DECEMBER 30, 1911 SCIENTIFIC AMERICAN SUPPLEMENT No. l878 427 the sun's heat, particles are detached from the nucleus, their density is negligible, 'as can be readily shDwn. thing over 1,000 kilometer s,* and the particles which and the comet fritters down, so to speak. When the The contrary might be sup'posed, in view of the light we are considering measure one-thousandth of a milli particles are detached, their very lightness exposes which they emit. Even if we admit the whole of this meter in diameter. If, therefore, we 'were to fill the them to the repulsion of the sun's light, and they light is reflected sunlight, and that no ·cathode phe volume of the moo·n with p ar ticles of this magnitude recede into space and are lost. The tail would soon nomena such as may occur in highly rarefied space, in such manner that the total density were one mil disappe,ar entirely if it were n ot continually regener enters into the -case, there really is no cause for lion million times less than that of the moon, the light ated anew. anxiety. which wou.ld be reflected would still have the same Under these circumstances :it is readily intelligible If we consider a given mass lighted up ·by the sun, brilHancy as that which we receive from t'he moon. If that a·n encounter with suoh a taB need oause us no the amount of light whic,h it reflects will be the we viewed ,this collection of particles at Ithe dis'banee anxiety. In the first p.lace, the mass of comets is not 'greater, the more highly divided its subst'ance. If this of the moon, they would present just the same ap very considerable. It 'has now been observed that it mass is for med of a lar·ge number of small spheres, p ea rance as the moon. If we were fart'her away we does not exercise the slightest pel'turbating influences the reflected light wiII be the more intense, the would see them smaller, but with the same bright UI)On the planetary or bits. A comet on a certain occa smaller the spheres. It is easy to realize this; let us ness. As a m atter of fact, the brightness of the sion )l3Jssed between Jupiter ,and its satellites. Its imagine larger spheres of ,two centimeters radius, and 'comet's -tail cannot ,be compared with that of the trajectory was strongly modified, but neither Jupiter smaller spheres of one centimeter radius; the volume moon. It is, maybe, one hundred times less, .perhaps nor its 'satellites seemed to be in the slightest degree or mass of the larger spheres will be eight times that one thousand tilmes-I am not aware that any meas affected. La P,la,ce went so far as to say that the ,of the smaller spheres , but the surface of the larger urements have b-een made. We must, therefore, con mass of a comet is only a few kilogr ammes. In this he spheres wiLl be only four times that of the smaller. clude ,that the density of the particles is 10" times e vidently exaggerate d. An encounter of a comet's Eight small sphereS:, therefore, will be ·equivalent to ,less than that of water; we might ,as 'Well say that nucleus with the earth would no doubt cause some one of the larger ones in point of mass, 'but they will we have, in the comet's tail, nothing but empty space, damage, but such an event is extremely jmpr'obable, have twice the surface area and will there·fore r·eflect since it represents ,a density over one thousand mil for the nuclei are relatively very small, and we rea.lly twice as much li'glht. The moon has a radius of some- lion times smaller than the most extr·emely rarefied stand very little ·ohance of hitting snch a small tar gas which we are able to produce in a vacuum appa • The eminent French mathematician has here taken consid get. The same is not true as regards the tails, which erable Iiberti�s in rounding oil' his figures. As our readers know, ratus with the most ·perfect mean·s whi.ch modern spread over an immense sp,ace in the sky, but then the ·Moon's radius is 1081 miles.-ED_ technique place.s at our disposal.
Wheels, Ancient and Modern-II.* From Log Roller to Wire-spoKe Motor Car Wheel
By Henry L. Heathcote, 8.Sc.
