CONTROL LINE SPEED LAPPING IS METHOD getting parts really round absolutely flat can also method create special shapes remove material specific areas surfaces cylinders and/or improve surface finishes According Marks Mechanical Engineering Handbook lapping process producing extremely smooth accurate surfaces means lap fine abrasive part lapped final accurate dimension mating form softer material such soft close-grained cast iron copper brass lead made up job very thin coating abrasive mixed lard oil machine oil kerosene grease placed between two surfaces rubbed together column Ill try explain use laps model engines improve performance Telescope lenses eyeglasses water-pump seals dowel pins engine valves lappedto get accurate dimension shape flatness get make seal pressed against mating surface lapped pistons create seal between moving metal surfaces benefit piston rings instance Any lathe mill grinding machine will vibrate making part pieces come out accurate would like Hones can make cylinders nearly round its difficult achieve tapered bore lap engine What mean say lap piston sleeve Can lap piston sleeve toothpaste various household abrasive cleaners Lets start simple thing rotary valve DRILL TAP TO SLOT FOR SHORT 10-32 SET SCREW MAZE SLUG SAMR LENGTH AND DIAMETER AS PISTON FILE OR GRIND GROOVES 1/32 DEEP FIGURE 1 MAFE TWO PLATE5 PDRILL ONE PLATE TAP TOP FLANGE OF SLEEVEONE PLATE FOR 632 BETWEEN THEMSCREWS 002 0 00 APPROX 3/16 4 U-BORE TO FIT SLEEVE IOUTSIDE DIAMETER FIGURE 2 driven crankshaft makes intermittent seal between carburetor crankcase piston goes up down backplate rotary valve openings oriented open close correct time give maximum breathing suit particular engine intake timing will different engines depending end use Speed engines have different timing RC engines instance valves must flat smooth seal against backplate crankcase compressionour two-stroke engines cant run have rear-intake Speed engine uses flat rotor check backplate sure flat smooth arent lap flat piece glass using fine aluminum oxide grit mixed light oil move figure-eight pattern grind telescope lens use straight backand-forth motion end up dished part dont have aluminum oxide grit can use 400A 600A oiled sandpaper placed glass Abrasive-coated Mylar much better will give flatter surface available lapidary stores comes fine grits down micron millionth meter sizes Front-intake rotary valves must seal too depend close fit between crankshaft crankcase Lapping usually necessary unless touch during running should remove metal spots rub Fine sandpaper stick will job sleeve-and-piston combination important part engine maximum performance must have proper materials proper shapes correct fit Correct lapping about way remove metal certain areas achieve shape fit want some companies making newest Speed Racing engines CNC computer-controlled machines still lap some parts get round fit correctly recognize need proper geometry fit must understand what goes engine during operation piston comes up locks charge fuel air compresses glow plug ignites mixture blast hot gases impinge against top piston dont have tight seal lose benefits high compression lose power heat combustion causes tip piston expand almost instantly need some clearance prevent binding against cylinder wall some time delay heat transfer before moves down sidewalls piston must have clearance piston moves downward sleeve DRILL AND TAP FOR 1/420 CLAMP BOLTSAW FLEX SLOTS PISTON 00 FIGURE 3 122 Model Aviation NTLY LONGER nAN PISTON Additionally friction between sleeve piston creates heat also causes piston expand So piston goes down expands need clearance eliminate binding nonessential friction time combustion gases have less pressure dont need tight seal top bottom stroke fuel-air mixture crankcase cools piston next sequence reasons taper bore sleeve tight top stroke extremely loose bottom also put taper top piston wall period Speed engine development sleeve least 005 larger bottom tapered piston seals top 20% stroke doesnt touch sleeve anywhere else during stroke rides loosely oil film top piston wall also tapered bottom half relieved about 001 engines come way have lap bore until round has enough clearance check piston roundness clearance taper whether wrist pin square sides major differences allow engine go much faster another engine same type laps made various materials such brass cast iron copper Aluminum steel will sometimes gall dont use usually make brass internal laps sleeve brass wears faster chrome sleeve end up tapered lapexactly what want lap made cast iron sharp corners can easily go through thin chrome platingbe careful Too much pressure lap can also damage sleeve take easy let abrasive work Cast iron makes excellent external lap pistons will last longer bore will stay straighter know lapping necessary needed Run engine flying prop slightly smaller pitch diameter few minutes note rpm can has flown okay too Disassemble engine look bore