tool mesury gaule barrel

8/22/2019 Tool Mesury Gaule Barrel

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AD-769 272

A NEW TOOL FOR ACCURATELY MEASURING THE INSIDEDIAMETER OF A GUN BARREL, LONG TUBE, OR SIMILAR

NAVAL ORDNANCE LABORATORY

AUGUST 1973

Distributed By:

National Technical Information ServiceU. S. DEPARTMENT OF COMMERCE

Best Available Copy


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NOLTR 73174

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Q) A NEW TOOL FOIl ACCURATELY MEASURING TH E INSIDE DIAMETER OF A GU N BARREL.I-ONG TUBE, OR SIMILAREly1J PPAuWSNAVAL OHNNANCE LABORATORYWHITEI OAK, SILVER SPRING, MD, 20910

0 Approved tot put~ic ittleaso, distribution unlimited

NAVAL ORDNANCE LABORATORYWHITE OAK. SILVER SPRING, MARYLAND 20910SI))~~ ~,,,,.,

NATIONA'. TECHNICALINFORMATION SERVICE


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AS NOTED IN THE NTIS ANNOUNCEMENT,PORTIONS OF THIS REPORT ARE NOTLEGIBLE. HOWEVER, IT IS THE BESTREPRODUCTION AVAILABLE FROM THECOPY FURNISHED NTIS BY THE CONTRIB-UTOR.


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4e ~1" 1 . _T aI aN (Pro b *Ilto,wthen ih, Mal-o t eDIOrC14'kp, .611CAI IONaNAVU. (1-ki'uil'o 1.,tborntory W'Ah1XEI:.ilvei' SprinLg, M.-Iryl a.lt[ I o2' .( i Q\A1EW "oOI, P011 A, CTIJAIT.LY MEASUULINO f111E INSIDE DIAMETEIR "2At~1 N1I(R1 , NU iTUBE , OR 1IMII.AIl'

Is, TO~TAL NO. Of ' PAGIRS KraOOP

Slb.OT WN aIomY NOISI (Any oth~er nuaobrliot Mth mamy . aooldnedd.10 YMflhT SU ON SASIApproved foir public release, distribution unlimited.

II U~P (M Nr~ i SONOPIINO MILItYANY - T V YJaalOrdnaboratorySler Sp ring, Maryland 2001011 AIPSTNA CY1,11.1 voport de~3crlbe:3 a newly devel~oped tool or gage for accuratel1yin~~rLgthe10 ill:idc, di1ameter of' gun barrel,. or anmy long tube wheretLho ratio of the insiIde dliamneter anid length io. large, for example,I hi 1.00 or more.

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NOLTR 73-174

A NEW TOOL FOR ACCURATELY MEASURING TIlE INSIDEDIAM1tER OF A GUN BARREL, LONGTUBE, OR SIMILAR

Prepared by:J. Paauwe

ABSTRACT: This report describes a newly developed tool or gage fo raccurately measuring th e inside diameter of gun barrels or any longtube where th e ratio of th e inside diameter and length is large,for example, 1 in 100 or more.

NAVAL ORDNANCE LABORATORY"SILVER SPRING, MARYLAND

M SPR.ING,


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NOLTR 73-174. 29 August 1973

A NEW TOOL FOR ACCURATELY MEASURING THE INSIDE DIAMETER OF A GUNBARREL, LONG TUBE, OR SIMILARThe design and development of this new gage was the fulfi l lment ofa long-time need. The necessity of the knowledge of the insidediameter and profile of a two-stage gun barrel gets more importantwith increasing launch velocit ies. Also, the number of shots pergun barrel is important (the longer a gun barrel can be used, themore economical the operation will be). When th e shape of a gunbarrel can be kept in th e right condition, an important steptoward successful launchings has been taken.The development of this gage was done under th e Naval OrdnanceLaboratory, Ballistics Department's Maintenance and ImprovementProgram.The author wishes to express his appreciation to Messrs. E. L. Whiteand J. F. Meek for their assistance in Lhe experimental part and theactual measuring operations.