Continued from Supplement No. 1877, page 415
MOJ)��ltN Wln;J::LS. position, the decrease becomes, of course, all increase, 1I' Uw avt.ragu I,ellsion on tltO N spukes is t, when trans The S'IiS7JUII8'iou lVhed_--We willllulV pass on to t1w having its maximum for sp ukes on the upper part uf mitting the torque T the tangent eircle will have a IlPxt �tag() in wheo! develupment, which dltto� frum the the whenl pointing in the direcUun of the compression. radlus- 1ISI\ of bieyeks_ During this gap of about 2Jj()O yf'ars Obviously the spoke tension shuuld never fall tu zeru '1' tho only challges of any impurtance were the dishing of nor rise above the elastic limit, and these limits help r = - approx. wheels to resist lateral stresses dm; to ruts and rounding to regulate the choice of the imtial spoke tension. Nt corners,' and arranging the spokes on two cones instead The Tangent-Spoke Wheel.-The tangent-spoke wheel Applying this to a bicycle wheel with fifty spukes, of UIH'_ This last, was dune as e�rly as 1828, and is still in which the spokes are tangent to a circle having its and assuming the pull in the chain to be 300 pounds practised at Wuolwieh Arsenal in building ambulance center at the axle and are not normal to the rim. prub (which is about that due to a vigorous jerk), the chain wagon wht",l s. Strange thuugh it may appear, wheds ahly owes its origin to the curved arms used in driving ring tu be 3 inches diameter and the hub flange 1 % wpre not llSt'ti glllll'rally for facilitating transit in Britain pulleys and fly-wheels for transmitting considerahle inc:lws diameter, if the average final spoke tension be till (Jomparativeiy reel'lIt tinws. '1'he very first carriage torque_ Both ancient and modern rruiiaZ spoke wheels SO pounds, it is easy to show that the hub will twist wa� made for Queen T�lizabeth in 1568; the first that are capable of transmitting a certain amount of torque, 73fi degrees relatively to the rim. plied for hire in London were in 162fi, and the first but the amount is limited, and depends not only on the In a l;angent-spoke wheel the hub must also turn stage coaches were in 16,",9. Broadly speaking, all the bending strength of the spoke, but on the rigidity of its relatively to the rim, but the angular movement is far early wheels were cumpression wheels with radial spokes. attachment to both rim and hub. Since no material less. In this case torque has the effect of increasing the The introduction of the suspension wheel for bicycles has an infinite elasticity, it follows that however thick tension on half the spokes and decreasing it on the marked a great advance in the shock-absorbing powers of the spokes may be there must be a certain amount of uther half. Reverting to Fig_ 1, if the initial tension wh"els. The first bicycle wheels were compression twist of the hub (in the plane of the wheel) relatively on A Band C D be t and the added and subtracted wheels. and had wooden spokes and rim with an iron to the rim, or no drive can be transmitted. When the lension be p, the torque due to- tyro. The wheels were just· ordinary light carriage torque is considerable-as in a motor car wheel-the A B will be (I + p) 1', and to w]wols. The Clurved Ilwmher (Jonnecting the back axle actual twist sooner or later rises above that currespond C D will be (t - ]i) r_ tu the top of the front wheel is not altogether unlike ing to the elastiC limit at some or all of the spoke attach 'l'hc difft'rence of these is the resultant torque due to that used in the ehariots of the ancients. Later bicycle ments, and this leads to gradual loss of rigidity and tu this element- wheels had radial-wire spokes which, being in tension, creaking, and, in some cases, even to charring, owing N kept rim in position. In the older wheels the rim to ruhbing. In a radial-spoke bicycle wheel subjected tu the ."