Precision Mensuration
Last updated on Friday, December 14, 2018 06:01:40 AM Mountain US Time Zone


Definitions, Surface Plates, IndicatorsComparator Stands, Z-Offset Gages, Depth Gages, Height Gages, Universal Gage,
Inside Diameter Gages, Pin Gages, Runout & Bore Gages, Calipers, Micrometers, Dial Test Indicators, Coaxial, Indicator Holders,
Thread Gages, Angle Meter, Angle Gages, Radius Gages, Infrared Thermometer, Tachometer, Sound Level Meter

Made so as to vary minimally from a set standard.
- The act, process, or art of measuring. Measurement of geometric quantities.
- Smallest difference between indications of a displaying device that can be meaningfully distinguished.
For a digital display device, this is the change in the indication when the least significant digit changes by one step.
Accuracy - Closeness of the agreement between the result of the measurement & the true value of the measurand.
Measurand - A quantity that is being determined by measurement.

See Layout Tools Section.
Decimal Equivalents of Fractions   Decimal Equivalents of # Drills   Decimal Equivalents of Letter Drills
Inch to mm Conversion   mm to Inch Conversion   Metric & Inch Equivalents   Machinist Calculator

Surface Plates

Granite surface plates (+/-0.0001") in 18"x12"x3" (85-lbs.) & 12"x9"x2" (30-lbs.) sizes.
Use surface plate cleaning fluid to remove dirt, oil, & marks left by (aluminum) parts.



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Mitutoyo electronic indicator
(1/2" range). Resolution is 0.00005" (50 millionths). A linear encoder, it always
displays the spindle's absolute position from the origin at power-on. Digimatic indicator manual & drawing.






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Mitutoyo electronic indicators
(1/2" range) with a Noga magnetic base indicator holder (both from Japan).
Both are best in class. See digital indicator manual.

A wooden holder for 3/8" stemmed digital & dial indicator gages. Many tools are supplied with their
own indicator. Two came with dial indicator comparator stands & two with gun cartridge measurement
fixtures. 2nd from the front is my first digital-style gage which was replaced by the front gage that has much
higher resolution. The gages vary by their respective measurement ranges, accuracies, & resolutions.

Their positions are offset to accommodate the lug back mounts.
The plungers of the more costly units are not compressed while stored.

Mill & Router Spindle Square

A spindle square used to align a CNC router. Eighteen inches long. To setup, mount in the chuck, place a
spacer under one indicator & zero then swing the other indicator around to the same spacer & zero.
The bar has to be very straight, rigid & the center dowel must be perfectly perpendicular. 

One-half inch interference fit shank using a precision ground steel dowel.

Dowel pins come in a huge variety of sizes & precision.
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Comparator Stands

Two, dial indicator comparator stands. Used for quality assurance (QA) size
measurements of many parts. Serrated anvils are purportedly more accurate.

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Several two-inch range gages were used on various machines before changing to advanced DROs.
For example, I used two gages just for the Taig micro lathe & to good effect, providing excellent control.
I liked it so much I went digital for both X & Z-axes but later extensively modified the lathe to be CNC.
Surprising accuracy & repeatability though low durability, but given the cost, acceptable if on a budget.

A two-inch range digital indicator that reads to 0.0005" resolution. It has an 8mm stem.

The fine adjustment mechanism for the stand.

A collar was made to adapt the 8mm stem to 3/8". The screw is threaded through to directly contact the stem.

Heavy, Brown & Sharpe No. 731 10" x 3" x 1-3/4" (L x W x H) inspection holder (USA).

Note the robust adjustments.

Different types of dial gage interchangeable 4-48 threaded indicator points.
To keep from straining or breaking a gage's internal alignment pin, completely depress the plunger
so the rack absorbs the loosening & tightening forces before changing the points. Never use Loctite.

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Z-Offset Gages

4.000" height, Z-axis tool length setting gage (USA). One-inch contact face picks-up all the flutes of
large end mills, easy to read 2.2" dial face, a setting repeatability of 0.0002", & hard, red anodize.
Needle-based Z-setting gages are not damaged by over travel like some electronic types.
The unit's overall ergonomic & mechanical design is excellent & has a good, heavy feel.