ROBERT WILLIAMSON IICaptain, USNCommander

A. E. SEIG2LBy direction


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NOLTR 7 3 -174

CONTENTSPage

INTRODUCTION . . . . . . . . . . . . . . . . . . 1BORE TOOL . . . . . . . . .... a a ... 2

General . . . . . . . . . . o . . . . . . . . . . . 2Description . . . .. . . . . . . .. . . . . 3

PRINCIPLE OF MEASURING AND RECORDING . . ..... . . 3METHOD OF MEASURING . . . . . . . . . . o o . 9. . . . . . . 4RESULTS AND CONCLUSION o... e . .. .... . ..... 5

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NOLTR 73-174

I LLUS TRATIONSFigure Title

I Prcfiiu of insiae liameLe,, of Two-ich barrel2 Strain Gage Beam3 Bore Tool or Bore Gage4 Bore Gage5 Exploded Drawing of Bore Gage6 Gage in Standard (Calibration) Cylinder withDigital Voltmeter7 Electric Diagram of Strain Gages8 Cylinders for Calibration9 Adjustment Cylinder with Micrometer Screw Translator10 Calibration Diagram

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NOLTR 73-174

INTRODUCTIONMeasuring the inside diameter of the barrel of a two-stagelauncher is a difficult and almost impossible job. The results withthe available tools, such as a dial bore gage, Starr gage, or Spidergage, are questionable. As long as the length of a barrel is, forexample, ten feet, one can measure the inside diameter fairlyaccurately, assuming it is possible to measure from both ends andthe length to cover from each end is not more than, for example,five feet. Up to this length, it is reasonable to accept andexpect an accurate measurement, within plus or minus 0.0005 inch.Yet, it is difficult, needs skill, and is time-consuming. Largertubes and lengths over ten feet can still be measured with th e

aforementioned Starr or Spider gages, but the accuracy obtained isnot high. Repeatability is poor, and if one needs real and truedimensions, there is no instrument available which gives the desireddata in a short time, if at all. A good and accurate profile of theinside diameter of a long tube is very difficult to obtain.One of the barrels in use in the Ballistics Department has atwo-inch inside diameter and a length of eighty-one feet. Thismeans a ratio of diameter and length of almost 1:500. in the past,measurements of th e inside diameter were done with a Starr gage upto approximately three feet from the breech and three feet from themuzzle end inward. It is possible to go six or more feet inside,but the accuracy of measurements goes down proportionally with the

length or depth of measuring inside the barrel and th e uncertaintyis larger. Then a good-fitting phenolic or polyethylene plug wasmade and pulled through the barrel , and th e force to pul l the plugthrough was measured. This "pull force" and the markings on theoutside diameter of th e plug were an indication of the condition ofthe inside diameter of th e barrel.It is clear -that this method does not produce any accurate dataat all and is only a rough estimate of the shape and conditions ofthe barrel. The only thing which can be proved is the minimum orsmallest diameter of the barrel bore. It is interesting to notethat different people obtained different results, and the variousmeasurements even resulted in conflicting data.Another method for measuring and checking the inside shape ofthe barrel is an optical system, whereby a so-called backlight targetis used. The backlight target with cross-hair l ines is pulled througtht barrel, and t-he deflections are measured with a scope. This.;y:;tem i, in particular, used for straightness measurements and'tlignment of the barrel, but occasionally is fried for diametermeasurements. This system is complicated, tinmeconsuming, and

I


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NOLTR 73-174"repeat" accuracy is difficult to obtain. When the barrel is notstraight, diameter measurements are not possible.

The newly developed measuring tool not only is an answer toth e question of measuring th e inside diameter, but proves to be atool which really gives a clear view of th e inside condition of th ebarrel. For example, there had been a difference of opinion aboutth e "crimping" effect of a heavy bracket clamped around the barrel.According to some, th e inside diameter was measurably smaller atth e location of th e bracket. This thought was definitely notaccepted by others. The "pro's" measured th e effect of the outerbracket by carefully measuring th e inside diameter with th e bracketbolts tightened and with th e bolts just hand t ight, thus arrivingat their observations. The next time th e barrel was measured, th e"opposite" party did th e measurements and promptly came up with adifferent resul t and measured no effect of th e bracket at all.Interesting enough, nobody ever complained about th e joints of th ebarrel sections, and as we wil l see, this should have been done.

