US1330660A

US1330660A - Method and apparatus for casting propeller-wheels

Info

Publication number: US1330660A
Application number: US302145A
Authority: US
Inventors: Thacher Thomas Oxenbridge
Original assignee: THACHER PROPELLER AND FOUNDRY
Current assignee: THACHER PROPELLER AND FOUNDRY; THACHER PROPELLER AND FOUNDRY Corp
Priority date: 1919-06-06
Filing date: 1919-06-06
Publication date: 1920-02-10
Anticipated expiration: 1937-02-10

Description

T. 0. THACHER.

METHOD AND APPARATUS FOR CASTING PROPELLER WHEELS.

APPLICATION FILED JUNE 6,!919. 1,330,660. Patented Feb.1(),1920.

3 SHEEIS' SHEEI I.

l l l INVENTOR 01 91M?" BY QJZWL I 4 M ATTORNEYS T. O. THACHER. METHOD AND APPARATUS FOR CASTING PROPELLER WHEELS.

,APFLICATION FILED JUNE 6, 1919- -1, 33O,660. Patented Feb. 10,1920.

* 3 SHEETS-SHEET 2.

f /%n 5 O INVENTOR 7% WMZV 1 BY W,AM,MWZ

ATTORNEY TLO. THACHER.

METHOD AND APPARATUS FOR CASTING PROPELLER WHEELS.

APPLICATION FILED JUNE 6,1919.

1,330,660. Patented Feb. 10,1920.

3 SHEETSSHEET 3.

INVENTOR @gm W, 4%, K mai iamza ATTORNEYS o i i v UNITED STATES PATENT onrrcn. THOMAS OXENBRIDGE THAC HER, OF ALBANY, NEW YORK, ASS'IGNOF. TO THACHER PROPELLER AND FOUNDRY CORPORATION, OF ALBANY, NEW YORK, A coRro- BATION' or NEW YORK.

METHOD AND APPARATUS FOR CASTING PROPELLERQWHEELS.

Application filed June 6, 1919. Serial No. 302,145.

To all whom it may-concern:

Be it known that I, THOMAS O. THAGHER, a citizen of theUnited States, residing at Albany, in the county of Albany, State of New York, have invented certain new and useful Improvements in Methods and Appaart to which it appertains to make and use the same.

This invention relates to method and apparatus for casting propeller wheels, and blades, which has for its object to provide a propeller in which the blades, whether cast separately or as an integral propeller wheel, will be so accurate in their position, pitch and dimensions as to require little or no finishing to secure a wheel which is balanced and symmetrical.

A 'further object of the invention is to provide a method and apparatus of casting propeller wheels and blades by means of which accurate blades or propellers may be made in any quantity from the same set of patterns without requiring greater skillon the part of the foundryman than possessed by the ordinary labor employed for the pur ose.

p A further object of the invention is to provide a method and apparatus for forming molds for propeller wheels and blades whereby exact replicas of the pattern wheel or blade may be made Without the usual inaccuracies resulting from shrinkage of the sand, dilierences in the degree of tamping, shifting of the pattern, etc., which are inevitable when the individual skill of the molder is depended upon.

The invention of this application constitutes an improvement or a modification of the invention disclosed in my copcndi'ng application No. 259,493, filed October 24;, 1918,

and is directed particularly to the application of the general principles of the method there disclosed to the production of single propeller blades and propellers of smaller size which may be cast in a single flask.

The invention of this application also comprises improvements in the method of producing the molds in the flasks and. improvements' in the apparatus employed whereby a singleset of flasks and pattern boxes may be employed with a series of patterns for the production of various sizes and shapes of propellers and blades.

The invention of this application also in cludes improvements in the method of castmg the wheel or blade so as to carry the inevitable surface dust "on the face of the molds into a portion of the blade where it may be readily removed, leaving the finlshed blade symmetrical and with a smooth surface free from impurities. Another feature of my invention of the greatest importance is that the stepsof filling the flasksand withdrawin the patterns may be performed by molding machines of the standard types now on the market-without interferlng in any way with the accuracy or quallty of the work, thereby reducing the tune required for producing the casting to a fraction of the time formerl 1 required and correspondingly-reducing t e cost of manufacture.

In the accompanying drawings I have Patented Feb. 10, 1920.

illustrated my improved method as applied to the production of separate blades and also to integral propellers.

