A fixture for sharpening thread chasers consisting of a block of seven-sided configuration and a latch secured by a thumbscrew. The block has a base surface which rest on the table of a grinder, and an inclined front surface. There are slanting grooves in the front surface, and locating pins in the grooves. The latch can be swung clear of the grooves to allow a chaser to be inserted. One groove is intended for right hand chasers and the other for left hand chasers. When a chaser is positioned in the appropriate groove with its cutting tip facing upward, the face of the first tooth is parallel to the table so that it can be ground. By placing the same chaser in the other groove facing either upward or downward, and laying the block in its side, the hook of the chaser is presented in position to be ground.
What is claimed is
1. A fixture having means for selectively holding for sharpening right and left hand thread chasers of the type having a shank with a locating slot and a cutting tip with a hook and a tooth face at one end of the hook, said tooth face being at a first predetermined angle to the axis of said shank and said hook being at a second predetermined angle to said shank axis, said means comprising: a block having a base surface, side surfaces, an upper surface, and a front surface, said base surface being disposed obliquely with respect to said upper and front surfaces, said block having therein only two chaser shank receiving grooves for positioning said chasers for sharpening both the hook and tooth faces thereof, said grooves being substantially rectangular, and each having an upper and a lower end, formed in said front surface angularly to each other and obliquely with respect to said side surfaces, the upper end of said grooves extending through said upper surface, said grooves being each adapted to receive a said shank in sliding engagement, fixed locating means in each groove engageable with said slot for locating said shank of a chaser in said groove with its tip projecting a predetermined distance from said upper surface and fixedly retaining said chaser against axial movement, said grooves being respectively at an angle to said base surface which is substantially 90° minus said first predetermined angle and having their upper ends uniformly spaced from said base surface to cause said tooth face of chasers of opposite hand located therein respectively to lie parallel to said base surface in position suitable for grinding with said fixture supported on said base surface, said grooves being at an angle to said side surfaces which is substantially equal to said second predetermined angle to cause the end of said hook adjacent said tooth face of chasers of opposite hand located therein respectively to lie parallel to respective ones of said side surfaces in position suitable for grinding with said fixture supported on said respective side surfaces, each of said side surfaces, in their entire supporting position, lying in a single plane, and means for locking said shanks in said grooves.
2. A fixture as described in claim 1, said locating means comprising a pin disposed in said groove and engageable in said slot.
3. A fixture as described in claim 1, which includes an under surface parallel to said upper surface, and wherein the other end of said grooves extends through said under surface, said positioning means being so located in said grooves as to permit also locating chaser shanks in said grooves with their tips projecting from said under surface for grinding the hooks thereof.
This invention relates to fixtures for sharpening thread chasers of both the right and the left hand type.
BACKGROUND OF THE INVENTION
Most devices now used for mounting thread chasers to be sharpened are complicated and expensive, and require adjustment to present the chaser at the proper angle to the grinding wheel. The adjustments call for skill on the part of the operator and introduce the possibility of human error. Ordinarily, different fixtures are used to sharpen the cutting face and the hook of the chaser. The principal object of this invention is to provide a fixture which is simple and inexpensive to manufacture, which automatically positions the chaser so that the cutting face is ground to the optimum angle, and which can be used for sharpening the hook as well as the cutting face of the chaser. Other objects, advantages and novel features will be apparent from the following description.
The fixture here described consists principally of a metal block of seven-sided configuration having a base surface which rests on the grinder table and an oblique front surface. There are two grooves in the front surface disposed in converging arrangement and of a depth and width to receive the shank of a chaser. A latch is mounted on the front face and can be swung to clear the grooves, so that a chaser can be inserted, and to cover the grooves to hold the chaser in place. The latch is locked in position by a thumb screw. Locating pins in the bases of the grooves engage in the locating slots normally provided on thread chasers for positioning them in the die. The left groove is intended for left hand chasers and the right groove for right hand chasers when the faces of the cutting tooth are to be sharpened. By reversing the chasers in the grooves, and laying the block on one of its sides, the hook of a chaser is placed in the correct position for grinding.