When accurate measurements were taken with th e new tool, wefound an interesting phenomenon. The inside diameter of th e barrelshowed two areas where the diameter changes were larger and moreirregular than the average pattern. These bad spots were exactlyat the joints of th e barrel sections, and th e joints definitelyaffected th e inside diameter over a length of several feet beforeand after th e joint . The diameter at th e bracket location did notchange, whether the bracket was tightened on the barrel or not.Figure 1 shows th e results of th e inside diameter measurements takenat six-inch intervals.

BORE TOOLGeneral

The new tool which has been developed for measurement of th einside diameters of long barrels, tubes, etc., overcomes all theproblems of the other systems. The new tool can be used in anylocation and gives very high accuracy in th e diameter measurements.Its use reduces the time of measurements considerably and does notneed special handling or skilled hands. The important thing is thatit is possible now to measure accurately any spot or area inside th ebarrel. The length of th e barrel, pipe, or tube is not important,arnd there is no restriction anymore for reliable and accuratemeasurements. Measurements can be repeated within very smalltc>i=~ec, depending on the recording or readout instruments used.There are a few conditions for operation. The bore has to be cleanand without heavy damages or grooves, and th e surface of the insidediiLameter should be smooth, preferably honed. Secondly, the boretool has to be adjusted and made, ready for the particular diameter.Tr-i measuring range is small in comparison with other instruments.T'h dly for accurate measurements, the bore tool has to be cali-br',ted before and after the "measuring run."

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NOLTR 73-174In measuring the inside diameter of a tube or barrel, the tool.is slowly pulled through the tube (barrel) and can give an auto-matic continuous readout on tape of the inside diameter (writing orpen recorder). The bore tool can be stopped and read at any distanceor interval. Six-inch intervals are very attractive and give a real

inside pattern of the barrel. The diameter can be read on a digitalvoltmeter or can be directly transferred in actual dimensions. Also,punch cards can be used, and via a computer, an accurate readout canbe obtained later.Description

The instrument consists of a body holding a strain gage beamof certain length, Figure 2. The beam has a smaller area whereon both sides (top and bottom) strain gages have been attached. Th estrain gage beam at one side is solidly tightened to the main toolbody, whereas the opposite side is free to move up and down. Thisend of the beam has a button which, as said, can move a certainrestricted distance up and down. The restriction is to prevent thebeam from overstressing and causing permanent deflection.The body at one end is supported by two solid bearing buttonsand a third one is spring-loaded (this side is the opposite sidefrom the moving beam button and on the same side where the beamhas been fixed to the main body). The two bottom buttons areassembled in a movable or rotating bearing block in order to preventthe tool from "lifting" or "floating" on one dide. The other sideof the main body is the side where tl- measuring action takes plJ-v(see Figures 3, 4., and 5).The strain gage beam is provided on both sides with a doubleset of strain gages which are temperature-balanced and wired in such

a way that when the beam is slightly pushed down, the top straingages under tension and the bottom strain gages under compressionadd displacement values. In this way, even the smallest amount ofdeflection is easily readable. The most simple form of readout isa digital voltmeter where the changes are recorded as microvolts.A calibration and simple calculation wilJ transfer the digitalreadings into actual diameter readings. Since the muzzle end ofthe barrel is usually the biggest diameter, it is easy to adjust thetool fo r this diameter, thus assuring uninterrupted contact of thebeam button with the inside diameter of the barrel (see Figure 6).PRINCIPLE OF MEASURING AND RECORDING

