Tar removing mechanism for pneumatic nailing machine

A pneumatic nailing machine for driving a nail to a work, comprising: a main unit having a body; a cylinder disposed in the body of the main unit; a nose portion being hollow and continously extending from the main unit, the nose portion having a driver guide hole; a piston slidably inserted in the cylinder; and a driver coupled to the piston in the cylinder, and being slidable between a uppermost position and a lowermost position, wherein the driver and the piston are driven by high pressure compressed air supplied into the cylinder, and the nail supplied to the nose portion is hammered by the driver, the driver including, a base portion positioned near the piston and having a relatively large diamter so as to be substantially equal to an inner diameter of the driver guide hole, wherein the base portion is fitted into the driver guide hole when the driver reaches the lowermost position, and a tip end portion has a diameter so as to be smaller than an inner diameter of the nose portion, wherein the driver is loosely guided by the driver guide hole so as to swing during hammering, and the tip end portion of the swinging driver scrapes off tar adhering to an inner wall of the nose portion.

BACKGROUND OF INVENTION 
The invention relates to a pneumatic nailing machine in which, even when 
actual hammering is repeatedly conducted on asphalt roofing shingles or 
the like, tar adhering to a driver is prevented from sticking to the 
interior of a nose portion. 
When an asphalt roofing shingle which is formed into a sheet-like shape is 
to be attached to a roof base member, usually, nails are driven via the 
asphalt roofing shingle into the roof base member. 
In a conventional nailing machine, when actual hammering is conducted on 
asphalt roofing shingles, tar easily sticks to the tip end of a driver, 
particularly during the hot season. When the driver which has been once 
driven by compressed air is returned to its initial position, therefore, 
the tar is pulled into a nose portion. When actual hammering is repeated 
for a long time period, the tar is stickingly deposited on the inner wall 
of the nose portion, so that the sliding resistance between the driver and 
the nose portion is increased. As a result, there may take place a 
phenomenon in which the returning operation of the piston (the operation 
of returning the piston to the initial position) is disabled. 
Conventionaly, therefore, a nailing machine must be periodically cleaned by 
gasoline or the like in order to remove tar. 
However, the cleaning of a nailing machine must be frequently conducted 
during the nailing work. Furthermore, the cleaning must be conducted also 
after the nailing work is ended, because, when a nailing machine is left 
to stand overnight, tar is hardened and such hardened tar is hardly 
removed away. It is very cumbersome to clean a nailing machine after the 
nailing work is ended. 
SUMMARY OF INVENTION 
It is an object of the invention to provide a nailing machine which can 
solve the above-discussed problem and in which tar in a nose portion can 
be removed away during the nailing operation. 
In order to attain the object of the invention, the present invention 
provides a pneumatic nailing machine for driving a nail to a work, 
comprising: a main unit having a body; a cylinder disposed in the body of 
the main unit; a nose portion being hollow and continously extending from 
the main unit, the nose portion having a driver guide hole; a piston 
slidably inserted in the cylinder; and a driver coupled to the piston in 
the cylinder, and being slidable between a uppermost position and a 
lowermost position, wherein the driver and the piston are driven by high 
pressure compressed air supplied into the cylinder, and the nail supplied 
to the nose portion is hammered by the driver, the driver including, a 
base portion positioned near the piston and having a relatively large 
diamter so as to be substantially equal to an inner diameter of the driver 
guide hole, wherein the base portion is fitted into the driver guide hole 
when the driver reaches the lowermost position, and a tip end portion has 
a diameter so as to be smaller than an inner diameter of the nose portion, 
wherein the driver is loosely guided by the driver guide hole so as to 
swing during hammering, and the tip end portion of the swinging driver 
scrapes off tar adhering to an inner wall of the nose portion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a main unit 1 of a nailing machine according to an embodiment 
of the present invention. A cylinder 2 is disposed in the nailing machine 
main unit 1, a piston 3 is slidably housed in the cylinder 2, and a driver 
4 is integrally coupled with the piston 3. A hollow nose portion 6 is 
formed below the cylinder 2 so as to be continuous therefrom via a driver 
guide hole 5. One side of the nose portion 6 defining a nose portion hole 
20 is opened. A nail feeding mechanism which supplies a nail 8 via the 
opening 7 to the nose portion 6 is disposed in the nailing machine main 
unit 1. The driver 4 is vertically driven together with the piston 3 by 
supplying high pressure compressed air into the cylinder 2. The nail 8 
supplied to the nose portion 6 is hammered out by the driver 4. 
A blow-back air chamber 9 is formed outside the lower portion of the 
cylinder 2. The cylinder 2 is communicated with the blow-back air chamber 
9 via upper and lower through holes 10 and 11. A check valve 12 configured 
by an elastic member is disposed in the upper through hole 10 and on the 
side of the blow-back air chamber 9. A damper 13 is disposed in the bottom 
portion of the cylinder 2. 
The dimensions of the driver 4, the driver guide hole 5, and the nose 
portion 6 are set so as to have the following relationships. 
