This invention relates to a portable perforating

unit, particularly for sheet metal work.

In order to make holes, in particular in sheet

metal, it is known to use drills or punching machines. Drills are generally provided with a tool, knov/n as

a drill bit, mounted in a chuck rotated by an electric or

pneumatic motor.

However, they have certain drawbacks, and in

particular:

- they are highly uncon ortable to operate in determined

positions, for example when making holes in sheet .metal

located a certain height above the operator,

- they are operationally slow,

the operator can be harmed by the drillings formed during

working,

the tool is subjected to considerable wear and is easily

broken,

it is impossible to form non-circular holes,

a certain pressure has always to be exerted in order to make the hole.

Punching machines generally comprise a tool, -

commonly known as a punch, and a die on which the sheet

metal in which the hole is to be made is rested.

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These machines, v/hich enable holes of any profile

to be- made, have however other drav/backs and in particular

operational slov/ness, the need for the workpiece in which the hole is to be made to be placed on the actual punching machine, which is nearly alv/ays fixed, and the impossibility

of using the die in the case of tubes or closed sections.

An object of the invention is to obviate the

drav/backs jointly or separately present in knov/n drills and

knov/n punching machines, by providing a perforating unit

which enables holes of any profile co be made at high speed.

A further object of the invention is -to provide a

perforating unit which is safe and reliable in use even in

the most uncomfortable positions.

These and further objects v/hich will be apparent

from the description given hereinafter are attained

according to the invention by a portable perforating unit,

particularly for sheet metal work, characterised by

comprising:

an outer casing provided with a handgrip,

- a tool consisting of a punch axially mobile betv/een a

rest position, in correspondence v/ith v/hich it is

completely housed within said casing, an a working

position, in correspondence v/ith which its end emerges

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from said casing,

- means v/hich, v/hen activated by the operator, cause the

impelling displacement of the tool from its rest position

to its working position, and to then return to its rest position.

The present invention is described hereinafter with

reference to the accompanying drav/ings in which:

Figure 1 is a longitudinal section through a perforating

unit according to the invention in its rest

configuration,

Figure 2 is a view thereof similar to Figure 1 but in its

working con iguration, and

Figure 3 is a diagrammatic section through the valved

firing mechanism of the perforating unit according to the invention.

As can be seen from the ^' figures, the perforating unit according to the invention comprises an outer casing 1

p: ovided with a handgrip 2 and a guiding nosepiece 3 for a

punch 4. ^■ -

l.ithin the handgrip 2 there is provided a chamber

5, having a compressed air feed connector ύ. The chamber 5

is also provided with a valved firing mechanism 7 operated

by a trigger 3 pivoted to the casing 1.

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The valved firing mechanism 7 comprises

substantially an opened backward cylindrical chamber 9 provided at the front end v/ith an aperture 10 crossed by a

ste 11 operable by the trigger 3. A helical spring 12

acting on the inner end of the stem causes the partial exit

of this from the casing 1; a suit annular ring 13, bound to

the stem 11 ensure the seal between the stem 11 and its

seat, and therefore the front seal of the cylindrical

chamber . Inside the cylindrical chamber 9 a piston 14 is foreseen, the hollow stem 15 of which houses in the chamber

5 and is provided with a hole 16 v/hich puts said chamber 5

into communication v/ith the chamber 9 .

The other end of the stem 15 houses in a seat 17

having an annular seal 13. A duct 19 outs the seat 17 into

communication v/ith the rear zone of a chamber 20 housing a

valve 21 , with a longitudinal hollow 22, and having its

^• front surface facing a cylinder 23, in which a piston 24

slides under sealed conditions.

The cylinder 23, the inner diameter of which is

less than the outer diameter of the valve 21 , is v/ound by an

annular chamber 25 communicating with said cylinder by v/ay _.

of apertures 26 and 27 disposed along tv/o circumferential

D ORIGINAL

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lines. The position of said apertures 26 and 27 is such that

v/hen the piston 24 is in its front end-of-travel position

(see Figure 2), the former are disposed downstream and the

latter are disposed upstream thereof. In particular, the apertures 27 consist of holes

formed in a semi-cylindrical seat provided in an outer

circumferential projection on the cylinder 23 and are closed

by an elastic 0-rir.g 28, v/hich forms v/ith said apertures 27

non-return valves, the purposes of which is described

hereinafter. The front end of the cylinder 23 is closed by

an annular rubber plug 29 against which the piston 24 * halts

on reaching its front end-of-travel. Inside the cylinder 23

a pin 30 is provided having its axis parallel to the axis of

the same cylinder 23, for the guide of the piston 24.

