Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 7
The present invention relates to manually operated
rotary disc sanders and more in particular to an abra-
sive disc assembly for these machines.
A sander, as intended throughout this specification,
may be any rotary disc machine for manual use wherein a
disc bearing pad is rotated at a high speed by an elec-
tric or c~mpressed air operated motor contained inside
an ergonomically shaped machine body provided with
suitably shaped handle means and to which this bearing
pad a consumable abrasive or polishing disc may be
fastened. As an example, such a rotary disc sanding ma-
chine provided with an abrasive disc assembly will be
particularly suited for sanding a car body.
Heretofore commercially available sanders are pro-
vided with a relatively flexible disc bearing pad inthe form of a diYc of rubbery material having a substan-
tially flat surface wherein an abrasive disc is
fastened, although in same- applications e.g. for
sandin~ wood, the disc bearing rotary pad may also be
substantially rigid. Abrasive discs ~ear rapidly ~ith
use and must be replaced frequently by the operator.
Consumable a~rasive discs are normally composed of a
backing or support layer, normally a reinforced paper
sheet or a synthetic sheet material, on a face of which
abrasive particles are cemented for proviæing a suffi-
ciently durable abrasive surface of a graded granu-
larity (finess). The other face of the abrasive discs
may be provided with a self-adhesive layer, customarily
protected by means of a protection foil to be peeled
off before adhering a new disc on the flat smooth sur-
face of the rubbery pad of the machine. Another type of
abrasive disc assembly available on the market utilizes
a Velcro ~T.M.) fastener. The abrasive discs are pro-
duced with a felt layer over the fastening surface of
the disc and the rubbery disc pad of the sander is pro-
vided with tiny Velcro hooks for gripping on the felt
2 ~
surface of the replaceable abrasive disc. Other ma-
chines are known which utilize semirigid consumable
abrasive discs which may be fastened directly to the
pad by means of a central screw passing through a cen-
tral hole of the disc. However these abrasive disc as-
semblies are not so satisfactory in use and have had a
limited diffusion.
Notably hand operated sanders are coupled by means
of a flexible hose to a vacuum generating apparatus for
sucking the dust produced while sanding. To this pur-
pose the rotary disc support also when provided with a
cushoning rubber pad on the surface thereof have a
series of apertures and the abrasive discs are also pro-
duced with similarly located holes which must be
aligned with the holes of the disc pad when placing a
new abrasive disc on the surface of the pad. Through
these passages the dust produced in the working area
may be sucked by the dust control system to which the
sander is coupled. These known abrasive disk assemblies
have drawbacks. The flexible consumable abrasive discs
must be produced with a special backing: be it an
adhesive back surface or a felt back surface. This has
a marked influence (from ~100% to ~200%~ on production
costs and selling prices of these discs. Notwith-
standing the presence of apertures through the substan-
tially flat surface of the abrading disc for sucking
the dust produced, collection of the dust by the dust
removal system is unsatisfactory because upon maneu-
vering the rotary disc sander over a flat surface, the
suction through the apertures may be throttled to a
point where dust is no longer sucked in and tends to
cause gumming and overheating of the abrading surface
of the disc which is accompanied by the release of very
fine abrasive particles which are harmful for the
operator.
The present invention provides a solution to the
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above mentioned drawbacks.
Basically the abrasive disc assembly for a rotary
disc sander object of the present invention utili~es a
rotary pad for supporting the abrasive disk, having an
inner concentric receqs and at least two angularly
spaced apart grooves or channels which extend from said
inner recess zone to the outer circumference of the
pad. The abrasive disk may have an inner concentric
hole or a plurality of apertures about its center point
which operatively match the recessed zone of the pad
and may have a simple backing layer, advantageously
without any purposely made adhesive or fastening layer.
The abrasive disc placed on the surface of the pad is
retained thereon by means of a compressively acting re-
taining element which may be fastened to the rotarydisc supporting pad or to the end of the spindle of the
driving motor, provided with angularly spaced apart
arms which fit-into said grooves or channels of the pad
and are capable upon the tightening of the fastener of
the retaining element of warping and compressing said
abrasive di~c into said grooves of the pad, thus
securely retaining the abrasive disc in place.
The rotary di~c supporting pad has apertures formed
within the perimeter of said inner concentric recess of
the pad surface for providing therethrough a dust suc-
tion path which is advatageously in communication with
the radially extending channels defined by the surface
of the abrasive disc portions which have been warped
into the grooves of the pad by the arms of the re-
taining member.
