PRECISION MEASUREMENT FOR THE AMATEUR MACHINIST
MY PERSONAL DEFINITION OF PRECISION IS MEASURING TO AN ACCURACY OF LESS THAN ONE THOUSANDTH OF AN INCH, 0.001".IN THIS BLOG I WILL DESCRIBE 0.001 INCH AS "ONE THOU".
THE METRIC EQUIVALENT IS 0.025 MM.
REMEMBERING THAT THIS BLOG IS INTENDED TO HELP ENTHUSIASTS WITH LIMITED MEANS, SO THAT I WON`T BE TALKING ABOUT INSTRUMENTS THAT ARE TOO EXPENSIVE FOR US TO BUY BUT TO DISCUSS HOW ACCURACY CAN BE ACHIEVED ON A LOW BUDGET.
THE METRIC EQUIVALENT IS 0.025 MM.
REMEMBERING THAT THIS BLOG IS INTENDED TO HELP ENTHUSIASTS WITH LIMITED MEANS, SO THAT I WON`T BE TALKING ABOUT INSTRUMENTS THAT ARE TOO EXPENSIVE FOR US TO BUY BUT TO DISCUSS HOW ACCURACY CAN BE ACHIEVED ON A LOW BUDGET.
THIS IS A DESCRIPTION OF HOW TO MEASURE DIMENSIONS WITH PRECISION WHEN MACHINING.
MY APPRENTICESHIP AT THE COVENTRY GAUGE AND TOOL CO TAUGHT ME ALL ABOUT PRECISION MEASUREMENT AS THEY WERE THE MAIN UK MANUFACTURERS OF HIGH PRECISION MEASURING INSTRUMENTS SELLING THEM UNDER THEIR TRADE NAME OF "MATRIX".
MY APPRENTICESHIP AT THE COVENTRY GAUGE AND TOOL CO TAUGHT ME ALL ABOUT PRECISION MEASUREMENT AS THEY WERE THE MAIN UK MANUFACTURERS OF HIGH PRECISION MEASURING INSTRUMENTS SELLING THEM UNDER THEIR TRADE NAME OF "MATRIX".
ABOVE IS SHOWN PAGES 2 AND 22 OF THE WARTIME BROCHURE PRODUCED BY MATRIX. THEY PRODUCED AN INCREDIBLE RANGE OF PRODUCTS AND AFTER WW2 EXPONENTIALLY INCREASED THEIR RANGE.
NORMALLY THESE PRODUCTS WERE PRICED OUT OF THE REACH OF AMATEURS BUT MODERN TECHNOLOGY HAS PRODUCED MACHINES THAT CARRY OUT THE PRECISION MEASUREMENT IN FACTORIES THAT HAS LED TO THE MANUAL MEASURING DEVICES TO BE PENSIONED OFF.
THIS HAS CREATED A WONDERFUL OPPORTUNITY TO BUY THESE PENSIONERS AT AN AFFORDABLE PRICE AND THE BEST PLACE TO FIND THEM IS NORMALLY ON EBAY UK.
NORMALLY THESE PRODUCTS WERE PRICED OUT OF THE REACH OF AMATEURS BUT MODERN TECHNOLOGY HAS PRODUCED MACHINES THAT CARRY OUT THE PRECISION MEASUREMENT IN FACTORIES THAT HAS LED TO THE MANUAL MEASURING DEVICES TO BE PENSIONED OFF.
THIS HAS CREATED A WONDERFUL OPPORTUNITY TO BUY THESE PENSIONERS AT AN AFFORDABLE PRICE AND THE BEST PLACE TO FIND THEM IS NORMALLY ON EBAY UK.
TEMPERATURE
TEMPERATURE CAN HAVE AN UNDESIRED EFFECT ON ACCURACY. MOST TOOLROOMS IN A FACTORY WILL BE HEATED TO AROUND 20 DEGREES CELCIUS. TO GIVE AN EXAMPLE, IF YOU ARE USING LARGE CUTS TO REDUCE THE DIAMETER OF A SHAFT AND YOU ARE NOT USING COOLANT AS MOST OF WE AMATEURS DONT, THEN THE TEMPERATURE OF THE SHAFT WILL BE TOO HIGH FOR AN ACCURATE MEASUREMENT TO BE MADE IF WORKING TO CLOSE TOLERANCES, SAY TO FIT A BALL BEARING, SO IT MUST BE ALLOWED TO COOL DOWN BEFORE TAKING THE FINAL CUTS.