The piston 24 is in front provided v/itn an

internally threaded cylindrical seat into which the rear

flanged end 31 of the punch 4 is inserted. This flanged end

31 is held against the front surface of the piston 24 by a

hollow screw 32 disposed coaxially to the punch 4 and engaged in the cylindrical seat.

The nosepiece 3 comprises a shell 48 screwed on to

a portion 35 which inserts into the casing 1 of the

perforating unit and is bound to this by tv/o little screv/s

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44. The nosepiece 3 also comprises a cap 33 screv/ed on to a

flange-shaped sleeve 34.

The sleeve 34 v/ith its cap 33 are axially movable

v/ith respect to the shell 43 and are kept, by means of a

spring 36, projecting beyond the end of the punch 4 v/hen in

its working state.

A rod 37 is connected to the sleeve 34, parallel to

the axis of the punch 4 and acting v/ith its back inclined

plane on the end of a pushe " 33 having the other end in

contact v/ith a spring lever 39. The arm 40 of the lever 39

not touching the pusher 33 drives a little rod articulated

to the trigger 8.

The operation of the perforating unit according to

the invention is as follow:

In rest state (see Figure 1 ) the pressure in the chamber 5

is transmitted through the hole 16 into the chamber 9 of the

valved firing mechanism 7 and keeps the ste 1 in its back

enc-of-travel, v/ith an annular seal 46 closing the way

towards the duct 45- Tn this state the compressed air fills

the seat 17 and, through the duct 19, can fill the rear

chamber 20 of the valve 21.

As the rear surface area of the valve 21 is greater

than its front surface area, the valve 21 is kept pressed

BAD ORIGINAL

against. the rear aperture of the cylinder 23, to seal it by way of a seal ring 42.

In this rest configuration, the piston 24 is at its

rear end-of-travel position, and the punch 4 is completely retracted into the nosepiece 3.

In order to effectively operate the trigger 3 and

therefore to cause the punch 4 to go out, first of all it is

necessary to rest, against the sheet metal to be perforated,

the cap 33 and to cause it to go back with the flange-shape

sleeve 34. Due to this displacement, the rod 37 causes v/ith

its inclined plane the lowering of the pusher 33 which in

its turn operates the lever 3D and put the little rod 39

into touch with the stem 11 (see Figure 2}.

n operating the trigger 3, the stem 11 goes back

and displaces its seal 13, and enables that the air of the

chamber 9 to discharge to atmosphere through the play around

the s em 11.

Λs the air altering the chamber 9 through the hole

16 is lesser than the air coming out from said play, the

chamber 9 has a pressure lesser than the pressure of the

chamber 5- Therefore the piston 14 advances and its stem 15

closes backward, with its seal 13, the annular aperture of

the seat 17, no longer allowing the inlet of the air into

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the chamber 20 and at the same time causing the compressed air, there housed, to discharge through the duct 45.

Uov the pressure difference betv/een the chamber 5

and the chamber 20 causes the backwards displacement of the

valve 21 and its separation from the cylinder 23. The air

violently enters the interior of this latter through its

rear aperture, to suddenly thrust the piston 24 and the punch 4 rigid with it.

After a very short distance of travel the valve 22

closes its rear aperture against the plug 43. In this

manner, the compressed air from trie ^* chamber 5, after

entering the cylinder 24, is prevented from passing to

atmosphere through the axial cavity 22 of the valve 21 and

the ducts 47-

The sudden advancement of the piston 24 causes the air in the front part of the cylinder 23 to pass into the annular chamber 25 ^* through the holes 26 and 27 and to

undergo com-pression. It should be noted that in this stage,

in v/hich the trigger 5 is almost certainly still being

pressed, when the piston 24 has reached its front

end-of-travel position, the air from the chamber 5 and also

the air which is still being fed through the connector 6

enter the cylinder 23 through its rear aperture, to thus

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enter the annular chamber 25 through the holes 27, so

increasing the pressure therein.

V/hen the operator releases the trigger 3, the

elastic reaction of the spring 12 returns the stem 11 to

adhere v/ith the seal 13 to its seat, preventing the further

exit of air through the play around the stem 11.

