AU602413B2 - Tapping screw - Google Patents

Description

To" The ommissioner of Patents APPLICATION ACCEPTED AND AMENDMENTS A LLO W ED *.1

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION Form

(ORIGINAL)

FOR OFFICE USE Uz 4 1 Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: This document contains the amendments made under Sect ion '9 and is correct for printing Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: YAO SEIBYO CO. LTD.

246 KANAN-CHO YAMASHIRO

MINAMIKAWACHI-GUN

OSAKA

JAPAN

GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Actual Inventor: Address for Service: Complete Specification for the invention entitled: TAPPING SCREW The following statemenc is a full description of this invention including the best method of performing it known to me:- Position President GRIFFITH HACK CO PATENT AN D TRADE MARK

ATTORNEYS

MELBOUR NE SYDNEY PERTH TAPPING SCREW The present invention relates to a tapping screw.

A conventional tapping screw has a thread with a substantially uniform lead angle on the periphery of its shank over its entire length. In order to drive the screw into the material, it has to be turned while pressing very hard from the start. Further, it takes much time -t drive t t t the screw deep enough for it to stand on its own. Only a little relaxing of the driving force may cause the screw to S skid, making it difficult to further drive the screw.

In order to solve the abovesaid problems, the present applicant proposed a tapping screw (Japanese Unexamined #4 SUtility Model Publication No. 62-16992) in which the lead #4 angle of its thread 10 increases toward the tip of the c' tapered po'tion 11, as shown in Fig. 5. With this prior art tapplng screv, a thread 10' on the tip of the shank has such a lead as to be convergent to the axis of the screw so that the thread 10' will act as a drill edge. This considerably improves the drilling capacity of the screw and permits driving with a smaller force.

But, since the threau 10 has a uniform diameter over the entire length of the straight shank portion of the screw, when the screw is driven deep into a material, it tends to seize owing to a heat buildup resulting from a long

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contact distance between the thread and the material. If the material is a hard wood, this tendency will be marked and the possibility that the screw gets broken will increase.

Further, owing to a large lead angle of thread at the tip of the tapered port' a great force is needed for initial driving of tb screw and the screw is difficult to stand on its own. After a bore has been drilled by the tapered tip portion, the thread with a small lead angle has t.r to bite into the bore with a large diameter. Thus, a large 9 torque is required to turn the screw and the thread is liable to slip and idle against the hard clamp face, thus inhiLiting further driving of the screw.

An object of the present invention is to provide a tapping screw which obviates the abovesaid shortcomings and which can be driven positively even into a rather hard clamp face with a relatively small force.

In accordance with the present invention, there is provided a tapping screw having a shank having a tapered portion at one end thereof and a head at the other end thereof, the shank and the tapered portion having threads formed thereon, two ribs of a triangular section being formed at the rear of the tapered portion so as to be separate from the threads on the shank and the threads on the tapered portion and to be twisted in the axial direction, the ribs having an arcuate ridge line, the maximum diameter between the highest points of the ridge lines of the ribs being substantially equal to or smaller than the diameter of the threads on the shank and larger than the maximum diameter of the threads on the tapered portion, the ridge line forming a larger angle with respect to a plane perpendicular to the axis of the tapping screw than the lead the tapered portion.

The tapping screw is firstly driven into the material with its thread on the tapered tip. As the screw is further driven in, the ribs having a maximum diameter which is larger than the maximum thread diameter at the tapered portion serve to expand the threaded hole tapped by the thread on the tapered portion. At the same time, the ribs chip off part of the thread on the hole to form two helically extending grooves. The thread at the rear portion t of the screw then bites into the hole thus formed.

The grooves formed by the ribs serve to reduce the circumferential length to be tapped by the thread at the rear of the shank, thus allowing tapping with a small torque. The grooves will also contribute to a reduction in the heat buildup in the trailing thread, thus preventing it from seizing. Also, the grooves will act for chip ejecti on, preventing the screw from being clogged with the chips.

Further, since the thread on the tapered tip has a small lead angle, the screw can be driven even into a -ather hard clamp surface with a small torque.

According to the present ivention, the ribs have helically extending ridge lines instead of straight ridge lines. This is because if the ribs have straight ridge lines, they will act as drill edges, chipping off almost completely the thread on the hole tapped by the thread on the tapered end of the screw. The hole formed by the straight-ridged ribs would be too large for the thread at the rear of the shank to bite thereinto.

rQ.4* By virtue of the helical ridges, long contact lines between the ribs and the tapped hole are obtained. The ribs 4 t can continuously and smoothly bite into the tapped hole.

Other features and objects of the present invention 44 will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a front view of the tapping screw in accordance with the present invention; Fig. 2 is a sectional view taken along line II-II of Fig. 1; Figs. 3 and 4 are views of portions of the same; and Fig, 5 is a front view of a prior art tapping screw.