surfaces reflected light will see piston has rubbing chrome will polished marked want have piston touch seal top stroke approximately 1/ inch no 20% stroke Most likely will see shiny spots shiny areas around exhaust bypass ports walls shiny spots piston rubbingthe sleeve out round doesnt have clearance areas Make lap like shown Figure 1 make sleeve holder like Figure 2 lap sleeve applying mixture oil aluminum-oxide grit 600 size finer both parts rotating other adjusting diameter surfaces wear away use aluminum oxide grit because breaks down can washed out easily Some abrasives like diamond carborundum can imbed themselves surfaces keep wearing parts Cross-hatching makes lap cut lot faster grooves dont have fancyjust file use grinder Deburr lap before use must have patience chrome hard wear-resistant dont try hurry things applying too much pressure lap you can warp sleeve score plating both sleeve holder keeps squeezing sleeve out round lapping Put marker stop some kind shaft lap dont go too deep lap area pistons seals usually insert lap proper depth wrap shaft electrical tape bottom sleeve As lap wears chro removed adjust diameter screw must have tight fit top stroke dont remove chrome course light inspection shows sleeve out round may have lap until round get new piston fit Run lap lathe drill press gets hot going too fast hard Reverse rotation once can think have removed enough chrome clean sleeve soap water toothbrush make sure have removed abrasive Look piston skirt too scored marked up will need lap round polish marks off s trips 600-grit sandpaper Just dont mess top seals sleeve will have get new oversized piston Oil reassemble engine Run fly check increase rpm speed take apart check sleeve again still shiny spots lap some times necessary takes 20 times want go fast what must go through chrome will likely have send engine someone can strip rechrome start over Its much easier taper stripped sleeve before chrome have done way too never said cheap easy its Speed nuts spend time 996 123 WEST BRAND EPOXY Custom blend evey batch meet specific application Resin Four Hardeners Seven Fillers THE SOLID SOLUTION Send $5 Product Guide Technical Manual OST Price List Sale Announcement lIII HUE Composite Structures Technology P0 Box 642 Dept JM Tehachapi CA 93581 Order Desk 1-800-338-1278 Technical Information 1-805-822-4162 aviation EaIe 435-9232 6042 Norwell Drive West Carroilton Ohio 45449
Edition: Model Aviation - 1996/05
Page Numbers: 122, 123
Edition: Model Aviation - 1996/05
Page Numbers: 122, 123
CONTROL LINE SPEED LAPPING IS METHOD getting parts really round absolutely flat can also method create special shapes remove material specific areas surfaces cylinders and/or improve surface finishes According Marks Mechanical Engineering Handbook lapping process producing extremely smooth accurate surfaces means lap fine abrasive part lapped final accurate dimension mating form softer material such soft close-grained cast iron copper brass lead made up job very thin coating abrasive mixed lard oil machine oil kerosene grease placed between two surfaces rubbed together column Ill try explain use laps model engines improve performance Telescope lenses eyeglasses water-pump seals dowel pins engine valves lappedto get accurate dimension shape flatness get make seal pressed against mating surface lapped pistons create seal between moving metal surfaces benefit piston rings instance Any lathe mill grinding machine will vibrate making part pieces come out accurate would like Hones can make cylinders nearly round its difficult achieve tapered bore lap engine What mean say lap piston sleeve Can lap piston sleeve toothpaste various household abrasive cleaners Lets start simple thing rotary valve DRILL TAP TO SLOT FOR SHORT 10-32 SET SCREW MAZE SLUG SAMR LENGTH AND DIAMETER AS PISTON FILE OR GRIND GROOVES 1/32 DEEP FIGURE 1 MAFE TWO PLATE5 PDRILL ONE PLATE TAP TOP FLANGE OF SLEEVEONE PLATE FOR 632 BETWEEN THEMSCREWS 002 0 00 APPROX 3/16 4 U-BORE TO FIT SLEEVE IOUTSIDE DIAMETER FIGURE 2 driven crankshaft makes intermittent seal between carburetor crankcase piston goes up down backplate rotary valve openings oriented open close correct time give maximum breathing suit particular engine intake timing will different engines depending end use Speed engines have different timing RC engines instance valves must flat smooth seal against backplate crankcase compressionour two-stroke engines cant run have rear-intake Speed engine uses flat rotor check backplate sure flat smooth arent lap flat piece glass using fine aluminum oxide grit mixed light oil move figure-eight pattern grind telescope lens use straight backand-forth motion end up dished part dont have aluminum oxide grit can use 400A 600A oiled sandpaper placed glass Abrasive-coated Mylar much better will give flatter surface available lapidary stores comes fine grits down micron millionth meter sizes Front-intake rotary valves must seal too depend