Preferably the rotary disc supporting pad is com-
posite and may be advantageously formed by a semirigid
rotary disc support, e.g. a nylon disc, which may have
a central reinforcement steel "washer" or cap and a
cushioning pad of rubbery material permanently bonded
to the semirigid "backing" disc. In this case the
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central recess and the radially extending grooves may
be formed in the cushioning rubbery layer, or the
latter may be conveniently formecl by separate and
suitably spaced circular sectors of rubbery material
bonded onto a semirigid or rigid backing disc support,
thus defining said recess and said channels
therebetween.
The abrading surface, though remaining susbtantially
flat, will presen-t radially ~xtending channels extend-
ing from the area of said inner concentric recess tothe outer circumference of the abrading disc surface.
The radial discontinuities of the abrading disc surface
defined by the channels formed by the warping of the
abrasive disc into the radial grooves of the supporting
pad (by means of the arms of the retaining member) have
been found effective in promoting the collection of the
dust produced and in f~voring the suction of the dust
through the apertures present within the recessed inner
concentric zone of the disc pad. Thus suction is no
lon~er throttled when the sander is moneuvered more or
less parallel to a flat surface, as happened with the
abrasive disc assemblies o~ the prior art.
Even in machines which are not coupled to a suction
system, the novel abrasive disc assembly of the inven-
2~ tion offer advantages. The dust generated in theworking area tends to be collected into the radially
extending channels from where it is easily ejected by
centrifugal force, thus also in this case retention and
accumulation of dust on the abrading surface leading to
gumming is effectively prevented. The working surface
i9 less likely to overheat exce~sively and the abrasive
discs last longer.
An attendant advantage of the assembly of the inven-
tion is represented by the possibility of momentarily
loosening the retaining member sufficiently and ro-
tating the abrasive disc relatively to the pad surface
2 ~ & ~
before retightening the retaining member. This permits
to continue to use a partially damaged (gummed) disc by
expo~ing fresh portions of abrading surface which were
previously warped into the radial channels by the arms
o~ the retaining member.
The parts of the assembly may be functionally joined
together in various ways. One way is to utili~e a sin-
gle pin passing through a central hole of the compo-
nents of the assembly (i.e. retaining member, abrasive
disc, pad and/or a rotary disc support or a central re-
inforcing washer ther~of~ for fastening the assembly to
the end of the sander's spindle. Alternatively a rotary
disc support or a central reinforcing washer thereof
may be separately fix~d to the end of the spindle and
the abrasive disc retaining memher may be fastened to
the disc support or washer by specifically designed
fastening means.
The radially extending grooves or channels on the
surface of said pad may be straight or may describe a
curve. Advanta~eously in a sander provided with dust
suction means the grooves may be involute-shaped ac-
cording to the sense of rotation in order to promote a
conveyance of the dust toward the axis of rotation.
i.e. the recessed central zone wherein the apertures in
the abrasive disk and in the rotary disk support pro-
vide for suction passages of the vacuum system. Con-
versely in a sander without dust sucking means, the
grooves may be involute-shaped, contrary to the sense
of rotation for promoting a centrifugal discharge of
dust collected into the channels. Of course the radius
of curvature must be large enough for the warpable abra-
sive disc to be forcibly adaptable into slightly curved
channels without problems of overstretching.
The different aspects and advantages of the inven-
tion will appear more clearly through the following de-
scription of preferred embodiments and reference to the
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attached drawings, wherein:
Figure 1 is a partly sectioned view of an abrasive
disc assembly of the invention;
Figure 2 is a view of the abrading surface of the
abrasive disc showing the retaining means of the
invention;
Figure 3 is an exploded view showing an alternative
embodiment of the cushoning pad, abrasive disc and
retaining member; and
Figures 4a and ~h show alternative embodiments of
the abrasive disc retaining fixture.
Figure 5 is an exploded view showing an alternative
embodiment wherein the radially extending grooves and
the arms of the retaining element are curved;
Figure 6 is an exploded view showing another embodi-
ment of the abrasive disc assembly of the invention.
An abrasive disc assembly 1, made in accordance with
the present invention, is depicted in Figures 1 and 2.
The assembly comprise a rotary disc 6, typically of
a semirigid plastic material, e.g. a nylon disc, which
may be provided with a reinforcing central metal cap
(or washer~ 5 for mounting the disc onto the spindle 4.
To the rotary disc support ~, a cushoning pad 7 of rela-
tively soft rubbery material may be permanently bonded.
The cushoniny pad 7 has an inner concentrical reces~ 12
and four radial grooves 13 which extend from the cen-
tral recessed zone 12 to the outer circumference of the
pad. The groo~es 13 in the example shown are angularly
spaced by 90 from each other. A Elexible abrasive disc
2 which may have an annular shape as shown in Fig. 2 is
placed on the surface of the cushoning pad 7 and is re-
tained thereon by a compressively acting retaining fix-
ture 3 having a spider-shape. ~he retaining fixture 3
is formed in the example shown by a central square-
shaped washer piece 11 from which four angularly spacedarms 8 extend. The arms engage the abrasive disc 2 and
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warp the flexible material of the abrasive disc inside
the radial channel of the pad 7, thu6 firmly retaining
the abrasive disc 2 in place. The retaining element 3
is secured to the end of the spindle ~ by means of a
fastening screw 9, which may be -tightened into a
threaded axial hole of the driving spindle 4.
