New Measurement Uncertainty Requirements
Effective January 1st, 2012, all ISO/IEC 17025:2005 calibration laboratories are required to begin reporting measurement uncertainties for each measurement result. Fox Valley Metrology prides itself on being one of, if not the only lab to offer this via automated software. This automation allows us to provide this service at no additional cost.
For calibration laboratories, ISO/IEC 17025:2005 (clause 5.10.4.2) requires that “if a statement of compliance with a specification is made, this shall identify which clauses of the specification are met or not met”.
When compliance with a specification is made it should be clear to the customer which coverage probability for the expanded uncertainty has been used. Unless otherwise noted, the coverage probability will be 95%.
An explanation of In Tolerance, Out of Tolerance, and Within Uncertainty:
(Case 1) In Tolerance: If the specification limit is not breached by the measurement result plus the expanded uncertainty with a 95% coverage probability, then compliance with the specification can be stated. This can be reported as “In Tolerance”.
(Case 4) Out of Tolerance: If the specification limit is exceeded by the measurement result minus the expanded uncertainty with a 95% coverage probability, then noncompliance with the specification can be stated. This can be reported as “Out of Tolerance”.
(Case 2 & 3) Within Uncertainty: If the measurement result plus/minus the expanded uncertainty with a 95 % coverage probability overlaps the limit, it is not possible to state compliance or non-compliance. The measurement result and the expanded uncertainty with a 95 % coverage probability should then be reported together with a statement indicating that neither compliance nor non-compliance was demonstrated. A suitable statement to cover these situations would be “Within Uncertainty”.
Using a horizontal taper measuring block to inspect tapered plug gages
Thread Check Inc offers both horizontal and vertical tapered blocks specially designed to calibrate tapered plug gages. Instructions are referenced below.
INSTRUCTIONS FOR USE OF HORIZONTAL TAPER MEASURING BLOCK
In order to check the Major Diameter, the gage block setup is the small end major diameter divided by 1.000489. Then add the constant, marked on the block.
In order to check the Pitch Diameter, the gage block setup is the small end pitch diameter plus the best wire constant and that total divided by 1.000489. Then add the constant, marked on the block.
Place the block on the measuring device, with the back of the block against the floating anvil. Place the plug, to be checked, small end down. Move the plug into measuring position. You must now square the floating anvil to the measuring block. Turn the block slowly, first left and then right, until you achieve the smallest reading possible. When you reach the smallest reading, the block will be square. You may now take a measurement.
A hold down clamp has been provided but its use is not recommended unless necessary. The plug gages will sit on the small end without issue.
Calculating Pre Plate Screw Threads & Gages
It is important to understand how various plating affects manufactured parts featuring internal and external threads. All too often component parts are manufactured without taking into account the correct plating requirements. This results in rejection in final and incoming inspection or even in the field resulting in a recall. Either way proves to be very costly and time consuming.
Manufacturers of threaded components should understand the specific plating specifications and make specific allowances to the threads prior to the plating process. If this is not done or done incorrectly there is high probability that the thread will be too tight or too loose. This pre- plating allowance must be considered for both of the mating parts.
When working with the common 60 degree thread, the ratio is 4:1, meaning the plating thickness will build up 4 times the applied amount as each flank on both sides of the thread is affected.
The first part of making pre plate threads is to determine how much plating build up will be applied to the thread. This is determined by the plating specification as well as where the screw thread is located on the part. There may be cases where an internal thread is located deep down in a bored cavity and it may be difficult to apply the full amount of plating. It may be a good idea to discuss this with a qualified plating company.
To ensure the parts will assemble and fit correctly, the manufacturer should utilize pre plate thread gages so that the thread can be controlled correctly. This investment will pay dividends assuming the correct amount of plating is applied. This can be confirmed with standard or after plate thread gages. It may be a good idea to supply the plating facility with these gages so they can confirm that their plating process is correct and deliver back parts that are in tolerance.