In said drawings,

Figure 1 is a vertical section showing one-' half of the two-part pattern box employed in forming the molds before the blade pattern is applied;

Fig. 2' is a similar view of the other half of the pattern box;

Fig. 3 is a sectional view of the pattern box shown in Fig. 1 showing one step in the process of making the patterns;

Fig. 4 is a sectional view on line 4-4 of Fig. 5, showing the blade pattern in the pattern box;

Fig. 5* is a plan view of the core pattern part shown in Fig. 4:;

Fig 6 is a sectional view similar to Fig.

2 but showing the blade pattern in place;

Fig. 7 is a plan view of the pattern-box part shown in Fig. 6; v

Fig. 8 is a side elevation of the pattern box part shown in Fig. .63

Fig. 9 is a perspective view of the piece from which the pattern-supporting blocks are cut;

Fig. 10 is a side elevation of a gage employed in shaping the pattern-supporting blocks;

Fig. 11 is a vertical sectional view showing the method of molding the impression of the blade in the flask;

Fig. 12 is a similar view showing the two halves of the flask assembled together and showing the impression of the blade therein;

Fig. 13 is a view similar to Fig.7 but of a modified type of propeller blade;

Fig. 14L is a vertical sectional view of a pattern-box used for molding entire propellers in a single flask;

Fig. 15 is a plan view of the pattern box shown in Fig. 14;

' Fig. 16 is a vertical section of the flask containing the impression of an entire blade, and

Fig. 17 is a side elevation of a modified gage for measuring the pitchplane surfaces of the blocks.

In Figs. 1 to 13 of the accompanying drawings I have shown an apparatus whereby a single pattern-box and a single flask may be employed for producing blades of different sizes and pitch by the employment of detachable pattern blocks. As shown, the pattern-box consists of a boxlike part 1 preferably formed of metal and with its interior of circular cross section and with its side walls tapering so that the interior of the pattern-box when the pattern section is removed has the outline of a frustu1n of a cone, with the base of the cone at the open side of the box.

The bottom of the box is formed of a metal plate having its upper surface machined ofi' to a true surface at right angles to the axis of the cone, the bottom being provided at its center with a dowel pin 3 to hold the detachablepattern 4 in place.

In the detail drawings I have shown my apparatus as designed for forming single propeller blades to be separately attached to the hub on the propeller shaft and for this ,purpose one side of the pattern box 1 has a flat portion 5 perpendicular to the face of the base of the box and of a width slightly larger than the attaching flanges of the largest size blade for which the pattern box is designed.

The upper edge of the pattern box sur' rounding the open side is-formed as a flange 6 of rectangular outline and with its upper surface machined off to a true plane parallel with the inner surface of the bottom plate of the box 1.

The other half of the pattern box consists simply of a metal plate 7 having one surface machined off to a true plane. The cover plate 7 is provided at the center with a dowel pin 3 for holding the pattern block in place. The plate 7 has also attached to it near one side-a vertical bar or plate 14., the face of the plate 14 being the same distance from the center of the dowel pin as the fiat surface 9 of the pattern box 1. The pattern blocks are preferably not attached directly to the bottom of the box land to the plate 7 but are separated therefrom by

spacers

2 and 13 respectively for a purpose which will be later described.

The flange of plate 7 will preferably be provided with marginal holes 8 for facilitating their attachment to the flask section when the mold is to be formed in the flask.

One of the important features of my invention is my improved method of forming the pattern block sections. one of which is to be set in the part 1 of the patternbox while the other is attached to the machined face of the plate 7. The two pattern blocks which are numbered 4 ands, respectively, are preferably formed of wood, either of single blocks or by building up separate pieces, to avoid too extensive cutting, as mayv be preferable in practice, particularly for larger size blades. For simplicity of illustration I have shown each section of the pattern block out out of a single block of wood. The block before cutting is shown in Fig. 9, and will be of a thickness substantially as great orgreater than the depth of the box 1, with one transverse face 9 cut to a true plane surface and with one vertical face 10 cut to a plane surface normal to the face 9 and of a width at least equal to the width of the flat side formed in pattern box 1. The face 9 of the block is provided with a hole 11 for receiving'the dowel pin 3, the

hole being located in the block with respect to the face 10 to fit the dowel pin when the face is in engagement with the flat face form-ed in-the pattern box. In its other dimensions the block will be larger than the corresponding dimensions of the pattern box. I

The surface of the plate opposite the face 9 is then cut down to the desired pitch plane of the wheel to be cast, the pitch plane being determined from a center set back of the fiat face 10 a distance equal to the distance from the center of the propeller shaft to the face of the hub to which the blade is to be i attached. The proper surface may be readily determined by means of the apparatus as shown in Fig. 10.