The washer piece 11 is completely received into the
central recess 12 of the pad 7 and the radially ex-
tending arms B are completely received in the grooves
13 of the pad 7, as may be better seen in Fig. 3.
In dust suction equipped sanders, the dust produced
by the sanding operation on the abrading surface of the
replaceable abrasive disc 2 is partly collected in the
channels defined by the warped in portions of the abra-
sive disc inside the grooves of the pad 7 of the as-
sembly and suction i8 exerted through the passages 14
of the reinforcing metal cap 5 of the assembly, the cen-
tral hole 12 of the semirigid backing support 6, the
central hole of the padding layer constituting said re-
cessed zone of the abrading sruface 7 and the radialchannels 13. As may be easily seen in Fig. 2, the a~ra-
sive disc retaining fixture (11-8) leaves an ample free
cross-~ection for dust ~ucking paths.
In the exploded view of Fig. 3, an alternative em-
bodiment is shown. The rubbery pad 7 has three equallyspaced grooves 13 extending from the central recess 12
to the outer circumference. The abrasive disc 2 is an-
nularly shaped and is provided with a central hole 15
matching the perimeter of the central recessed portion
12 of the padded disc support. The spider-shaped re-
taining element 3 is composed of a central washer 11provided with openings 16 for dust suction passages and
has three radial arms 8 fitting the channels 13 of the
padded disc support. A socket head screw 9 is used for
tightening the abrasive disc retaining fixture 11 to
the end of the machine spindle.
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The assembly washer piece 11 of the retaining fix-
ture 3 may be provided with radial wings or vanes in
order to act as a fan and thus assist in creating a suc-
tion effect, in sanders equipped with dust collecting
means, or a centrifugally blowing eEfect useful in
sanders which are not equipped with dust suction means
for assisting in ejecting dust radially out of the chan-
nels of the abrading surface.
As said before, the radially extending channels may
also be involute-shaped instead of being straight for
promoting dust removal from the abrading surface, as
shown in Fig. 5, wherein functionally similar parts are
indicated with the same numbers.
As schematically shown in Fig. 9a, the retaining
arms 8 may also be bent over the back surface of the
rotary disc assembly and shaped as a hook for engaging
with anchoring pins 18 provided thereon.
Yet another alternative embodiment of the invention
is schematically depicted in Fig. 4b. According to thi~
alternative embodiment, each radial arm 8 of the abra-
sive disc retaining fixture may be individually mounted
on a respective hinge 19 provided on the rear face of
the rotary disc assembly and each arm 3 may be swung
from a closed position whereby an inner end of each arm
is fastened to a central washer piece of the retaining
fixture and an open released position for discarding a
worn out abrasive disc 2 and installing a new disc.
Another preferred embodiment of the abrasive disc
assembly oE the invention is depicted in the exploded
view of Fig. 6, wherein functionally similar parts are
indicated with the same numbers.
In accordance with this embodiment, a composite
rotary pad is formed by a semirigid disc 6, having an
inner reinforcement metal washer 6a having apertures 14
and a central assembly hole 6b, all contained within an
imaginary inner circular zone which superimposes onto
~6?~
the inner recess of the pad. An assembly screw 6c pas-
sing through the central hole 5d of the reinforcement
washer 6a is tightened into a threaded hole 4a of the
machine spindle 4. The assembly screw Sc is provided in
turn with an axial threaded hole 6d.
According to this preferred embodiment the abrasive
disc 2 has a central assembly hole 2a which is engaged
by the assembly screw 9 which is used for tighteniny
the retaining element 3 and which tightens into the
threaded hole 6d of the disc assembly screw 6c. The
engagement of the abrasive disc by the central screw 9
provides a self-centering function thus releving the
operator from the need of carefully keeping the
abrasive disc in place on the pad surface until the re-
taining element 3 is set in place and tightened. Thisgreatly simplifies the replacement of the worn-out
æiscs. This self-centering function is realized by
forming a plurality of apertures 2b in a central zone
of the abrasive disc 2 so that the apertures 2b super-
impose on the recessed zone 12 of the supporting pad toprovide for du~t suction passages.
Of course, the arrangement may also be different
from a "spoke-wheel" configuration of the inner portion
of the abrasiYe disc 2, as depicted in Fig. S.
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