JPS6234636A - Manufacture of crank for bicycle - Google Patents

Abstract

PURPOSE:To increase force transferred to a gear from a crank by fixing a wheel gear by a dowel which is fixed to a crank arm by welding. CONSTITUTION:A cold finished round steel bar is cut to a fixed size, and a center part 2 and a pair of right and left large diameter parts 3, 4, a pair of side parts 5, 6 connected to its outside, and large and small flanges 7, 8 formed in a connecting part of one large diameter part 4 and its side part 6 are pressed and formed by a hydraulic press. Both ends are cut and formed to spherical parts, pedal fitting face parts 11, 12 are formed, and also both the side parts 5, 6 are formed flatly. Subsequently, crank arms 17, 18 are formed by bending both the side parts 5, 6 to each opposite direction by a hydraulic bender, and the center part 2 and the large diameter parts 3, 4 become a crank shaft 19. In the large diameter parts 3, 4, screw parts 24, 25 are formed, and a dowel 26 is welded to the inside face of the crank arm 18. In the end parts of the crank arms 17, 18, pedal fitting holes 27, 28 are formed, and also a tip 31 of the dowel 26 is worked to a wheel gear engaged diameter, and a key groove 32 is cut in the screw part 25.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a bicycle crank from a polished round steel bar.

(Prior Art) “As a manufacturing method of this kind of single crank, for example, the method described in Japanese Patent Publication No. 49-21233 is known. This conventional method uses polished round steel bar as a material and performs upset processing. A pair of large-diameter parts each having a large-diameter part and a large and small flange are formed in the central part, and then the parts on both sides connected to these large-diameter parts are pressed flat, and the flattened parts on both sides are bent in opposite directions. Then, a crank material having a crankshaft and a pair of crank arms is made, and then each screw is machined on the large diameter part and drilling is carried out on both crank arm heads, and a wheel is engaged with the large and small flanges of the one large diameter part. A single crank characterized in that a single crank made of polished steel bar and with an integrated wheel engaging plate is obtained by fitting a separate wheel engaging plate with a protrusion. It was a cold manufacturing method.

(Problems to be Solved by the Invention) Although the crank itself obtained by the above-mentioned conventional manufacturing method is excellent in strength, it is a separate wheel-engaging crank that has wheel-engaging protrusions on the large and small flanges of the large-diameter part. Since the plate is fitted, there is a limit to the transmission force from the crank to the wheel gear, and play is likely to occur between the wheel engagement plate and the crank.

Therefore, an object of the present invention is to provide a method for manufacturing a single crank that can transmit a large force from the crank to a wheel gear.

(Means for Solving the Problems) A feature of the present invention for achieving the above object is to use a polished round bar steel cut to a fixed size, press the central part, and both sides of the central part. A large-diameter portion that is connected to the large-diameter portion, both side portions that are continuous to the outside of the large-diameter portion, and large and small flanges formed at the connecting portion between one of the large-diameter portions and the side portions, each having a circular cross section with a predetermined diameter. Next, the outer end surfaces of both sides are cut into spherical surfaces using a cutting machine, and then pins are driven into the outer ends of both sides using a press to form the pedal mounting surface, and both sides are flattened. Next, by bending both sides in opposite directions with a bender, the both sides are formed into a crank arm, and the center and large diameter parts are formed into a crankshaft. The outer diameter of the small flange is cut to the gear fitting diameter, and both large diameter parts are cut to the lower thread diameter. Next, a thread is formed on both large diameter parts using a thread rolling machine, and then a welding machine is used to cut the outer diameter of the small flange. Using a transfer machine, weld a dowel to the crank arm on the large flange side. Next, use a transfer machine to drill and tap a pedal mounting hole at both ends of the crank arm, and cut the tip of the dowel to the gear engagement diameter. , cut a keyway into the threaded part of the large diameter part.
The point is to get this crank.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

As shown in FIG. 1, in the present invention, a polished round steel bar 1 is cut to a fixed size, and a material obtained by chamfering both ends is used as a crank material.

This round steel bar l is pressed in a hydraulic press as shown in Figure 2.
A central portion 2, a pair of left and right large diameter portions 3.4 continuous to both sides of the central portion 2, a pair of left and right side portions 5.6 continuous to the outside of the large diameter portion 3.4, and one large diameter portion. 4 and the large and small flanges 7.8 formed at the connecting portions with the side portions 6 are pressed into circular cross-sections each having a predetermined diameter.