Z-axis offset animation showing a 3/4" end mill being set at 4.000" above the vise bed.
Starrett also makes a superior (expensive) 4-inch special dial depth gage for Z-height setting.

A 3.000" height offset gage using a 40 mm (1.5") diameter face Mahr dial indicator (GER) that reads to 0.0005".
Mahr is a top quality, durable, made in Germany, dial test gage; highly recommended instrument.
Stem is 8mm (.315"). The 7.5mm (0.295") diameter flat tip is an ideal shape. The bracket is all steel construction.
All critical surfaces of the parts, including the round post ends, were precision surface ground for high accuracy.
An adjustable, brass, over-travel stop was added so the needle can only turn about one revolution.
This height gage design has excellent sensitivity for delicate end mills & does not require a lot of Z.

The bottom of this Z-offset gage needed lapping which was performed on a granite surface plate first using
320 followed 400 & 600 grit silicon carbide papers. Moved the part in a figure-8 pattern to insure an even
removal of material. Significant surface improvement resulted. The edges were deburred with an India stone.



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This offset gage has a magnetic bottom which attracts debris & the spring is too strong for very small end mills.

1-2-3 Jo-blocks bolted together make a very accurate, rigid, low-cost zeroing fixture.
Jo-blocks are indispensible for use in mill setups, too.





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2" high Z-offset gage. A 3" micrometer & a 1-2-3 Jo-block were used to set the gage's zero at 2.0000".
The recessed bottom required a Jo-block. The micrometer was first locked at 3.0000" using the gage block.

Mill Z-offset gage (instructions) used to set tool lengths. Needle-based, Z-offset gages set the
 mill more quickly & accurately than illuminated types plus they are not damaged by over travel.

Animation showing a 2.000" Z-offset height being set on the Taig CNC Z-axis using the Mach3 MPG step mode.

Electric-type Z-offset gage with 0.0002" repeatability. It has a 1" x 2" x 3" form factor. Uses 2, LR44 batteries.
Aluminum faces do not chip brittle carbide end mills. May not work properly on anodized surfaces (e.g., Taig).
The analog dial-type with a needle have superior setting ease, accuracy, & repeatability.

Checking the height & light/battery circuit. Z-offset gage instructions.

An animation showing a 1.0000" Z-offset being set.

With the gage light illuminated, the value (1.0000") was then entered into the Z-axis of the mill DRO.

Here the electric gage is working on the CNC Taig mill's anodized table. The connection was
completed by grinding off the black anodize on the T-nut inner face & making multiple punch marks.
The vise should not clamp the gage that is deep in the jaws as that would short-out the upper & lower plates.

The punch marks are raised & sharp thereby piercing the table's inner T-slot anodized surface to complete
the connection. Though maybe not necessary, this can be done for all the T-nuts that hold the vise in place.

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A tooling plate is mounted onto the anodized table where a 0.2 ohm conductivity is realized via 6, T-nuts.

The gage can also be used with parallels & lightly clamped into the vise.

Depth Gages

Baker dial depth indicator (India) with a 0" to 10" range & where one gradation = 0.001". Rod extension chart.

The dial indicator gage itself has a 0 to 0.5" measurement range.
Example: Measured Depth = 0.1840" (dial reading) + 0" (extension rod length) = 0.1840".

Micrometer depth gage with a 0-6" range & where one gradation = 0.001". Depth = reading + rod length.


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A Mitutoyo digital micrometer head combined with a hardened & precision-ground depth base.
Note: Over tightening the set screw can distort the mounting flange & bind the mechanism.

The scale is not reversed like its mechanical counterpart, but digital micrometers can
be zeroed at any location & then the negative sign is simply ignored for the readings.

Hardened & precision-ground depth base attached to a Mitutoyo digital caliper.

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Digital depth gage with a large base. See digital caliper manual.