_ Tutal torque = - X (11' + p" -- Ir X prj was normally in tension, and the spokes and hub in a torque in its plane, the hub must rotate relatiyely to 2 compression. In a suspen�iun wheel the spokes and hub the rim until the spokes arE! tangent to a small circle. .". T = N p T_ are in extension, while the rim is in compression. It is a common, though not unnatural error to suppose that thll spokes of a modern bicycle wheel are sometimes in compressiun. As a mattor ot fact, they are always in tension, even those hetwnen the hub and the ground, wh('n a heavy rider is in the saddle. Fig. I represen ts one element uf a wire wheel. If tension he applied to the spukes, the rim and huh would move toward eaoh another lV"ro it not for tho I'/t,'e t of" the ot]--I'I' segments; 1.lw rusi.;tall(Jc tu tlte compressiull forre3 in tlJe nm, and to the bursting strf'S, in the hub shell prevents this movement. When eOI\lI)Tp�sjul1 i" applierl botwl'l'n till' hot tom of the rim and the huh uI'n Ll'r or "Iwh l1 whppl, t.he tonsioll of pac!! spokp will, il' the rim i, inflexible, deercasc propurtiunately to the
Fig. l-The Torque App.lied at the Hub Must be Trans mitted Along the Wire Spokes to Overcome the Resistance at the Circumference_ l<�ig. 2. cosine of the angle between the spoke, or, rather, the ji'ixed Wood Fixed Symmet Rudge - Wh itwo r t h Rudge - Whitwo r t h projection of the Rpok(' in th!' plane of the wheel, and Wheel. rical Wire Paten t Detachab-le Patent Detachable tho rlimeLioTl of COlllJlrPssioll. Wlu'Jl 1.111' eosinl' hnmnnf'R A Very Common Wheel. Win'> Whep-I, p.at W:ire Wheel, Pat h IIng-ative, as wlwn til,' spol;o is 'Lhov() its . ori'lollL
© 1911 SCIENTIFIC AMERICAN, INC. 428 SCIENTIFIC AMERICAN SUPPLEMENT No. J878
Whillll is iuJejJew\onL of the illilial LcUt;iell provided It is not to be supposed that even a wheel of this advanced J;VOL(,TION OF THE MO'f(lIL-CAIt WIIO, W II (>gL. (t - p) is a positive quanLity. type is capable of absorbing as much shock as a tyre. '1'he first wire wheels to be used for motor-cars wuru If the tangent circle be of the �allle diameter as the The air pressure in the inner tube of a motor tyre ranges bi-Iaterally symmetrical like the front wheel of a hieyele. Hange in the previous case, it is easy to show that, for usually from about 60 to 90 pounds per square inch, but The spokes were headed and bent near tho Jlead througb tifteen-gage spokes elasticity 10,000 tons per square the corresponding normal pressure on a Rudge-Whit 90 degrees (see Fig. 2). The holes in the hub flanges Wl'I'U ineh, the twist of the hub for the same push as before worth wire wheel rim ranges from about 150 to 200 drilled parallel to the axle, and the spo ke� threadeJ will he 0. 11, degrees or about one-seventieth that with ra pounds per square inch. This, combined with the fact through these holes were attached to tite rilll hy nipplns dial spokes. '1'his greater rigidity in torque transmission screwed on to the other end of the spoke. ilut, a� ill places the tangent-spoke suspension wheel far ahead of both radial compression and radial tension wheels. It
.'
. (
z o . � : f 1 ". u� 1------1 .. w
o' . .-. ' . . .. .1...... ••. .• .. J/ , - - T.!�__ -'-- ______ Fig. ;)-J)iagralll Showing the Tem;iou of Two Diamet· };'ig. "-' Tlw I"ull Line Indicates lhu 111 i tilLi TI�II;.;ioli 011 1,'ig. ,J--·Polar Diagram of the Ten� iolJ 011 the Spokes rically Opposite Spokes as a Funetion of the Hw Out.�ide Spokes, the Dotted LillO that on of a Rudge-Whitworth Detaehable Wheel. Time, Und8r Various Conditions. the Inside Svokes. The ])ot� Show thl) )£ffect Oil the Tension l'ro(lllccd that the rim is not nearly so flexible as a tyre cover, has 10llg I>eon universally u�ed for bicycles and motor by a Combined Load accounts for its inferiority to the tyre as a shock absorber, hi(,yele�, l1nd i� now enjoying unrivaled popularity in and Torque. though the much larger diameter of the wheel operates its applinatioll to motor car�. in the other direction. Large diameter wheels-like The radial wheel has to be Hubjected to great radial living �trueturos, so in engincering (,onstJ'lwtiolls, evolu large section covers-are, ceteris paribus, better shock tension or compression in order to impart the necessary tion brings gradual morphological dilfe['(lntiatioll of absorbers than small ones. The superiority of this type torque rigidity. In the tangent wheel the necessary structure and further division uf laLlOr. tlto oady of wire wheel as a shock absorber, compared with com In torque rigidity can be attained without imparting exces hi-laterally