an autobiography-第95章

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f　taking　a　much　deeper　cut；　there　being　an　entire　absence　of　any　source　of　springing　or　elasticity　in　its　structure。　　This　not　only　enabled　the　machine　to　perform　its　work　with　more　rapidity；　but　also　with　more　precision。　　Besides；　it　occupied　much　less　space　in　the　workshop；　and　did　not　cost　above　one…third　of　the　machines　formerly　in　use。　　It　gave　the　highest　satisfaction　to　those　who　availed　themselves　of　its　effective　Services。

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A　comparison　of　Fig。　1which　represents　the　general　arrangement　of　the　machine　in　use　previous　to　the　introduction　of　minewith　that　of　Fig。　2；　may　serve　to　convey　some　idea　of　their　relative　sizes。　　Fig。　1　shows　a　limit　to　the　admission　of　wheels　exceeding　6　feet　diameter；　Fig。　2　shows　an　unlimited　capability　in　that　respect。


1836。　An　Instrument　for　finding　and　marking　the　Centres　of　Cylindrical　　　　　　　Rods　or　Bolts　about　to　be　turned　on　the　Lathe。

One　of　the　most　numerous　details　in　the　structure　of　all　classes　of　machines　is　the　bolts　which　serve　to　hold　the　various　parts　together。　As　it　is　most　important　that　each　bolt　fits　perfectly　the　hole　it　belongs　to；　it　is　requisite　that　each　bolt　should；　by　the　process　of　turning；　be　made　perfectly　cylindrical。　　In　preparing　such　bolts；　as　they　come　from　the　forge；　in　order　to　undergo　the　process　of　turning；　they　have　to　be　〃centred；〃　that　is；　each　end　has　to　receive　a　hollow　conical　indent；　which　must　agree　with　the　axis　of　the　bolt。　To　find　this　in　the　usual　mode；　by　trial　and　frequent　error；　is　a　most　tedious　process；　and　consumes　much　valuable　time　of　the　workman　as　well　as　his　lathe。

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In　order　to　obviate　the　necessity　for　this　costly　process；　I　devised　the　simple　instrument；　a　drawing　of　which　is　annexed。　　The　use　of　this　enabled　any　boy　to　find　and　mark　with　absolute　exactness　and　rapidity　the　centres　of　each　end　of　bolts；　or　suchlike　　objects。　　All　that　was　required　was　to　place　the　body　of　the　bolt　in　the　V…shaped　supports；　and　to　gently　cause　it　to　revolve；　pressing　it　longitudinally　against　the　steel…pointed　marker；　which　scratched　a　neat　small　circle　in　the　true　centre　or　axis　of　the　bolt。　　This　small　circle　had　its　centre　easily　marked　by　the　indent　of　a　punch；　and　the　work　was　thus　ready　for　the　lathe。　　This　humble　but　really　important　process　was　accomplished　with　ease；　rapidity；　and　great　economy。


1836。　Improvement　in　Steam…Engine　Pistons；　and　in　Water　and　Air…Pump　　　　　　　Buckets；　so　as　to　lessen　Friction　and　dispense　with　Packing。

The　desire　to　make　the　pistons　of　steam…engines　and　air…pump　buckets　of　condensing　engines　perfectly　steam　and　water　tight　has　led　to　the　contrivance　of　many　complex　and　costly　constructions　for　the　purpose　of　packing　them。　　When　we　take　a　commonsense　view　of　the　subject；　we　find　that　in　most　cases　the　loss　of　power　resulting　from　the　extra　friction　neutralises　the　expected　saving。　　This　is　especially　the　case　with　the　air…pump　bucket　of　a　condensing　steam…engine；　as　it　is　in　reality　much　more　a　water　than　an　air　pump。　　But　when　it　is　constructed　with　a　deep　well…fitted　bucket；　entirely　without　packing；　the　loss　sustained　by　such　an　insignificant　amount　of　leakage　as　may　occur　from　the　want　of　packing　is　more　than　compensated　by　the　saving　of　power　resulting　from　the　total　absence　of　friction。

The　first　condensing　steam…engine　to　which　I　applied　an　air…pump　bucket；　entirely　without　packing；　was　the　forty　horsepower　engine；　which　I　constructed　for　the　Bridgewater　Foundry。　　It　answered　its　purpose　so　well　that；　after　twenty　years'　constant　working；　the　air…pump　cover　was　taken　off；　out　of　curiosity；　to　examine　the　bucket；　when　it　was　found　in　perfect　order。　　This　system；　in　which　I　dispensed　with　the　packing　for　air…pump　buckets　of　condensing　steam…engines；　I　have　also　applied　to　the　pistons　of　the　steam　cylinders；　especially　those　of　high…pressure　engines　of　the　smaller　vertical　construction；　the　stroke　of　which　is　generally　short　and　rapid。　　Provided　the　cylinder　is　bored　true；　and　the　piston　is　carefully　fitted；　and　of　a　considerable　depth　in　proportion　to　its　diameter；　such　pistons　will　be　found　to　perform　perfectly　all　their　functions；　and　with　a　total　absence　of　friction　as　a　direct　result　of　the　absence　of　packing。　　By　the　aid　of　our　improved　machine　tools；　cylinders　can　now　be　bored　with　such　perfect　accuracy；　and　the　pistons　be　fitted　to　them　with　such　absolute　exactness；　that　the　small　quantity　of　water　which　the　steam　always　deposits　on　the　upper　side　of　the　piston；　not　only　serves　as　a　frictionless　packing；　but　also　serves　as　a　lubricant　of　the　most　appropriate　kind。　　I　have　applied　the　same　kind　of　piston　to　ordinary　water…pumps；　with　similar　excellent　results。　　In　most　cases　of　right　packed　pistons　we　spend　a　shillingto　save　sixpence　a　not　unfrequent　result　of　〃so…called〃　refined　improvements。