DESCRIPTION OF THE DRAWINGS
In the drawings illustrating the invention:
FIG. 1 is a side elevation of a fixture constructed according to the invention;
FIG. 2 is a cross-section taken along line 2 -- 2 of FIG. 3;
FIG. 3 is a view of the front surface taken in the direction of the arrow 3 in FIG. 1, showing a left hand chaser in place for sharpening the tooth face and the hook; and
FIG. 4 is a bottom view of a typical chaser.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The body of the fixture is a metal block 10, having a front surface 11, a rear surface 12 parallel to the front surface, an upper surface 13 perpendicular to the front and rear surfaces, an under surface 14 parallel to surface 13, parallel side surfaces 15 and 16, and a base surface 17 disposed obliquely with respect to surfaces 11, 12, 13, and 14. The base surface is intended to rest on the table 18 of a grinder.
Extending into the block from surface 11 is a pair of converging grooves 19 and 20, said grooves being substantially rectangular as shown. The left groove (as seen in FIG. 3) is intended for left hand chasers, and the right groove for right hand chasers, when the tooth surfaces are to be ground. Locating pins 21 and 22 are disposed in the bases of the grooves. A latch bar 23 is mounted against surface 11 and is swingable about a thumb screw 24 threaded into the block. The bar can be swung from the open position, shown in full line in FIG. 3, to the closed position indicated by the dot and dash line 25. A coil spring 26, mounted in a counterbored hole 27 under the latch bar, pushes the bar out to swing freely when the thumb screw is loosened.
A typical thread chaser 28 has a hook 29, a series of teeth 30, and a locating slot 31 on its side. The upper surface 30 a of the first tooth is the surface which is ground to sharpen the chaser.
To sharpen the chaser, the chaser is placed in the appropriate groove, the left groove as here illustrated for a left hand chaser, with the pin 21 in slot 31. Bar 23 is swung to closed position and locked by the thumb screw. The groove is made to a close sliding fit with the shank portion 28a of the chaser and is of the same depth, so that the chaser is accurately positioned with its hook projecting beyond the upper end 19a of the groove, and surface 30a, which is the face of the principal cutting tooth, parallel to base surface 17 and thus to the grinding table. Face 30a is also parallel to the side to side direction of the block. If the chaser were placed in the wrong groove, for example in the position of the dotted outline 32, the error would be at once apparent.
Tooth face 30a, as shown, is at about a 35° angle to the chaser shank axis. So that it will be parallel to base surface 17 from front to rear, the grooves 19 and 20 should hold the chaser shank axis at an angle of about 90° minus the angle of the tooth face to the shank axis, or, in the drawing about the 55° angle of rear surface 12 to base surface 17, front surface 11 and the grooves 19 and 20 therein being parallel to surface 12. So that tooth face 30a is parallel to the side-to-side direction of the block, the upper ends 19a and 20a of the grooves are, as shown, uniformly distanced from base surface 17.
To sharpen the hook 29, which is disposed at an angle to the shank, for example 15°, the left hand chaser is placed in the right groove. The chaser can be placed with the hook projecting from the upper end 20a of this groove, and the block laid on its side surface 16. In that case the chaser would be in the position indicated by the dotted outline 32. Alternatively the chaser can be reversed and placed in the position indicated by the full line 33, with its hook projecting from the lower end 20b of slot 20, and the block laid on its side surface 15. In either case the end part of the hook is parallel to the grinding table, since the grooves, as shown, are at about the same angle to the respective side surfaces 15 and 16 as the angle of the hook to the shank axis.
It is understood that a right hand chaser can be similarly placed in the right groove 20 for sharpening the tooth face, and in the left groove 19 for sharpening the hook. If this chaser is placed with its hook projecting from the upper end 19a of groove 19, the block is laid on side surface 15. If the chaser is placed with its hook projecting from the lower end 19b, the block is laid on side surface 16. In either case the hook face to be ground will be parallel to the grinding table.
A single fixture of this type will accomodate a range of right and left hand chasers having the same shank size, both for grinding the tooth faces and for grinding the hooks. As no adjustments are required there is no possibility of error, and considerable time is saved in setting up the chasers for sharpening. The fixture can also be made up in different sizes to accommodate chasers of various shank sizes.