The basic principle of the new bore tool is that very small...... in diameter of the bore introduce a change in current. Incur prototype, - semi-conductor strain gage bridge is used, Pigure 7.T!. 'Pi'inge in diameter of the barrel, when the tool i.; slowly PulledLtrrIuiq the barrel, will change the current through the Jegs of thohr ... , ,nd these changes produce, an unbalance vo.tri c whi(,h i',oc rc:1,: by a digi tal voltmeter. The change; in curnrm t Qan a):;o be

73


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NOLTR 73-174recorded by other -eans. Also, it is possible to use other devicessuch as three terminal capacitors instead of strain gages. Threeterminal capacitors have often been used as transducers to measureaccurately small displacements in air by measuring the change ofcapacitance as a guarded electrode moves with respect to a secondelectrode. Another way is measuring a straightforward electricalresistance change in a leg of a Wheatstone bridge. In this case,the changes in diameter move a contact over a current-carrying wirand the wire is one of the legs of a Wheatstone bridge. Because othe small diameter changes, the movements are enlarged by a leversys tern.

METHOD OF MEASURINGThe actual measuring operation, as said, is simple, considerina few preparations which have to be taken.a. The tool has to be adjusted for the particular bore size.Once this has been done, it does not need to be repeated until th echanges in diameter become too large and the tool cannot cover themeasuring range. In the case of a barrel, it is easy to accomplissince the muzzle end usually is the largest diameter and, as it isin our case also, the side where honing and cleaning operationsstart. Measurements are taken of the muzzle end (or the largestpart of the barrel) with the tool adjusted accordingly.b. Special calibration cylinders have been made to adjust ancalibrate the tool. Two of these "standard" cylinders have adifferent inside diameter: Cylinder 1 has an inside diameter of2.0228 inches, and cylinder 2 has an inside diameter of 2.0028inches rusulting in a difference in diameter of 0.0200 inch (seeFigure 8). These two cylinders serve fo r calibration of the boretool, whereas a third cylinder is used fo r diameter adjustment andconfirmation of the calibration. The third cylinder has at oneend a micrometer screw and, as said, is in the first place used fodiameter range control, but can also be used for direct calibrationpurposes (see Figures 9 and 10).c. The barrel should be cleaned and honed before the measure-ment operation. When the bore measuring tool or bore gage has beenadjusted and calibrated, the measurement can take place. A tape of.;ufficient length, for example, 100 feet, is brought into th ebirrel and at the other side attached to the bore gage. Then slow:;tcp by step, the tool can be -ulled through the barrel. Intervals!,'ix inches are small enough steps to obtain an accurate pattern-f' he inside diameter of the barrel. After the bore gage has beenpoIllcA through, it is good pract-ice to check the calibration and

'.;ure, the barrel a second time. Since the sensitivity is high,;iitly different readings might be observed also due to a small, fcrc',ce in actual location of the bore gage, 0.0003 inch. An/,:r":Pc value can be taken fo r the computation of the diameters.

,.l:;o, it i, ; preferred to move the bore gage in one directionr irn. to prevent shattering of the gage beam. Pulling the bore14


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SNOLTR 73-17L4

gage back and forth has been done without difficulty; as long as thegage beam can relax., there seems to be no problem. Relaxing thegage beam can easily be done by pulling in the "wrong" direction,for example, eight inches, and pulling back in the right directiontwo inches.

RESULTS AND CONCLUSIONWith the availability of the new tool or gage, an excellentpattern of the inside diameter of a barrel can be obtained. Whenthe gage is adjusted correctly, the measuring operation of an 80-foot barrel would not take more than one hour. With six-inchintervals, a total of 160 diameter measurements gives the profileof the inside diameter and shape of the barrel. The result is anauthoritative answer to a question which never before could beanswered or only estimated at the best.The results of the measurements depend on the calibration andelectronic instruments used. The accuracy of measurements can bebetter than 0.0002 inch. When the average accuracy over the totallength of a barrel is between 0.0005 inch and 0.001 inch, anexcellent profile of the inside diameter has been obtained. Thereare no more guesses or estimates of the inside diameter, and withthe availability of new honing tools, the honing operation itself isgoing to be much more effective and efficient. The barrel can bekept in a better condition than before and, consequently, can be usedmuch longer.

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