symmetrical wire wheels both inside out pression wheels with radial wood spokes, is a matter of and �ive radial rigidity. As a result of this the tangent sus side spokes transmitted the drive. In the present I�urlgo actual experience as well as of conjecture, and is noticed pension wheel can be made capable of absorbmg shock. Whitworth wire wheels, to prevent the �tresses rising in their more constant contact with the ground under A eomparison of a su�pension wheel with a section of a too high when rounding corners or when skidding, tho similar conditions of use. Lyre will bring this out more clearly. wheels are dished and the outside spokes arc relieved of' I;U"P�;NSION WHEEiL AND TYRE SEGMEN'r COMPARED. the whole or greater part of their share in transmitting The deformation of a tyre by load is resisted because drive. Thi., is done in some types by making the hub the radially-acting air pressure puts the tube and cover of much larglr diameter at the end near the car than at in considerable tension. The rim of a suspension wheel the other end. As a result of this the displacement or is the reciprocal of this, being in compression due to the the inside spoke heads under torque is greater than tho radial components of the spoke tension. The rim flattens displacement of the outside spoke heads, the ratio of the like a tyre under load or shock. the radial tension in the displacement in the direction of the spokes (and there one case acts like the air pressure in the other; the fore of the added tf\nsion) being the ratio of the rliarnn(,nn; greater the tension the less the rim flattens, and the less of the circles to which the spokes are tangent. III othel' the tension the "softer" is the wheel. types the end of the hub to which the outside spokes Wheel building is the counterpart of tyre inflating, are attached is .revoluble, so no torque is transmitted hy and the art produces its best when sufficient tension to them and their whole strength is reserved for resisting produce torque rigidity is combined with conditions that side-thrusts. develop in the wheel a maximum cushioning effect. Such Another departure from symmetry which soeul'OS a wheel, by co-operating in the duties of the tyre, length greater strength for the inside or driving spoko cone is ens its life and lessens its liability to wear, cuts, and the employment of 50 per cent more spokes inside than punctures. To obtain maximum cushioning from a outside. In the hub shells the spoke holes are not drilled wheel of this type, moderate spoke tension needs to be parallel to the axle, but perpendicular to it. This enahles combined with a flexible and resilient rim and thin spokes bent through a small angle to be used; for in spokes. This in its turn implies not only careful choice stance, the inside spokes that transmit the drive arc only of materials, but appropriate design to neutralize the bent through 45 degrees, and this, with a special way Fig. 6-Denison Testing Machine to Imitate Stresses reduction of resistance to torque perpendicular to the of producing the bend and careful scrutiny in the firms' Set Up in Rounding Corners or in Side-slipping. plane of the wheel entailed by lightening the rim. Both laboratory, has enabled the strength at the bend to I)[) the wheels of antiquity, modern artillery wheels, and increased from about 60percent (with the 90 degrees bcn(!) wheels for motor-cars, owe much of their lateral strength to over 90 per cent that of the body of the spoke. Tho to the high moment of inertia of their heavy wooden outside spokes are bent through less: than 45 degrees so tho felloes, the disadvantage of which is their inflexibility strength at the bend is still less impaired. Another and consequent inability to absorb shock. The Rudge improvement is the addition of another cone of spokes, Whitworth wire wheel for motor-cars (Fig. 2) is the making three in all, so that the drive is transmitted to first wheel in which these requirements were adequately both sides of the rim. The same device enables t.ho met. This is done by making the outside spokes, that point of contact with the ground to be more nearly under are much dished, enter the rim near its edges and not the bearing or steering knuckle (see Fig. 2). at its center, as was formerly considered correct. In The diagram of Fig. 3 illustrates the fluctuations of this way members are provided to oppose the twisting spoke tension (or compression in a compression wheel) of the rim due to sideways shearing of the tyre when under some of the conditions of use, assuming that the l ... t - t • rounding corners. 