Height Gages
A Mitutoyo, 8", 543-244 digital height gage with fine adjustment mechanism. The height gage & a granite surface
plate make an accurate combination for measuring parts or laying out precisely scribed lines. Resolution: 0.0005".
Absolute electrostatic capacitance type linear encoder. A fine adjustment carriage is a requirement for fast, accurate
See Mitutoyo 543-244 digital height gage manual & dimensional drawing. For accurate, repeatable
measurements, insure the surface plate, height gage, & scribe working surfaces are free of debris/grit. Check to
see if the scribe bracket is tight. Periodically inspect the adjustable ways of the transducer for excessive play.

The heavy base has an excellent ergonomic design. The bottom surface is ground & lapped to perfection.

Mitutoyo depth & center-finder attachments for the height gage.

Hole center-finder attachment.

Hole center finder animation showing how the fine adjustment of the height gage is used to zero the needle.
This tool allows comparative QC measurements of many holes in production.

Using a test gage in conjunction with a height gage allows measurements of both dimensions & tolerances
without having to use separate instruments. See instructions on how to set tip geometry & see illustration.

Height gage with digital indicator for both height & tolerance measurements.

Starrett No. 3751 digital height gage. Auto-off in 5 minutes but retains zero; auto-on when the slide
is moved. Zero to 6.45" max range, 0.0005" (0.01mm) resolution & +/-0.001" (+/-0.03mm) accuracy.
Supplied with an extra scribe & clamp plus an excellent, padded, aluminum hard case. The vertical
column is set-in from the tip of the base's nose for better stability. This height gage's compact size
 is especially valuable when measuring parts with very small features or using it on my two mills.
The scribes are not carbide-tipped. The fine-edged, HSS scribes are limited to semi-hard metals &
the rounded tips limit scratch depth. This height gage is ideally suited for use on small, delicate work.

Starrett No. 3751 digital height gage manual.

Adjusting to a specific height can be accomplished by picking it up & using it much like a regular caliper.
 Slightly increasing the slide resistance of the transducer (a small, side set screw) helps adjustability.
Setting an exact numerical value with this type of adjustment mechanism is slower than
that of a height gage equipped with a fine adjustment carriage mechanism.

A Starrett Last Word DTI mounted onto the small, 3715 height gage using the 711-49 bar attachment.

A carbide-tipped (Mitutoyo) 10", dial height gage on a granite surface plate (+/-0.0001").
High accuracy can be achieved using gage blocks to set specified heights.
Use layout die to make the scribe marks easier to see. Mitutoyo height gage manual.
Surface plates are useful for precision alignment when assembling parts, too.

Mitutoyo OEM wooden case.

Depth attachment. Rod accepts different 4-48 threaded indicator points. This was my first height gage.
It is easier to miss-read an analog dial than a digital readout though analog scales can be interpolated.

Measuring distances between holes using a center-finder attachment from Mitutoyo.

Height gage with digital indicator for both height & tolerance measurements.

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Universal Gage

Starrett No. 995E (USA) Universal Precision Gage set is best in class. This gage has multiple uses:
height gage, scriber, planer/shaper setup, an adjustable parallel to measure a gap, transfer
measurements, precision level, & layout work on a surface plate using gage blocks or a sine bar.
Starrett  Model No. 995E Universal Gage exploded diagram.

Nominal dimensions of the base are 5.25" x  2.5" x 0.75" (W x H x D). Hardened & precision ground.
The slide has a combination of both a flat & a V-way to provide excellent accuracy.

The slide has a fine adjustment mechanism allowing faster & more accurate settings.
No other similar gages have this important feature. Note the mineral spirits bubble level.

Offset attachment with clamp bolt extends the nose for a minimum height of 0.17" allowing use in tight areas.

One-inch & three-inch extension rods can be screwed in at four different locations.

A post clamp holds a hardened HSS scribe which is being set at 3.0000" height using a gage block.

A Starrett Last Word DTI mounted onto the 995E Universal Gage using the 711-49 bar attachment.