This apparatus consists of a bed-plate 15 having a vertical shaft 16 set therein, the shaft being formed with a spiral key or thread 17 of -the desired pitch of the propeller blade. Near the base of the shaft the plate 15 has a shoulder 18 against which the flat side 10 of the block will be clamped in any suitable manner, a dowel pin also being provided in the plate for registering with the hole in the block. The shaft 16 may be adjustable toward and from the shoulder in a line normal to its face so that the same apparatus may be used for blades of different proportions. The shaft 16 carries a straight edge 19 with its hub threaded on the spiral key 17, so that when the straight edge is revolved around the shaft its lower edge will describe the pitch plane corresponding to the thread of the shaft. The block will pitch plane determined by the rotation of.

the straight edge of the spiral thread 17'.

After one

block

4, 4 is completed to this extent, a similar block will have one surface .dressed to a true pitch plane in the same manner, and the two blocks thus partially completed will then be placed with their pitch planes in contact, which, if truly cut,

' will coincide throughout their entire surfaces. The two blocks thus matched together will then be clamped in a lathe with the spindles centered on the dowel pin holes and turned down to a tapering periphery until, the smaller diameter is just equal to the diameter of the spacer 2 at the bottom of the pattern box 1. This block will then formthe completed pattern block 4 except for the pattern section, and will fit accurately in the bottom of the pattern box.

The other block will also fit in the pattern box with its pitch plane surface resting on the pitch plane surface of the lower section 4. In practice the combined thickness of the blocks will preferably be originally somewhat greater than the depth of the pattern box 1 so that the pitch plane surfaces may be dressed ofi until absolutely accurate if the first cutting is imperfect, without making the block too small. After the two block sections are set in the pattern box 1 the extra thickness of theblock 4", if any, will bedressed off so that the filled plate 13 will just fill the pattern box flush with the flange. The block 4 will then be withdrawn from the pattern box and its base set on the face of the plate 13 which it should accurately fit. The

filler plates

2 and 13 may be dispensed with if desired and the pattern blocks attached directly to the cover plateand the bottom of the pattern box respectivelyfbut in an outfit forproducing blades of varying dimensions with the same pattern-boxes and flasks, a set of filler plates of varying thickness may be used with advantage in fitting the blocks in the pattern boxes without excessive trimming of the blocks.

The next step in my improved method is to apply to the pitch plane surfaces the parts of the blade pattern which it is dethe propeller has a sufficiently smooth sursired to reproduce. The specimen blade or pattern, which may be of wood or aluminum, is cut in two parts along the pitch Y plane, as indicated. at 21 and 22. I I One part of the blade pattern, for instance, part 21, will then be attached to the pitch plane surface of one pattern block, say the art 4, while the other pattern will be simi arly attached to the block 4.

The. two sections of the pattern box will now be finished and may be used for forming the blade molds. For this purpose I employ a flask in' two parts, 23 and 24, respectively, the part 23 being preferably, but not necessarily, not-so deep as the part 24, the meeting flanges of the two parts being accurately machined and provided with corner holes corresponding with the holes 8 in the pattern-box sections. The pattern-box 1 will be attached with its flange clamped 85 against the flan e of the deeper half 24 of the flask, and W1 1 be rammed upwith sand mixture and the pattern-box withdrawn and the mold baked in the" usual manner. The other section of the pattern-box will then be clamped to the deeper section of the flask and the core molded in the deeper section and also baked, suitable holes being formed in the mold for the pouring of the metal.

The two parts, of the flask are then clamped together and the mold will be ready for pouring, which may be accomplished in any approved manner, for instance, in the manner described in my co-p'ending application above referred to.

The pattern-box formed in the above manner may be used repeatedly for forming molds for identical blades and the blades may-not only be identical with each other, but each will necessarily have its driving surface accurately coinciding with the de' sired pitch plane of the propeller and its hub section faced off accurately with relation to the axis of the blade so that no machining of the blade will be necessary or desirable to form a finished propeller of most accurate dimensions and balance.

By using baked molds in place of green sand for the casting, the entire surface of face for skin friction to be negligible, even on the driving face.