0- made In rim is flexible. When the wheel is jacked up, revolv �hc�1 -r:�� RII�geiW�t�orth L�borato,ry not Solid. RlnlS all 111 It is only fair to add that this method of spoking has shown 8IS oS?- ing does not appreciably alter the spoke tension whinh, I 1-,-- the effect of localizing the bending stresses, due to the - �J therefore, does not vary with time, and so is represf\Ilted • _ • _ l� d ._ M"I;metr�$ pull of the tyre bead, in the edge of the rim. This is Ocflecllan In by a horizontal line, as shown in the first section or met by strengthening the rim bead, which at the same Fig. 3. When the car is in steady motion and freo time strengthens the whole wheel very considerably. r-- wheeling the tension on each spoke will increase and There is another point of similarity between the wire IT ' decrease, the values following a cosine curve (as already "J 0' wheel and a tyre segment. If the radial compression /' explained), the axis of which should be below tIl(' . -- X on tyre walls gradu�lly decreases owing to air escaping - .. ' .. ' I- minimum points. The zig-zag, which occurs at differont r-�-f-- . , < ":':" - 3V 1,'<' ':":" from the stressed condition, the flexed part of the tyre I a . .r.. points of the curve in Fig. 3, illustrates the effect of' e - will be increased, and a point arrives at which this has � �3f- · ) shock due to the wheel leaving the ground and falling !, r . -n�� to IIButralized by inflating. Similarly, if the spoke ,. 1- back suddenly to its former condition. The dotted lille be "� <'.-"f- j � J).. tellsion of the wire whcel should fall the flattening of the -c-- shows the instantaneous condition of a spoke diamotri § -. - rim would increase, and migh t even reduce the spoke C- --f- cally opposite. .. tension to zero. �[..--. � In the third section we see the variations in tension ,,- , I . . . ,.,. I'-- o� Fortunately, solids are more easy to manage than . . . of the spokes of a driving wheel traveling straight; and •.• ;;,\� I--�� " gases, and by employing spokes of high elastic limH, and i%�:�: � ' the fourth shows the variations when the wheel is heing - hy cok! working the metal of the hub shell round the j ',." driven round a corner. It is important to nolice that >Ill, s_rou spoke heads, and of the rim round the nipple holes by 1 m -I�-t--- the effect <;>f the samfl shock is very different in t.he dir f-:; I.. ,,,, ... hammering and bulging (coupled, o(course, with proper �",��T ferent cases, and depends on the instantaneous valuo of design and materials), the vibration elastic limit above �� , �-lli the spoke tflnsion as well as on the posi('iou of the spokp, - - I _ 1 which pflrmanflnt m;�apfl amI IORR of tflnsion would �Cfmr, t �I r in the wheel. 'l'he v:1.l'iatioll slOt up ill :� woorl wll('''' will is made so high that arter a slight initial bedding the follow t.he diagrams pretty dosel.\'. hut [tntual experi ordinary stresSflR arfl insufficient to "soften" the wheel. 1"ig. 7-Curves Representing Tests Made with the ments with wire wheels show that tilt' increment of s In any event, the spoke ten ion oan be adjusted readily. Denison Machine. tension due to load, torque, and load and torque COID. © 1911 SCIENTIFIC AMERICAN, INC. SCIENTIFIC AMERICAN SUPPLEMENT No. 1878 429 el)J.·ll!·/'>; biJll'U, i� !JoL /H'arly SII grc;�L at; (,lllI�l' di;'I,graJlls iudicate. 