As shown in FIG. 3, both ends of the forged crank material are cut into spherical parts 9.10 using a cutting machine.

As shown in Fig. 4, the above molded crank material is
Using an FP press, pins are driven into both ends to form pedal mounting surface portions 11.12, and both side portions 5.6 are formed flat. At this time, the side indicated by reference numeral 13.14 in FIG. 4 is formed in a planar shape, and the side indicated by 15.16 in FIG. 4 is formed in a chevron shape.

Next, as shown in FIG. 5, both sides 5.
6 are bent in opposite directions so that both side portions 5.6 serve as a crank arm 17.1B, and the central portion 2 and large diameter portion 3.4 serve as a crankshaft 19.

Next, as shown in FIG. 6, the fitting portion 20 is formed by cutting the outer diameter of the small flange 8 to a wheel gear fitting diameter using an outer cutting machine. Further, a relief portion 21 is formed at the connecting portion between the small flange 8 and the large diameter portion 4 by cutting the outside diameter. Furthermore,
The outer diameter of one of the large diameter portions 4 is cut into a right-handed threaded lower diameter portion 22, and the outer diameter of the other large diameter portion 3 is cut into a left-handed threaded lower diameter portion 23.

Next, as shown in FIG. 7, threads are rolled on the lower diameter portions 22.23 of both threads using a thread rolling machine to form threaded portions 24.25.

Next, as shown in FIG. 8, a dowel 26 is welded to the inner surface of the crankshaft 8 on the large flange 8 side using a welding machine.

Next, as shown in Fig. 9, in the transfer machine,
Pedal mounting surface 11 at the end of the crank arm 17.18
Drill a hole at ゜12, tap it, and make the pedal mounting hole 27.
28 and a pedal mounting recess 29.30 at its end to hole 27.28.

Further, the tip 31 of the dowel 26 is cut to a wheel gear engagement diameter, and a key groove 32 is further cut into the threaded portion 25.

Through the above steps, one crank is completed as shown in FIG. 9.

(Effects of the Invention) According to the present invention, since the wheel gear is fixed by a dowel fixed to the crank arm by welding, the force transmitted from the crank to the gear can be transmitted from the conventional wheel engagement plate. This increases the strength of the single crank and increases the transmission force.

[Brief explanation of the drawing]

FIGS. 1 to 9 are explanatory diagrams showing processing steps from a raw material to a finished product according to the method of the present invention. 1... Polished round steel bar, 2... Center part, 3.4... Large diameter part, 5.6... Side part, 7... Large flange, 8...
・Small flange, 9, lO... Spherical part, 11.12...
・Pedal mounting surface, 17.18...Crank arm,
19... Crankshaft, 20... Fitting portion, 21
... Relief part, 22.23 ... Thread lower diameter part, 24.2
5... Threaded part, 26... Dowel, 27.28... Pedal mounting hole, 29°30... Counterbore, 31... Dowel tip, 32... Keyway. Patent applicant Sugino Techno Co., Ltd. Figure 1 ■ ○■■ ■ Figure 3 0@00゛

Claims (1)

[Claims] 1. Using a polished round bar steel cut to a specified size, press a central part, a large diameter part continuous to both sides of the central part, and both sides continuous to the outside of the large diameter part. , the large and small flanges formed at the connecting part between one large diameter part and its side part are pressed into circular cross-sections with predetermined diameters, and then the outer end surfaces of both sides are cut into spherical shapes using a cutting machine. Next, pins are driven into the outer ends of both sides using a press to form the pedal mounting surface, and both sides are formed flat, and then both sides are bent in opposite directions using a bender. Then, use an outside diameter cutting machine to cut the outside diameter of the small flange to the gear fitting diameter, and screw both large diameter parts together. Cut it to the lower diameter, then use a thread rolling machine to form threads on both large diameter parts, then use a welding machine to weld a dowel to the crank arm on the large flange side, and then transfer it to a transfer machine. Then, drill and tap holes for pedal attachment on both ends of the crank arm, cut the tip of the dowel to the gear engagement diameter, and cut a keyway in the threaded part of the large diameter part to obtain a single crank. A unique method for manufacturing bicycle cranks.