THE BASIC MUST HAVE MEASURING TOOLS
NOT EVERYONE IS GOING TO AGREE WITH MY CHOICE OF MEASURING TOOLS. CHOICES ARE NORMALLY BASED ON PERSONAL EXPERIENCE GAINED FROM THE TOOLS THAT WE HAVE USED DURING OUR WORKING LIFE OR FROM ARTICLES PUBLISHED IN THE MODEL MAKING MAGAZINES OR ON VIDEOS SHOWN ON "YOU TUBE".
SLIP GAUGES
OTHERWISE KNOWN AS GAGE BLOCKS,. THESE WERE INVENTED BY THE SWEDISH ENGINEER C. E. JOHANSON.
ABOVE, AN 81 PIECE SET OF IMPERIAL SLIP GAUGES MADE BY MATRIX. THERE WERE TWO GRADES AVAILABLE. THE WORKSHOP AND THE INSPECTION GRADE. THIS IS A WORKSHOP SET THAT COST ME LESS THAN A HUNDRED GBP.
THIS IS A BOX THAT`S PACKED WITH POWER, ACCURATE TO MILLIONS OF AN INCH THAT YOU CAN USE TO CALIBRATE ALL OF YOUR OTHER MEASURING INSTRUMENTS, THEIR USES ARE INFINITE AND ONCE USED, I PROMISE YOU, THAT YOU WILL NEVER WANT TO BE WITHOUT HAVING THEM IN YOUR WORKSHOP.
THEY ARE LAPPED TO SUCH A FINE SURFACE FINISH, THAT WHEN WRUNG TOGETHER, THEY WILL STICK TO EACH OTHER DUE TO ATMOSPHERIC PRESSURE ACTING ON THEM. DON`T WORRY IF SOME OF YOURS DON`T, AS THEY ARE STILL INCREDIBLY ACCURATE.
THIS IS A BOX THAT`S PACKED WITH POWER, ACCURATE TO MILLIONS OF AN INCH THAT YOU CAN USE TO CALIBRATE ALL OF YOUR OTHER MEASURING INSTRUMENTS, THEIR USES ARE INFINITE AND ONCE USED, I PROMISE YOU, THAT YOU WILL NEVER WANT TO BE WITHOUT HAVING THEM IN YOUR WORKSHOP.
THEY ARE LAPPED TO SUCH A FINE SURFACE FINISH, THAT WHEN WRUNG TOGETHER, THEY WILL STICK TO EACH OTHER DUE TO ATMOSPHERIC PRESSURE ACTING ON THEM. DON`T WORRY IF SOME OF YOURS DON`T, AS THEY ARE STILL INCREDIBLY ACCURATE.
ABOVE LEFT AND CENTRE, AN IMPERIAL AMERICAN 81 PIECE SET MADE BY THE DEARBORN GAGE CO. THE DATE OF MANUFACTURE IS STATED AS 1942, PROBABLY SENT TO THE UK VIA A CROSS ATLANTIC CONVOY DURING WW2. I PAID 40 GBP FOR THEM AND USE THEM FOR ROUGH WORK BUT THEY ARE STILL ACCURATE ENOUGH FOR ALL OF MY NEEDS.
I ONCE PICKED UP A HALF SET OF METRIC SLIPS, SHOWN IN THE RIGHT IMAGE, AT THE BEAULIEU AUTOJUMBLE FOR 10 GBP, THERE WERE FOUR MISSING BUT SO CHEAP AND SO VERY USEFUL!
I ONCE PICKED UP A HALF SET OF METRIC SLIPS, SHOWN IN THE RIGHT IMAGE, AT THE BEAULIEU AUTOJUMBLE FOR 10 GBP, THERE WERE FOUR MISSING BUT SO CHEAP AND SO VERY USEFUL!
