Note: Descriptions are shown in the official language in which they were submitted.
CA 02076330 2002-10-15 L°11 / 7 1
DRYWALL SANDER
FIELD OF THE INVENTION
This invention relates to motorized sanders and in
particular to rotary power driven sanders.
DESCRIPTION OF THE PRIOR ART
In drywall construction it is necessary, after taping
and filling the joints between the panels, to sand the joint
to reduce it to the same level as the adjacent panels and thus
obscure any evidence of a joint.
In the past this had been done with manual sanders
consisting simply of a supporting block and a section of
abrasive material on the block. An improved power operated
sander was disclosed and claimed in U.S. Patent No.4,782,632
issued July 11, 1988.
While the sander disclosed in that patent has proved
useful, there are certain improvements which we have since
evolved which improve its operation and convenience. In part-
icular, the presence of the vacuum hose makesthe apparatus
disclosed in that patent somewhat clumsy. Replacement of the
sanding surface was not discussed but required the operator
to remove a retaining bolt which held the sanding disc in place.
This obviously caused some delays in operating the sander.
Extraction of the dust during operation of the sander
is of great importance and design of the areas through which
the dust passes determines the continuing effectiveness of
the extraction system as does also the selection of the vacuum
system.
There are also certain peculiarities to the sanding of
drywall which may not be of the same importance in other
sanding applications. The material used to cover the tape and
fill the joint is easily abraded and care must be taken to
avoid scoring the surface. The paper surface of the plaster
board is also easily damaged when sanding. Selection of suitable
chacteristics of the abrasive material becomes of great imp-
ortance.
The amount of force applied to the surface by the rot-
ating disc of the sander and concentration of force on part-
icular areas also affects the final result.
a tW.~:3.
SUMMARY OF THE INVENTION
In accordance with the present invention the vacuum
line is incorporated into the handle of the sander thus elim-
inating the loose vacuum line ajacent the head. The shroud
surrounding the sanding disc is contoured to provide a smooth
substantialy constant crossectioned duct for air flow from
the head into the handle and out to the vacuum system which
is selected to handle the large quantities of dust produced
during the sanding of drywall.
The abrasive disc used for sanding is specialy designed
in view of the nature of the surface being sanded. In the case
of drywall the abrasive disc has a foam backing and is faced
with a grit of suitable size. Preferably the grit is coated
directly on the foam but in any case the disc must retain its
flexibility. The foam is selected to have a non-linear comp-
ression chacteristic so that when compressed, the force required
to produce a given deflection increases as the foam is comp-
ressed. The foam also has what may be termed a quick memory,
that is, when compressed and released the foam quickly recovers
its original thickness.
The diameter of the abrasive disc and its associated
drive plate is selected to operate over as large an area as
possible while recognizing the limitations of motor horse-
power and weight in a hand tool and the hazard of excessive
peripheral velocity. Suitable diameters may be 6 to 10 inches.
Finally, to increase efficiency the disc is held on trie drive
plate by a quick release high compression locking device which
permits rapid and positive replacement of worn abrasive discs.
A clearer understanding of our invention may be had
from a consideration of the following description and drawings
in whicha
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a view, partialy in section, of a sander
in accordance with the invention.
Figure 2 is ase~tional view of the sanding head 10
of figure 1 on section line II-II of figure 3.
Figure3 is a plan view of the bottom of the sanding
head 10 of figure 1.
Figure 4 is an enlarged view of the locking device
used to retain the abrasive disc.
~~'Q,~l~~~~~
-3-
DESCRIPTION OF THE PREFERED EMBODIMENT
Considering first figure l,it will be seen that a motor
1, having a housing 2 and a rear extension 3 behind the motor,
is connected to a wand 4. The shaft of the motor is connected
to a flexible drive 5 comprising a flexible drive shaft 6 supp-
orted by bearings within a flexible sheath 7 which passes thro-
ugh a seal 8 within wand 4 which separates the junction of the
motor shaft and the flexible drive from the interior of the
wand 4. A hole 9 on the motor side of seal 8 allows the flex-
ible drive to be at atmospheric pressure.