The chamber 9 fills v/ith air v/hich, after having

pushed the stem 15 to its rear end-of-travel position, enters into the chamber 20 through the duct 19. Vhen. the

chambers 20 and 5 have the same pressure, the valve 22 closes the cylinder ^" 23 at its rear, and on the other hand

enables the air accumulated in the cylinder 23 to pass

through the inner cavity 22 of said valve 21 and to leave to

atmosphere through ducts 47-

As a result of this, the compressed air contained

in the annular chamber 25 can discharge through the aperture

26 to urge the piston 24 rearwards and with it the punch 4,

which is rigid therewith, this latter entering the nosepiece 3 ready for the next operation. It should be noted that

during this stage the compressed air v/hich has accumulated

in ^' the annular chamber 25 is unable to leave through the

aperture 27 because of the presence of the 0-ring 28.

V/hen the piston 24 is in its rear end-of-travel

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position, the further compressed air housed inside the cylinder 23 comes out through the several plays present betv/een the reciprocally moving parts. As this air has been previously added with oil, it lubricates the several parts. As already said, the operating of the trigger 8

requires the preventive backwards displacement of the cap 33

and therefore the operating of the perforating unit is not

allowed in the case in v/hich the cap 33 has not been rest

against the metal sheet to be perforated. If moreover, due to accidental reasons, such an

operating of the trigger will equally occur and cause the

operating of the perforating unit, the cap 33 of the

nosepiece 3, v/hich elastically projects forwards by an

extent greater than the emerging portion of the punch 4,

would be in any case a further "safety".

Because the tool needs to be periodically

resharpenea with use, and the effect of the resharpening is

to shorten it, it is necessary occasionally to screw the cap

33 around the sleeve 34 to maintain the punch portion projecting thereform constant.

V/hen it is no longer possible to resharpen the

punch 4 and it thus has to be replaced, the nosepiece 3 is

disengaged from the member 1 by operating on the screws 44.

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The hollow screv/ 32 is then disengaged from its seat in the piston 24, _. the punch 4 ₌ is withdrawn therefrom and is

replaced v/ith a new one.

From the aforegoing it is clear that the

perforating unit according to the invention has numerous

advantages, and in particular:

it enables holes of any profile to be quickly formed; it

should be noted that the slight deformation of the

perforated metal sheet around the hole is insignificant as the edge of the hole is generally covered by a washer

or by the ^' neac of the screv/ v/hich is to be inserted through the hole,

- it is safe and reliable in use, even in a very

uncomfortable position, as it requires practically no pressure to be exerted against the surface of the sheet metal to be perforated,

- it cannot harm the operator, as the punch emerges from

the nosepiece only when this is rested against the

v/orkpiece to be perforated,

- ic car alόo be u_. d for perforating tubes or closed

sections.

From tests carried out with a perforating unit of

dimensions corresponding to those of a conventional

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commercial hobby drill, 100 holes of 5 mm diameter were made

in one minute in a section 1.5 mm thick v/ithout any noticeable wear of the punch.

The same test carried out v/ith a professional drill

5 of about 350 v/atts positioned on a bench and thus under more

comfortable conditions for the operator, required a time of

eighteen minutes.

In uncomfortable positions (walls, ceilings) this time is certainly greater. o The invention can also use conventional valved firing mechanisms of other types v/hich provide for the

automatic return of the piston 24 and of the punch 4 rigid therewith into their rest position, independently of whether

.he trigger d has been released or not. In addition, the

5 tool for its next actuation must require the trigger 3 to be operated again.

The described embodiment of the perforating unit is

fed v/ith compressed air. However, the invention also covers

perforating units operated by an explosive charge. This

0embodimen , which doubtlessly is more costly to produce and

more noisy in use, can be preferred where compressed air

feed is not available or if the thickness of the workpieces to be perforated is so large as to otherwise require

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excessively bulky perforating units operated by compressed

air.

The invention also covers a perforating unit

operated by electric charge. Again in this case, as in the

previous case, compressed air is not required but the unit

has the drawback of slov/ operation and of considerable

v/eight and overall size.

Finally, the invention also covers a perforating unit operated by manual charge. In this case, no external

eed connection is required, but the unit has the drawback-

of slov/ operation due to the need for manual recharging.