Inside Diameter Gages

Telescoping & half-ball Mitutoyo inside gage sets (Japan). The half-ball type can get into a shallow, blind
hole better than a ball type. Expand into hole, lock & then measure the gage with a micrometer or caliper.

Left: The small (half-ball) hole gage is expanded by the center wedge.
Right: The telescoping inside gage posts spring outward, self-center & are then locked via a knob on the handle.
They can then be accurately measured with a caliper or a micrometer.

Mitutoyo (Japan) tools have superior accuracy, repeatability, quality & durability.

This steel part is being held in a lathe.

The hole measured 1.6296". I then updated the lathe's DRO X-axis setting for further boring.

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Full-ball, small hole gage set.

Half-ball compared to full-ball small hole gage types.

Pin Gages

 Pin/plug Gage Sets - ID type gages for measuring hole diameters & slot widths.
0.011" to 0.060" x 0.001" minus Class ZZ pin-gage set (50 pieces).
Tolerance +.0000" -.0002".  10mm finish or better.  Hardness 60-62 RC.

 0.061" to 0.250" x 0.001" minus Class ZZ pin-gage set (190 pieces).
Tolerance +.0000" -.0002".  10mm finish or better.  Hardness 60-62 RC.

Detail of the 0.061" to 0.250" x 0.001", minus pin gage set (still in the grease). Two-inches overall lengths.

0.251" to 0.500" x 0.001", minus Class ZZ pin-gage set (250 pieces).
Tolerance +.0000" -.0002". 10mm finish or better. Hardness 60-62 RC.

0.501" to 0.625" x 0.001", minus Class ZZ pin-gage set (125 pieces).
Tolerance +.0000" -.0002". 10mm finish or better. Hardness 60-62 RC.

Dowel pins come in a huge variety of sizes & precision.
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Go/no go pin gage handles. Shown holding 0.25" & 0.050" pin gages.

Runout & Bore Gages

Back-plunger dial indicator set (India) with 'G' clamp, universal clamp, swinging-arm assembly, tool post holder,
 holding rod, Tommy bar & 2nd anvil. Swinging-arm assembly enables the back-plunger dial gage for use on internal
work to a depth of 1.6" (40mm); similar to a lever-type gage. Allows multiple types of mounting possibilities for
gaging applications like concentricity checks, alignment of machine tools, testing parallelism, & surface-plate work.

Back-plunger dial gage with swinging-arm attachment.

Measuring the eccentricity & runout of the ID of a bored cylinder.

A self-centering, 1.4" to 6" cylinder bore gage (instructions).
The gage is first set up to measure a specific size (zeroed) then run through the bore to measure its variation.
To keep the extensions in order, a vibrator engraver was used to label each size on a non-critical surface.

The dial gage must be inserted deep enough to preload (or move) the needle about 1 revolution (0.050").
The black plastic shroud can be installed after calibration to protect the head under heavy shop use.

These 1/2" travel digital indicators, preloaded to 0.050" depth, can also be utilized but others may not work.

Exploded view of the 1.4" to 2" measurement head, the 1.4" range anvil & knurled anvil lock nut.
The pointed rod end (at the lower left) engages a rod inside the handle.

Anvil installation animation.

The center measurement anvil moves in & out.
The outside mechanism depresses under spring tension to center the head.

Small anvil animation.

Assemble the appropriate anvils & spacers (left side) for the target measurement size.
Then, using a gage block, set a micrometer (e.g., 2") to the bore size & zero the dial scale.
The gage is then run through the cylinder & the variation from set size, noted.

Bore gage measurement animation.
Note the small measurement anvil (left) depresses & the self-centering guide mechanism slides to the right.

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Mitutoyo Absolute Digimatic caliper (Japan).
An excellent digital caliper that is very accurate throughout its entire measurement range.
Always maintains zero, large LC display, greater than 3 years battery life. No irritating auto-off.

Mitutoyo digital caliper manual.