Sanding head 10 is mounted on a bracket 11 which con-
sists of a pair of arms extending from wand 4. The ends of the
arms are pivotaly connected to a pair of legs 12 which extend
from plate 13. A shroud, preferably formed from transparent
plastic,encloses the drive plate 15 and abrasive disc 18.
As shown in figure 2, the drive plate 15 is mounted on
a shaft 16 supported in bearing 17 which in turn is mounted
on plate 13. Shaft 16 is connected to flexible drive shaft 6
Abrasive disc 18 comprise an annulus of open-celled
foam 19 coated on its surface with a suitable abrasive 20.
The abrasive 20 is fastened to the foam 19 by means of a soft
flexible adhesive which ensures that the whole disc remains
flexible. The surface of drive plate 15 is provided with a
frictional drive surface 21 for engaging the foam 19. This
drive surface may consist of a coarse abrasive or some other
surface treatment capable of engaging the open cells of foam
19 in such a manner as to reliably drive the abrasive disc 18.
A typical alternative treatment would be a portion of hook
material such as is used in hook and loop fasteners sold
under the trademark VELCRO.
The drive plate 15 is mounted on a hub 22 which in
turn is mounted on shaft 16. The abrasive disc 18 is held
down on drive plate 15 by retainer disc 23 which includes a
plurality of protuberances 24 which cause localized compression
of the foam 19. The retainer disc 23 is held in place by
a twist lock bayonet type fastener 25 shown in more detail
in figure 4.
The periphery of shroud 14 includes a resilient mat-
erial but as shown, unlike the sander of 4,782,632 , the
resilient material is made up of bristles 26 which not only
a -., s~ r'3 ~.a
~~ fJ
-4-
provide a resilient partial air seal but also scrub the surface
to assist in dislodging the dust.
Vacuum line 27 is connected to the shroud 14 and an
air passage is therefore provided from the periphery of the
the shroud,around the abrasive disc, between the plate 13 and
the shroud 14, past bearing 17 and into vacuum line 27 through
wand 4 and out through stub tube 28 and into vacuum hose 29.
Air is also drawn in through hole 9 through flexible drive
sheath 7 and out through bearing 17 and into the shroud 14 thus
producing a clean air flush for the flexible drive preventing
the entry of abrasive drywall dust into the flexible drive and
its bearings.
As has been indicated a suitable vacuum source must be
provided recognizing the quantity and nature of the dust. A
canister type vacuum cleaner with a collector bag ( not shown)
is connected to vacuum hose 29.
To ensure proper movement of the dust through the
system it is desirable that the air velocity be maintained
as uniform as possible with minimal eddy formation, Corners
of the shroud are therefor curved as shown in figure 2 and
the crossectional area of the air path is maintained as cons-
tant as possible. The gap around the edge of the periphery of
the abrasive disc must also be maintained small to produce
a high velocity for effective pickup of dust.
It will be seen that the pivot points of the sanding
head 10 on legs 12 are further from the end of wand 4 than the
center of the head where theflexible drive 5 and the vacuum line
27 enter the head. The forces imparted by the compressed
vacuum line and the flexible drive tend to cause a clockwise
rotation of the head on the pivots thus tending to cause the
rear edge of the head to encounter the wall surface being
sanded before the front edge. This will be found to facilitate
proper operation of the sander.
Because the shroud is not attached to plate 13 but is
free to slide up and down on legs 12 the location of the
abrasive disc relative to the shroud is not fixed but depends
on the force applied to plate 13 from the wand through legs 12.
It is therefor possible for the operator to vary the pressure
on the abrasive disc by varying the force he applies to the
wand without necessarily distorting the bristles 26 and the
y~ t F r ~.
~~~ ~~~au
-5-
shroud does not interfere with the application of pressure to
the abrasive disc.