'rim ,;Ln::;b",· �('t I U ) IVhL!! 1'()UlldlJlg withuut :C;XPJ<;lUl>n;N'l'tl Wl'fH W]HE WHE�Lo. skidding have beeu very fully investigated by J. V. Pugh (A pages and When traveling at I<'ig. 4 shows a polar diagram of the tension on the utocw', 1906, 910 U4g). spokes of a Rudgn-Whitworth detachable wheel fitted twenty miles per hour round a curve 30 feet radius, tho with a t,yre sustaining a load of one ton. About one side-thrust on an outside wheel, at the tyre, may be as quarter of the spokes have their tension relieved, but much as 134 times the load on the wheel when traveling straight. When skidding, the side-thrust may be con tlHl others experi mlCe nothing liko the same increase, and it is distributed fairly evenly all round. siderable, not only when stopped by a curb-stone, but To test thtl enect of combined load and torque, the also when the side-slipping II'h eels are arrested by a dry, plIll was applieu to a dummy tyre made of iron, so that sandy, or rough part of the road. the rear wheels of a car weighing one ton side its line of aetion did not pass through the center of the If skid whod. By varying the distance between the wheel cen- ways at a corner, and are brought to rest by the outer torque wheel running on to a dry, rough, or sloping part of the t.er and the line of pull the ratio --- could be varied road, and if two-thirds of the load is borne by the rear load wheels, and they attain a sideways velocity of five miles per hour, and stop after sliding three inches beyund the at will . In this way tests imi tating all sorts of condi tions of road surface, ear load, and horse-power engine slippery part, then, taking moments about the front wheels, the retarding force is hav() heen carriod out. diagram Fig. 5 shows a polar for a wheel having the v' 2 W 2 2240 X [>3.:-; Ibs. approx. on same number of outside and inside spokes, the outside Def/uti,," If1 Ml/fImefrU [,020 ;.j • -2ys =;;' li4 X 0.:15 spolws of whieh transmit their pull to the hub and not one wheel. /e 1.0 :t rovolub ring. The outer dotted line indicates t.he On a smooth surface, even if dry, LIIC groul1ll woulrl i in tial tension on the inside spokes, the inner that on not exert so great a force 011 the tyre, hut when rough the uutside ones. The dots show the effect on the tension and sloping, even greater forces can be exerted, of the combinea load and torque. In this test the inner (To be Continued. ) hub, bub-shell nipples, and rim are all tested, and the results demonstrate beyond controversion the enormous strength of these wheels for forces and couples in the Motor-Driven Circular Saw Bench plalle of tho wheel. '1'he puint to which I would particu OUR il lustration , adapted from 'l'he Engineer, shows larly call attentiun is the great advantage of a flexible a portable motor-driven circular saw lJendl sppdalJy rim which, as these results show, quite obviates the high designed for use on battleshipH, large liners, a.m] so t()lIsion8 ur compressions which would otherwise obtain, forth. On s u ch vessels there is always a (;o llsideraille :tlld w hwh would prove so destructive every time the amount of caqJentry work to be done , and it is l·on· whoo! wa!' jl'rlwd off the ground. sid ered that such a t{)ol will also be found useful for III addition to uetllrmining the effect of load and yard work and in other cases where it is more ('on torque, separately and combined, we have subjected venient to take the machine to the timber than to both woo(l and wire wheels to a side-pull applied at the convey the timber to the mill. The mac'hine iH, as a rinl or to.a dummy tyre. Fig. 6 shows a Denison testing fad, parti·cularly adallted for worK in the op en by maclliue, adapted to imitate the stres�es set up in round reason of its st rong design, and as the motor is inside ing a Hllarp corner at very high speed or in a bad side the main framing and totally inclosed, no trollbll' is slip. 'The results of some of these tests will be seen in li kely to arise either through dllst or from the pllN:ts ["ig. 7. In nearly every instance the deflection of the I of the weather. r- WC)(HI whod for the same pull is greater, and in every . I The main framing, which is of solid c:ollstrudioTl, is a rtl e so the wood wllt�]el sustained permanent damage at a / I . \ , I mounted on a trolley running on wheels for purposes lower pull than in the wire wheel. The same applies to \ / I I " I . of transport. Pr{)vision is also maue for IJulting t1w s wot-llte wheels. The arrangement of the sp kfls r,]le I e\ o mathine to a deck or founda.tion if desi red. The tOIl Rudge-Whitworth wire wlwtll hall been the sub i"n the part of the machine is made to swi vel on a tnrntalJh', (,areful design and experiment. Fig. shows the ." jc:nt of 8 ..