Pre Plate Ratios for Various Threads
60° Unified thread = 4:1
29° Acme thread = 8:1
7°/ 45° Buttress thread = 4.3138:1
10° Square thread = 23:1
Based on the ratios above you can see how much affect a specific amount of plating can build up on a thread. There are several screw thread engineering programs that will handle the calculations for pre plating , including ThreadTech v2.24. You can download a free trial version of the ThreadTech software at www.threadcheck.com .
The rule for determining pre plate pitch diameters, major diameters, and minor diameters of parts and gages is as follows:
To determine pre plating dimensions for external threaded parts: For external threads subtract the max plating thickness from the parts high limit P.D.. Then subtract the minimum plating from the parts low limit P.D. For the minor and major diameters reduce the Parts maximum diameters by half the maximum plating and reduce the parts minimum diameter by half the minimum plating.
To determine pre plating dimensions for internal threaded parts: For internal threads add the max plating thickness to the low limit P.D. Then add the minimum plating thickness to the high limit P.D.. For minor and major diameters increase the minimum minor diameters by half the maximum plating and increase the maximum minor diameter by half the minimum plating.
To determine pre plating dimensions for thread ring gages: For thread ring gages subtract the max plating thickness from the P.D. of the Go thread ring gage. Then subtract the minimum plating from the P.D. of the No Go thread ring gage. For the minor diameter reduce the Go ring minor diameter by half the maximum plating and reduce the No Go ring minor diameter by half the minimum plating.
To determine pre plating dimensions for thread plug gages: For thread plug gages add the max plating thickness to the P.D. of the Go thread plug gage. Add the minimum plating thickness to the P.D. of the No Go thread plug gage. Increase the major diameter of the Go thread plug by half the maximum plating and increase the No Go thread plug major diameter by half the minimum plating.
Example for Thread Plug Gage:
Plating of .0002” - .0003” allowance per side multiple x 4
.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min
½ - 20 UNF 2B P/P
Basic Go P.D. = .4675” + .0012” = .4687” Go P/P pitch diameter
Basic No Go P.D. = .4731” + .0008” = .4739” No Go P/P pitch diameter
Basic Go Major Diameter = .5000” + .0006” = .5006” Go P/P major diameter
Basic No Go Major Diameter = .4948” + .0004” = .4952” No Go P/P major diameter
Example for Thread Ring gages:
Plating of .0002” - .0003” allowance per side multiple x 4
.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min
.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min
½ - 20 UNF 2A P/P
Basic Go P.D. = .4662” - .0012” = .4650” Go P/P pitch diameter
Basic No Go P.D. = .4619” - .0008” = .4611” No Go P/P pitch diameter
Basic Go Minor Diameter = .4446” - .0006” = .4440” Go minor Diameter
Basic No Go Minor Diameter = .4511” - .0004” = .4507” No Go minor Diameter
If no minimum and maximum plating thickness is given , then the given plating thickness is considered nominal or minimum plus 50% to determine maximum plating.
Thread Check Inc now offers a complete line of high precision feeler gauges
Our feeler gauges are widely used by many industries as gages to precisely measure clearances and gaps in machinery, dies, and component parts and as shims to accurately set spacing. They can be supplied in thicknesses ranging from .0005” up to .125” in various lengths and widths. They are conveniently available in 6" and 12" strips, 25' coils, as well as standard and custom blade sets. Our steel blades are offered in the highest quality carbon steel or stainless steel for outstanding resistance to corrosion and all blades are permanently marked with the thickness size for easy identification. The standard tolerance on all blades is +/- .0005" (+/-.0127mm). Tighter thickness tolerances of +/- .0001” are available if required. We also offer custom bending and stamping solutions to design a way around obstructions. The option of adding a step creates two gauges in one and can be used as a Go/No-Go gauge or for different applications. We commonly provide air gap gages for power and utility companies in 24", 36", and 48" lengths
Feeler Gauges are a close relative to plug gages. One of the most common applications of a feeler gage is for use with spark plugs on engines to establish the gap between the distributor points. Feeler gauges of 24", 36", and 48" lengths are also used by power and utility companies to inspect air gaps in their equipment. Stainless Steel feeler gauges are commonly used to check critical medical dimensional characteristics.
