US 2367637 A
Description (OCR text may contain errors)
Jan. 16, 1945. ZUBUN 2,367,637 I DRILLING BIT Filed Aug. 13, 1941 zfoHA/A. Z054 W,
[N VE N TOR atented Jan. 16, 1945 STATES PATENT OFFICE 4 Claims.
This invention relates to drilling bits, and more particularly to drilling bits of the type involving a body rotatable about the axis of the hole and a plurality of rollers carrying cutting surfaces mounted on the bit body.
In the design of rollers with cutting surfaces for bits of this type, it is possible to vary the cutting effect of an individual cutting surface by so shaping it, and so disposing the axis of its roller that it either has true rolling motion on the hole bottom, or has a rolling motion accompanied by slippage on the formation. In thecase of conical cutting surfaces or frusto-conical cutting surfaces, the degree of scraping which accompanies the rolling is governed by how far the shape of the surface departs from a cone having its apex at the axis of rotation of the bit. It is obvious that the only shape of cutting surface which will have a true rolling motion on the hole bottom is a conical, or frusto-conical surface, with the apex of the cone at the bit axis. All other shapes of surface or deviations of apex have a rolling motion accompanied by a slipping or scraping motion.
It is a well known fact that all bits involving rollers with cutting surfaces have a tendency to leave a pattern on the hole bottom. In nonbrittle formations with great crushing strength, this pattern is almost a true picture of the tooth arrangement of the cutting surface, causing the roller to gear with this pattern to such an extent that drilling progress almost comes to a standstill. If now all rollers with frusto-conical cutting surfaces assembled on one bit have the same apex relative to the bit axis, then all of them will partake in this gearing effect with the bottom of the hole, holding up drilling progress.
Previous attempts to minimize this effect have been limited to variation in the shape or position of the teeth, so that, of a plurality of rollers, the cutting surface of one roller makes one pattern, and the cutting surface of another roller superimposes a different pattern over it. However, although this may result in a finer pattern, the various patterns do not completely obliterate each other. Consequently, the tracking of the teeth in the pattern is never entirely eliminated.
It is therefore an object of the present invention to provide a bit in which the pattern-forming tendency is minimized.
It is a further object of the present invention to provide a drilling bit in which a given zone of the hole bottom is subjected to a rolling cutting action having a low degree of scraping motion,
followed by another rolling cutting action involving a greater degree of scraping motion.
It is a further object of the present invention to Provide a drilling bit in which a first roller. with different cutting surfaces drills with one cutting surface on one zone of the hole bottom with a. cutting action with a givendegree of scraping motion, and drills with another cutting surface of the same roller on another zone of the hole bottom with another given degree of scraping motion; while a second roller of the same bit has cutting surfaces which drill the same zones with cutting surfaces having different degrees of scraping motion, thus making it possible for a plurality of cutting surfaces on different rollers to remove the formation in one and the same zone simultaneously but with a different degree of scraping motion.
Briefly, it is proposed to provide a plurality of rollers of which some at least will have a cutting surface in contact with the hole bottom rolling thereover with one degree of scraping motion while other rollers have a cutting surface in contact with the zone of the hole bottom traversed by the first mentioned surface and having Figure 3 is asimilar" section of a modified bit embodying the present invention.
The bit shown in Figures land 2 has been illustrated by taking the section to show the rollers as having their axes parallel to the plane of the paper, ,to facilitate illustration of the principle involved, it being understood, however, that the bit actually consists of three rollers spaced around the bit axis. As showma bit body l0 provided with a threaded pin I l for connection to the drill collar, supports three rollers, l2, l3, and I4, the roller l3 appearing in both figures.
Each roller is provided with a reaming surface l5, which is conventional, and is merely for the purpose of assuring a full gauge bore. The bottom engaging cutting surfaces of the rollers are, however, different. Roller I3 has a cutting surface [6 in contact with the outermost zone of the hole bottom, the cutting surface being so formed that its apex is a point A. This surface l6 thus has a true rolling motion over the zone X of the hole bottom. Cutting surface I! of this roller, on the other hand, is in the form of a plane, and thus obviously scrapes over zone Y of the hole bottom.
Roller l2, as shown in Figure 1, has its axis at a different angle to the axis of the hole than the roller I3. Therefore, as the apex of the cutting surface I8 of the roller does not fall atthe axis of rotation of the bit, but to the right, point B, the cutting surface I8 of the roller I2 scrapes the formation as it traverses the zone X of the hole bottom. The cutting surface I 9, on the other hand, has its apex at the axis of rotation of the bit, at C, and thus has a true rolling motion over zone Y of the hole bottom.