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A digital caliper (manual) that measures & displays inches, millimeters & fractions to 1/64th-inch.
Handy for wood work & sifting through raw stock. This LCD has a somewhat narrow optimal viewing angle.

Chromed, dial caliper gage with a 0 to 0.8" measurement range & a 0.0005" resolution (China).
The jaws are spring-loaded closed & are opened with the lever. Custom wooden box storage.

Ball bearing tips.

Before use, calibrate the dial scale against a gage block of appropriate size.

I bought these gages to allow me to make measurements in tight mill setups.


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A snap thickness gage. Close & zero the scale first.

8-inch digital linear scale for instrumenting tools like drill presses, mills, & lathes.

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This open-weave drawer liner has (Microban) antimicrobial properties that prevent bacterial growth.
The non-slip black cushion protects the instruments & keeps them from moving (banging) around, too.

Mitutoyo digital measurement tools: depth gage, caliper & micrometer (older models).


Superior quality Mitutoyo (Japan) digital micrometer that reads down to 0.00005" or 0.001mm.
The scales are engraved, not chemically etched thus have superior readability & durability.
Even if the battery is removed, the micrometer's scales allow it to be used as a standard instrument.
It has a micro-polished, carbide-faced working surfaces & an effective spindle lock.
DO NOT store a micrometer (any style) with its measurement anvils touching.

See micrometer manual.

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The holder adjusts to different angles & has rubber pads that protect the instrument from clamping damage.

Another style micrometer stand/holder. This model has a nice, heavy base.

Mechanical digital-type outside micrometer, 1-2" range. Standard & adjustment tool, included.

Mechanical digital-type outside micrometers, 2-3" range (above) & 3-4" range (below).
Standard & adjustment tool, included. Digit Micrometer Manual.

The one ten-thousandths-inch (0.0001") measurements are read off the (barrel) vernier.

All three shown for size comparisons; size standards included.

Small, 0.6" (non-locking) & standard 1" micrometers. The smaller micrometer's scales are chemically etched,
the larger micrometer's scales, engraved. Superior instruments have engraved scales for clarity & durability.

2-inch mechanical micrometer.

Micrometer set zero through six-inches with its wooden storage case (import).
One, two, three, four & five-inch sized standards plus adjustment wrench are included.
The plastic insulating grips on the standards reduce warming effects (expansion) due to handling.
Acquired for use mainly on the 9x20 lathe. Excellent accuracy, engraved scales, & a good value.
All micrometers read to 0.0001". The wooden case was re-glued in places & then sanded.
See micrometer scale reading instructions.

Though low-cost, the scales are engraved, the positive locking lever is metal, & the ratchet thimble is precise.
A good value for light use.

Detail of the 1" to 5" standards for the 0" to 6" micrometer set.

6" to 12" micrometer set. The smaller wooden case holds size standards 6" through 11".
All micrometers read to 0.0001".

6" micrometer, shown.

12" micrometer shown with the standards case, open. The holes lighten the instrument for easier handling.
I needed the 7", 8", & 9" micrometers (for e.g., a flywheel) so it was more economical to buy the whole set.

I needed four, aluminum rods to be exactly 9.6250" in length so the 9"-10" micrometer was used.

Two micrometer sets covering the 0" through 12" range. Eleven size standards; 1" through 11".
Two separate sets can make handling/storing the boxes easier than one big heavy 0" ~ 12" set.

A 0.6" micrometer compared to a 12" micrometer.

A micrometer head that can be incorporated into other devices e.g., an adjustable lathe carriage stop.
1/2" range. The tip of the 0.2" diameter anvil is rounded & hardened. The collar is 3/8" diameter x 0.32" long.

Mitutoyo digital micrometer head.

Hub micrometer that measures 0-1" to 0.0001" & designed to clear through a 3/4" hole.
Handy in tight places especially in milling setups.

A 6" throated micrometer having a measurement range of 0 to 1" maximum with a 0.0001" scale.

Locking levers made of metal are a plus for durability & precision of the mechanism movement.

