TURNING. 



fully explained m the article Rosii-£«^inf. It is the moa 

 convenient method of all others for cutting fcrews, and very- 

 accurate, if the pattern fcrews which are fixed on the man- 

 drel are corrcdly cut. For all purpofes of wood turning, 

 it is undoubtedly the beft method, and far preferable to 

 the common one of cutting fcrews flying, as it is called, 

 that is, by means of the tools 32 and 33, which are applied 

 to the work, and moved along endways at tlie fame time 

 that the work turns round, fo that they cut a fpiral. ( See 

 RoSK-Engine. ) The rapidity and accuracy with which fome 

 workmen cut fcrews in this way exceed belief; but it is 

 only by long experience that this habit can be acquired, and 

 for thofe who have not had fuch experience, fome mechanical 

 help is neceflary. The objedions made by accurate work- 

 men to the flying or fcrew mandrel are, that as the necks 

 muft be cylindrical, it cannot be kept fo perfeftly fitted in 

 its collars as the common mandrels, which have a point at 

 the extremity, and the neck at the other end is made flightly 

 conical, fo that it can always be fcrewed up to fit in the 

 collar. Meffrs. Holtzapfels mandrels are made of har- 

 dened fteel at the necks, and the collars are alfo hard ; 

 they are accurately fitted, and have no fliake when new. 

 From the hardnefs of the materials, they will wear a long 

 time before they get any loofenefs. 



Mr. Maudflay has the moft complete fet of tools for all 

 kinds of mechanical works at his manufaftory, and is par- 

 ticularly well provided with turning apparatus. All his 

 lathes are made with triangular bars, fuch as is defcribed in 

 our article Lathe, and the mandrels are all formed with 

 conical necks and collars. The bar lathes are very accurate, 

 particularly when the flide-reft is applied to them, as tliere 

 defcribed. The bed lathe may alfo have a flide-reft applied, 

 as is fliewn under RosE.-£ngine. 



If a piece of metal, after being propt'rly turned, is to be 

 bored hollow within, like a gun-barrel, tlie back puppet is 

 to be removed from the bed of the lathe, and another fub- 

 ftituted in its place, having a hole or collar through it, into 

 which the neck or end of the iron is to be corredlly fitted, 

 the other end of the iron being fupported and turned round 

 by being fitted into a chuck at the end of the mandrel, or 

 elfe by means of the centre point at the end of the mandrtl, 

 and with a driver, as \n figs. 8. and 9. The reil is to be fet op- 

 pofite the end of the piece where it comes through the collar, 

 and drills or borers are to be applied, fimilar to thofe ufed by 

 lockfmiths in boring keys, beginning with a fmall one and 

 afterwards ufing larger ones, until the hole is made as wide 

 and deep as neceifary. The borers muil be held very firm 

 on the reft, othervvife there is danger of not boring the hole 

 ftraight. The borer fhould be withdrawn from time to time, 

 to oil it and clean the hole. As it is difficult to make a 

 hole quite round or concentric with the outfide by means of 

 borers alone, it is neceffary to have alfo a turning tool con- 

 siderably fmaller than the hole, one of the fides of which is 

 iharp, very well tempered, and a little hollow in the middle. 

 This inftrument being fixed in a long handle, is to be intro- 

 duced into the hollow, and applied with fteadinefs to the 

 inner furface of the hole, and it will entirely remove every 

 inequality that may have been there before its application. 



The collar puppet is only reforted to, when the piece which 

 is to be bored is of confiderable length; for if it is fliort, it will 

 be held fufficiently faft in the chuck, without the neceffity 

 of fupporting the extreme end. 



