what is the best way to measure deep internal grooves

   THREAD INSPECTION OF PITCH DIAMETER

   MTG, Inc. decided to look for answers by studying one of the most successful methods of gaging external threads, the 3-wire system. No one had ever seriously considered this system for internal threads before , it was obvious  the concrete characteristics of wires made it impossible to deploy and  seat them in the tight convolutions of a female person thread. But the principle was sound, so we overcame the physical issues past substituting " floating balls" of Best Wire sizes for the actual wires. Held captive in caliper fingers and mounted on an indicating gage frame, the balls could exist made to simulate 3-wire inspection in internal threads, Figure 1.

LESS GAGING Pressure level
The apply of balls, incidentally, eliminates perhaps the only significant shortcoming of wires. The problem is spelled out in Spiral Thread Standards for Federal Services, under the heading Limitations of Three-Wire Measurement of External Threads: "When the lead bending and bore of a thread are such that double contact of the measuring wires occurs, it will exist necessary to bank check the pitch diameter by means of balls rather than wires. For authentic measurement with wires, single contact on each flank must occur. Measuring wires tin can be used if the following formula is satisfied for a specific thread." And then follows a lengthy bounty formula adult past Werner F Vogel of The Van Keuren Co.

    Considering of the possibility that wires may brand double contact in threads of sure lead and diameter combinations, Vogel's equation calls for increased gaging pressure to seat the wires--as much as 2 1/2 Ib. in a ane/2-twenty thread. This may upshot in deformation of the wire , the thread or both  ! ! ! !

    Replacing the wires with balls every bit nosotros have done eliminates seating problems by making spheres rather than cylinders the method of contact. Gaging force per unit area need exist only about 1 oz., or enough to satisfy the inspector that contact pressure level is sufficient to register the size.

HOW ERROR IS ISOLATED
To empathize how the ball principle isolates thread aspects for errorless measurement, let u.s. first consider the key dimension in any thread; the pitch diameter. By definition, the pitch diameter is an imaginary cylinder along which each cutting thread and each web of intervening metal take the aforementioned width: one-half the pitch, or P/2.

     Traditionally, the pitch diameter has been checked with thread plug gages. If an inspector could enter the "Become" plug just not the "No Become," the pitch bore was considered to be inside tolerance. Should the "Go" neglect to enter, general practice was to deepen the cut until information technology did. Conversely, should the "No Become'' enter, the cutting would be made shallower to prevent its entry.

    The blind spot in this procedure was that it assumed perfection in all other aspects of the internal thread. It ignored the fact that a thread cut to perfect depth will gage undersize if there is lead error, because the mis-matched leads of the thread and the plug gage will have interference. By the same token, a thread cut oversize and having atomic number 82 error can pass thread plug inspection if the interference is not enough to block the "Go" but does forbid the "No Go" from entering.

    The floating brawl system cannot be deceived by errors in lead or helix, no matter how astringent or erratic (as in drunken threads), because the balls float laterally to discover a perfect seat in the cuts regardless of the width of the metal between cuts, Figure 2. The balls are solid carbide, finished to Best Wire sizes, and will positively establish whether the tool is cutting to PD tolerance, since they measure out diametrically across the threaded pigsty from cut to cut, not from cutting to metal.

   What is the importance of gaging from cutting to cutting? Simply stated, all diameters of a thread are functions of depth of cut. The cutting is the constant, an exact matrix of the cutter at every point along the thread. The metal between cuts, however, is an unknown remainder whose P/2 width is a linear role dependent on the accuracy of the pb. A lead with a plus error volition widen the metallic betwixt cuts; a minus mistake will narrow information technology; an erratic lead volition event in inconstant widths. Unless the lead has been proved perfect in advance, checking the pitch bore by using the metal as a gaging indicate is futile.

ane. Section drawing shows three balls in contact with pitch line of internal thread. ii. Floating action of the balls cancels out pitch errors in the metal betwixt cuts (5) whether the error is minus every bit at (A) or plus as at (B).

ISOLATING SUBSEQUENT ASPECTS With the ability to isolate and accurately check the pitch diameter, information technology becomes a uncomplicated matter to inspect the remaining thread factors i at a fourth dimension, isolating extraneous errors at each footstep. In our organization, the same gage frame is provided with boosted pairs of fingers, each with a dissever function. HOW ACCURATE? In this arrangement, much thought has been given to the elimination of normally inherited errors. For case, the gage does not measure. It compares the work slice confronting an accepted reference such as a patently ring cuff or gage blocks, and shows whatsoever variation on a dial indicator or electronic comparator. Fingers motion on one airplane merely, along the axis of the indicator, so no radial or angular "scissors effect" errors can exist introduced.     Problems of taper and out-of-circular will not fool the system considering its point-contact fingers reveal such conditions by displaying various readings when they are moved from ane location to another around or forth the thread. Repeatability of the MTG cuff is excellent, since in that location is null to change successive readings except surface contaminants, and careful cleaning of disquisitional parts can overcome this. The system is and so accurate information technology can exist used to certify thread band gages on the job. In bodily tests, it has detected and confirmed errors even in make new adaptable thread band gages.

Dorsum to Peak

                                           INTERNAL THREAD INSPECTION

Thread plug gages can neither isolate compound errors in female threads nor reveal the amount of error. They merely suggest that "something is wrong." Now the ''MTG Organization'' lets the producer of internal threads brand his own footstep-by-footstep analysis with a manus-held cuff in a few minutes. Required data is obtained by use of interchangeable fingers shown on the chart below. Most significant of the fingers is ''J'', which contains ii floating assurance of "All-time Wire Size''. These assurance make contact at the P/2 width, or pitch circle of the thread grooves. Considering they float, the balls will seat at the pitch circle whether the atomic number 82 is brusque, long, correct or drunken. Finger "J" is used in conjunction with every upper finger in the thread series except the "Functional", and provides an identical base of operations line in every case!