\ so that it ean lJe swung round and secured at any angle rosults of om thesfl experiments, and makes it elear ill p S i the The 111<1- s e of �- 1-=YJ- withont ehanging the O t on of ba�e. Fig. 8-'rests Show'ing the Influence of D€sign of Hu II i that strength attained, even wit,h precisely similar tho and Spokes when the Material is the Same. ('hine carries sa"'s up to 2(; inehes in diameter, and rims, hubs and spo o material, depends greatly on the k will cut through a depth of 8 ilH:hes. It is fittt'd with e chlsign sol eted. '1'hese tosts have given valuable data an adjustable fence, arranged to ('ant to any ;)nglP for as o materials instanee, the forees that turn a car round a corner reside to t h hpst (l<:signs and for the rims, spokes, bevel cutting, and made to turn ove r the end of the shu lis. in the round. It is quite a mistake to suppose that the and hub It does not follow, however, that bench to leave the table clear for c'ross·(,lItting. A closigns anI! nmtorials proved suitable for withstanding driver at the steering-wheel really steers the car; the eross-cut slide with a quadrant adjuslable to any anglp a stm.cly also suitable for impulsive forees, so path followed may be indicated by the steerer, but it is Foree ar() is also provided for miter l:lltting. e n investigated by the ground. The most the driver can do is the various types of whl'lli h:wf) b e under dictated The saw spindle runs in hardened I'all-bearing jour to turn the wheels into such a position that, if the ground illl pact. nals, and has a double ball thrust bearing for taking 1"01' this purpose i of an impact pendulum, permits, the forces developed under and near the wheels use s made up end play. The armature of the motor is fittl'd whic,h is rolpasild against the top of the rim of the tyretl will alt-f)r the direetion of the car to the desired extent. direct to the saw s pindle, and the eleetrkal parts, wlwl'1. 'l'he length of the pen ulum about 12 feet, d is Ilrushes, etc., are a('cessib le from the top lJy means of thn hob weighs nearly a quarter of a tou. In somn " n,nc\ a re movalJle br'ass covel' fittl'd in the table illlmediately (psts incrC'asing hlows were appli d the same part of -I - - e to '.-- -I� over the motor. The main standard in which tlJ(' " LiJ(l \Vhl'd. in oth('rs a moderate eonstant blow, e. g., - - - , -1- motor is fitted is made with a large l'adi�Lting SlIl'f<1('(' - ;20() 1'()()�-jlOlll](ls--w�tS applied at sllccessive points on - I to keep the motor cool. " - tho rim f'1C'vllll-thirtit'ths of tho whole circumference -- - - c- An au tomatie feed motion is pfovillecJ. T ll is con· apart;. �'ig. shows eharact rist c diagrams for wood, - - \l ll i - -- \ sists of two horizont al rollers plac:pcl Oil" i n front amI : sllC'pt-st.PP\ w\t(,(,1s wc\ sllhj('(:t,p(l to inc:reasing blows - wirn - one behind the saw. and c·onnc'c'tl·.(] with ea(,h other o s "r-c- -f-r- Sa,IlHl a l I;·l�. s w the r!'sults of � - - at til(' phwe; l (I J() h the r- 1- wood all(\ wheds with similar hlows, - - - \.<·st.ill� wiw " - � - - - i-I I 1-'I- lwing eleven-thirtit'tllo of the way roun(l whl'd turnen - -- - � -c- aftor: Raeh hlow. " r- I 'b� I Tho q lwstion will probably suggest itself as to whether n is ever call1ld upon to stand sido r-- Jrloj,or-mr wlted " .j-1-1---1-1- Lhl'lIst.s and groat as LlllIse rl'prlls{mted by the ->-r-c-r hlows as - - uPI)('r part of \<'igs. 7 and 9. 'l'ho magn itude of' t,he strc'ss ,. . on � - dO)l(·nds in uvnl'y ease, not entirely, but primarily, T�r--- f,hl' i'o]'('tl t.hat t.he gmull d can exert on tho wh('(\\. "'or r':r-I--r-� � 1 f-- H -i--r- ._.=.-=-..-r- �-, -,- "100 \- 'II)!:e.. 5"1 "-_/. R \ . 1150 I - 11001 3 4- :> 6Det�"!8 C:bl� !) 'l ,-1- ,cr 2 rff4�17 -11 10 \'r 12 13 14 ,� i ' - \�l Number of Blow � � t Iry �I !)50 ... , ;/1 -- r ... � � ; 23 Portable Circular Saw Benc'I). :::\' J}:'�I:f·�1(1'r�,,�� ""J 17 U50� I Ily a driving chain. The rollers are driven through n totally inclosed worm gearing, by a f r iction disl" a d t ntly stopped or started. The feed can be �700- 1 ran be ins a / varied from 5 feet to 45 feet p er minu'te lJy traversing ,,',0 ", © 1911 SCIENTIFIC AMERICAN, INC.