http://www.threadcheck.com/feeler-gauge-gage/
Thread Tech Software for Windows
Thread Tech complies with the following standards and specification. We are continuing to improve the program by adding more thread information and updating the standards when the standard committees make changes. Thread Tech will soon be available to purchase by download. This will be a positive change for our customers as it will eliminate shipping costs particularly for our international customers.
http://www.threadcheck.com/content/software.asp
- Unified inch screw threads-parts: ASME B1.1
- Unified inch screw threads-gages: ASME B1.2
- Unified inch screw threads (UNJ Thread Form): ASME B1.15
- Screw threads - UNJ profile, inch: AS8879D
- Unified inch taps: ASME B94.9
- S.T.I. screw thread plug gages: MIL-T-211309 / A-A-59158
- Metric screw threads M profile-parts: ASME B1.13M
- Metric screw threads M profile-gages: ASME B1.16
- Metric screw threads MJ profile-parts: ASME B1.21M
- Metric screw threads MJ profile-gages: ASME B1.22M
- Metric taps: ASME B94.9
- Buttress inch screw threads-parts and gages: ANSI B1.9
- NPT pipe threads: ASME B1.20.1
- ANPT pipe threads: SAE AS7105
- NPSC pipe threads: ASME B1.20.1
- NPTR pipe threads: ASME B1.20.1
- NPSM pipe threads: ASME B1.20.1
- NPTF pipe threads-parts: ASME B1.20.3
- NPTF pipe threads-gages: ASME B1.20.3
- Pipe threads where pressure-tight joints are not made on the threads-Parts: ISO 228-1
- Pipe threads where pressure-tight joints are not made on the threads-Gages: ISO 228-2
- Pipe threads where pressure-tight joints are made on the threads Parts: ISO 7-1
- Pipe threads where pressure-tight joints are made on the threads Gages: ISO 7-2
- Worm threads: Vogel Formula, Buckingham Formula
- Acme screw threads-general purpose and centralizing-parts and gages: ASME B1.5
- Stub acme screw threads-parts and gages: ASME B1.8
- ISO metric trapezoidal-parts: DIN 103 part 3
- SO metric trapezoidal-gages: DIN 103 part 9'
- Universal Screw Thread Program: EA-10/10 Berndt equation, Vogel exact equation
Three Wire thread Measuring Systems from Thread Check Inc
The traditional three-wire method is the most accurate method of measuring the effective or pitch diameter of an external screw thread. Unfortunately in the past, holding and correctly positioning three wires against a thread while simultaneously taking an accurate measurement had been an extremely difficult task. Now, Thread Check's 3-Wire Thread Measuring System provides a simple and precise way for determining the pitch diameter for threaded parts and thread plug gages. The system enhances Repeatability and Reproducibility ( R & R ) and reduces measurement time to a fraction of the time normally taken using the traditional three-wire method. Thread Check offers specially designed wire holders and wires and base assemblies that make thread measurement fast and accurate. Thread Check's holders are fitted with certified full length thread measuring wires that meet or exceed the requirements of the ASME/ANSI B1.2, and B1.16M, thread standards as well as ASME B89.1.17-2001, Federal Spec. GGG-W-366b and ISO standards. All wire holder sets include the actual wire size, NIST traceable number, and the constant required for determining the pitch diameter.
Thread measuring holders are precision made to predetermined thread pitches. The wires are held in a predetermined position by light pressure clips. The holders rotate freely on the spindle/anvil of the measuring instrument so as to engage the lead angle of a thread. Holders can be purchased without wires for companies that have existing wires. Wires can be easily installed. Thread measuring holders are available in a full range of Standard, Metric, and Acme sizes. Thread Check's engineering department can design wire holders for multiple start threads, helical gears, worms, and other special thread measurement applications. Thread measuring holders and wires available for a wide selection of measuring instruments.