MICROMETERS
THESE COME IN ALL SHAPES AND SIZES AND ARE THE NEXT MOST ACCURATE MEASURING DEVICE AFTER SLIP GAUGES IF KEPT CALIBRATED BY USING YOUR SLIP GAUGES. THE MORE EXPENSIVE MICS COME WITH A CALIBRATING PIECE BUT THIS WILL ONLY ENSURE THAT THE MIC IS ACCURATE AT ONE POINT IN IT`S RANGE OF MOVEMENT. MICS WEAR JUST LIKE ANY OTHER MECHANICAL DEVICE AND THE SCREW CAN BE WORN IN THE AREA OF MOST USE, WHICH CAN LEAD TO A N INCORRECT READING BEING TAKEN .
ABOVE LEFT, A TABLE FULL OF MEASURING INSTRUMENTS AT AN AUCTION SALE OF THE CONTENTS OF A FACTORY CLOSURE IN OSLO. I WAS ABLE TO SKIM OFF MANY OF THE BEST INSTRUMENTS AT INCREDIBLY LOW PRICES. SOME I WILL PROBABLY NEVER USE BUT THEY ARE THERE IF I EVER NEED THEM.
ABOVE RIGHT, A SELECTION OF MICS THAT WERE ON MY DESK. A/ A MOORE AND WRIGHT 0-1" DEPTH MIC.
B/ A DINKY MOORE AND WRIGHT 0-0.5" MIC. C/ A MOORE AND WRIGHT 0-2" MIC. D/ A JAPANESE NSK DIGITAL MIC THAT I BOUGHT AROUND THIRTY YEARS AGO. IT`S EXACTLY THE SAME AS THE MITUTOYO. THE PROBLEM WITH THESE MECHANICAL DIGITAL MICS IS THAT THE MINI GEARS IN THE MECHANISM CAN BECOME WORN AND THE DIGITS NOT LINE UP TOGETHER.
ABOVE RIGHT, A SELECTION OF MICS THAT WERE ON MY DESK. A/ A MOORE AND WRIGHT 0-1" DEPTH MIC.
B/ A DINKY MOORE AND WRIGHT 0-0.5" MIC. C/ A MOORE AND WRIGHT 0-2" MIC. D/ A JAPANESE NSK DIGITAL MIC THAT I BOUGHT AROUND THIRTY YEARS AGO. IT`S EXACTLY THE SAME AS THE MITUTOYO. THE PROBLEM WITH THESE MECHANICAL DIGITAL MICS IS THAT THE MINI GEARS IN THE MECHANISM CAN BECOME WORN AND THE DIGITS NOT LINE UP TOGETHER.
MICROMETERS ARE THE STEADFAST SOLDIERS OF OUR COLLECTION OF MEASURING TOOLS. YOU CAN MEASURE TO WITHIN ONE TENTH OF A THOU EASILY ONCE YOU HAVE MASTERED THE USE OF THEM BY DEVELOPING YOUR OWN "FEEL" DURING USE. YOUR INCREDIBLY SENSITIVE HANDS ARE THE NATURAL GAUGES OF YOUR BODY AND MEASURING INSTRUMENTS ARE THE EXTENSION OF THEM. I WILL EXPAND ON THIS LATER.
BUYING A MICROMETER
NEW MICS CAN BE CHEAP TO BUY AND ARE AVAILABLE AS A STANDARD MECHANICAL OR AN ELECTRONIC VERSION. ALWAYS REMEMBER THAT ELECTRONICS CAN GO HAYWIRE AND CHEAP VERSIONS CAN CONSUME BATTERIES AT AN ALARMING RATE AS THEY DON`T HAVE AN AUTOMATIC SHUT OFF FACILITY. THE MECHANICAL TYPE SHOULD BE THE ONE OF CHOICE.
SECOND HAND MICS CAN BE BOUGHT CHEAPLY FROM SITES SUCH AS EBAY UK BUT THERE IS NO WAY THAT THESE CAN BE CHECKED OUT BEFORE PURCHASE AND THE SELLER MAY NOT BE AN ENGINEER AND CANNOT CHECK THEM OUT HIMSELF. MICS ARE EASILY DAMAGED BY CARELESS HANDLING SUCH AS DROPPING THEM OR USING TOO MUCH PRESSURE WHEN TAKING READINGS. THEY ARE DELICATE, SO TREAT THEM WITH RESPECT!