MTG ZONAL METHOD

PITCH (MINIMUM Textile) Diameter
Fingers "A" and "J" both have tungsten carbide balls of "Best Wire Size", and requite a reading which excludes lead error but not angular errors. PD fingers tin be used for right or left hand threads. TAPER AND OVALITY
Use fingers "A" and "J" at intervals along thread for taper and effectually the thread for ovality. INCLUDED ANGLE
Utilise fingers "D" and "J". The ball in "D" is smaller than in pitch diameter finger "A", and should seat a prescribed distance deeper. If information technology does not, athwart fault is present. The degree of fault and its effect on P.D. can be adamant past a formula.

MAJOR Diameter
Apply fingers "B" and "J"

UNEQUAL HALF ANGLES
Opposite finger "J", use "E"; so either "F" or "Thou". "E" has full flanks, while "F" and "Thou" are limited to 0.1H contact. Where half-angles are unequal, the thread groove volition be tilted, and ''E'' will seat more shallow because its broader contact surfaces will meet greater interference from the tilted groove. The degree of tilt and its consequence on PD is available through thread specification publications. MINOR Bore
Concentricity betwixt pocket-sized and PD is measured by using fingers "C" and "J" .  Minor diameter size, roundness and taper are checked with a pair of "C" fingers. FUNCTIONAL (MAXIMUM Material) DIAMETER
Paired fingers "L" are helically ground for a single PD, pitch/pb combination which will mensurate the net result of all errors.

SIMPLE SETTING METHOD (60 degree threads) The MTG gage is gear up "over the balls" or "over the crests" with gage blocks, micrometers, super micrometers, or plain cylindrical ring gages. No threaded masters are needed.     The pitch diameter setting equals the pitch diameter (depression, nominal or high) plus the ball radius. The ball diameter is etched on the pitch diameter fingers. All contacts (except small-scale diameter) that are used opposite contact "J" are marked with a constant dimension thus: CD +.0214 or CD -.0261. Setting size is equal to the PD. setting plus or minus the constant dimension.     Functional fingers are marked with a specific setting size thus; OD .7501. Paired pocket-size diameter fingers are set exactly to the minor diameter size. When a single minor diameter finger is used opposite a ''J'' finger to bank check concentricity, no precise setting is required.

INTERNAL   THREAD

PITCH DIAMETER SETTING SIZE CALCULATORS

( CLICK ON Pick-- And so CLICK ON "ENABLE EDITING" TO ENTER  YOUR Data )

UNIFIED & METRIC SETTING SIZE.xlsx

Summit THREAD SETTING SIZE.xlsx

WHITWORTH THREAD SETTING SIZE.xlsx

BUTTRESS THREAD SETTING SIZE.xlsx

(Important! BUTTRESS FORMULA FOR vii/45 DEG ONLY)

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EXTERNAL THREAD INSPECTION

MTG ZONAL METHOD

PITCH (MINIMUM Material) Diameter
Inserts "A" and "J" both incorporate balls of Best Wire size, and give a reading which excludes pb error but not angular errors. The PD inserts tin can be used for both left hand and right hand threads.

TAPER AND OVALITY
Utilise inserts "A" and "J" at intervals forth the thread for taper, and around the thread for ovality.

INCLUDED Bending
Use inserts "D" and "J". The brawl in "D" is smaller than that in Pitch Diameter insert "A", and should seat a prescribed distance deeper. If it does not, angular error is present. The caste of error and its issue on PD tin be adamant by using a formula.

UNEQUAL Half-ANGLES
Reverse insert "J", use "Eastward"; then either "F" or "G". "E" has full flanks, while "F" and "Thousand" are limited to 0.1H contact. Where half-angles are diff the thread groove will be tilted, and "E" volition seat more shallow considering its broader contact surfaces will run across greater interference from the tilted groove. The degree of tilt and its effect on PD. is bachelor through thread spec. publications.

Minor Diameter
Employ inserts "B" and "J".

MAJOR DIAMETER
Concentricity between major and PD is checked past using inserts "C" and "J".    Major Diameter size, roundness and taper are checked by a pair of "C" inserts.

FUNCTIONAL (MAXIMUM) MATERIAL Diameter
Paired inserts (C) (functional) are Helically Manufactured for a single PD/Pitch/Atomic number 82 combination. A separate pair is required for each combination.

SIMPLE SETTING METHOD (60 degree threads)
The PD inserts are set up "between the balls".   The Pitch Bore setting equals the depression, nominal, or high PD minus the brawl radius.  The Functional Inserts are prepare with a supplied master.

    All contacts (except Major Bore) that are used reverse contact J are marked with a constant dimension thus: CD +.0214; or CD -.0261. Setting size is equal to the PD setting plus or minus the constant dimension.

    Paired Major Diameter inserts are set exactly to Major Diameter size. When a unmarried Major Bore insert is used opposite a J insert to check concentricity, no precise setting is required. The inserts are brought into contact with the workpiece and the indicator is read for runout.

EXTERNAL THREAD

 PITCH Bore SETTING SIZE CALCULATORS

     (CLICK ON Choice--And then CLICK ON "ENABLE EDITING"  TO ENTER YOUR INFORMATION)

O.D. UNIFIED & METRIC SETTING SIZE.xlsx

O.D. Meridian THREAD SETTING SIZE.xlsx

O.D. WHITWORTH THREAD SETTING SIZE.xlsx

O.D. BUTTRESS THREAD SETTING SIZE.xlsx

(Important! BUTTRESS FORMULA FOR 7/45 DEG ONLY)

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Source: http://www.mtggage.com/thread-inspection.html

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