This invention concerns dressing equipment for finishing the surfaces of manufactured articles or for preparing them for some further treatment.

Ordinary dressers, especially of the disc type, apply an abrasive part, in particular disc-shaped, to the sur¬ face of a structure such as the bodywork of a car or an article of wooden furniture or else a stone or wooden floor or threshold, to give it a finished appearance or to prepare the surface for further treatment such as paint ing .

Devices are present to draw up the dust produced by the abrasive part on the work surface, and to carry it into receptacles provided for the purpose so as to ensure a clean and healthy working environment. Suction and removal of dust produced by this type of process

is an aspect of first class importance.

For this purpose a fan is fixed onto the shaft of the motor that rotates the plate and its abrasive disc, so that dust may be drawn up through a set of holes in the plate and in the abrasive disc, and from there carried through a pipe to a collecting receptacle.

To improve suction of dust other methods have been adop¬ ted such as mounting a separate electric aspirator whose pipe is connected to the dressing machine. In all cases the plate contains within it radial tubes through which the holes on the working surface of the plate communicate with a chamber made inside the head of the dresser that supports both the electric motor and the plate itself. Dressing is done by glueing abrasive discs onto the plate. Clearly the abrasive discs must also have holes in them the same as those on the plate and in corresponding po¬ sitions . As the abrasive surface of the disc is subjected to such hard wear it needs frequent changing, a task attended with a certain amount of difficulty.

If the adhesive between plate and disk is weak, though easy to detach from the plate, it would be liable to shift during work considering the high speed, up to 8000 revs per minute, at which the plate rotates.

But if the glue is strong, detaching the worn disc, clean¬ ing the surface of the plate and fixing a new disc are all time-consuming operations. Once the glue has begun to harden it is obviously i pos- sible to adjust the position of the disc which may be necessary to see that its holes fit over those in the plate.

As an alternative to glue there is another fixing method consisting of pairs of velcro pads placed on the working surface of the plate and on the back surface of the re¬ placeable discs. One way of doing this is to glue a piece of male velcro permanently onto the plate and to fix pieces of female velcro onto the surface of the disc.

A worn disc can therefore be pulled off the plate and a new one put on by simply pressing it into place. But even this does not solve all the problems as fixing by velcro is inevvtably rough and inaccurate and does not ensure stable adherence between plate and disc. In addition it is practically impossible to align the holes in the plate with those in the disc as it is difficult to make said holes coincide and to match up the pieces of male and female velcro. This means that several attempts may have to be made before getting both disc and plate in their correct positions. Application of velcro to the discs obviously implies a considerable increase in cost.

When discs are worn their disposal raises a problem since they would thus contain polluting properties. Another proposal is to bend the outer rim of the disc onto a groove made all round the sides of the plate. An elastic ring placed round the bent rim of the disc determines its insertion inside this groove in the plate to give stability This being a difficult operation, a loading means has been proposed consisting of a disc with a flexible rim on which the elastic ring is placed; the disc has pins to fit into the holes in the plate and these pins guide the disc.

But neither does this suggestion solve the problem as the

rim of the abrasive disc is generally not easy to bend. There would therefore have to be a disc with a flexible rim. Even so the operation would be lengthy and complex. The above invention offers a solution that deals with all problems: those of securing a strong connection but easy disc changing and those regarding a precise fit be¬ tween the holes in the disc and the holes in the plate. Subject of the invention is a method for mounting replace¬ able abrasive discs on the elastic plates of rotating dressing equipment.

Means for a mechanical hold between both parts are placed on the plates and on the discs.

Said means are respectively placed on the cylindrical or truncated-cone shaped sides of the plate and on the rim of the discs but projecting outward from said rim so as to avoid interference with the piece to be dressed. The means placed on the sides of the plate are pins while those placed on the rim of the disc are perforated radial tongue-shaped pieces turning outwards. Radial positions of the tongues corresponds to that of the pins on the plates.

Hole diameter in the tongues corresponds to that of the pins. Having fitted together one tongue and one pin and having used the fingers to bend the edge of the elastic plate at the point where a second pin lies diametrically opposite to the first pin so that the second pin coincides with the hole in the second tongue on the disc, it therefore becomes possible to fix this second tongue onto said second pin. Spontaneous return of the elastic rim of the plate to its former configuration fixes the disc to the plate.

The same is done for the other pins on the plate and for the other tongues on the disc.

If the plate has- truncated-cone shaped sides, the pins stand substantially orthogonal to its working surface. The pins can be in one piece with the plate or else stably fixed in holes made for them in its sides. Alternatively the means for establishing a mechanical hold between plate and disc may be pairs of velcro pads firmly attached by glue or some other substance onto the sides of the plate and on radial toague-shaped pro¬ jections facing outward from the rim of the disc. Radial positioning of each corresponding pair of velcro pads is substantially the same on both plate and disc. Preferably the plate is given a piece of male velcro and the disc a piece of female velcro. To make sure that the disc is firmly held to the plate and is able to withstand working stress, the surface of the plate to which the replaceable disc will be applied is made as rough as possible. This is done to create maximum friction between plate and discs and therefore the greater is the working pressure the stronger will be the connection.