Caliper-type micrometer measures to 0.0001".  Measuring anvils are approximately 3/4" above the micrometer.
The thread mechanism that keeps the anvil from rotating also acts as a somewhat effective lock.

Disk micrometer with a 0.0001" scale.

0-1" range, 0.07" diameter anvil, tube wall thickness micrometer that measures to 0.0001".

0-1" range, 0.19" diameter anvil, tube wall thickness micrometer that measures to 0.0001".

Carbide-faced electronic blade micrometer for measuring in narrow slots & recesses.
The thread mechanism that keeps the anvil from rotating also acts as a lock.
 A 0.00005" minimum readout. Digital blade micrometer manual.

The blades are 0.030" thick.

1 to 2-inch blade micrometer supplied with a 1-inch standard & adjustment wrench.

Carbide-tipped, small faces or spline micrometer for measuring in tight areas. 0-1" range with 0.0001 scale.
The anvils are 0.0775" diameter.

Carbide-tipped, point micrometer for measuring in very tight areas. 0-1" range with 0.0001 scale.
Points have a radius of approximately 0.012".

Screw thread micrometer with five different anvil pairs measure both unified & metric external pitch diameters.
0" to 1" measurement range with a 0.0001" scale. The left anvil holder floats back & forth to allow zeroing then
 it is locked into place. However, the anvil itself always floats rotationally to maintain ease of measurement.









64 - 48

44 - 28

24 - 14

13 - 9

8 - 5


0.4 - 0.5

0.6 - 0.9

1 - 1.75

2 - 3

3.5 - 5

Anvil pairs are clearly marked for pitch range.

Example measurement of a 1/4-20 screw. The micrometer reading is 0.2160". Table pitch value is 0.2164" max.
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.

Carbide-faced inside micrometer gages with locking mechanisms. The top gage range is 1"-2" & the bottom
gage range is 0.2"-1.2". Supplied with 1" & 0.2" inside ring standards, respectively. One gradation = 0.001".


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Dial Test Indicators (DTI)

Interapid 312B-1 (Swiss). Best in class dial test indicator having: a monobloc metal housing with two dovetails,
jeweled movement, ball-bearing lever system, micro-polished carbide tip, large tilted dial face, & an additional
revolution counter. Bi-directional measuring with automatic reversal inside the movement & extra wide +/-0.060"
range makes it especially versatile. True readings when the angle between the stylus & work piece surface is 12 deg.

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Interapid Model 312B-1 Horizontal Style DTI
Graduation 0.0005"
Dial Reading 0-15-0
Range +/-0.060"
Point Length 0.687"
Point Diameter 0.080"
Dial Face Diameter 1.5"
Stem Diameter 0.156" (4mm) 5/32"
TESA Number 74.111370

Accessories (Swiss): slotted reduction sleeve 3/8" to 5/32", height gage bar w/clamp, contact point wrench &
axial support with 3/8" diameter stem. The white tube in the gray fitted storage box holds extra contact points.

Note the small (right of center) secondary revolution counter needle used to track the wide +/-0.060" range.

5/32" (0.15625" or 4mm) pivoting stem, dovetail mount, & monobloc metal housing.

Tramming a steel part before boring in the mill. Zeroed at front, back, left, right; X & Y tables then locked.

Starrett surface gage & Interapid dial test indicator on the granite surface plate being zeroed
 using a 1" gage block. If possible, move the part not the gage when measuring a surface
unless, of course, the surface is being swept.

For highest accuracy, the angle between the stylist & part surface should be as close to 12 deg as possible.

The wide-range (+/-0.060") Interapid held by the rigid, precise Starrett is an accurate combination on a surface plate.

Indicating the Parlec vise solid jaw, animation. The slot on the top of the solid jaw can also be used.
The Interapid indicator has 0.0005" resolution. See instructions on how to set tip geometry & see illustration.
Here, the needle moves <0.0001" in the center which is well below the manufacturer's vise spec.

An excellent BesTest Brown & Sharpe (Swiss) dial test indicator set. One gradation = 0.0005". This model
incorporates an auto-reversing feature & dovetail mounting. The Swiss instruments are quite sensitive.

