miter cuts with the saw according to the 
invention, the saw blade swings or tilts in a direction toward the guide 
rail edge, so that it is necessary to shift the handheld circular saw in a 
direction crosswise to the guide rail edge. Such an adjustment is possible 
according to the invention so that the present circular saw may be used 
for prescoring and for carrying out angular or miter cuts also with 
prescoring.

DETAILED DESCRIPTION OF A PREFERRED EXAMPLE EMBODIMENT AND OF THE BEST MODE 
OF THE INVENTION 
FIG. 1 is a front view of a handheld circular saw 1 which is, for example, 
a so-called plunge saw having a motor housing 2 tiltably mounted on a base 
plate 3, whereby the tilting allows an adjustment of the cutting depth of 
the saw blade 4. The saw blade 4 in the saw according to the invention 
serves both for prescoring a cover layer 5 of a work piece, such as a 
panel 6 and for cutting through the entire thickness of a substrate 6' of 
the work piece 6. For example, the substrate 6' may be a wooden panel or 
plywood sheet and the cover layer 5 is a plastic laminate bonded to the 
substrate 6' to form the panel 6 with a decorative or finish coating. 
In order to guide the saw 1 for making straight cuts, a guide edge 7 may be 
placed on the surface of the panel 6 in an appropriate priate position. 
The downwardly facing side of the guide edge 7 has friction pads 7a or the 
like for securely holding the guide edge 7 on the surface of the panel. 
The saw 1 has a guide groove 9 which engages a guide rib 8 of the guide 
edge 7 to slide along the guide edge 7. Specifically, a guide shoe 10 
connected to the base plate 3 of the saw is provided with the groove 9. 
As shown in the detail view of FIG. 2, a console 11 holds the guide shoe 
10. The console 11 is removably secured to the base plate 3 by screws 12. 
The console 11 includes a threaded bore 13 into which a threaded bolt 14 
is screwed to engage the threaded hole 13 in the console 11. The outer end 
of the threaded bolt 14 ends in a lug received in an eye 16 and a lever 15 
extending therefrom. The bolt 14 passes through a block 17 connected to 
the guide shoe 10 and through a stack of disk springs or Belleville 
springs 18 arranged between the block 17 and the console 11, whereby the 
disk springs 18 constantly urge the block 17 and the console 11 apart from 
each other so as to urge the block 17 against the eye 16 of the bolt 14. 
An adjustment plate 19 is arranged between the guide shoe 10 and the 
console 11 and carries the block 17 attached to the adjustment plate 19. 
Two guide bolts 20 are connected to the adjustment plate 19 and are 
slidingly inserted in guide bores 21 of the console 11. In this manner, 
the guide shoe 10 is slideably supported on the base plate 3 and may be 
slidingly adjusted in a direction perpendicular to the saw blade 4 by 
turning the bolt 14 by means of its operating lever 15. The adjustment 
plate 19 further comprises preferably two slots 22 elongated in a 
direction perpendicular to the saw blade 4. Screws 23, which are screwed 
into or connected to the guide shoe 10, pass through the slots 22 and 
adjustably engage the adjustment plate 19. The guide shoe 10 is further 
provided with stop members 24 which are positioned within cutout grooves 
or recesses 25 of the adjustment plate 19. The stop members have elongated 
holes 26. An angle scale 27 is marked on the adjustment plate 19 along the 
edge of each groove 25 to cooperate with an angle pointer mark 27' marked 
onto each stop member 24 for indicating the position of the stop to 
thereby function as an angle indicator for miter cuts. 
In order to prevent too much play between the guide rail edge 7 and the 
guide shoe 10, an insert 28 made of an elastic, synthetic plastic material 
is arranged in a cutout of the guide shoe 10 in such a manner that a thin 
wall portion 29 of the insert 28 forms a part of the side wall 30 of the 
guide shoe 10. Thus, as shown in FIGS. 1 and 2, the guide rib 8 of the 
guide rail edge 7 is slidingly engaged by the side wall 30 of the guide 
shoe 10, whereby the side wall 30 is at least partially formed by the 
plastic insert 28. An adjustment screw 31 is arranged in the guide shoe 10 
so that its end acts on the thin wall region 29 of the plastic insert 28, 
whereby the wall portion 29 of the insert 28 may be adjusted as desired in 
a direction toward or away from the guide rib 8 to virtually completely 
eliminate any play between the guide rib 8 and the plastic insert 28 
forming the side wall 30 of the guide shoe 10. 