Propeller blades of different sizes and pitch may be readily made from the same set of pattern-boxes, and flasks, by making up

different blocks

4, 4 for each type of blade to be manufactured. The apparatus for gaging the pitch plane shown in Fig. 10 may be used for all different sizes by having the shaft carriage adjustable in the manner described, the shafts themselves being detachable so that shafts of different pitch ma be substituted. The apparatus shown inFig. 10 is suitable for measuring the surfaces of pattern blocks for blades of mod- 1? metal: lplate;

erate size and small pitch but for large blades and blades of steep pitch, I prefer to use the apparatus disclosed in Fig. 17. This apparatus may also be employed to advan- 5 tage for cutting a number of duplicate pattern blocks at once, either for the single blade molds or for molding the solid wheels as shown in Figs. 14, and 16. This device consists of a bedplate 15 havinga true surface and supporting at its center a smooth vertical shaft lo A straight edge 19 is mounted on the shaft 16 for free rotation about the center of the shaft, the end of the straight edge resting on an arcuate cam 18 whose edge is cut to the desired pitch plane.

This apparatus may be used to gage a number of blocks at once, for instance three, by merely adding to the hub of the straight edge. additional arms 19 projecting from 20 the hub at the proper angles, the three blocks being held in proper place by dowel pins set in the face of the base plate at points separated to the same extent as the straight e and the additional arms 19 f desired, the bolt holes 26 in the hub sections of the blades may be cast in the blades byzrsmeans of corresponding projections formed on a. small separate core 27 which re is-aset in the flask to fill the space formed bi the vertical plate 14.

.. Inathe above described figures I have shown my improved method as applied to the;manufacture of separate blades to be a r: .1 attached to a separately formed lmb, but my improved procedure of making the patterns innit tribe employed with equal advantage in @foniningg'kthe molds for a propeller to be .foianed" In: a single casting, The onlysuba stantial; ange necessary for this purpose late t substitution of a pair of plates ela hfor a .miectiugua. an angle corresponding with the l nihiseotzion ,of the propeller to be included are; qinsericliitrrflaski The pattern-box 1 may also abe:a'anoditieel'cby having its transverse partition 5 of V-shape instead of flat. fs'flfllf; a vla ggegnimiber of con'iparatively small rep, lens a o be cast I may with advani -tage; take up ,,;a pattern-box designed to uform,, mhld for the entire propeller, as

illustrated in Figs. 14 and 15. I preferably ;cmplo,yi.a roundgpattcrnsbox which may be sirn-plytfiameund,{flask section such as shown :giiirllig.

'16....rnd, gwith .itsiopen face provided in l l edgehaving a flange iefinishm ;b.v in s of which it 18 to be tern-box consists of a afimvi roles in its margin corthemars 29 of the. box porn i, and provided at z e-quallynspaoedepoints symmetrical with its *nenteii wiitliuholes 30,- in jwhich are inserted 'ih 'i ithez doweliupirisi l projecting from the bottom of the pattern blocks 32, one of which single plate 14, the plates 14 is provided for each blade, here shown as three in number. The pattern blocks 82 will preferably be made by the procedure above described, and will be identical with each other, and will have their dowel holes carefully positioned so that the three pitch plane surfaces will occupy exactly symmetrical positions with relation to the center of the plate.

Before the pattern pieces for the blades or hub wheels are attached to the blocks 32 the plate will be attached to the box portion and the box will be filled with a plaster Paris or some other suitable plastic molding composition so that there will be formed in the box an exact replica of the pattern blocks 31. Preferably when this procedure is employed the pattern blocks 32 will not extend to the center of the plate but instead the plate will be provided at the center with a detachable cylindrical block 33 for forming in the mold produced in the pattern-box a central recess large enough to receive the separate hub pattern when the mold is used as a pattern for molding the cores in the flask sections.

After the top plate of the pattern-box has been used to form the plaster mold in the box portion of the pattern-box there will be attached to the pitch plane faces of the pattern blocks on the plate and also the molded surfaces in the pattern-box the blade pattern sections 36 formed by dividing the pattern blades in the manner above described. A separate hub section for each part of the pattern-box will also be provided so that when the two half cores are formed in the sections of the flask a mold for the complete propeller with the hub Will be formed.