OPERATION
In operation the user places an abrasive disc on the
drive plate l5,inserts the retainer disc 23 and the fastener
25 and forces the bayonets of the fastener downonto matching
pins 30 on hub 22 ( see figure 4), thus locking the retainer
disc down on the abrasive disc ensuring that it is firmly
retained. The friction drive surface of drive plate 15 engages
the foam backing 19 and provides a constant uniform drive for
the abrasive disc. The user then presses switch 31 on the motor
causing the motor to drive the flexible drive shaft 6 and
drive plate 15 and places the sander against the wall. The
couple produced by the location of legs 12 and the location
of the compressed vacuum line 27 cause the rear edge of the
sanding head to contact the wall first but as the user in-
creases the pressure applied by the wand the front edge of
the sanding head engages the wall, thus providing a gentle
approach to the surface to minimize gouging and scratching
of the surface of the paper. With increasing pressure the
shroud is pushed back or the bristles are deflected and
increasing pressure is applied to the abrasive disc. As the
abrasive disc encounters the crown of the joint which is
being sanded or other bumps or lumps of speckle the foam
backing is compressed localy and, due to its non-linear
compression characteristic,the pressure applied to the high
points is substantialy greater than the pressure applied to
the surface of the paper. The quick memory of the foam however
ensures that, as the disc leaves the high point the foam quickly
returns to its original shape and uncompressed state.
If, at the same time as the user presses switch 31 he
also activates the vacuum system, the air at the wall surface
will be drawn under the shroud 14 through the vacuum line 27,
down wand 4 and out through vacuum hose 29 and into the can-
ister. Air will also be drawn in through hole 9, through flexible
drivesheath 7 and through bearing 17 into the shroud.
~ ~~ '~
Continued mavement, in the normal sanding action will
ensure that a smooth surface is produced with almost no free
dust and, if the abrasive is properly selected, the surface
will have a finish superior to that produced by hand sanding.
The finish produced can closely match the texture of the paper
surface of the drywall, thus resulting in a uniform appearance
when the wall is painted, even with gloss or semigloss paint.
Selection of the grit size of the abrasive will depend upon
variables such as the nature of the spackle, desired smoothness
and the -time element. Such grit size may vary between 60 and
280 grit but for most applications sizes between 100 and 180
will be found most suitable.The transparent shroud allows the
user to see how much dust is being removed thus providing a
direct indication of the abrasive disc cut rate and vacuum
Performance and a guide of how quickly to progress in the
sanding operation.
Thickness of the foam backing will normaly lie between
3/8" and 1". Thickness less than 3/8" will not provide suffic-
ient flexibility while thicknesses greater than 1" are waste-
full and may exhbit undesirable response to drive energy.
Since the rear edge of the surface of the abrasive
disc is primarily in contact with the wall, there is a tendency
for the head to move sideways in response to the direction of
rotation of the disc. This may be advantageous when working
into corners and may cause the head to move into the corner
and maintain light pressuxe:against the adjacent wall. It is also
convenient when sanding large surfaces. If the wand is held in
a transverseposition the frictional engagement of the abrasive
disc with the wall surface will cause a lifting action on the
sander counteracting gravity and reducing fatigue of the user.
It will also be evident that in working along the top
edge of a wall adjacent the ceiling, the sander can be position-
ed in a manner such as to cause the head to gently contact the
ceiling while sanding the wall portion adjacent the ceiling. If
the clearance between the abrasive disc and the shroud is kept
small to improve dust pick-up it will also provide maximum
acces to the corner surfaces leaving minimum areas to be hand
sanded.
While other drive system may be possible, it appears
that electric drive is most advantageous since it is relat-
ively light, requires no auxiliary equipment and may provide
~i y ~A '.~
ig '~ ~ t~ ?:t t.7
'j
variable speed. It has been found that a small universal motor,
of fractional horsepower, such as is normaly used for electric
drills, is quite adequate to drive the sanding disc at sufficient
speed to permit .rapid sanding with acceptable finish.
while described with particular reference to drywall
sanding it will be understood that the device may find app-
lication in other situations where large quantities of dust are
produced in a sanding operation and the surfaces being sanded
are relatively delicate.
A lamp such as lamp 33 which contains its own recharg-
able energy source or is powered from the motor power source
may be found of particular advantage when working in poorly
illuminated locations.
Because of the length of the wand 4 and the weights
involved it may be found to be desirable to apply a coating
or sleeve, such as sleeve 32 over the wand to provide a better
grip for the user. A resilient rubbery material,such as an
adhesive backed,vinyl, textured traction material may be
found to add to the convenience of the user.