Applications:
- Certify working thread plug gages & setplug gages
- Monitor the wear on working thread plug gages
- Monitor and control pitch diameter variation during thread fabrication
- Use in conjunction with “GO” and “NOGO” ring gages to control thread size to the most demanding specifications
- Determine out of roundness and taper that may exist in threaded parts
- Applications for preplating & postplating thread measurement
- Eliminate the cost and time involved in using outside calibration services
- Reduce measurement time to a fraction of the time normally taken using the traditional three-wire method.
PATENT NO. 5,317,809
PATENT NO. 5,383,286
FOREIGN PATENT
The Three Wire Method
The three wire method is recommended for universal use in the direct measurement of thread gages and components. It has been found to be the most accepatble and universally recognized method of measuring pitch diameter.
The pitch diameter is the diameter where the thread thickness is equal to the space between the threads. If the flats at the top and the bottom of the thread are the same, the pict diameter will coincide with the middle of the sloping side of the thread.
The pitch diameter is represented by the letter E
E=D - depth of thread = D - h
How to determine the proper gagemaker tolerance for a GO/NO GO cylindrical gaging application.
One of our most frequently asked question is “Which gagemaker class of tolerance should be used for selecting plain plug and ring gages to check internal and external diameters of parts?”
The industry standard is referred to as the Ten Percent Rule. This common rule of practice requires that 10% of the product tolerance is divided between the GO and NO GO gauges. For plug gages a plus tolerance is applied to the GO member and a minus tolerance is applied to the No Go member. Ring Gauges receive the reverse tolerance direction so that the GO member is minus and the NO GO member is plus.
10 Percent Rule results in gauge tolerance always being included in the part tolerance by up to 10%. This rule results in the possibility that 10% of good product may fail inspection but that no bad product would ever pass inspection.
Example
A part has a hole diameter requirement of .500” +/- .001”. Thus the hole diameter is .4990” - .5010”. The product has a tolerance of .002”. 10% of the product tolerance is .0002”. Divide .0002” by 2 = .0001”. On the industry standard gagemaker chart, .0001” is classified as a class Z tolerance. The Go member would be specified as .4990” plus .0001” tolerance and the No Go would be specified as .5010”minus .0001”. The gage would be assembled and marked as .4990”- .5010” Class Z Go/No Go Plug Gage w/handle.
Selecting higher precision gagemaker tolerances for cylindrical plug and ring gages such as class X or XX will consume less product tolerance and will allow the acceptance of slightly more product but with less gage wear life and at greater expense.
Thread Check’s engineering staff can make recommendations in selecting the correct gagemaker tolerances for a given application.
Gage maker Chart
View our complete product listing of cylindrical products here
Depth Micrometer Masters
Depth micrometer masters are used to calibrate depth micrometers. The Depth Micrometer Master is superior to gage block calibration because they do not require block stacks so it is much faster to inspect the linear range of the tool.
http://www.threadcheck.com/depth-micrometer-masters-dm-1m-metric/surveillance-masters/
Knoop Hardness Testing
![knoop-hardness-testing[1]](http://blog.threadcheck.com/wp-content/uploads/2011/01/knoop-hardness-testing12.jpg "knoop-hardness-testing[1]")
In the Knoop hardness test, a diamond pyramid indenter, which has a rhombic base with included angles of 172°30' and 130°, is pressed onto the specimen under a test force F (kgf). The hardness number (HK) is obtained by dividing the test force F by the projected area, A (mm2), of the identation. The area is calculated from the longer diagonal length, d (mm), of the indentation when the indenter is removed.
The Knoop hardness scale is generally used when shallower depth indentions are required. Knoop hardness can be measured by installing a Knoop indenter on the Macro-Vickers hard- ness testing machine.