close fit between crankshaft crankcase Lapping usually necessary unless touch during running should remove metal spots rub Fine sandpaper stick will job sleeve-and-piston combination important part engine maximum performance must have proper materials proper shapes correct fit Correct lapping about way remove metal certain areas achieve shape fit want some companies making newest Speed Racing engines CNC computer-controlled machines still lap some parts get round fit correctly recognize need proper geometry fit must understand what goes engine during operation piston comes up locks charge fuel air compresses glow plug ignites mixture blast hot gases impinge against top piston dont have tight seal lose benefits high compression lose power heat combustion causes tip piston expand almost instantly need some clearance prevent binding against cylinder wall some time delay heat transfer before moves down sidewalls piston must have clearance piston moves downward sleeve DRILL AND TAP FOR 1/420 CLAMP BOLTSAW FLEX SLOTS PISTON 00 FIGURE 3 122 Model Aviation NTLY LONGER nAN PISTON Additionally friction between sleeve piston creates heat also causes piston expand So piston goes down expands need clearance eliminate binding nonessential friction time combustion gases have less pressure dont need tight seal top bottom stroke fuel-air mixture crankcase cools piston next sequence reasons taper bore sleeve tight top stroke extremely loose bottom also put taper top piston wall period Speed engine development sleeve least 005 larger bottom tapered piston seals top 20% stroke doesnt touch sleeve anywhere else during stroke rides loosely oil film top piston wall also tapered bottom half relieved about 001 engines come way have lap bore until round has enough clearance check piston roundness clearance taper whether wrist pin square sides major differences allow engine go much faster another engine same type laps made various materials such brass cast iron copper Aluminum steel will sometimes gall dont use usually make brass internal laps sleeve brass wears faster chrome sleeve end up tapered lapexactly what want lap made cast iron sharp corners can easily go through thin chrome platingbe careful Too much pressure lap can also damage sleeve take easy let abrasive work Cast iron makes excellent external lap pistons will last longer bore will stay straighter know lapping necessary needed Run engine flying prop slightly smaller pitch diameter few minutes note rpm can has flown okay too Disassemble engine look bore surfaces reflected light will see piston has rubbing chrome will polished marked want have piston touch seal top stroke approximately 1/ inch no 20% stroke Most likely will see shiny spots shiny areas around exhaust bypass ports walls shiny spots piston rubbingthe sleeve out round doesnt have clearance areas Make lap like shown Figure 1 make sleeve holder like Figure 2 lap sleeve applying mixture oil aluminum-oxide grit 600 size finer both parts rotating other adjusting diameter surfaces wear away use aluminum oxide grit because breaks down can washed out easily Some abrasives like diamond carborundum can imbed themselves surfaces keep wearing parts Cross-hatching makes lap cut lot faster grooves dont have fancyjust file use grinder Deburr lap before use must have patience chrome hard wear-resistant dont try hurry things applying too much pressure lap you can warp sleeve score plating both sleeve holder keeps squeezing sleeve out round lapping Put marker stop some kind shaft lap dont go too deep lap area pistons seals usually insert lap proper depth wrap shaft electrical tape bottom sleeve As lap wears chro removed adjust diameter screw must have tight fit top stroke dont remove chrome course light inspection shows sleeve out round may have lap until round get new piston fit Run lap lathe drill press gets hot going too fast hard Reverse rotation once can think have removed enough chrome clean sleeve soap water toothbrush make sure have removed abrasive Look piston skirt too scored marked up will need lap round polish marks off s trips 600-grit sandpaper Just dont mess top seals sleeve will have get new oversized piston Oil reassemble engine Run fly check increase rpm speed take apart check sleeve again still shiny spots lap some times necessary takes 20 times want go fast what must go through chrome will likely have send engine someone can strip rechrome start over Its much easier taper stripped sleeve before chrome have done way too never said cheap easy its Speed nuts spend time 996 123 WEST BRAND EPOXY Custom blend evey batch meet specific application Resin Four Hardeners Seven Fillers THE SOLID SOLUTION Send $5 Product Guide Technical Manual OST Price List Sale Announcement lIII HUE Composite Structures Technology P0 Box 642 Dept JM Tehachapi CA 93581 Order Desk 1-800-338-1278 Technical Information 1-805-822-4162 aviation EaIe 435-9232 6042 Norwell Drive West Carroilton Ohio 45449