IF DROPPED, THE MIC WILL PROBABLY LOOK PERFECT BUT THE IMPACT FORCES MAY HAVE DISTORTED THE FRAME SO THAT THE FACES OF THE SPINDLE AND ANVIL ARE NOT EXACTLY ON THE SAME AXIS. YOU CAN FEEL THIS WHEN CLOSING THEM TOGETHER, AS YOU WILL FEEL THEM TOUCHING TOGETHER AND A LITTLE MORE FORCE WILL CLOSE THEM TOGETHER. THEY CAN STILL BE USED FOR ACCURATE WORK IF USED IN CONJUNCTION WITH SLIP GAUGES AS I WILL EXPLAIN.
SECOND HAND MICS CAN BE BOUGHT CHEAPLY FROM SITES SUCH AS EBAY UK BUT THERE IS NO WAY THAT THESE CAN BE CHECKED OUT BEFORE PURCHASE AND THE SELLER MAY NOT BE AN ENGINEER AND CANNOT CHECK THEM OUT HIMSELF. MICS ARE EASILY DAMAGED BY CARELESS HANDLING SUCH AS DROPPING THEM OR USING TOO MUCH PRESSURE WHEN TAKING READINGS. THEY ARE DELICATE, SO TREAT THEM WITH RESPECT!
IF DROPPED, THE MIC WILL PROBABLY LOOK PERFECT BUT THE IMPACT FORCES MAY HAVE DISTORTED THE FRAME SO THAT THE FACES OF THE SPINDLE AND ANVIL ARE NOT EXACTLY ON THE SAME AXIS. YOU CAN FEEL THIS WHEN CLOSING THEM TOGETHER, AS YOU WILL FEEL THEM TOUCHING TOGETHER AND A LITTLE MORE FORCE WILL CLOSE THEM TOGETHER. THEY CAN STILL BE USED FOR ACCURATE WORK IF USED IN CONJUNCTION WITH SLIP GAUGES AS I WILL EXPLAIN.
CALIPERS
ABOVE LEFT, A MITUTOYO ELECTRONIC CALIPER. THE RIGHT HAND IMAGE SHOWS TWO OTHER VARIANTS, THE UPPER ONE IS A SIMPLE IMPERIAL/METRIC VERSION, USEFUL FOR TAKING QUICK MEASUREMENTS AND BELOW A JAPANESE VERSION THAT HAS A VERNIER FUNCTION THAT CAN MEASURE TO PLUS AND MINUS A THOU. THERE IS ANOTHER TYPE THAT HAS A DIAL JUST LIKE A DIAL INDICATOR, THESE ARE MORE DIFFICULT TO READ AND AS THEY ARE OPERATED BY A TINY RACK ALONG THE SHAFT. SMALL PIECES OF METAL CAN BECOME LODGED IN THIS RACK AND PREVENT A GOOD READING BEING OBTAINED.
CALIPERS COME IN MANY VARIETIES BUT THEY ARE NOT PRECISION DEVICES, SOME ELECTRONIC ONES SHOW A READOUT OF HALF A THOU BUT THEY ARE NORMALLY ONLY GUARANTEED TO BE ACCURATE TO PLUS OR MINUS A THOU IF YOU READ THE SMALL PRINT. THE MECHANICAL ONES ARE OBVIOUSLY MORE RELIABLE THAN THE ELECTRONIC ONES BUT THE ADVANTAGE WITH THE ELECTRONIC ONES ARE THAT THEY ARE QUICKER TO USE AND MORE EASY TO READ, IDEAL FOR CHECKING THE DIAMETER OF A BAR WHILE TURNING DOWN TO SIZE BUT FOR ACCURACY A MICROMETER SHOULD BE USED TO CHECK THE FINAL CUTS.
I HAVE TWO MITUTOYO ELECTRONIC 8 INCH CALIPERS BOTH OF THEM HAVE DEVELOPED PROBLEMS WITH THEIR ELECTRONICS AND ARE OF NO USE AND WILL HAVE TO BE REPAIRED IF THAT IS FOUND TO BE A COST EFFECTIVE SOLUTION? I WILL PROBABLY BUY ANOTHER ONE BUT THESE ARE MADE IN CHINA AND UNFORTUNATELY, THERE ARE INFERIOR COPIES, ALSO MADE IN CHINA, THAT ARE PASSED OFF AS ORIGINALS, SO BE AWARE!
