JPS6341694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drill that has excellent drilling ability and is capable of processing the inner wall of the hole with high precision.

In conventional drills, the outer diameter of the shank having the helical groove and the outer diameter of the cutting edge are generally the same. For this reason, during hole drilling, the outer circumferential portion of the shank rubs against the inner wall of the drilled hole, causing flaws on both the inner wall and the outer circumferential surface of the shank, and also resulting in an increase in the rotational resistance of the drill. To eliminate this inconvenience, the outer diameter of the shank can be made smaller than the outer diameter of the tip cutting edge, but in that case, chips may be trapped between the outer circumferential surface of the shank and the inner wall of the machined hole. There is a risk.

In view of these points, it is an object of the present invention to provide a drill that has low cutting resistance and can improve the finishing accuracy of the inner wall of a machined hole. That is, the present invention provides a drill having a helical groove in which the outer diameter of the tip cutting edge is larger than the outer diameter of the shank by 0.04 to 0.30 mm. If the outer diameter of the tip cutting edge is increased within this range, the outer diameter of the shank will not come into contact with the inner wall of the machined hole, and furthermore, in this range, chips may become trapped between the outer peripheral surface of the shank and the inner wall of the machined hole. Prevented.

Hereinafter, the present invention will be explained with reference to drawings of embodiments. 1 is a shank of a drill; 2, 2 are a pair of chips having cutting edges 6; 3 is a helical groove; 4 is an outer peripheral surface of the shank; and 5 is an inner wall of a machined hole. This cutting edge has a curve that is convex in the rotation direction, and is a spiral curve whose curvature increases as it approaches the center from the outer periphery. When such a cutting edge shape is adopted, chips are thinner at the center than at the outer periphery, cutting resistance is small, and the chips are not pressed against the cutting blade, so they are smoothly discharged. In addition, in the present invention, the shape of the cutting edge is not necessarily limited to this embodiment, and various shapes can be adopted.

The outer diameter of the cutting edge 6 is larger than the outer diameter of the shank 1, and therefore a gap t is formed between the inner wall 5 of the machined hole and the outer peripheral surface 4 of the shank. This gap t
It is necessary to make the gap as large as possible to prevent the outer peripheral surface 4 of the shank from coming into contact with the inner wall 5 of the machined hole, but if the gap is too large, there is a risk that chips rising in the helical groove 3 will be caught in this gap. There is. Conventionally, it was thought that if this gap was formed, chips would be trapped, so a so-called margin part was formed on the rear ridge line 8 of the helical groove 3 in the direction of rotation, and this part was made to contact the machined hole. The outer diameter was formed to be the same size as the outer diameter of the cutting blade 6.

As a result, there were various drawbacks as mentioned above, but
In the present invention, no margin portion is provided, and the outer diameter of the shank is set to be smaller than the outer diameter of the cutting edge within a range of 0.04 to 0.30 mm. This range, that is, the gap t
When the thickness is in the range of 0.02 to 0.15 mm, it is possible to prevent chips from being entrapped and to prevent the outer circumferential surface 4 of the shank from coming into contact with the inner wall 5 of the machined hole.

Example 1 For a drill with a diameter of 16 mm (drill A) and a drill with a diameter of 20 mm (drill B), the diameter of the tip cutting edge was set to be larger than the outer diameter of the shank in various dimensions, and a hole with a depth of 40 mm was made under the following conditions. Work material S45C for drilling
and SS41. The above drill is made of cemented carbide (JISM20 series) and has the structure shown in Figures 1 and 2, and water-soluble emulsion type cutting oil is used as the cutting oil.
It was diluted 5 times and used. OKK, NC this drill
Processed using a milling machine (15 horsepower).

(A) Drill A: S50C: Number of revolutions 1250 rpm, feed 0.30 mm, SS41: Number of revolutions 1400 rpm, feed 0.32 mm, (B) Drill B: S50C: Number of revolutions 1000 rpm, feed 0.30 mm, SS41: Number of revolutions 1100 rpm, feed 0.38 mm, (a) If the outer diameter of the tip cutting edge is set to D + 0.02 mm with respect to the shank diameter (D), the drill shaft of both drill A and drill B will seize into the machined hole, resulting in machining. It became impossible.

(b) When the outer diameter of the tip cutting edge was set to D + 0.04 mm with respect to the diameter (D) of the shank, both drill A and drill B formed holes with smooth inner wall surfaces. The surface roughness of the inner wall surface depends on the work material.
Rmax8 for S50C, Rmax8 for SS41
It was Rmax12.

(c) When the outer diameter of the tip cutting edge was set to D + 0.12 mm with respect to the diameter (D) of the shank, holes with smooth inner walls were formed for both drill A and drill B. The surface roughness of the inner wall surface depends on the work material.
Rmax4 for S50C, Rmax4 for SS41
It was Rmax6.

(d) When the outer diameter of the tip cutting edge was set to D + 0.30 mm with respect to the diameter (D) of the shank, both drill A and drill B formed holes with smooth inner wall surfaces. The surface roughness of the inner wall surface depends on the work material.
Rmax9 for S50C, Rmax9 for SS41
It was Rmax11.

(e) When the outer diameter of the tip cutting edge is set to D + 0.35 mm with respect to the shank diameter (D), chip fragments will be welded to the outer periphery of the shaft of both Drill A and Drill B. In addition, a flaw occurred on the inner wall surface of the drilled hole, and the drill caused a walking phenomenon, creating a large spiral flaw on the inner wall, making it unnecessary to measure the surface roughness. The reason why such a large flaw occurred on the inner wall surface was because chips were caught between the shank and the inner wall.

The above-mentioned gap may be appropriately set within the above-mentioned range depending on the material of the workpiece, the dimensions of the drill, etc., but it is generally particularly preferable that the gap t is in the range of 0.08 to 0.12 mm.

In this way, the present invention prevents the outer circumferential surface of the shank from coming into contact with the inner wall of the machined hole while preventing chips from getting caught by making the outer diameter of the shank smaller than the outer diameter of the cutting edge within a certain range. and
Therefore, the rotational resistance is small, and the finishing accuracy of the inner wall of the machined hole can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line -2. 1... Shank, 2... Chip, 4... Outer peripheral surface of shank, 5... Inner wall of machined hole, 6... Cutting edge,
t...Gap.

Claims (1)

[Claims] 1. A drill having a helical groove, characterized in that the outer diameter of the tip cutting edge is larger in the range of 0.04 to 0.30 mm than the outer diameter of the shank.