A cylindrical two-part flask 35 such as shown in Fig. 16 will be employed, the molds being'formed in the flask sections in the same manner as when molding a single blade. The propeller may be cast with a solid hub to be later' bored for the propeller shaft, or acenter core such as described in my c0- pending application above referred to, may be used to form the shaft opening in the cast propeller.

Instead of molding the lower part of the pattern-box in plaster in the manner described to obtain accurate replicas of pitch plane surfaces of the upper part, the pattern blocks may be formed of wood or other material in any desired manner, for instance, separate sectors for each blade, by the procedure above described, and assembled in the box. Also, the pattern for the hub section of the propeller may be integral with the blade sections instead of formed in a separate piece. The metal will be poured in any approved manner, for instance that described in my above mentioned co-pending application.

When the metal is poured into a mold, even when the mold is formed of hard baked mixture such as Iemploy, a small amount of surface dust and other impurities are takenup by the metal and carried to the edge of the blade sothat in the finished ropeller the surface atthe edge of the b ade may be undesirably rough. To obviate this difliculty and provide for the ready removal of this unavoidable'surface dirt, I preferably form the molds with-a shallow recess, I as shown at 41 in Fig. 12, around the edge of the blade into which the dirt will be carried by the molten metal when the blade is cast, the metal forming a thin fin around the edge of the blade. This fin can be readily broken off the edge of the blade after the metal is cold, the line of breakage accurately following the edge of the blade proper. The recess may be readily formed in the mold by attachin a thin strip to the faceof the pattern b ock around the edge of the blade pattern.

I have P as cut out of wood as the preferable I method of making a permanent durable pattern but the patterns may obviously be made. by other methods and of different materials.

For instance, the blocks may be] made of" plastic material and the revoluble straight;

. to the truepitch plane. I I In the foregoing description I have described the manner of carrying out the va-' rious steps of my improved method injde tail, and also the details of construction of apparatus preferably employed. Itwillbe.

understood, however, thatthe invention is not limited to the details 'of such method and apparatus, but that they may be variously modified without departing-from the spirit of the invention.

I claim:

1. The method of forming a pattern for propeller blade molds which consists in forming on a piece of suitable material a surface shaped to the pitch plane of the propeller, and attaching to said surface a portion of a propeller blade pattern similar to that formed by dividing the complete blade pattern on its pitch plane.

2. The method of forming patterns for ropeller blade molds' which consists in orming one surface of a block of suitable material to conform to the desired pitch plane, forming a replica of such surface on another block of material and then attaching to the pitch plane surfaces so formed the two parts of a pattern blade similar to that formed by dividing the blade along its pitch plane. 7 Y

3. The method of forming patterns for molding propeller blades which consists in providing a box having a pluralit of secv ti0ns,- attaching to one $90. 9. erect a lar to that forme describedthe pattern blocks 4 and,

- pitch edge used as a tool to sweepup the surface block of attern-forming material with an exposed ace shaped to the desired pitch lane, attachin to another section'of the ox a second b ock of pattern-forming material having its surface shaped to the pitch plane and fitting the pitch plane surface of the first-mentioned section, shaping the other surfaces of the blocks so that when the blocks are fitted together they fill the box, then separatin the box sections and attaching to the pitc plane surface of eachblock a portion of a pro eller blade pattern simi- II by dividing the pattern along its pitch plan j 4. The method of forming the patterns so for propeller blade molds which consists in providing a two-part box, attaching to one portion of the box a" block of pattern-forming material havin its exposed face shaped to'the desired pitc plane, attaching to them;

other part of the box a second block of pattern-formin material having its surface shaped to t e itch plane and fitting the pitch plane sur ace of the other block, shaping the other surfaces of the two blocks so that the matched blocks fill the box, then separating the box parts and attaching to the plane surface of each one portion of a propel er blade pattern similar to that pitch lplane. I 5. he method of forming the patterns formed by dividing the pattern along its for propeller blade. molds which consists in providing a two-part box, attaching to one,

portion of the box a block of pattern-form-1Qo I ing material having its exposed face shaped to the desired pitch plane, attaching to the. other part of the box a second block of at-' tern-forming material having its sur ace shaped to the" itch plane and fitting the pitch plane sur ace of the other block, shap- .ing the other surfaces of the two blocks so that the matched blocks fill the box, then separating the box parts and attaching to the pitch plane surface of each one portion of a propeller blade pattern similar to that formed by dividing a pattern of smaller dimensions than the pitch plane surfaces along its pitch plane.