This Starrett Model No. 711 DTI has a small side lever to select the needle direction. No dovetail mounts.








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The carbide tips have multiple spring-loaded detent positions. Quick & easy tip changes.

Rugged LS Starrett No. 711 Last Word DTI & attachments (USA). One gradation = 0.001".

Starrett 711-49 attachment: 2-5/8" OAL, 1/8" x 5/16" x 1-7/8" rectangular shank, & a 3/4" long x 15/16" round tip.
Used to affix the Starrett 711 Last Word DTI to either the 3751 Height Gage or the 995E Universal Gage.

Gem DTI (USA). One gradation = 0.001". Rod & dovetail mounting.  Gem dial indicators & accessories.
See instructions on how to set tip geometry & illustration. Essentially a copy of the
Starrett No. 711 but with slightly different dimensions so accessories are not interchangeable.

Federal Testmaster DTI (USA). One gradation = 0.0001". Note needle reversing lever & dovetail mounting.

Various DTIs showing dovetails. Top to bottom: Brown & Sharpe (Swiss), Federal, & Gem (USA).

Fowler DTI set (import). One gradation = 0.0005". Dovetail mounts.

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Using Dial Test Indicators - Test indicators are primarily used for the testing or checking of parts & for machine setups.
Test indicators come in two types; the plunger style & the lever style. The lever style is more adaptable to smaller,
confined working areas. The lever style differs in measuring because the lever contact moves in an arc rather than in a
straight line, as in the plunger style. This can cause a slight inaccuracy called cosine error, if reasonable care is not
 used in setting the angle of the lever to the work piece. If, for example, a lever was set off 20 deg more at the start of a
reading than it should have been, there could be an error of .0006" in a .010" range (0.012mm in a 0.2mm range).
This is not important when zeroing-out, but only when looking for a measurement. It is best to keep the contact at or near
90 deg to the direction of movement unless the manufacturer specifies another angle (see illustration). Test indicators
 should always be 1/10 to 1/4 of a turn before measuring. Test indicators are not hand-held absolute measuring
tools. They are comparative instruments that check & compare to known standards or that are used to zero-out setups.

Coaxial Indicator

Coaxial indicator (import) that takes measurements while the spindle is spinning (800 RPM maximum).
The point can be used to locate a punch mark. See centering indicator instructions.
Different length probes affect the scale's absolute readout values. Good for large parts.


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Indicator Holders

Sparro 1st Word dial test indicator holder (USA).

Using a Sparro 1st Word holder & an LS Starrett Last Word DTI
to check the alignment of the mill/drill. Nicely made, very rigid indicator holder.

Animation showing how to check alignment by indicating the Rong Fu RF-25 mill table
& 1-2-3 blocks.

Noga indicator holder (Japan) for both dovetail & 3/8" stem types. Note the fine adjustment mechanism.

Noga NF1018 indicator arm (Japan) with 3/8" & dovetail clamp.
This style arm is very quick & easy to set up plus it has very good rigidity.

Noga arm held by a modified, V-groove tool post, mounted off the headstock side T-slot of the Taig mill.
Setup shows indicating a work piece before rotating to a specific cutting angle.
The Noga arm is good for aligning mills, lathes & rotary tables.

Zero-set universal dial test gage attachment (import).

A Federal 0.0001", dovetail mount, DTI being used to indicate the Parlec vise's solid jaw.

This style universal DTI holder gives a broad sweep of the small 18" mill table.

IndicOL #178 (USA) DTI holder attaches an indicator to the mill's spindle. Best in class attachment.
Dovetail or stem-style test dial indicators can be attached to this holder.



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Half-round combination DTI (dovetail & stem) with a 1/4" shank.

Modified an indicator clamp to hold various stemmed DTIs; close to the center; rigid, compact, & quick.
Reamed two, 3/16" holes & the thumbscrews are 6-32 SS cap-head screws with pressed-on plastic caps.

Added another set screw to hold the half-round combination DTI holder.