1836。　An　instantaneous　Mode　of　producing　graceful　Curves；　suitable　for　　　　　　　designing　Vases　and　other　graceful　objects　in　Pottery　and　Glass。

The　mode　referred　to　consists　in　giving　a　rapid　〃switch〃　motion　to　a　pencil　upon　a　piece　of　paper；　or　a　cardboard；　or　a　smooth　metal　plate；　and　then　cutting　out　the　curve　so　produced；　and　employing　it　as　a　pattern　or　〃template；〃　to　enable　copies　to　be　traced　from　it。　When　placed　at　equal　distances；　and　at　equal　angles　on　each　side　of　a　central　line；　so　as　to　secure　perfect　symmetry　of　form　according　to　the　nature　of　the　required　design；　the　beauty　of　these　〃instantaneous〃　curves；　as　I　term　them；　arises　from　the　entire　absence　of　any　sudden　variation　in　their　course。　　This　is　due　to　the　momentum　of　the　hand　when　〃switching〃　the　pencil　at　a　high　velocity　over　the　paper。　By　such　simple　means　was　the　beautiful　curve　produced；　which　is　given　on　the　following　page。　　It　was　produced　〃in　a　twinkling；〃　if　I　may　use　the　term　to　express　the　rapidity　with　which　it　was　〃switched。〃　The　chief　source　of　the　gracefulness　of　these　curves　consists　in　the　almost　imperceptible　manner　in　which　they　pass　in　their　course　from　one　degree　of　curvature　into　another。　　I　have　had　the　pleasure　of　showing　this　simple　mode　of　producing　graceful　curves　to　several　potters；　who　have　turned　the　idea　to　good　account。　　The　illustrative　figures　on　the　next　page　have　all　been　drawn　from　〃templates〃　whose　curves　were　〃switched〃　in　the　manner　of　Fig。　A。

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1836。　A　Machine　for　planing　the　smaller　or　detail　parts　of　Machinery；　　　　　　　whether　Flat　or　Cylindrical。

Although　the　introduction　of　the　planing　machine　into　the　workshops　of　mechanical　engineers　yielded　results　of　the　highest　importance　in　perfecting　and　economising　the　production　of　machinery　generally；　yet；　as　the　employment　of　these　valuable　machine　tools　was　chiefly　intended　to　assist　in　the　execution　of　the　larger　parts　of　machine　manufacture；　a　very　considerable　proportion　of　the　detail　parts　still　continued　to　be　executed　by　hand　labour；　in　which　the　chisel　and　the　file　were　the　chief　instruments　employed。　　The　results　were　consequently　very　unsatisfactory；　both　as　regards　inaccuracy　and　costliness。

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With　the　desire　of　rendering　the　valuable　services　of　the　Planing　Machine　applicable　to　the　smallest　detail　parts　of　machine　manufacture；　I　designed　a　simple　and　compact　modification　of　it；　such　as　should　enable　any　attentive　lad　to　execute　all　the　detail　parts　of　the　machines　in　so　unerring　and　perfect　a　manner　as　not　only　to　rival　the　hand　work　of　the　most　skilful　mechanic；　but　also　at　such　a　reduced　cost　as　to　place　the　most　active　hand　workman　far　into　the　background。　The　contrivance　I　refer　to　is　usually　known　as　〃Nasmyth's　Steam　Arm。〃　None　but　those　who　have　had　ample　opportunities　of　watching　the　process　of　executing　the　detail　parts　of　machines；　can　form　a　correct　idea　of　the　great　amount　of　time　that　is　practically　wasted　and　unproductive；　even　when　highly…skilled　and　careful　workmen　are　employed。　　They　have　so　frequently　to　stop　working；　in　order　to　examine　the　work　in　hand；　to　use　the　straight　edge；　the　square；　or　the　calipers；　to　ascertain　whether　they　are　〃working　correctly。〃　　During　that　interval；　the　work　is　making　no　progress：　and　the　loss　of　time　on　this　account　is　not　less　than　one…sixth　of　the　working　hours；　and　sometimes　much　more；　though　all　this　lost　time　is　fully