viding a box co prising-a box portion having tapering w lls, a cover plate having its surface fitting the open side of said box portion, then forming a pattern block fitting 120 the bottom of said box portion with-its upper surface shaped. to the pitch p ane of thepropeller, attaching to the face of the plate a second attern block shaped to fill I 6. The method 'f forming patterns for propeller blade yids which consists in prothe portion of t e box above the first-men- 126 tioned block with a pitch plane surface accurately matching the pitch plane surface of the first-mentioned block, then separating the box parts and attaching to the pitch plane surfaces respectively the portions of m I I part having its open face shaped to fit the said face of the pattern-box section, whereby the mold of the pattern in the pattern-box section is accurately positioned inthe flask part.

8. The method of formingmolds forpropeller blades which consists in providing a,

sectional pattern-box having pattern-carrying portions divided on the pitch line of the blade to be molded and with partial blade patterns provided on the face of each section, attaching each section to the open face of one part of a sectional flask, filling the flask with sand mixture to thereby form in each a mold of the corresponding portion of the propeller blade accurately positioned in the flask section with relation to its open side, whereby the flask sections when connected together form a complete propeller blade mold.

9. In the method of forming molds for propeller blades, the step which consists in providing a two-part box, each part having a partial blade pattern set therein in a position predetermined with reference to a face of said -core-box, attaching said box part to a flask section having its open face shaped to fit the said face of the box part,

whereby the mold of the pattern in the box part is accurately positioned in the flask art. p 10. The method .of forming molds for propeller blades which consists in providing a two-part box having a pattern-carrying portion divided on the pitch line of the blade to be molded and with partial blade patterns secured to the face of each part, attaching each part to the open face of a two-part flask, filling the flask with sand mixture to thereby form in each a mold of the corresponding face of the propeller blade accurately positioned in the flask section with relation to its open side, whereby the two flask sections when connected together, form a complete propeller blade mold.

11. The method of forming molds for prope ler blades which consists in providing a two part box, each part having a patterncarryil g portion with its exposed surface shape to the pitch line of the blade to be molded and with a partial blade pattern secured? to the face of each pattern-carrying portion, the pattern-carrying portion being accurately positioned in the box with relation to one face thereof; attaching each part of the box to the open face of the twopart flask; filling the flask sections with sand mixture to thereby form in each a mold of the corresponding face of the propeller aceurately positioned in the flask section with relation to its open side, and then baking the flasks to bake the sand mixture into a hard mold.

12. A pattern-box for forming molds for propeller blades comprising a box portion and a cover portion, a pattern-supporting block detachably connected to each portion w1th its pattern-supporting surface shaped to the pitch plane of the propeller, and a partial blade pattern secured to each pattern-supporting surface.

13. A pattern-box for forming molds for propeller blades comprising a box portion and a cover portion, a pattern supporting block detachably connected to each portion with its pattern-supporting surface shaped propeller, a second pattern block secured to the cover section, said block havin its face shaped to conform tothe pitch p ane surface of the lower block and with dimensions to exactly fill the box section, and partial blade patterns similar to that formed by dividing a pattern of the blade to be cast on its pitch plane secured to each of said pattern blocks.

15. The method of forming patterns for molding propellers which consists in providing a two-part box, one part havin its surface shaped to conform to the pitch p ane surfaces of the blades of the propeller, then filling the other portion of the box with molding material to form an impression therein of the pattern surface of the other section, and then attaching to the pitch plane surfaces of both sections sectional patterns similanto that formed by dividing the blades along their pitch planes.

16. The method of forming patterns for molding propellers which consists in providing a two-part box, forming on one section raised pattern blocks having their surfaces shaped to conform to the pitch plane of the propeller, forming in the other section depressions conforming to the shape of the raised pattern blocks so that when the two sections are placed together the raised sections will exactly fill the depressions, and

then fastening to the pitch plane surfaces of the raised sections and the depressions pattern blade sections similar to that formed by dividing the blade patterns along their pitczh lane.

propeller blades to provide a smooth, clean surface, which consists in forming in the mold around the edge of the blade a narrow he method of casting propellers or channel of inaterialg less depth than the thickness of the bla to be cast, whereby the free surface particles in the mold will be carried into the channel forming a fin around the blade containing impurities which may be readily broken ofi.

In testimony whereofI afiix my signature.

THOMAS OXENBRIDGE TEACHER.