Detail of the close-fitting brass bushing (3/8" OD, 1/4" ID) that is held in using red Loctite.
Added a 5/32" hole & set screw for the Interapid stem size.

Tramming a 6", 4-jaw chuck on a rotary table.  See Rotary Tables.

A Mighty Mag (USA) magnet holds 3/8" (or smaller) stemmed indicators. Very powerful magnet.

Click on linked thumbnails

Accurate low-cost 2" range analog positional readout. Gage blocks can be used to extend range.

Thread Gages

Left to right: imperial & metric (yellow) screw thread gages (2), fractional, & numbered drill bit gages.
These plate-type thread gages would be more accurate if they were two or three times thicker.
Having just a few threads, it is easy to make an error. For example, 10-32 & M6-1 are very similar threads.

Click on linked thumbnail

This metric thread gage is 0.11" thick whereas the others are 0.08" thick.

Fractional, numbered, & metric drill bit gages.

A metric drill bit gage 1mm to 13mm by 1/2mm. A 1/4" hole is on the far right end.

These gages check both nuts & bolts. Metric are black oxide & imperial are galvanized. Sizes are clearly
stamped & colored. Superior to plate-type gages which use only a few threads per size for testing.

Standard imperial & metric thread gages.



Click on linked thumbnails

Angle Meter

Starrett AM-2 angle meter (USA). The RF-25 mill X-axis is shown being level.

Back label of the AM-2 angle meter.




Click on linked thumbnails

Also see Protractors Section

Angle Gages

Angle gage set 5 deg to 90 deg every 5 deg.

Multiple edges provided for a given angle.

Countersink gage with 1/32" scales.

Radius Gages

Radius gage set 1/64" to 17/64" by 1/64" & 9/32" to 1/2" by 1/32" with handle.

Five edges provided to measure a given inside/outside radius.

Click on linked thumbnail

Infrared Thermometer

Infrared Thermometer Model 96451

Measurement Range - 4 deg F to 968 deg F - 20 deg C to 520 deg C
Measurement Accuracy +/-4 deg F below 212 deg F +/-2% above 212 deg F
Response Time 500 msec
Distance to Spot Size 8:1
Battery Requirement Standard 9V

The red laser beam is used solely for aiming. An infrared (IR) sensor actually measures the temperature.
The distance to spot ratio is 8:1., so for e.g., at a 16" (407mm) distance the measurement area is 2" (51mm).


Click on linked thumbnails


Sampo Digital Tachometer: five digits 18mm (0.6") White backlight LCD.

Sampo Digital Tachometer DT6234B Manual

Accuracy +/-(0.05%+1 digit)
Sampling Time 0.5 sec (over 120 RPM)
Range Select Auto-Ranging
Memory Max., Min., Last. Stores 96 sec of data
Time Base 6 MHz Quartz crystal
Detecting Distance 50~500mm
Power Consumption Approx. 55mA
Measuring Range 2.5~99,999 RPM
Resolution 0.1 RPM (2.5~999.9 RPM), 1 RPM (over 1K RPM)
Total Test Range 1~99,999
Frequency Range 1~1,666.6Hz
Resolution 0.01Hz
Battery 4x1.5V AA or external 6VDC regulated power supply

Measuring RPM of the 9x20 lathe variable DC motor. Works best using a small patch of retro-reflective tape.

Sound Level Meter

Sometimes I want to know sound pressure changes of equipment or re-equalize my home theater systems.
 See the lathe sound pressure levels for the variable speed drive as an example. Sound level meter manual.

The meter's microphone.

Click on linked thumbnail

Definitions, Surface Plates, IndicatorsComparator Stands, Z-Offset Gages, Depth Gages, Height Gages, Universal Gage,
Inside Diameter Gages, Pin Gages, Runout & Bore Gages, Calipers, Micrometers, Dial Test Indicators, Coaxial, Indicator Holders,
Thread Gages, Angle Meter, Angle Gages, Radius Gages, Infrared Thermometer, Tachometer, Sound Level Meter