Large-diameter portions 4a and 4b which have a relatively large diameters 
are formed in the tip end and base portions of the driver 4, respectively. 
The outer diameters of the large-diameter portions 4a and 4b are 
substantially equal to the inner diameter of the driver guide hole 5, and 
slightly smaller than the inner diameter of the nose portion hole 20 of 
the nose portion 6. According to this configuration, when the driver 4 is 
at the uppermost position as shown in FIG. 1, the tip end portion 4a of 
the driver 4 is closely fitted into the driver guide hole 5. When the 
driver 4 is in the course of operation as shown in FIG. 2, gaps are formed 
between the driver 4, and the driver guide hole 5 and the nose portion 6. 
When the driver 4 reaches the lowermost position as shown in FIG. 3, the 
base portion 4b of the driver 4 is closely fitted into the driver guide 
hole 5. A gap is formed between the tip end portion 4a of the driver 4 and 
the nose portion 6 irrespective of the position of the driver 4. 
Next, an example in which a nail is driven via an asphalt roofing shingle 
into a roof base member by the thus configured nailing machine will be 
described. First, a trigger lever which is not shown is pulled to supply 
compressed air into the cylinder 2. As shown in FIGS. 1 to 3, the driver 4 
is then driven together with the piston 3 from the uppermost position 
toward the lowermost position. A nail 8 supplied into the nose portion 6 
is hammered, so that an asphalt roofing shingle 14 is fixed to a roof base 
member 15. 
During the movement of the driver 4 toward the lowermost position, the air 
under the piston 3 is compressed. As shown in FIG. 2, therefore, part of 
the air is supplied into the blow-back air chamber 9 via the lower through 
hole 11, and other part of the air is discharged to the outside via a gap 
between the driver guide hole 5 and the driver 4. As a result, the 
pressure rise under the piston is suppressed so that the reduction of the 
driving force due to the back pressure is prevented from occurring. When 
the driver 4 reaches the lowermost position as shown in FIG. 3, the 
expanded portion 4b of the base portion of the driver 4 is fitted into the 
driver guide hole 5, and hence the compressed air cannot escape to the 
outside via the driver guide hole 5. Therefore, the compressed air which 
is supplied into the blow-back air chamber 9 and increased in pressure 
remains in the chamber 9. Furthermore, compressed air is supplied into the 
blow-back air chamber 9 via the upper through hole 10 after the piston 
passes over the upper through hole 10, so that compressed air of an amount 
sufficient for returning the piston to the initial position is ensured in 
the blow-back air chamber 9. The check valve 12 prevents the compressed 
air in the blow-back air chamber 9 from reversely flowing into the 
cylinder 2 via the upper through hole 10. 
When the trigger lever is then released, the compressed air supplied to the 
cylinder 2 is discharged, so that the pressure on the upper side of the 
piston 3 is reduced and, as shown in FIG. 4, the pressure of the 
compressed air supplied into the cylinder 2 acts on the lower side of the 
piston from the blow-back air chamber 9 via the lower through hole 11. 
Therefore, the piston 3 is returned toward the uppermost position and the 
nail driving operation is ended. When the piston 3 is upward moved, tar of 
the asphalt roofing shingle adheres to the tip end of the driver 4. 
Therefore, the upward movement of the driver 4 may cause the tar to adhere 
to the inner wall of the nose portion 6. 
When, in the next nail driving operation, the driver 4 is driven together 
with the piston 3 from the uppermost position toward the lowermost 
position, the driver 4 swings during the operation in a direction 
perpendicular to the center axis of the driver because the outer diameter 
of the driver 4 is smaller than the inner diameter of the nose portion 6 
and the driver is loosely guided only by the driver guide hole 5. Since 
the driver 4 swings, the tip end of the driver 4 bumps against the inner 
wall of the nose portion 6 so as to move while rubbing the inner wall as 
shown in FIG. 2. As a result, tar 16 adhering to the inner wall is scraped 
off by the driver 4 as shown in FIG. 5. The swing direction of the driver 
4 is variously changed every time hammering is conducted, and repeated 
nailing works result in that the tip end of the driver 4 bumps against 
various portions of the inner wall of the nose portion 6. Consequently, 
tar is thoroughly scraped off and removed away during nail driving 
operations. Therefore, it is not required to wash the nailing machine 
during the nailing work and after the end of the nailing work. 
In the embodiment described above, the tip end portion 4a of the driver is 
expanded. The tip end portion is not restricted to the expanded one and 
may be configured in any manner as far as the tip end portion 4a can rub 
the inner wall of the nose portion 6. 
Since the outer diameter of the driver 4 is substantially equal to the 
inner diameter of the driver guide hole 5, a gap is not formed between the 
driver 4 and the driver guide hole 5 when the driver 4 reaches the 
lowermost position, and hence the air compressed under the piston 3 cannot 
escape to the outside via the driver guide hole 5. Therefore, most of the 
compressed air in the blow-back air chamber 9 which flows into the 
cylinder 2 via the lower through hole is used for the upward movement of 
the piston 3, with the result that the returning performance of the piston 
3 is not impaired.