FIG. 3 shows the motor side view of the plunge saw or handheld circular saw 
1 according to the invention, whereby a handle 1a is connected to the 
motor housing 2. A conventional trigger switch 1b is provided on the 
inside of the handle 1a while a thumb switch 1c is provided on the outside 
of the handle for locking the trigger switch 1b in an operating position, 
if desired. A power cable 1d leads into the handle 1a. The just described 
elements 1, 2 including the saw blade 4 are tiltably connected to the base 
plate 3 by a tilting axle 32 so as to be tiltable about the axis of the 
axle 32. The blade 4 can assume several positions which are adjustable as 
will be described in more detail below. For example, position 4a is a 
scoring position while position 4b is a through cutting position of the 
blade 4. 
A protective blade guard 33 is rigidly connected to the base plate 3 to 
surround the saw blade 4 in all of its tilted positions. A prescoring stop 
in the form of a tilt lever 34 is tiltably connected to the blade guard 33 
in order to allow the saw blade 4 to be adjusted to the desired prescoring 
depth 4a by tilting the motor housing about the tilting axle 32. 
As is further shown in FIG. 4 in conjunction with FIG. 3, a guide plate 36 
comprising an elongated hole 37, is connected to the blade guard 33, for 
example, by screws extending into holes 35 in the blade guard 33. The tilt 
lever 34 is adjustably supported by an adjustment screw 38 in the 
elongated hole 37 so as to be tiltable and adjustable in a substantially 
vertical direction. The tilt lever 34 is urged in a direction toward the 
motor housing 2, by a tension spring 39 attached to the guide plate 36 
until the lever 34 comes to rest against a surface 40 forming a stop 
element on the guide plate 36. A further stop element 41 is connected to 
the motor housing 2 in a position so that the stop element 41 contacts a 
stop nose 42 of the tilt lever 34 when the saw blade 4 is in its 
prescoring position 4a as shown especially in FIG. 3 by a dashed line 
circle. 
In order to carry out the final cut through the entire thickness of the 
work piece or panel 6, the tilt lever 34 is pushed in a counterclockwise 
direction so that the stop nose 42 releases the stop element 41 and so 
that the motor housing 2 may be tilted into the desired full plunge 
cutting depth position 4b shown by a dash-dotted line circle in FIG. 3, by 
tilting about axle 32. Tilt lever 34 further comprises a slanted run-up 
surface 43 which cooperates with or contacts the stop element 41 during 
the return tilting of the motor housing 2 for moving the tilt lever 34 
outwardly so that the stop element 41 can again pass over the stop nose 
42. 
As shown in FIG. 4, the blade guard 33 is provided with a guide surface 44 
which forms with the guide plate 36 a guide slot 45. A stop element 41 
reaches into and slidingly engages the guide slot 45 in such a manner that 
the motor housing 2 and thus the saw blade 4 is reliably guided during the 
cutting movement. 
In order to carry out the method according to the invention, the present 
handheld circular saw 1 is first shifted transversely to the base plate 3 
approximately 0.6 mm by pushing the lever 15 into the position shown in 
FIG. 2. Then, the motor housing 2 is tilted from its resting position in a 
counterclockwise direction until stop element 41 contacts stop nose 42 as 
shown in FIG. 3. In this position 4a the saw blade 4 protrudes downwardly 
by about 3 mm beyond the guide rail 7. In this position of the saw blade 
4, the circular saw 1 is pulled along the guide rail 7 in the direction of 
the arrow 46 shown in FIG. 3, so that the cover layer or coating 5 of the 
work piece or panel 6 is prescored in the same direction as the rotation 
direction 4' of the saw blade 4. Then, by turning lever 15 by 180.degree., 
the circular saw 1 is shifted transversely to the base plate 3 into a 
second lateral prescoring position in which the saw 1 is again moved along 
the guide rail 7 in a synchronous cutting direction shown by arrow 46 to 
prescore the cover layer or coating 5 along a line parallel to and 
adjacent to the first prescoring line. In this manner, a groove has been 
formed in the cover layer 5 which is wider than the blade thickness of saw 
blade 4 by a maximum of 0.3 mm on each side of the saw blade 4, thereby 
providing the clearance required for avoiding marring the finish surface 
of the coating 5. 
Finally, lever 15 is turned into a vertical position so that the circular 
saw 1 is moved laterally into a centered position between the first and 
second prescoring positions. Then, the prescoring stop 34 is manually 
tilted in a counterclockwise direction, whereby the motor housing 2 and 
the saw blade 4 are also tilted about the tilting axle 32, shown in FIG. 
3, in a counterclockwise direction, for example, against a maximum cutting 
depth stop which is not shown, to place the blade and the saw into the 
dash-dotted position 4b so that the final full depth cut can be made 
through the work piece or panel 6 in a counter cutting direction shown by 
arrow 47. 
As shown in FIG. 3, the blade rotation direction at the down side of the 
saw blade 4 is directed against or counter to the advance direction 46 of 
the saw during scoring cut. However, at the upper blade side the blade 
rotation direction is directed in the same direction as the saw advance 
direction 46. The same considerations apply to the arrow 47 representing 
the full cut moving direction of the saw. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.