A collar puppet is fomctimes neceffary in turning centre 

 work when the work is long, and fo flender, that it bends or 

 fprings by the ftrefs of the tools: the collar is then applied 

 to fupport the work at the part where it is weakeft and 

 befids moft. 



rurnws of elliptical nr oval Work, fuch m FidureframiSt 

 Snuff-boxes, £5"^.— This is performed in the fame lathe, and 

 with the fame tools, as the circular work; but the lathe is 

 provided with a chuck, which caufes the work to traverfe in 

 a very curious manner, by a motion given to it in a diredion to 

 and from the centre of the mandrel as it revolves ; fo that a 

 tool held up againft the work will cut an elliptical figure 

 inftead of a circle. Elliptical work has a very fingular 

 appearance when in motion ; for after the work has been 

 turned truly elliptical, every part of the circumference, ex- 

 cept the exaft point where the tool was applied, appears to 

 vibrate, or be excentric in a great degree, but that one point 

 of the circumference runs perfedly true and regular, the fame 

 as the whole circumference of a piece of circular work does. 

 The mode of aftion of this ingenious apparatus is rather diffi- 

 cult to defcribe, and it is firft necefl'ary to underftand the prin- 

 ciple of its adion. This is the fame as the trammel or elliptic 

 compaffes ; fee fg. 29. An oftagonal or fquare board 

 A A, B B, has two grooves cut in its furface, which inter- 

 fed each other at right angles ; this board is held down 

 upon the furface where the ellipfe is to be defcribed, with 

 the centre lines of the crofs grooves coincident with the 

 two diameters of the intended eUipfis, and of courfe their 

 interfedion will be its centre. The curve D D is traced be- 

 yond the circumference of the board, by means of a pen or 

 pencil, which is fixed at F, to a radical bar or beam F G H ; 

 this bar carries two other points or pins, G and H, which 

 are attached to lliders, inferted into the crofs grooves of the 

 board, as fhewn in the figure : the Aiders are fitted in truly^ 

 fo that each of them will have a motion in its refpedive 

 grooves : thus the flider of the pin H will move along A A ; 

 and the flider of G, along the groove B B. By turning 

 about the beam F G H, the Aiders go backwards and for- 

 wards in their crofs grooves with a fimultaneous motion ; fo 

 that when the beam has gone one -fourth way about, one of the 

 Aiders will have moved from the circuniferencc of tlic board 

 A B, to the common centre of the crofs grooves; and when 

 the beam has gone half round, the fame flider will have pro-, 

 ceeded the whole length of the crofs, and arrived at the 

 oppofite fide of the circumference. The fame applies to the. 

 otlicr flider, and when one flider is at the centre, the other 

 will always be at the circumference. 



The pins F and G H can be fixed at any part of the 

 beam at plcafiire, (though this is not fo reprcfcnted in the 

 drawing, ) for the purpofe of fetting the trammel to draw .iny 

 particular ellipfis : thus, place the beam in the diredion of the 

 line A A, then the pin G will be in the centre of the crofs 

 grooves ; now fix F at fuch a diftance from the centre, as 

 is equal to half the finall diameter of the elfipfe, and fet H fo 

 far diftant from G, as the difference of the two diameters ; 

 confequently, from F to H will be equal to half the longeft 

 diameter. Now, in turning the beam round from the direc- 

 tion A A, till it comes to the diredion B B, the point G will 

 depart from the centre along B B, and H will approach it 

 along A A, till it gets to the centre. Then wfll the pencil 

 F be fo much farther from the- centre, as G is diftant from 

 H, and the pin has in its circuit traced one-fourth of an 

 ellipfe. The beam being turned quite round, will complete 

 the whole curve. 



This apparatus may be applied to turning by fome modifi- 

 cation. Suppofe the two crofs grooves made^ in a round 

 board, as large again as that reprefented in the figure ; then, 

 if the whole apparatus be inverted, and the beam F G held 

 faft in a vice, or otherwife, the bo'ard with the crofs may be 

 traverfed round upon the fixed fliders, in the faiiK- manner as 

 the beam could be traverfed round upon the fixed board. 

 Suppofe a tracing point is held to the back of the board. 