The principle of operation should be clear from the above description. In fact, a two cone bit embodying theabove cutters would demonstrate the principle correctly. The surface I6 of the roller I3 has a true rolling motion on zone X of the hole bottom and surface I8 of roller I2 has a scraping motion on the same zone of the hole bottom. Surface I9 of roller I2 has a true rolling motion over zone Y of the hole bottom while surface I! of roller I3 scrapes this zone. Thus, each zone of the hole bottom is alternately cut by a true rolling surface and then by a scraping surface.
The cutting surfaces I6 and I! of roller I3 have a true rolling motion and a full scraping motion respectively. This is merely the extreme limit to which the differentiation in cutting action might be pushed. The essential thing to be pointed out by this arrangement is that one cutting surface Cutting surface has its apex D closer to the axis of the bit than that of cutting surface I8 of the roller I 2 and the apex E of the cutting surface 2I is slightly removed from the bit axis. Thus, the motion of surface 20 of roller I4, is
intermediate the motion of cutting surfaces I8 and I6 of the rollers I2 and I3. Likewise the motion of surface 2I of the roller I4 is intermediate the motion.of the cutting surfaces I9 and ll of rollers I2 and I3.
As a modification, the construction shown in Figure 3 may be employed. In this form a bit body supports a pair of rollers 3| and 32 for rotation. The surface of roller 3| has true rolling contact with the entire hole bottom, zone X thus extending across the entire hole bottom. Roller 32 has its cutting surface with a certain degree of scraping over the portion of the bottom it contacts. This form of bit also subjects the hole bottom to a true rolling cutting action caused by the cutting surface of one roller, followed by a scraping motion of the cutting surface of the other roller.
It is to be understood that this form also is idealized with the roller 3| having its cutting surface in the form of a true rolling cone, while in practice it need only have a lesser degree of scraping motion than the surface of the roller 32.
The constructions shown thus both achieve a different type of cutting on all or substantially all of the hole bottom. The surfaces of the rollers in scraping contact with the bottom tend to effectually obliterate any pattern which cutting surfaces in truer rolling relation with the hole bottom may tend to form, by slicing or knocking off the high portions of the pattern. There is thus no opportunity for the pattern to develop a sufficient depth to interfere with proper cutting. At the same time, such pattern as it does develop is easily broken by the cutting surfaces in scraping relation to the hole bottom, and these surfaces are therefore protected from undue wear. In addition to this, the presence of the two different kinds of cutting action in the bit over the entire hole bottom surface permits the bit to make progress through a larger number of different types of formation than would be the case if the cutting surfaces traversing a given zone of the formation were to perform with the same degree of scraping motion.
Although I have used the term true rolling" in this description, I wish it clearly understood that this term is intended to be relative rather than absolute. Many rollers are made with their cutting surfaces doubly curved, which give no true rolling motion at all, but since even cutting surfaces that have considerable scraping motion leave some pattern, it is the difference in scraping motion that is intended, as far as possible, to obliterate with the cutting surface of one roller any patterns which might be formed in the hole bottom by the cutting surface of another roller. For the purpose of clarity of illustration, the present device is illustrated without the teeth which are actually present on the cutting surfaces, and it is to be understood that these teeth may be inside, outside, or extend through the illustrated "cutting surfaces."
1. In a rotary drilling bit, a plurality of rollers having individual frusto-conical cutting surfaces in simultan. cus contact with the hole bottom, an individual cutting surface of one roller rolling over the same zone of the hole bottom as an individual cutting surface of another roller, the apices of said individual 'frusto-conical cutting surfaces being differently spaced from the hole axis, whereby said cutting surfaces roll over this zone with different degrees of scraping motion.
2. In a rotary drilling bit, a plurality of rollers having individual cutting surfaces in simultaneous contact with the hole bottom, one of said rollers having a plurality of individual cutting surfaces rolling over concentric zones on the hole bottom, the cutting surface rolling on the outer zone with a greater degree of scraping motion than the surface rolling on the inner zone, and another roller having cutting surfaces rolling over substantially the same zones, with a greater degree of scraping motion on the inner zone than on the outer zone.
3. In a rotary drilling bit, a plurality of rollers having individual cutting surfaces in simultaneous contact with the hole bottom, one of said rollers having a frusto-conical cutting surface with its apex at the hole axis and a plane cutting surface perpendicular to the axis of the roller, and a second roller having a conical cutting surface engaging the zone of the hole bottom traversed by said plane cutting surface.
4. In a rotary drilling hit, three rollers having individual cutting surfaces in simultaneous contact with the hole bottom, the cutting surfaces of all three rollers defining a pair of concentric zones on the hole bottom, the individual cutting surfaces of any one roller rolling over said zones with different degrees of scraping motion, and the individual cutting surfaces of the different rollers in contact with any one zone having different degrees of scraping motion.
JOHN A. ZUBLDI.