US83469A - Peters - Google Patents

Description

esteem HORACE I. CRANDALL, OF NEW BED-FORD, MASSACHUSETTS.

Letters Patent No. 83,469, dated October 27, 1868. l i l INIPROVEMENT IN COG-WHEELS AIE'OR. lG-EARING;

wb- L The Schedule referred to in these Lettere Patent and making part of the same.

The nature of my invention consists of three distinct features, which, in combination, will produce such a form of tooth (for double-faced teeth) that any two bf the saine pitch can run equally correct together in all their various positions.

To enable those skilled in the arts to apply my invention, I will proceed to describe the saine.

The rule for making the old English -system of teeth is to space off the thickness of the Vteeth on the pitchline or circle from the radial centre-line of each tooth, then using the pitch for the radius for sweeping the faces of the teeth, the 'fixed leg ofthe compass resting uponV the pitch-line or circle, as represented in Figures l and .2, plate l. i Some makers have endeavored to overcome the eriors of the above system by adopting a new radius and locus-centre line on `whichto rest the fixed legof the compass, which reduces the thickness of the points, and increases the'thickness of the roots. (See dotted lines L L, iig. l, plate l.)

The teeth in Williss system of gears are formed by the use of an instrument called the odontgraph, iiomthe use of which the locus-centres and radii are derived.

By reference to fig. 2, plate 2, it will be seen that the pinion-teeth are just as thick as they can be at the pitch-circle to work into the rack. Now look at iig. 1- on same plate, where two such pinions are meshed into each other, and an error or a lack occurs in which the teeth do not ill the opposing cavities by about T-l-U of an inch, a portion of which is its error in angular velocity.

The same error will appear in any of the modifica tions of the English system, only to a greater degree than in Williss. y (Sue English, iigs. l and 2, plate l.)

In my system of gears, there are three peculiar and distinct features, neither of which has been used or claimed by any writer upon the subject previous to my invention.

'lhe irst of these features is, that the thickness of all teeth must be spaced at" right angles from the radial centre-line ofveach tooth, from the intersection of that line with the pitch-circle. (See B B, iigs. l and 2, plate 5.)

'lhis feature, when properly used, will give a universal condition of thickness, regardless of the curvayture of the pitch-circle, or of radii, or locus-centres.

The second feature of my system is, that the meeting-point of the root and point-faces is not at the pitchcircle, but inside of it, in proportion to the pitch and number of teeth. (This point will hereafter be called the knuckle.)

By reference to dotted lines L L on iig. 1, plate 3, also L L, plates 4 and 5, it will be seen that without this knuckle the teeth could never be tight in those positions; and referring to tooth A A of rack on iig. l, plate 3, it will be seen that without this feature ofthe knuckle K K, the tooth A A would not be in contact with either of the pinion-teeth, and that whichever was the driver, either rack or pinion, the operative points would be at M M, which is at an angle of twenty-two and a half degrees om the centre of motion, and the rack-tooth A A, which ought to be doing nearly all the work inv this position, would, without this feature of the knuckle, be doing nothing; and similar to this will be the result of all double-faced teeth that have their culminating points at the pitch-circle.

rlhe third feature of my system is, that the pinion which has the least number of teeth in the set, determines and furnishes the radius for sweeping the faces of all the teeth that are included in that set.

The three points necessary for forming a segment of this circle are found in thefollowing manner:

The point B BX, iig. 1, plate 3, and figs. l and 2, plates 4 and 5, indicating the thickness of teeth, as before described, is a fixed point.

. The second point of the segment is indicated at M Miig. 1, plate .3, and figs. l and 2, plate 4, which point cannot be deviated from and maintain constant contact of the teeth.

For the third point of the segment, reference must be had to point C O, figs. l and. 2, plate 4, which is likewise a fixed point in the segment of the circle which forms the faces'of the teeth; and from these three points are found the radius and locus-centre for the same.

For the obtaining of `the radius and locus-centres, reference must be had to the following rules and tables of coeiiicients:

Table of Coecients for Cfrandalls System of Gcars.-Ooe17cients for finding Faces of Points.

f3 .2 e .2 B 2 .2 8 .e B 3 B .2 s 5 25 'E 5 Qi 5 5 5 si o' 8 e e' e o' o v o' 5 z 8 z z z z z r3 z z Rule for the above.

Multiply the coeicients in the table corresponding' to the number of teeth by the pitch in inches and hundredths, and by the number lof teeth; the product will be in' lunulredths 0f an inch. This gives the distance inside of the pitch-circle or line, for the point face-loeus-centre line. All number of teeth above 200 to be calculated as 200.

Oocgcent for jndi'ng the locus-centre line for faces o f yroots, the distance outside of pitch-circle. Oce'ice'entjbr the distance outside of pitch-knuckle, 24,00.

Iinside of pttch-muckle, 24,00. RULE-Multiply by pitch and divide by No. teeth.

Ans. in ths.

RULE-Multiply by pitch.

Ans. in 100tl1s. .Depth of rlmt of teeth, 32,500, Zeng/th of points, 31,00. RULE-Multiplyby pitch.

Ans. in 100th`s.

RULE-Multiply by pitch.

E 1,85. Ans. in 100ths.

Rad/ias for sweeping faces of teeth., 61,75.

" Thickness of teeth at ptchJine for Ivery close gear, 40,0 Rm E Multiply by pitch ZI!- r I 1 For cast gea/rs, Vedwm 400 Ans. in 100ths.

ery open 48,0

NOTE-No teeth below fifteen in number can be strictly accurate.

At three-inch pitcln'the error of twelve teeth will be 3%, and ten teeth ,46 of an inch.

the Locus-Centre Line fm' I disclaim any and all systems folforrning the teeth of gears that are usually termed involute, in which 'the faces 0f the'teeth are formed with one continuous curve from point to root, and all systems which have not the three featmes which have been named and described in my system.

What I claim as my invention, and 'desire to secure by Letters Patent, is-

1. The teeth of cog-wheels, for gearing, constructed as hereinbefere. described.

2. The thickness of the teeth spaced at right angles from the centre line of the same, substantially as set forth.

3. The meeting-point of the root and point-face circles inside 0f the pitch-circle, in accordance with the rules as specified.

4. The radii, for sweeping the faces of the teeth, obtainediiom the wheel containing` the least number of teeth in a set, as so described.

-Witnesses:v HORACE I. CRANDALL.

J AMES LYLE, WILLIAM E. TIRRELL.

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