Referring to Fig. 1, the tapping screw of the present invention has a shank 1 having a tapered portion 2 at its r

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one end and a head 3 provided at the other end and formed with a groove or grooves to receive a driver tip.

The shank 1 is provided on its periphery with threads 4 and 4' having the same predetermined lead angles, interrupted with a threadless portion of a predetermined length. On the threadless portion are provided two ribs separate from the threads 4, 4' so as to diametrically t oppose to each other.

As shown in Fig. 2, the ribs 5 have a triangular section with an apex angle of about 60 degrees and extend in a twisted manner with respect to the axis of the screw.

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Further, the ribs 5 have an arcuate ridge line 6 extending in the direction of twist as shown in Fig. 3. The maximum 4 diameter d between the highest points of the ridge lines 6 1 4 of ribs 5 is set to be larger than the maximum diameter dl of the thread at the tapered portion 2 and substantially equal to or smaller than the maximum diameter d2 of the thread 4' at the rear shank.

"Substantially equal" is to be understood to allow some manufacturing error, but the maximum allowable upward deviation of the d value from the d2 value, i.e. d d2, is 0.15 mm.

As shown in Fig. 4, the ribs 5 should have their ridge lines 6 inclined at an angle oL of about 60 degrees with respect to a plane perpendicular to the axis of the screw at their central portion and extending helically toward both ends in a twisted manner. The angleo. should be 60 degrees and be larger than the lead angle( of the threads 4 and Thus, the screw will be driven into the clamping wood in such a manner that the ridge lines 6 of the ribs will bite helically and consecutively into the hole tapped by the threads 4.

SThe number of turns of the thread 4 on the tapered i portion should be two or three in view of the balance f between the ease of driving-in and the guiding effect after I driven in. The length and diameter of the ribs 5 should be determined according to the lead angle of the threads 4 and Normally, the length of the ribs 5 should be S:k substantially the same as that of the tapered portion 2.

In operation, the screw is driven into the material V firstly with the threads 4 on the tapered portion 2. Then the ribs 5 widen the hole tapped by the threads 4. The threads 4' formed on the main portion of the shank then bites into the material.

When the ribs 5 are driven into the material, they bite helically into the tapped hole with their arcuate ridge portions 6 having a larger maximum diameter than that of the thread 4 so as to form two helical grooves. Although the ribs 5 chip some amount of material, since the ribs 5 are not edged so sharply as shown in Fig. 2, they do not act as 6 m -I drill edges. It is presumed that as the ribs 5 bite into the wood, the material at the thread on the hole tapped by the thread 4 will not be chipped off exactly in conformity with the track of the ridge lines but the hole is somewhat expanded radially owing to the elasticity of the wood.

After passing of the ribs 5, the hole will shrink back to its original state. Thus, the diameter of the grooves formed by the ribs 5 will be smaller than the maximum diameter d of the ridge lines 6 of the ribs 5, thus allowing 0 the threads 4' to bite thereinto.

.4 00 Still, the grooves formed by the ribs 5 are deep enough Sto partially interrupt the thread on the starting hole 0 0ra tapped by the thread 4. Thus, the circumferential length to be tapped by the thread 4' will decrease. This will p r So. irAnimize the heat buildup, thus preventing the thread 4' *a from seizing, and also allow easy tapping by the thread 4' with a small torque. The grooves formed by the ribs 5 also serve as passages for the ehips, thus preventing the screw I from being clogged with the chips.

Since the ridge lines 6 of the ribs 5 are inclined at an angle larger than the lead angle of the threads 4 and 4', the ribs are drawn with a greater force than the threads 4 and 4' while the screw is being driven in, thus helping to draw in the thread 4' and thus the entire screw at a greater speed. Once the screw is driven in, the ribs will strongly resist unscrewing forces to keep the screw tightly gripped by the material.

On~ the other: hanc6, the thread 4 on the tapered end functions to guide and pull t1 1 e screw as it cuts into the wood, allowing the ribs 5 and thread 4' to bite iriLo the wood without Yail, and helping the screw to. stand alone quickly.

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Claims (1)

1. A tapping screw having a shank having a tapered portion at one end thereof and a head at the other end thereof, said shank and said tapered portion having threads formed thereon, two ribs of a triangular section being formed at the rear of said tapered portion so as to be separate from the threads on said shank and the threads on R said tapered portion and to be twisted in the axial A A direction, said ribs having an arcuate ridge line, the A, maximum diameter between the highest points of the ridge lines of said ribs being substantially equal to or smaller than the diameter of the threads on said shank and larger than the maximum diameter of the threads on said tapered portion, said ridge line forming a larger angle with respect t I to a plane perpendicular to the axis of the tapping screw than the lead angle of the threads on said shank and that of the threads on said tapered portion. DATED this 5th day of JULY 1988 YAO SEIBYO CO. LTD. By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. 9