I HAVE TWO MITUTOYO ELECTRONIC 8 INCH CALIPERS BOTH OF THEM HAVE DEVELOPED PROBLEMS WITH THEIR ELECTRONICS AND ARE OF NO USE AND WILL HAVE TO BE REPAIRED IF THAT IS FOUND TO BE A COST EFFECTIVE SOLUTION? I WILL PROBABLY BUY ANOTHER ONE BUT THESE ARE MADE IN CHINA AND UNFORTUNATELY, THERE ARE INFERIOR COPIES, ALSO MADE IN CHINA, THAT ARE PASSED OFF AS ORIGINALS, SO BE AWARE!
INTERNAL MEASUREMENT
ACCURATE INTERNAL MEASUREMENT OF A BORE IS MORE DIFFICULT THAN OUTSIDE MEASUREMENT MAINLY BECAUSE THE COST OF THE GAUGES WHICH CAN RUN INTO THOUSANDS OF GBP.
THE ELECTRONIC CALIPER IS FINE FOR QUICK READINGS BUT FOR MORE ACCURATE RESULTS VARIOUS METHODS WILL NEED TO BE USED ASSUMING THAT YOU DON`T HAVE ACCESS TO THE EXPENSIVE INSTRUMENTS.
THE ELECTRONIC CALIPER IS FINE FOR QUICK READINGS BUT FOR MORE ACCURATE RESULTS VARIOUS METHODS WILL NEED TO BE USED ASSUMING THAT YOU DON`T HAVE ACCESS TO THE EXPENSIVE INSTRUMENTS.
ABOVE LEFT, IS A VERY USEFUL MATRIX BOXED SET OF ACCESSORIES THAT USES SLIP GAUGES TO ACCURATELY MARK OUT WORK OR STACK A LINE OF THEM IN THE CLAMPS FOR CHECKING A DIMENSION. THIS CAN ALSO BE USED TO CREATE INDIVIDUAL GAUGES FOR CHECKING INSIDE AND OUTSIDE DIMENSIONS. THE RIGHT HAND IMAGE SHOWS A STACK OF SLIPS CLAMPED TOGETHER WITH TWO ROUNDED ENDS THAT CAN BE USED TO CHECK THE GAP BETWEEN THE ELECTRODES IN THIS DISTRIBUTOR CAP. OR TO MEASURE A BORE ACCURATELY. NO BATTERIES REQUIRED AND CAN MEASURE DOWN TO ONE TENTH OF A THOU (0.0001 OF AN INCH)
ABOVE, A VERY NICE SET OF MATRIX GAUGES THAT CAN BE USED TO MEASURE DIAMETERS AND GAPS
GETTING THE "FEEL" OF MEASUREMENT.
UNFORTUNATELY, GETTING ACCURATE MEASUREMENT REQUIRES TRAINING AND THE MOST IMPORTANT PART OF THIS IS TO DEVELOP A DELICATE FEEL FOR EACH INSTRUMENT OR GAUGE THAT YOU USE.
THE SLIP GAUGES WILL HELP YOU TO TRAIN YOURSELF TO DEVELOP THE FEEL.
THE SLIP GAUGES WILL HELP YOU TO TRAIN YOURSELF TO DEVELOP THE FEEL.
STARTING WITH THE MICROMETER, HOLD IT IN YOUR RIGHT HAND AS SHOWN ABOVE (LARGER MICS WILL NEED A DIFFERENT APPROACH) AND THE SLIP GAUGE IN YOUR LEFT AFTER MAKING SURE THAT THE ANVIL, SPINDLE FACES AND SLIP GAUGE FACES ARE CLEAN.THEN WIND THE SPINDLE DOWN TO GRIP THE SLIP LIGHTLY. YOU CAN USE THE RATCHET TO EXERT THE CORRECT PRESSURE OF THE ANVIL AND SPINDLE ON THE SLIP BUT THE RATCHET CAN BECOME WORN OR CLOGGED UP SO MOST PROFESSIONALS DO NOT USE IT BUT RELY ON THEIR OWN FEEL TO GET THE CORRECT PRESSURE. THIS IS HOW I WAS TRAINED TO USE A MIC. NOW LOOK AT THE THIMBLE AND READ OFF WHAT IT TELLS YOU.