The desired roughness is obtained by processing that sur¬ face of the die, used to make the plate, which corresponds to the working surface of the plate; otherwise by firmly glueing a disc with a rough outer face onto the working surface of the plate. Said disc can be one of the types of abrasive discs already known. The invention offers evident advantages.

Replacement of abrasive discs is quick and easy it being sufficient to bend one edge of the elastic plate to do it. Corresponding positions of the holes in the disc and the pins on the plate, of fundamental importance for the re¬ quirements of efficient dust collection, is automatically

ensured, there being no need for any special expedient. Even when the abrasive disc is subjected to greatest stress its position in relation to the plate does not vary. The greater are these stresses the greater is the grip of the disc on the plate with its roughened surface ob¬ tained by stable application of the abrasive disc glued over it .

The replaceable discs no longer need glue , adhes ive or velcro Cost of each disc is lower than those with velcro pads. In conclusion, the method described offers a considerable reduction in cost of production and in operating costs and times, as well as full correspondence between disc holes and plate pins, maximum simplicity and speed of the process. Characteristics and purposes of the invention will be made still clearer by the following examples of its execution illustrated by diagrammat ically drawn figures. Fig.1 Perspective view from above of the plate for dressers showing pins for holding the abrasive disc. Fig.2 Perspective view of the disc with perforated tongues. Fig.3 Perspective view of the disc mounted on the plate. Fig. Cross section of the abrasive disc at the start of its application onto the plate. Fig.5 Completion of the operation in Fig. 4 also showing the dresser's motor-driven head. Fig.6 Perspective view from above of dresser plate with stably fixed separately made pins. Fig.7 Cross section of the plate in Fig. 6 and its abrasive disc, fixed to the dresser's motor-driven head. Fig.8 Perspective view from above of dresser plate with male velcro pads for fixing on the abrasive disc.

Fig.9 Perspective view from above of abrasive disc with tongues coated with pads of female velcro.

Fig.10 The abrasive disc with tongues coated with fe¬ male velcro pads placed upon the plate with male velcro pads. Fig.11 Cross section showing the plate in Fig. 10 fixed to the motor-driven head of the dresser.

Fig.12 Perspective view from below of an abrasive disc with perforated tongues being placed over a dres¬ ser plate with fixing pins, fitted with an ordi¬ nary type of abrasive disc permanently glued on. Fig.13 The plate in Fig. 12 fixed to the motor-driven head of a dresser. The plate 10 with its elastic plastic body 11 has four pins 13-16 placed at equal angular distances on the plate's truncated-cone shaped sides 12, said pins being substantially orthogonal to the working surface.

The abrasive disc 20 with radial aspiration holes 22 and abrasive surface 21 has four ongue-shaped pieces 23-26 placed at an angular distance corresponding to that of the pins 13-16 on the plate 10. Through each tongue there is a hole 27 whose diameter cor¬ responds to that of the pins 13-16.

To fit the disc onto the plate it is sufficient to press one of the tongues, e.g. 24, onto the pin 14 and then, by bending the rim 17 of the side 12 with the fingers, fit the hole 27 in the tongue 26 onto the pin 16, this pin being in a position diametrically opposite to pin 14. Having now placed said pin 16 in the hole 27, and allow¬ ing the rim 17 to resume its original shape, and having done the same with the other pins and the other tongues,the abrasive disc 20 will be held firmly on the plate 10. (Figs. 3-5).

In place of the pins made in one piece with the body 11 of the plate 12, pins 33-36 can be stably inserted through holes 38 in the sides 32 of the body 31 of the plate 30. These pins function in the same way as those made in one piece with the body of the plate.

Alternatively to the pins, pieces 43-36 of male velcro are placed at equal radial distances on the side 42 of the body 41 of the plate 40. The abrasive disc 50 has tongues 53-56 bearing pieces of female velcroJ57. at a radial distance equal to that of the pins 43-46.

The disc is applied over the plate by simply matching up the pieces of female velcro on the disc with the pieces of male velcro on the plate (Figs. 10 and 11). Stresses on the abrasive disc are extremely high and be¬ come more severe as its speed of rotation and working pressure increases.

To ensure maximum stability between disc and plate, an ordinary abrasive disc 60 is mounted with glue 61, the abrasive face 62 of said disc 60 being placed against the plate 10, as shown in Figs. 12 and 13. The abrasive disc 20 is then fitted onto the pins 13-16 as already explained. Application of abrasive discs therefore becomes quick-and easy at the same time ensuring correspondence of position between the suction holes 15, 16 on the plate and those 27 on the abrasive disc, as well as maximum stability between plate and disc while work is proceeding. The motor-driven head of the rotating dresser is shown in the figures by the number 18.