IT SHOULD READ ROUGHLY THE SAME AS THE SIZE OF THE SLIP SO THAT THERE ARE TWO POSSIBILITIES THAT PRESENT THEMSELVES. FIRSTLY, YOU HAVE NOT EXERTED THE CORRECT PRESSURE ON THE SLIP OR SECONDLY, THE MIC IS OUT OF ADJUSTMENT!
IT SHOULD READ ROUGHLY THE SAME AS THE SIZE OF THE SLIP SO THAT THERE ARE TWO POSSIBILITIES THAT PRESENT THEMSELVES. FIRSTLY, YOU HAVE NOT EXERTED THE CORRECT PRESSURE ON THE SLIP OR SECONDLY, THE MIC IS OUT OF ADJUSTMENT!
GETTING THAT EXACT MEASUREMENT WITH A MICROMETER
ONCE YOU HAVE DEVELPED THE FEEL OF YOUR MIC THEN IT DOESN`T REALLY MATTER IF IT IS OUT OF ADJUSTMENT, WORN OR THE AXES OF THE SPINDLE AND THE ANVIL ARE SLIGHTLY OUT.
REMEMBER THAT YOU CAN HAVE A BRAND NEW MIC AND STILL GET A WRONG READING IF YOU DO NOT HAVE THE FEEL OF IT!
LET`S SAY YOU ARE TURNING DOWN A BAR TO A PRE DETERMINED DIAMETER AND WANT TO MEASURE WITHIN A TENTH OF A THOU. TAKE THAT WORN OUT MIC THAT YOU FOUND ON THE INTERNET, SELECT THE SLIP GAUGES THAT MAKE UP THE DIMENSION YOU ARE MACHINING DOWN TO, AND USING YOUR FEEL, MEASURE THE SLIPS AND READ OFF THE DIMENSION. YOU MAY FIND THAT THE READING IS SEVERAL TENTHS OF A THOU OVER OR UNDER THE DESIRED RESULT. ALL YOU HAVE TO DO IS TO USE THIS RESULT AS YOUR ORIGIN AND MACHINE THE BAR DOWN TO IT TO GET THE CORRECT DIMENSION. IT`S SO SIMPLE TO DO AND YOU DON`T NEED TO ADJUST YOUR MICS TO DO THIS, AS THIS METHOD, USED BY PROFESSIONALS, COMPENSATES FOR ANY WEAR THAT IS PRESENT IN YOU MIC OR ANY OTHER MEASURING INSTRUMENT.THAT YOU ARE USING.
REMEMBER THAT YOU CAN HAVE A BRAND NEW MIC AND STILL GET A WRONG READING IF YOU DO NOT HAVE THE FEEL OF IT!
LET`S SAY YOU ARE TURNING DOWN A BAR TO A PRE DETERMINED DIAMETER AND WANT TO MEASURE WITHIN A TENTH OF A THOU. TAKE THAT WORN OUT MIC THAT YOU FOUND ON THE INTERNET, SELECT THE SLIP GAUGES THAT MAKE UP THE DIMENSION YOU ARE MACHINING DOWN TO, AND USING YOUR FEEL, MEASURE THE SLIPS AND READ OFF THE DIMENSION. YOU MAY FIND THAT THE READING IS SEVERAL TENTHS OF A THOU OVER OR UNDER THE DESIRED RESULT. ALL YOU HAVE TO DO IS TO USE THIS RESULT AS YOUR ORIGIN AND MACHINE THE BAR DOWN TO IT TO GET THE CORRECT DIMENSION. IT`S SO SIMPLE TO DO AND YOU DON`T NEED TO ADJUST YOUR MICS TO DO THIS, AS THIS METHOD, USED BY PROFESSIONALS, COMPENSATES FOR ANY WEAR THAT IS PRESENT IN YOU MIC OR ANY OTHER MEASURING INSTRUMENT.THAT YOU ARE USING.
IN PROGRESS